Disable external link checking until the website branch is up-to-date with master again

This is a squash commit of the following previous commits:

---

Introduce `documentation-support` module to extract website data from source code

By adding a compilation `TaskListener` that extracts data from the Bug pattern
and Refaster rule collection (test) classes and writing to JSON output files
in the target directory. This extraction happens as part of the Maven build
using the `docgen` profile.

---

Improve website styling

Co-authored-by: japborst <japborst@gmail.com>
Co-authored-by: Gijs de Jong <berichtaangijs@gmail.com>

---

Generate Markdown files from existing content for the website

---

Upgrade dependencies to the latest versions

---

Compile and install project jars before docgen

---

Run validation in build and exclude self-url

---

Reintroduce `htmlproofer`, improve templates, cleanup setup and dependencies

---

Delete directory if it exists

---

Add SCSS for GitHub button and fix bug pattern sample rendering

---

Fix bug pattern GitHub link

---

Small styling tweaks (incl. for dark theme)

---

Use single mvn command

---

Move mustache templates

---

Hardcode anchors for headings

---

Add supression to bugpatterns

---

Remove self ignore for html-proofer

---

Add refaster supressions and use callouts

---

Use v0.4.1-SNAPSHOT

---

Revert "Use single mvn command"

This reverts commit 594471d1ed23a1c19d7fe88d925d1b7f828716cd.

---

Extract Refaster samples from source code instead of AST

---

Skip verification, for now

---

Add notes on disabling bugpatterns

---

Set default layout and image

---

Fix mobile navigation

---

Revert "Set default layout and image"

This reverts commit 67a4aa7b5b4d14c0f2b783f345f53affe6ef3ec5.

---

Add supression for refaster rules

---

Post-rebase fixes

---

Fix the tests

---

Doh

---

Version bump

---

Exclude ThirdPartyLibraryTest from Bug Pattern test output

---

Remove only last occurence of 'Test' in Bug Pattern tests doc generation

---

Move `MapRulesTest` resources

---

Add exclusion for docgen of `SourceCodeTest`

---

Bump version

---

Extra fixes after rebase

---

Delete custom nav footer and `assets/images/favicon.ico`

---

Post rebase fixes with version bump to `0.8.1-SNAPSHOT`

---

Use new BugPatternTest extraction method

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,51 @@
+---
+name: 🐛 Bug report
+about: Create a report to help us improve.
+title: ""
+labels: bug
+assignees: ""
+---
+
+### Describe the bug
+
+<!-- Provide a clear and concise description of what the bug or issue is. -->
+
+- [ ] I have verified that the issue is reproducible against the latest version
+      of the project.
+- [ ] I have searched through existing issues to verify that this issue is not
+      already known.
+
+### Minimal Reproducible Example
+
+<!-- Provide a clear and concise description of what happened. Please include
+steps on how to reproduce the issue. -->
+
+```java
+If applicable and possible, please replace this section with the code that
+triggered the isue.
+```
+
+<details>
+<summary>Logs</summary>
+
+```sh
+Please replace this sentence with log output, if applicable.
+```
+</details>
+
+### Expected behavior
+
+<!-- Provide a clear and concise description of what you expected to happen. -->
+
+### Setup
+
+<!-- Please complete the following information: -->
+
+- Operating system (e.g. MacOS Monterey).
+- Java version (i.e. `java --version`, e.g. `17.0.6`).
+- Error Prone version (e.g. `2.18.0`).
+- Error Prone Support version (e.g. `0.8.0`).
+
+### Additional context
+
+<!-- Provide any other context about the problem here. -->

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,58 @@
+---
+name: 🚀 Request a new feature
+about: Suggest a new feature.
+title: ""
+labels: new feature
+assignees: ""
+---
+
+### Problem
+
+<!-- Here, describe the context of the problem that you're facing, and which
+you'd like to be solved through Error Prone Support. -->
+
+### Description of the proposed new feature
+
+<!-- Please indicate the type of improvement. -->
+
+- [ ] Support a stylistic preference.
+- [ ] Avoid a common gotcha, or potential problem.
+- [ ] Improve performance.
+
+<!--
+Here, provide a clear and concise description of the desired change.
+
+If possible, provide a simple and minimal example using the following format:
+-->
+
+I would like to rewrite the following code:
+```java
+// XXX: Write the code to match here.
+```
+
+to:
+```java
+// XXX: Write the desired code here.
+```
+
+### Considerations
+
+<!--
+Here, mention any other aspects to consider. Relevant questions:
+
+- If applicable, is the rewrite operation a clear improvement in all cases?
+- Are there special cases to consider?
+- Can we further generalize the proposed solution?
+- Are there alternative solutions we should consider?
+-->
+
+### Participation
+
+<!-- Pull requests are very welcome, and we happily review contributions. Are
+you up for the challenge? :D -->
+
+- [ ] I am willing to submit a pull request to implement this improvement.
+
+### Additional context
+
+<!-- Provide any other context about the request here. -->

.github/release.yml

@@ -0,0 +1,29 @@
+changelog:
+  exclude:
+    labels:
+      - "ignore-changelog"
+  categories:
+    - title: ":rocket: New Error Prone checks and Refaster rules"
+      labels:
+        - "new feature"
+    - title: ":sparkles: Improvements"
+      labels:
+        - "improvement"
+    - title: ":warning: Update considerations and deprecations"
+      labels:
+        - "breaking change"
+        - "deprecation"
+    - title: ":bug: Bug fixes"
+      labels:
+        - "bug"
+        - "bug fix"
+    - title: ":books: Documentation, test and build improvements"
+      labels:
+        - "documentation"
+        - "chore"
+    - title: ":chart_with_upwards_trend: Dependency upgrades"
+      labels:
+        - "dependencies"
+    - title: "Other changes"
+      labels:
+        - "*"

.github/workflows/build.yaml

@@ -0,0 +1,57 @@
+name: Build and verify
+on:
+  pull_request:
+  push:
+    branches: [ master ]
+permissions:
+  contents: read
+jobs:
+  build:
+    strategy:
+      matrix:
+        os: [ ubuntu-22.04 ]
+        jdk: [ 11.0.18, 17.0.6, 19.0.2 ]
+        distribution: [ temurin ]
+        experimental: [ false ]
+        include:
+          - os: macos-12
+            jdk: 17.0.6
+            distribution: temurin
+            experimental: false
+          - os: windows-2022
+            jdk: 17.0.6
+            distribution: temurin
+            experimental: false
+          - os: ubuntu-22.04
+            jdk: 20-ea
+            distribution: zulu
+            experimental: true
+    runs-on: ${{ matrix.os }}
+    continue-on-error: ${{ matrix.experimental }}
+    steps:
+      # We run the build twice for each supported JDK: once against the
+      # original Error Prone release, using only Error Prone checks available
+      # on Maven Central, and once against the Picnic Error Prone fork,
+      # additionally enabling all checks defined in this project and any Error
+      # Prone checks available only from other artifact repositories.
+      - name: Check out code
+        uses: actions/checkout@v3.1.0
+        with:
+          persist-credentials: false
+      - name: Set up JDK
+        uses: actions/setup-java@v3.8.0
+        with:
+          java-version: ${{ matrix.jdk }}
+          distribution: ${{ matrix.distribution }}
+          cache: maven
+      - name: Display build environment details
+        run: mvn --version
+      - name: Build project against vanilla Error Prone, compile Javadoc
+        run: mvn -T1C install javadoc:jar
+      - name: Build project with self-check against Error Prone fork
+        run: mvn -T1C clean verify -Perror-prone-fork -Pnon-maven-central -Pself-check -s settings.xml
+      - name: Remove installed project artifacts
+        run: mvn build-helper:remove-project-artifact
+
+# XXX: Enable Codecov once we "go public".
+# XXX: Enable SonarCloud once we "go public".

.github/workflows/codeql.yml

@@ -0,0 +1,44 @@
+# Analyzes the code using GitHub's default CodeQL query database.
+# Identified issues are registered with GitHub's code scanning dashboard. When
+# a pull request is analyzed, any offending lines are annotated. See
+# https://codeql.github.com for details.
+name: CodeQL analysis
+on:
+  pull_request:
+  push:
+    branches: [ master ]
+  schedule:
+    - cron: '0 4 * * 1'
+permissions:
+  contents: read
+jobs:
+  analyze:
+    strategy:
+      matrix:
+        language: [ java, ruby ]
+    permissions:
+      contents: read
+      security-events: write
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3.1.0
+        with:
+          persist-credentials: false
+      - name: Set up JDK
+        uses: actions/setup-java@v3.8.0
+        with:
+          java-version: 17.0.6
+          distribution: temurin
+          cache: maven
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v2.2.11
+        with:
+          languages: ${{ matrix.language }}
+      - name: Perform minimal build
+        if: matrix.language == 'java'
+        run: mvn -T1C clean install -DskipTests -Dverification.skip
+      - name: Perform CodeQL analysis
+        uses: github/codeql-action/analyze@v2.2.11
+        with:
+          category: /language:${{ matrix.language }}

.github/workflows/deploy-website.yaml

@@ -0,0 +1,54 @@
+name: Update `error-prone.picnic.tech` website content
+on:
+  pull_request:
+  push:
+    branches: [ master, website ]
+permissions:
+  contents: read
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+jobs:
+  build:
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3.1.0
+        with:
+          persist-credentials: false
+      - uses: ruby/setup-ruby@v1.126.0
+        with:
+          working-directory: ./website
+          bundler-cache: true
+      - name: Configure Github Pages
+        uses: actions/configure-pages@v2.1.3
+      - name: Set up JDK
+        uses: actions/setup-java@v3.5.1
+        with:
+          java-version: 17.0.4
+          distribution: temurin
+          cache: maven
+      - name: Compile project and extract data
+        # XXX: Remove `-Dverification.skip` and update `website/README.md` once
+        # module `docgen` has no errors.
+        run: mvn -T1C clean install -DskipTests -Dverification.skip -Pdocgen
+      - name: Generate documentation
+        working-directory: ./website
+        run: bundle exec ruby generate-docs.rb
+      - name: Upload website as artifact
+        uses: actions/upload-pages-artifact@v1.0.5
+        with:
+          path: ./website/_site
+  deploy:
+    if: github.ref == 'refs/heads/website'
+    needs: build
+    permissions:
+      id-token: write
+      pages: write
+    runs-on: ubuntu-22.04
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v1.2.3

.github/workflows/openssf-scorecard.yml

@@ -0,0 +1,36 @@
+# Analyzes the code base and GitHub project configuration for adherence to
+# security best practices for open source software. Identified issues are
+# registered with GitHub's code scanning dashboard. When a pull request is
+# analyzed, any offending lines are annotated. See
+# https://securityscorecards.dev for details.
+name: OpenSSF Scorecard update
+on:
+  pull_request:
+  push:
+    branches: [ master ]
+  schedule:
+    - cron: '0 4 * * 1'
+permissions:
+  contents: read
+jobs:
+  analyze:
+    permissions:
+      contents: read
+      security-events: write
+      id-token: write
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3.1.0
+        with:
+          persist-credentials: false
+      - name: Run OpenSSF Scorecard analysis
+        uses: ossf/scorecard-action@v2.1.3
+        with:
+          results_file: results.sarif
+          results_format: sarif
+          publish_results: ${{ github.ref == 'refs/heads/master' }}
+      - name: Update GitHub's code scanning dashboard
+        uses: github/codeql-action/upload-sarif@v2.2.11
+        with:
+          sarif_file: results.sarif

.github/workflows/pitest-analyze-pr.yml

@@ -0,0 +1,38 @@
+# Performs mutation testing analysis on the files changed by a pull request and
+# uploads the results. The associated PR is subsequently updated by the
+# `pitest-update-pr.yml` workflow. See https://blog.pitest.org/oss-pitest-pr/
+# for details.
+name: "Mutation testing"
+on:
+  pull_request:
+permissions:
+  contents: read
+jobs:
+  analyze-pr:
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3.1.0
+        with:
+          fetch-depth: 2
+          persist-credentials: false
+      - name: Set up JDK
+        uses: actions/setup-java@v3.8.0
+        with:
+          java-version: 17.0.6
+          distribution: temurin
+          cache: maven
+      - name: Run Pitest
+        # By running with features `+GIT(from[HEAD~1]), +gitci`, Pitest only
+        # analyzes lines changed in the associated pull request, as GitHub
+        # exposes the changes unique to the PR as a single commit on top of the
+        # target branch. See https://blog.pitest.org/pitest-pr-setup for
+        # details.
+        run: mvn test pitest:mutationCoverage -DargLine.xmx=2048m -Dverification.skip -Dfeatures="+GIT(from[HEAD~1]), +gitci"
+      - name: Aggregate Pitest reports
+        run: mvn pitest-git:aggregate -DkilledEmoji=":tada:" -DmutantEmoji=":zombie:" -DtrailingText="Mutation testing report by [Pitest](https://pitest.org/). Review any surviving mutants by inspecting the line comments under [_Files changed_](${{ github.event.number }}/files)."
+      - name: Upload Pitest reports as artifact
+        uses: actions/upload-artifact@v3.1.1
+        with:
+          name: pitest-reports
+          path: ./target/pit-reports-ci

.github/workflows/pitest-update-pr.yml

@@ -0,0 +1,39 @@
+# Updates a pull request based on the corresponding mutation testing analysis
+# performed by the `pitest-analyze-pr.yml` workflow. See
+# https://blog.pitest.org/oss-pitest-pr/ for details.
+name: "Mutation testing: post results"
+on:
+  workflow_run:
+    workflows: ["Mutation testing"]
+    types:
+      - completed
+permissions:
+  actions: read
+jobs:
+  update-pr:
+    if: ${{ github.event.workflow_run.conclusion == 'success' }}
+    permissions:
+      actions: read
+      checks: write
+      contents: read
+      pull-requests: write
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3.1.0
+        with:
+          persist-credentials: false
+      - name: Set up JDK
+        uses: actions/setup-java@v3.8.0
+        with:
+          java-version: 17.0.6
+          distribution: temurin
+          cache: maven
+      - name: Download Pitest analysis artifact
+        uses: dawidd6/action-download-artifact@v2.24.2
+        with:
+          workflow: ${{ github.event.workflow_run.workflow_id }}
+          name: pitest-reports
+          path: ./target/pit-reports-ci
+      - name: Update PR
+        run: mvn -DrepoToken="${{ secrets.GITHUB_TOKEN }}" pitest-github:updatePR

.mvn/jvm.config

@@ -1,4 +1,8 @@
+-XX:ReservedCodeCacheSize=512m
+-XX:SoftRefLRUPolicyMSPerMB=10
+-XX:+UseParallelGC
 --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED
+--add-exports=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED
 --add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED
 --add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED
 --add-exports=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED
@@ -6,5 +10,4 @@
 --add-exports=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED
 --add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED
 --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED
---add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED
 --add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED

.mvn/maven.config

@@ -0,0 +1,3 @@
+--batch-mode
+--errors
+--strict-checksums

.renovaterc.json

@@ -0,0 +1,22 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "packageRules": [
+    {
+      "matchPackagePatterns": [
+        "^org\\.springframework:spring-framework-bom$",
+        "^org\\.springframework\\.boot:spring-boot[a-z-]*$"
+      ],
+      "separateMinorPatch": true
+    },
+    {
+      "matchPackagePatterns": [
+        "^ruby\\/setup-ruby$"
+      ],
+      "schedule": "* * 1 * *"
+    }
+  ],
+  "reviewers": [
+    "rickie",
+    "Stephan202"
+  ]
+}

.travis.yml

@@ -1,38 +0,0 @@
----
-dist: bionic
-language: java
-jdk: openjdk11
-addons:
-  sonarcloud:
-    organization: picnic-technologies
-    token: "${SONARCLOUD_TOKEN}"
-install:
-  - mvn io.takari:maven:wrapper
-script:
-  # We run the build twice: once against the original Error Prone release,
-  # using only Error Prone checks available on Maven Central, and once against
-  # the Picnic Error Prone fork, additionally enabling all checks defined in
-  # this project and any Error Prone checks available only from other artifact
-  # repositories.
-  - ./mvnw clean install
-  - ./mvnw clean install -Perror-prone-fork -Pnon-maven-central -Pself-check -s settings.xml
-  # XXX: Enable SonarCloud once we "go public".
-  # ./mvnw jacoco:prepare-agent surefire:test jacoco:report sonar:sonar
-  - ./mvnw jacoco:prepare-agent surefire:test jacoco:report
-before_cache:
-  # Don't cache the artifacts we just generated, for multiple reasons: (1) we
-  # shouldn't need them next time around and (2) if we do, that indicates a
-  # dependency issue which might otherwise go unnoticed until next time we bump
-  # the project's version (i.e., when tagging).
-  - find "${HOME}/.m2/repository" -depth -name '*-SNAPSHOT' -exec rm -r '{}' \;
-cache:
-  directories:
-    # The local Maven repository in which third party dependencies are stored.
-    - ${HOME}/.m2/repository
-    # The Takari Maven Wrapper's storage for downloaded Maven distributions.
-    - ${HOME}/.m2/wrapper
-    # The SonarQube analysis cache.
-    - ${HOME}/.sonar/cache
-# XXX: Enable Codecov once we "go public".
-#after_success:
-#  - bash <(curl -s https://codecov.io/bash)

CONTRIBUTING.md

@@ -0,0 +1,85 @@
+# Contributing
+
+Thank you for checking this document! This project is free software, and we
+(the maintainers) encourage and value any contribution.
+
+Here are some guidelines to help you get started.
+
+## 🐛 Reporting a bug
+
+Like any non-trivial piece of software, this library is probably not bug-free.
+If you found a bug, feel free to [report the issue][error-prone-support-issues]
+on GitHub.
+
+Before doing so, please:
+- Verify that the issue is reproducible against the latest version of the
+  project.
+- Search through the existing set of issues to see whether the problem is
+  already known. With some luck a solution is already in place, or a workaround
+  may have been provided.
+
+When filing a bug report, please include the following:
+- Any relevant information about your environment. This should generally
+  include the output of `java --version`, as well as the version of Error Prone
+  you're using.
+- A description of what is going on (e.g. logging output, stacktraces).
+- A minimum reproducible example, so that other developers can try to reproduce
+  (and optionally fix) the bug.
+- Any additional information that may be relevant.
+
+## 💡 Reporting an improvement
+
+If you would like to see an improvement, you can file a [GitHub
+issue][error-prone-support-issues]. This is also a good idea when you're
+already working towards opening a pull request, as this allows for discussion
+around the idea.
+
+## 🚀 Opening a pull request
+
+All submissions, including submissions by project members, require approval by
+at least two reviewers. We use [GitHub pull
+requests][error-prone-support-pulls] for this purpose.
+
+Before opening a pull request, please check whether there are any existing
+(open or closed) issues or pull requests addressing the same problem. This
+avoids double work or lots of time spent on a solution that may ultimately not
+be accepted. When in doubt, make sure to first raise an
+[issue][error-prone-support-issues] to discuss the idea.
+
+To the extent possible, the pull request process guards our coding guidelines.
+Some pointers:
+- Try to make sure that the
+  [`./run-full-build.sh`][error-prone-support-full-build] script completes
+  successfully, ideally before opening a pull request. See the [development
+  instructions][error-prone-support-developing] for details on how to
+  efficiently resolve many of the errors and warnings that may be reported. (In
+  particular, make sure to run `mvn fmt:format` and
+  [`./apply-error-prone-suggestions.sh`][error-prone-support-patch].) That
+  said, if you feel that the build fails for invalid or debatable reasons, or
+  if you're unsure how to best resolve an issue, don't let that discourage you
+  from opening a PR with a failing build; we can have a look at the issue
+  together!
+- Checks should be _topical_: ideally they address a single concern.
+- Where possible checks should provide _fixes_, and ideally these are
+  completely behavior-preserving. In order for a check to be adopted by users
+  it must not "get in the way". So for a check that addresses a relatively
+  trivial stylistic concern it is doubly important that the violations it
+  detects can be auto-patched.
+- Make sure you have read Error Prone's [criteria for new
+  checks][error-prone-criteria]. Most guidelines described there apply to this
+  project as well, except that this project _does_ focus quite heavy on style
+  enforcement. But that just makes the previous point doubly important.
+- Make sure that a check's [(mutation) test
+  coverage][error-prone-support-mutation-tests] is or remains about as high as
+  it can be. Not only does this lead to better tests, it also points out
+  opportunities to simplify the code.
+- Please restrict the scope of a pull request to a single feature or fix. Don't
+  sneak in unrelated changes; instead just open more than one pull request 😉.
+
+[error-prone-criteria]: https://errorprone.info/docs/criteria
+[error-prone-support-developing]: https://github.com/PicnicSupermarket/error-prone-support/tree/master#-developing-error-prone-support
+[error-prone-support-full-build]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/run-full-build.sh
+[error-prone-support-issues]: https://github.com/PicnicSupermarket/error-prone-support/issues
+[error-prone-support-mutation-tests]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/run-mutation-tests.sh
+[error-prone-support-patch]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/apply-error-prone-suggestions.sh
+[error-prone-support-pulls]: https://github.com/PicnicSupermarket/error-prone-support/pulls

LICENSE.md

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2017-2023 Picnic Technologies BV
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -0,0 +1,282 @@
+<div align="center">
+  <picture>
+    <source media="(prefers-color-scheme: dark)" srcset="website/assets/images/logo-dark.svg">
+    <source media="(prefers-color-scheme: light)" srcset="website/assets/images/logo.svg">
+    <img alt="Error Prone Support logo" src="website/assets/images/logo.svg" width="50%">
+  </picture>
+</div>
+
+# Error Prone Support
+
+Error Prone Support is a [Picnic][picnic-blog]-opinionated extension of
+Google's [Error Prone][error-prone-orig-repo]. It aims to improve code quality,
+focussing on maintainability, consistency and avoidance of common pitfalls.
+
+> Error Prone is a static analysis tool for Java that catches common
+> programming mistakes at compile-time.
+
+Read more on how Picnic uses Error Prone (Support) in the blog post [_Picnic
+loves Error Prone: producing high-quality and consistent Java
+code_][picnic-blog-ep-post].
+
+[![Maven Central][maven-central-badge]][maven-central-search]
+[![Reproducible Builds][reproducible-builds-badge]][reproducible-builds-report]
+[![GitHub Actions][github-actions-build-badge]][github-actions-build-master]
+[![License][license-badge]][license]
+[![PRs Welcome][pr-badge]][contributing]
+
+[Getting started](#-getting-started) •
+[Developing Error Prone Support](#-developing-error-prone-support) •
+[How it works](#-how-it-works) • [Contributing](#%EF%B8%8F-contributing)
+
+---
+
+## ⚡ Getting started
+
+### Installation
+
+This library is built on top of [Error Prone][error-prone-orig-repo]. To use
+it, read the installation guide for Maven or Gradle below.
+
+#### Maven
+
+1. First, follow Error Prone's [installation
+   guide][error-prone-installation-guide].
+2. Next, edit your `pom.xml` file to add one or more Error Prone Support
+   modules to the `annotationProcessorPaths` of the `maven-compiler-plugin`:
+
+   ```xml
+   <build>
+       <pluginManagement>
+           <plugins>
+               <plugin>
+                   <groupId>org.apache.maven.plugins</groupId>
+                   <artifactId>maven-compiler-plugin</artifactId>
+                   <configuration>
+                       <annotationProcessorPaths>
+                           <!-- Error Prone itself. -->
+                           <path>
+                               <groupId>com.google.errorprone</groupId>
+                               <artifactId>error_prone_core</artifactId>
+                               <version>${error-prone.version}</version>
+                           </path>
+                           <!-- Error Prone Support's additional bug checkers. -->
+                           <path>
+                               <groupId>tech.picnic.error-prone-support</groupId>
+                               <artifactId>error-prone-contrib</artifactId>
+                               <version>${error-prone-support.version}</version>
+                           </path>
+                           <!-- Error Prone Support's Refaster rules. -->
+                           <path>
+                               <groupId>tech.picnic.error-prone-support</groupId>
+                               <artifactId>refaster-runner</artifactId>
+                               <version>${error-prone-support.version}</version>
+                           </path>
+                       </annotationProcessorPaths>
+                       <compilerArgs>
+                           <arg>
+                               -Xplugin:ErrorProne
+                               <!-- Add other Error Prone flags here. See
+                               https://errorprone.info/docs/flags. -->
+                           </arg>
+                           <arg>-XDcompilePolicy=simple</arg>
+                       </compilerArgs>
+                       <!-- Some checks raise warnings rather than errors. -->
+                       <showWarnings>true</showWarnings>
+                       <!-- Enable this if you'd like to fail your build upon warnings. -->
+                       <!-- <failOnWarning>true</failOnWarning> -->
+                   </configuration>
+               </plugin>
+           </plugins>
+       </pluginManagement>
+   </build>
+   ```
+
+<!-- XXX: Reference `oss-parent`'s `pom.xml` once that project also uses Error
+Prone Support. Alternatively reference this project's `self-check` profile
+definition. -->
+
+#### Gradle
+
+1. First, follow the [installation guide]
+   [error-prone-gradle-installation-guide] of the `gradle-errorprone-plugin`.
+2. Next, edit your `build.gradle` file to add one or more Error Prone Support
+   modules:
+
+   ```groovy
+   dependencies {
+       // Error Prone itself.
+       errorprone("com.google.errorprone:error_prone_core:${errorProneVersion}")
+       // Error Prone Support's additional bug checkers.
+       errorprone("tech.picnic.error-prone-support:error-prone-contrib:${errorProneSupportVersion}")
+       // Error Prone Support's Refaster rules.
+       errorprone("tech.picnic.error-prone-support:refaster-runner:${errorProneSupportVersion}")
+   }
+
+   tasks.withType(JavaCompile).configureEach {
+       options.errorprone.disableWarningsInGeneratedCode = true
+       // Add other Error Prone flags here. See:
+       // - https://github.com/tbroyer/gradle-errorprone-plugin#configuration
+       // - https://errorprone.info/docs/flags
+   }
+   ```
+
+### Seeing it in action
+
+Consider the following example code:
+
+```java
+import com.google.common.collect.ImmutableSet;
+import java.math.BigDecimal;
+
+public class Example {
+  static BigDecimal getNumber() {
+    return BigDecimal.valueOf(0);
+  }
+
+  public ImmutableSet<Integer> getSet() {
+    ImmutableSet<Integer> set = ImmutableSet.of(1);
+    return ImmutableSet.copyOf(set);
+  }
+}
+```
+
+If the [installation](#installation) was successful, then building the above
+code with Maven should yield two compiler warnings:
+
+```sh
+$ mvn clean install
+...
+[INFO] Example.java:[9,34] [Refaster Rule] BigDecimalRules.BigDecimalZero: Refactoring opportunity
+    (see https://error-prone.picnic.tech/refasterrules/BigDecimalRules#BigDecimalZero)
+  Did you mean 'return BigDecimal.ZERO;'?
+...
+[WARNING] Example.java:[13,35] [IdentityConversion] This method invocation appears redundant; remove it or suppress this warning and add a comment explaining its purpose
+    (see https://error-prone.picnic.tech/bugpatterns/IdentityConversion)
+  Did you mean 'return set;' or '@SuppressWarnings("IdentityConversion") public ImmutableSet<Integer> getSet() {'?
+...
+```
+
+Two things are kicking in here:
+
+1. An Error Prone [`BugChecker`][error-prone-bugchecker] that flags unnecessary
+   [identity conversions][bug-checks-identity-conversion].
+2. A [Refaster][refaster] rule capable of
+   [rewriting][refaster-rules-bigdecimal] expressions of the form
+   `BigDecimal.valueOf(0)` and `new BigDecimal(0)` to `BigDecimal.ZERO`.
+
+Be sure to check out all [bug checks][bug-checks] and [refaster
+rules][refaster-rules].
+
+## 👷 Developing Error Prone Support
+
+This is a [Maven][maven] project, so running `mvn clean install` performs a
+full clean build and installs the library to your local Maven repository.
+
+Once you've made changes, the build may fail due to a warning or error emitted
+by static code analysis. The flags and commands listed below allow you to
+suppress or (in a large subset of cases) automatically fix such cases. Make
+sure to carefully check the available options, as this can save you significant
+amounts of development time!
+
+Relevant Maven build parameters:
+
+- `-Dverification.warn` makes the warnings and errors emitted by various
+  plugins and the Java compiler non-fatal, where possible.
+- `-Dverification.skip` disables various non-essential plugins and compiles the
+  code with minimal checks (i.e. without linting, Error Prone checks, etc.).
+- `-Dversion.error-prone=some-version` runs the build using the specified
+  version of Error Prone. This is useful e.g. when testing a locally built
+  Error Prone SNAPSHOT.
+- `-Perror-prone-fork` runs the build using Picnic's [Error Prone
+  fork][error-prone-fork-repo], hosted on [Jitpack][error-prone-fork-jitpack].
+  This fork generally contains a few changes on top of the latest Error Prone
+  release.
+- `-Pself-check` runs the checks defined by this project against itself.
+  Pending a release of [google/error-prone#3301][error-prone-pull-3301], this
+  flag must currently be used in combination with `-Perror-prone-fork`.
+
+Other highly relevant commands:
+
+- `mvn fmt:format` formats the code using
+  [`google-java-format`][google-java-format].
+- [`./run-full-build.sh`][script-run-full-build] builds the project twice,
+  where the second pass validates compatbility with Picnic's [Error Prone
+  fork][error-prone-fork-repo] and compliance of the code with any rules
+  defined within this project. (Consider running this before [opening a pull
+  request][contributing-pull-request], as the PR checks also perform this
+  validation.)
+- [`./apply-error-prone-suggestions.sh`][script-apply-error-prone-suggestions]
+  applies Error Prone and Error Prone Support code suggestions to this project.
+  Before running this command, make sure to have installed the project (`mvn
+  clean install`) and make sure that the current working directory does not
+  contain unstaged or uncommited changes.
+- [`./run-mutation-tests.sh`][script-run-mutation-tests] runs mutation tests
+  using [Pitest][pitest]. The results can be reviewed by opening the respective
+  `target/pit-reports/index.html` files. For more information check the [PIT
+  Maven plugin][pitest-maven].
+
+When running the project's tests in IntelliJ IDEA, you might see the following
+error:
+
+```
+java: exporting a package from system module jdk.compiler is not allowed with --release
+```
+
+If this happens, go to _Settings -> Build, Execution, Deployment -> Compiler ->
+Java Compiler_ and deselect the option _Use '--release' option for
+cross-compilation (Java 9 and later)_. See [IDEA-288052][idea-288052] for
+details.
+
+## 💡 How it works
+
+This project provides additional [`BugChecker`][error-prone-bugchecker]
+implementations.
+
+<!-- XXX: Extend this section. -->
+
+## ✍️ Contributing
+
+Want to report or fix a bug, suggest or add a new feature, or improve the
+documentation? That's awesome! Please read our [contribution
+guidelines][contributing].
+
+### Security
+
+If you want to report a security vulnerablity, please do so through a private
+channel; please see our [security policy][security] for details.
+
+[bug-checks]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/
+[bug-checks-identity-conversion]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/IdentityConversion.java
+[contributing]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/CONTRIBUTING.md
+[contributing-pull-request]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/CONTRIBUTING.md#-opening-a-pull-request
+[error-prone-bugchecker]: https://github.com/google/error-prone/blob/master/check_api/src/main/java/com/google/errorprone/bugpatterns/BugChecker.java
+[error-prone-fork-jitpack]: https://jitpack.io/#PicnicSupermarket/error-prone
+[error-prone-fork-repo]: https://github.com/PicnicSupermarket/error-prone
+[error-prone-gradle-installation-guide]: https://github.com/tbroyer/gradle-errorprone-plugin
+[error-prone-installation-guide]: https://errorprone.info/docs/installation#maven
+[error-prone-orig-repo]: https://github.com/google/error-prone
+[error-prone-pull-3301]: https://github.com/google/error-prone/pull/3301
+[github-actions-build-badge]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/build.yaml/badge.svg
+[github-actions-build-master]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/build.yaml?query=branch%3Amaster
+[google-java-format]: https://github.com/google/google-java-format
+[idea-288052]: https://youtrack.jetbrains.com/issue/IDEA-288052
+[license-badge]: https://img.shields.io/github/license/PicnicSupermarket/error-prone-support
+[license]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/LICENSE.md
+[maven-central-badge]: https://img.shields.io/maven-central/v/tech.picnic.error-prone-support/error-prone-support?color=blue
+[maven-central-search]: https://search.maven.org/artifact/tech.picnic.error-prone-support/error-prone-support
+[maven]: https://maven.apache.org
+[picnic-blog-ep-post]: https://blog.picnic.nl/picnic-loves-error-prone-producing-high-quality-and-consistent-java-code-b8a566be6886
+[picnic-blog]: https://blog.picnic.nl
+[pitest]: https://pitest.org
+[pitest-maven]: https://pitest.org/quickstart/maven
+[pr-badge]: https://img.shields.io/badge/PRs-welcome-brightgreen.svg
+[refaster]: https://errorprone.info/docs/refaster
+[refaster-rules-bigdecimal]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/BigDecimalRules.java
+[refaster-rules]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/
+[reproducible-builds-badge]: https://img.shields.io/badge/Reproducible_Builds-ok-success?labelColor=1e5b96
+[reproducible-builds-report]: https://github.com/jvm-repo-rebuild/reproducible-central/blob/master/content/tech/picnic/error-prone-support/error-prone-support/README.md
+[script-apply-error-prone-suggestions]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/apply-error-prone-suggestions.sh
+[script-run-full-build]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/run-full-build.sh
+[script-run-mutation-tests]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/run-mutation-tests.sh
+[security]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/SECURITY.md

SECURITY.md

@@ -0,0 +1,23 @@
+# Security policy
+
+We take security seriously. We are mindful of Error Prone Support's place in
+the software supply chain, and the risks and responsibilities that come with
+this.
+
+## Supported versions
+
+This project uses [semantic versioning][semantic-versioning]. In general, only
+the latest version of this software is supported. That said, if users have a
+compelling reason to ask for patch release of an older major release, then we
+will seriously consider such a request. We do urge users to stay up-to-date and
+use the latest release where feasible.
+
+## Reporting a vulnerability
+
+To report a vulnerability, please visit the [security
+advisories][security-advisories] page and click _Report a vulnerability_. We
+will take such reports seriously and work with you to resolve the issue in a
+timely manner.
+
+[security-advisories]: https://github.com/PicnicSupermarket/error-prone-support/security/advisories
+[semantic-versioning]: https://semver.org

apply-error-prone-suggestions.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+# Compiles the code using Error Prone and applies its suggestions. The set of
+# checks applied can optionally be restricted by name.
+#
+# As this script may modify the project's code, it is important to execute it
+# in a clean Git working directory.
+
+set -e -u -o pipefail
+
+if [ "${#}" -gt 1 ]; then
+  echo "Usage: ${0} [PatchChecks]"
+  exit 1
+fi
+
+patchChecks=${1:-}
+
+mvn clean test-compile fmt:format \
+  -s "$(dirname "${0}")/settings.xml" \
+  -T 1.0C \
+  -Perror-prone \
+  -Perror-prone-fork \
+  -Ppatch \
+  -Pself-check \
+  -Derror-prone.patch-checks="${patchChecks}" \
+  -Dverification.skip

cdg-pitest-licence.txt

@@ -0,0 +1,7 @@
+# Arcmutate license for Error Prone Support, requested by sending an email to
+# support@arcmutate.com.
+expires=07/11/2023
+keyVersion=1
+signature=MhZxMbnO6UovNfllM0JuVWkZyvRT3/G5o/uT0Mm36c7200VpZNVu03gTAGivnl9W5RzvZhfpIHccuQ5ctjQkrqhsFSrl4fyqPqu3y5V2fsHIdFXP/G72EGj6Kay9ndLpaEHalqE0bEwxdnHMzEYq5y3O9vUPv8MhUl57xk+rvBo\=
+packages=tech.picnic.errorprone.*
+type=OSSS

documentation-support/pom.xml

@@ -0,0 +1,91 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>tech.picnic.error-prone-support</groupId>
+        <artifactId>error-prone-support</artifactId>
+        <version>0.9.1-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>documentation-support</artifactId>
+
+    <name>Picnic :: Error Prone Support :: Documentation Support</name>
+    <description>Data extraction support for the purpose of documentation generation.</description>
+
+    <dependencies>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_annotation</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_annotations</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_check_api</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_core</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_test_helpers</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-annotations</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>com.google.auto</groupId>
+            <artifactId>auto-common</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>com.google.auto.service</groupId>
+            <artifactId>auto-service-annotations</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.google.auto.value</groupId>
+            <artifactId>auto-value-annotations</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.jspecify</groupId>
+            <artifactId>jspecify</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-params</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+</project>

documentation-support/src/main/java/tech/picnic/errorprone/documentation/BugPatternExtractor.java

@@ -0,0 +1,114 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.common.base.Verify.verify;
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static java.util.Objects.requireNonNull;
+
+import com.google.auto.common.AnnotationMirrors;
+import com.google.auto.service.AutoService;
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.BugPattern.SeverityLevel;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.annotations.Immutable;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.ClassTree;
+import com.sun.tools.javac.code.Attribute;
+import com.sun.tools.javac.code.Symbol.ClassSymbol;
+import java.util.Optional;
+import javax.lang.model.element.AnnotationValue;
+import tech.picnic.errorprone.documentation.BugPatternExtractor.BugPatternDocumentation;
+
+/**
+ * An {@link Extractor} that describes how to extract data from a {@code @BugPattern} annotation.
+ */
+@Immutable
+@AutoService(Extractor.class)
+public final class BugPatternExtractor implements Extractor<BugPatternDocumentation> {
+  /** Instantiates a new {@link BugPatternExtractor} instance. */
+  public BugPatternExtractor() {}
+
+  @Override
+  public String identifier() {
+    return "bugpattern";
+  }
+
+  @Override
+  public Optional<BugPatternDocumentation> tryExtract(ClassTree tree, VisitorState state) {
+    ClassSymbol symbol = ASTHelpers.getSymbol(tree);
+    BugPattern annotation = symbol.getAnnotation(BugPattern.class);
+    if (annotation == null) {
+      return Optional.empty();
+    }
+
+    return Optional.of(
+        new AutoValue_BugPatternExtractor_BugPatternDocumentation(
+            symbol.getQualifiedName().toString(),
+            annotation.name().isEmpty() ? tree.getSimpleName().toString() : annotation.name(),
+            ImmutableList.copyOf(annotation.altNames()),
+            annotation.link(),
+            ImmutableList.copyOf(annotation.tags()),
+            annotation.summary(),
+            annotation.explanation(),
+            annotation.severity(),
+            annotation.disableable(),
+            annotation.documentSuppression()
+                ? getSuppressionAnnotations(tree)
+                : ImmutableList.of()));
+  }
+
+  /**
+   * Returns the fully-qualified class names of suppression annotations specified by the {@link
+   * BugPattern} annotation located on the given tree.
+   *
+   * @implNote This method cannot simply invoke {@link BugPattern#suppressionAnnotations()}, as that
+   *     will yield an "Attempt to access Class objects for TypeMirrors" exception.
+   */
+  private static ImmutableList<String> getSuppressionAnnotations(ClassTree tree) {
+    AnnotationTree annotationTree =
+        ASTHelpers.getAnnotationWithSimpleName(
+            ASTHelpers.getAnnotations(tree), BugPattern.class.getSimpleName());
+    requireNonNull(annotationTree, "BugPattern annotation must be present");
+
+    Attribute.Array types =
+        doCast(
+            AnnotationMirrors.getAnnotationValue(
+                ASTHelpers.getAnnotationMirror(annotationTree), "suppressionAnnotations"),
+            Attribute.Array.class);
+
+    return types.getValue().stream()
+        .map(v -> doCast(v, Attribute.Class.class).classType.toString())
+        .collect(toImmutableList());
+  }
+
+  @SuppressWarnings("unchecked")
+  private static <T extends AnnotationValue> T doCast(AnnotationValue value, Class<T> target) {
+    verify(target.isInstance(value), "Value '%s' is not of type '%s'", value, target);
+    return (T) value;
+  }
+
+  @AutoValue
+  abstract static class BugPatternDocumentation {
+    abstract String fullyQualifiedName();
+
+    abstract String name();
+
+    abstract ImmutableList<String> altNames();
+
+    abstract String link();
+
+    abstract ImmutableList<String> tags();
+
+    abstract String summary();
+
+    abstract String explanation();
+
+    abstract SeverityLevel severityLevel();
+
+    abstract boolean canDisable();
+
+    abstract ImmutableList<String> suppressionAnnotations();
+  }
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/BugPatternTestExtractor.java

@@ -0,0 +1,200 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.anything;
+import static com.google.errorprone.matchers.Matchers.argument;
+import static com.google.errorprone.matchers.Matchers.classLiteral;
+import static com.google.errorprone.matchers.Matchers.hasAnnotation;
+import static com.google.errorprone.matchers.Matchers.instanceMethod;
+import static com.google.errorprone.matchers.Matchers.toType;
+import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
+
+import com.google.auto.service.AutoService;
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.annotations.Immutable;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MemberSelectTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.source.tree.MethodTree;
+import com.sun.source.tree.Tree;
+import com.sun.source.util.TreeScanner;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.regex.Pattern;
+import org.jspecify.annotations.Nullable;
+import tech.picnic.errorprone.documentation.BugPatternTestExtractor.BugPatternTestDocumentation;
+
+/**
+ * An {@link Extractor} that describes how to extract data from classes that test a {@code
+ * BugChecker}.
+ */
+@Immutable
+@AutoService(Extractor.class)
+public final class BugPatternTestExtractor implements Extractor<BugPatternTestDocumentation> {
+  private static final Pattern TEST_CLASS_NAME_PATTERN = Pattern.compile("(.*)Test");
+  private static final Matcher<Tree> JUNIT_TEST_METHOD =
+      toType(MethodTree.class, hasAnnotation("org.junit.jupiter.api.Test"));
+  private static final Matcher<MethodInvocationTree> BUG_PATTERN_TEST_METHOD =
+      allOf(
+          staticMethod()
+              .onDescendantOfAny(
+                  "com.google.errorprone.CompilationTestHelper",
+                  "com.google.errorprone.BugCheckerRefactoringTestHelper")
+              .named("newInstance"),
+          argument(0, classLiteral(anything())));
+
+  /** Instantiates a new {@link BugPatternTestExtractor} instance. */
+  public BugPatternTestExtractor() {}
+
+  @Override
+  public String identifier() {
+    return "bugpattern-test";
+  }
+
+  // XXX: Improve support for correctly extracting multiple sources from a single
+  // `{BugCheckerRefactoring,Compilation}TestHelper` test.
+  @Override
+  public Optional<BugPatternTestDocumentation> tryExtract(ClassTree tree, VisitorState state) {
+    return getClassUnderTest(tree)
+        .filter(bugPatternName -> testsBugPattern(bugPatternName, tree, state))
+        .map(
+            bugPatternName -> {
+              CollectBugPatternTests scanner = new CollectBugPatternTests();
+
+              for (Tree m : tree.getMembers()) {
+                if (JUNIT_TEST_METHOD.matches(m, state)) {
+                  scanner.scan(m, state);
+                }
+              }
+
+              return new AutoValue_BugPatternTestExtractor_BugPatternTestDocumentation(
+                  bugPatternName, scanner.getIdentificationTests(), scanner.getReplacementTests());
+            });
+  }
+
+  private static boolean testsBugPattern(
+      String bugPatternName, ClassTree tree, VisitorState state) {
+    AtomicBoolean result = new AtomicBoolean(false);
+
+    new TreeScanner<@Nullable Void, @Nullable Void>() {
+      @Override
+      public @Nullable Void visitMethodInvocation(MethodInvocationTree node, @Nullable Void v) {
+        if (BUG_PATTERN_TEST_METHOD.matches(node, state)) {
+          MemberSelectTree firstArgumentTree = (MemberSelectTree) node.getArguments().get(0);
+          result.compareAndSet(
+              /* expectedValue= */ false,
+              bugPatternName.equals(firstArgumentTree.getExpression().toString()));
+        }
+
+        return super.visitMethodInvocation(node, v);
+      }
+    }.scan(tree, null);
+
+    return result.get();
+  }
+
+  private static Optional<String> getClassUnderTest(ClassTree tree) {
+    return Optional.of(TEST_CLASS_NAME_PATTERN.matcher(tree.getSimpleName().toString()))
+        .filter(java.util.regex.Matcher::matches)
+        .map(m -> m.group(1));
+  }
+
+  private static final class CollectBugPatternTests
+      extends TreeScanner<@Nullable Void, VisitorState> {
+    private static final Matcher<ExpressionTree> IDENTIFICATION_SOURCE_LINES =
+        instanceMethod()
+            .onDescendantOf("com.google.errorprone.CompilationTestHelper")
+            .named("addSourceLines");
+    private static final Matcher<ExpressionTree> REPLACEMENT_INPUT =
+        instanceMethod()
+            .onDescendantOf("com.google.errorprone.BugCheckerRefactoringTestHelper")
+            .named("addInputLines");
+    private static final Matcher<ExpressionTree> REPLACEMENT_OUTPUT =
+        instanceMethod()
+            .onDescendantOf("com.google.errorprone.BugCheckerRefactoringTestHelper.ExpectOutput")
+            .named("addOutputLines");
+
+    private final List<String> identificationTests = new ArrayList<>();
+    private final List<BugPatternReplacementTestDocumentation> replacementTests = new ArrayList<>();
+
+    public ImmutableList<String> getIdentificationTests() {
+      return ImmutableList.copyOf(identificationTests);
+    }
+
+    public ImmutableList<BugPatternReplacementTestDocumentation> getReplacementTests() {
+      return ImmutableList.copyOf(replacementTests);
+    }
+
+    // XXX: Consider:
+    // - Whether to omit or handle differently identification tests without `// BUG: Diagnostic
+    //   (contains|matches)` markers.
+    // - Whether to omit or handle differently replacement tests with identical input and output.
+    //   (Though arguably we should have a separate checker which replaces such cases with
+    //   `.expectUnchanged()`.)
+    // - Whether to track `.expectUnchanged()` test cases.
+    @Override
+    public @Nullable Void visitMethodInvocation(MethodInvocationTree node, VisitorState state) {
+      if (IDENTIFICATION_SOURCE_LINES.matches(node, state)) {
+        getSourceCode(node).ifPresent(identificationTests::add);
+      } else if (REPLACEMENT_OUTPUT.matches(node, state)) {
+        ExpressionTree receiver = ASTHelpers.getReceiver(node);
+        // XXX: Make this code nicer.
+        if (REPLACEMENT_INPUT.matches(receiver, state)) {
+          getSourceCode(node)
+              .ifPresent(
+                  output ->
+                      getSourceCode((MethodInvocationTree) receiver)
+                          .ifPresent(
+                              input ->
+                                  replacementTests.add(
+                                      new AutoValue_BugPatternTestExtractor_BugPatternReplacementTestDocumentation(
+                                          input, output))));
+        }
+      }
+
+      return super.visitMethodInvocation(node, state);
+    }
+
+    // XXX: Duplicated from `ErrorProneTestSourceFormat`. Can we do better?
+    private static Optional<String> getSourceCode(MethodInvocationTree tree) {
+      List<? extends ExpressionTree> sourceLines =
+          tree.getArguments().subList(1, tree.getArguments().size());
+      StringBuilder source = new StringBuilder();
+
+      for (ExpressionTree sourceLine : sourceLines) {
+        String value = ASTHelpers.constValue(sourceLine, String.class);
+        if (value == null) {
+          return Optional.empty();
+        }
+        source.append(value).append('\n');
+      }
+
+      return Optional.of(source.toString());
+    }
+  }
+
+  // XXX: Rename?
+  @AutoValue
+  abstract static class BugPatternTestDocumentation {
+    abstract String name();
+
+    abstract ImmutableList<String> identificationTests();
+
+    abstract ImmutableList<BugPatternReplacementTestDocumentation> replacementTests();
+  }
+
+  // XXX: Rename?
+  @AutoValue
+  abstract static class BugPatternReplacementTestDocumentation {
+    abstract String inputLines();
+
+    abstract String outputLines();
+  }
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/DocumentationGenerator.java

@@ -0,0 +1,56 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+import com.google.auto.service.AutoService;
+import com.google.common.annotations.VisibleForTesting;
+import com.sun.source.util.JavacTask;
+import com.sun.source.util.Plugin;
+import com.sun.tools.javac.api.BasicJavacTask;
+import java.nio.file.InvalidPathException;
+import java.nio.file.Path;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * A compiler {@link Plugin} that analyzes and extracts relevant information for documentation
+ * purposes from processed files.
+ */
+// XXX: Find a better name for this class; it doesn't generate documentation per se.
+@AutoService(Plugin.class)
+public final class DocumentationGenerator implements Plugin {
+  @VisibleForTesting static final String OUTPUT_DIRECTORY_FLAG = "-XoutputDirectory";
+  private static final Pattern OUTPUT_DIRECTORY_FLAG_PATTERN =
+      Pattern.compile(Pattern.quote(OUTPUT_DIRECTORY_FLAG) + "=(.*)");
+
+  /** Instantiates a new {@link DocumentationGenerator} instance. */
+  public DocumentationGenerator() {}
+
+  @Override
+  public String getName() {
+    return getClass().getSimpleName();
+  }
+
+  @Override
+  public void init(JavacTask javacTask, String... args) {
+    checkArgument(args.length == 1, "Precisely one path must be provided");
+
+    javacTask.addTaskListener(
+        new DocumentationGeneratorTaskListener(
+            ((BasicJavacTask) javacTask).getContext(), getOutputPath(args[0])));
+  }
+
+  @VisibleForTesting
+  static Path getOutputPath(String pathArg) {
+    Matcher matcher = OUTPUT_DIRECTORY_FLAG_PATTERN.matcher(pathArg);
+    checkArgument(
+        matcher.matches(), "'%s' must be of the form '%s=<value>'", pathArg, OUTPUT_DIRECTORY_FLAG);
+
+    String path = matcher.group(1);
+    try {
+      return Path.of(path);
+    } catch (InvalidPathException e) {
+      throw new IllegalArgumentException(String.format("Invalid path '%s'", path), e);
+    }
+  }
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/DocumentationGeneratorTaskListener.java

@@ -0,0 +1,109 @@
+package tech.picnic.errorprone.documentation;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
+import com.fasterxml.jackson.annotation.PropertyAccessor;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.VisitorState;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.CompilationUnitTree;
+import com.sun.source.util.TaskEvent;
+import com.sun.source.util.TaskEvent.Kind;
+import com.sun.source.util.TaskListener;
+import com.sun.source.util.TreePath;
+import com.sun.tools.javac.api.JavacTrees;
+import com.sun.tools.javac.util.Context;
+import java.io.File;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.net.URI;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ServiceLoader;
+import javax.tools.JavaFileObject;
+
+/**
+ * A {@link TaskListener} that identifies and extracts relevant content for documentation generation
+ * and writes it to disk.
+ */
+// XXX: Find a better name for this class; it doesn't generate documentation per se.
+final class DocumentationGeneratorTaskListener implements TaskListener {
+  @SuppressWarnings({"rawtypes", "unchecked"})
+  private static final ImmutableList<Extractor<?>> EXTRACTORS =
+      (ImmutableList)
+          ImmutableList.copyOf(
+              ServiceLoader.load(
+                  Extractor.class, DocumentationGeneratorTaskListener.class.getClassLoader()));
+
+  private static final ObjectMapper OBJECT_MAPPER =
+      new ObjectMapper().setVisibility(PropertyAccessor.FIELD, Visibility.ANY);
+
+  private final Context context;
+  private final Path docsPath;
+
+  DocumentationGeneratorTaskListener(Context context, Path path) {
+    this.context = context;
+    this.docsPath = path;
+  }
+
+  @Override
+  public void started(TaskEvent taskEvent) {
+    if (taskEvent.getKind() == Kind.ANALYZE) {
+      createDocsDirectory();
+    }
+  }
+
+  @Override
+  public void finished(TaskEvent taskEvent) {
+    if (taskEvent.getKind() != Kind.ANALYZE) {
+      return;
+    }
+
+    JavaFileObject sourceFile = taskEvent.getSourceFile();
+    CompilationUnitTree compilationUnit = taskEvent.getCompilationUnit();
+    ClassTree classTree = JavacTrees.instance(context).getTree(taskEvent.getTypeElement());
+    if (sourceFile == null || compilationUnit == null || classTree == null) {
+      return;
+    }
+
+    VisitorState state =
+        VisitorState.createForUtilityPurposes(context)
+            .withPath(new TreePath(new TreePath(compilationUnit), classTree));
+
+    for (Extractor<?> extractor : EXTRACTORS) {
+      extractor
+          .tryExtract(classTree, state)
+          .ifPresent(
+              data ->
+                  writeToFile(
+                      extractor.identifier(), getSimpleClassName(sourceFile.toUri()), data));
+    }
+  }
+
+  private void createDocsDirectory() {
+    try {
+      Files.createDirectories(docsPath);
+    } catch (IOException e) {
+      throw new IllegalStateException(
+          String.format("Error while creating directory with path '%s'", docsPath), e);
+    }
+  }
+
+  private <T> void writeToFile(String identifier, String className, T data) {
+    File file = docsPath.resolve(String.format("%s-%s.json", identifier, className)).toFile();
+
+    try (FileWriter fileWriter = new FileWriter(file, UTF_8)) {
+      OBJECT_MAPPER.writeValue(fileWriter, data);
+    } catch (IOException e) {
+      throw new UncheckedIOException(String.format("Cannot write to file '%s'", file.getPath()), e);
+    }
+  }
+
+  private static String getSimpleClassName(URI path) {
+    return Paths.get(path).getFileName().toString().replace(".java", "");
+  }
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/Extractor.java

@@ -0,0 +1,33 @@
+package tech.picnic.errorprone.documentation;
+
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.annotations.Immutable;
+import com.sun.source.tree.ClassTree;
+import java.util.Optional;
+
+/**
+ * Interface implemented by classes that define how to extract data of some type {@link T} from a
+ * given {@link ClassTree}.
+ *
+ * @param <T> The type of data that is extracted.
+ */
+@Immutable
+interface Extractor<T> {
+  /**
+   * Returns the unique identifier of this extractor.
+   *
+   * @return A non-{@code null} string.
+   */
+  String identifier();
+
+  /**
+   * Attempts to extract an instance of type {@link T} using the provided arguments.
+   *
+   * @param tree The {@link ClassTree} to analyze and from which to extract an instance of type
+   *     {@link T}.
+   * @param state A {@link VisitorState} describing the context in which the given {@link ClassTree}
+   *     is found.
+   * @return An instance of type {@link T}, if possible.
+   */
+  Optional<T> tryExtract(ClassTree tree, VisitorState state);
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/RefasterTestInputExtractor.java

@@ -0,0 +1,65 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.annotations.Immutable;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.MethodTree;
+import java.util.Optional;
+import java.util.regex.Pattern;
+import tech.picnic.errorprone.documentation.models.RefasterTemplateCollectionTestData;
+import tech.picnic.errorprone.documentation.models.RefasterTemplateTestData;
+
+@Immutable
+@AutoService(Extractor.class)
+public final class RefasterTestInputExtractor
+    implements Extractor<RefasterTemplateCollectionTestData> {
+  private static final Pattern TEST_CLASS_NAME_PATTERN = Pattern.compile("(.*)Test");
+
+  @Override
+  public String identifier() {
+    return "refaster-test-input";
+  }
+
+  @Override
+  public Optional<RefasterTemplateCollectionTestData> tryExtract(
+      ClassTree tree, VisitorState state) {
+    if (!state.getPath().getCompilationUnit().getPackageName().toString().contains("input")) {
+      return Optional.empty();
+    }
+
+    Optional<String> className = getClassUnderTest(tree);
+    if (className.isEmpty()) {
+      return Optional.empty();
+    }
+
+    ImmutableList<RefasterTemplateTestData> templateTests =
+        tree.getMembers().stream()
+            .filter(m -> m instanceof MethodTree)
+            .map(MethodTree.class::cast)
+            .filter(m -> m.getName().toString().startsWith("test"))
+            .map(
+                m ->
+                    RefasterTemplateTestData.create(
+                        m.getName().toString().replace("test", ""), getSourceCode(m, state)))
+            .collect(toImmutableList());
+
+    return Optional.of(
+        RefasterTemplateCollectionTestData.create(className.orElseThrow(), true, templateTests));
+  }
+
+  private static Optional<String> getClassUnderTest(ClassTree tree) {
+    return Optional.of(TEST_CLASS_NAME_PATTERN.matcher(tree.getSimpleName().toString()))
+        .filter(java.util.regex.Matcher::matches)
+        .map(m -> m.group(1));
+  }
+
+  // XXX: Duplicated from `SourceCode`. Can we do better?
+  private String getSourceCode(MethodTree tree, VisitorState state) {
+    String src = state.getSourceForNode(tree);
+    return src != null ? src : tree.toString();
+  }
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/RefasterTestOutputExtractor.java

@@ -0,0 +1,65 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.annotations.Immutable;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.MethodTree;
+import java.util.Optional;
+import java.util.regex.Pattern;
+import tech.picnic.errorprone.documentation.models.RefasterTemplateCollectionTestData;
+import tech.picnic.errorprone.documentation.models.RefasterTemplateTestData;
+
+@Immutable
+@AutoService(Extractor.class)
+public final class RefasterTestOutputExtractor
+    implements Extractor<RefasterTemplateCollectionTestData> {
+  private static final Pattern TEST_CLASS_NAME_PATTERN = Pattern.compile("(.*)Test");
+
+  @Override
+  public String identifier() {
+    return "refaster-test-output";
+  }
+
+  @Override
+  public Optional<RefasterTemplateCollectionTestData> tryExtract(
+      ClassTree tree, VisitorState state) {
+    if (!state.getPath().getCompilationUnit().getPackageName().toString().contains("output")) {
+      return Optional.empty();
+    }
+
+    Optional<String> className = getClassUnderTest(tree);
+    if (className.isEmpty()) {
+      return Optional.empty();
+    }
+
+    ImmutableList<RefasterTemplateTestData> templateTests =
+        tree.getMembers().stream()
+            .filter(m -> m instanceof MethodTree)
+            .map(MethodTree.class::cast)
+            .filter(m -> m.getName().toString().startsWith("test"))
+            .map(
+                m ->
+                    RefasterTemplateTestData.create(
+                        m.getName().toString().replace("test", ""), getSourceCode(m, state)))
+            .collect(toImmutableList());
+
+    return Optional.of(
+        RefasterTemplateCollectionTestData.create(className.orElseThrow(), true, templateTests));
+  }
+
+  private static Optional<String> getClassUnderTest(ClassTree tree) {
+    return Optional.of(TEST_CLASS_NAME_PATTERN.matcher(tree.getSimpleName().toString()))
+        .filter(java.util.regex.Matcher::matches)
+        .map(m -> m.group(1));
+  }
+
+  // XXX: Duplicated from `SourceCode`. Can we do better?
+  private String getSourceCode(MethodTree tree, VisitorState state) {
+    String src = state.getSourceForNode(tree);
+    return src != null ? src : tree.toString();
+  }
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/models/RefasterTemplateCollectionData.java

@@ -0,0 +1,25 @@
+package tech.picnic.errorprone.documentation.models;
+
+import com.google.auto.value.AutoValue;
+import java.util.List;
+import tech.picnic.errorprone.documentation.models.AutoValue_RefasterTemplateCollectionData;
+
+/**
+ * Object containing all data related to a Refaster template collection. This is solely used for
+ * serialization.
+ */
+@AutoValue
+public abstract class RefasterTemplateCollectionData {
+  public static RefasterTemplateCollectionData create(
+      String name, String description, String link, List<RefasterTemplateData> templates) {
+    return new AutoValue_RefasterTemplateCollectionData(name, description, link, templates);
+  }
+
+  abstract String name();
+
+  abstract String description();
+
+  abstract String link();
+
+  abstract List<RefasterTemplateData> templates();
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/models/RefasterTemplateCollectionTestData.java

@@ -0,0 +1,20 @@
+package tech.picnic.errorprone.documentation.models;
+
+import com.google.auto.value.AutoValue;
+import java.util.List;
+import tech.picnic.errorprone.documentation.models.AutoValue_RefasterTemplateCollectionTestData;
+
+@AutoValue
+public abstract class RefasterTemplateCollectionTestData {
+  public static RefasterTemplateCollectionTestData create(
+      String templateCollection, boolean isInput, List<RefasterTemplateTestData> templatesTests) {
+    return new AutoValue_RefasterTemplateCollectionTestData(
+        templateCollection, isInput, templatesTests);
+  }
+
+  abstract String templateCollection();
+
+  abstract boolean isInput();
+
+  abstract List<RefasterTemplateTestData> templateTests();
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/models/RefasterTemplateData.java

@@ -0,0 +1,21 @@
+package tech.picnic.errorprone.documentation.models;
+
+import com.google.auto.value.AutoValue;
+import com.google.errorprone.BugPattern.SeverityLevel;
+import tech.picnic.errorprone.documentation.models.AutoValue_RefasterTemplateData;
+
+@AutoValue
+public abstract class RefasterTemplateData {
+  public static RefasterTemplateData create(
+      String name, String description, String link, SeverityLevel severityLevel) {
+    return new AutoValue_RefasterTemplateData(name, description, link, severityLevel);
+  }
+
+  abstract String name();
+
+  abstract String description();
+
+  abstract String link();
+
+  abstract SeverityLevel severityLevel();
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/models/RefasterTemplateTestData.java

@@ -0,0 +1,15 @@
+package tech.picnic.errorprone.documentation.models;
+
+import com.google.auto.value.AutoValue;
+import tech.picnic.errorprone.documentation.models.AutoValue_RefasterTemplateTestData;
+
+@AutoValue
+public abstract class RefasterTemplateTestData {
+  public static RefasterTemplateTestData create(String templateName, String templateTestContent) {
+    return new AutoValue_RefasterTemplateTestData(templateName, templateTestContent);
+  }
+
+  abstract String templateName();
+
+  abstract String templateTestContent();
+}

documentation-support/src/main/java/tech/picnic/errorprone/documentation/package-info.java

@@ -0,0 +1,7 @@
+/**
+ * A Java compiler plugin that extracts data from compiled classes, in support of the Error Prone
+ * Support documentation.
+ */
+@com.google.errorprone.annotations.CheckReturnValue
+@org.jspecify.annotations.NullMarked
+package tech.picnic.errorprone.documentation;

documentation-support/src/test/java/tech/picnic/errorprone/documentation/BugPatternExtractorTest.java

@@ -0,0 +1,148 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.io.Resources;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.CompilationTestHelper;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.sun.source.tree.ClassTree;
+import java.io.IOException;
+import java.nio.file.Path;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+final class BugPatternExtractorTest {
+  @Test
+  void noBugPattern(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerWithoutAnnotation.java",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "public final class TestCheckerWithoutAnnotation extends BugChecker {}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void minimalBugPattern(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "MinimalBugChecker.java",
+        "package pkg;",
+        "",
+        "import com.google.errorprone.BugPattern;",
+        "import com.google.errorprone.BugPattern.SeverityLevel;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "@BugPattern(summary = \"MinimalBugChecker summary\", severity = SeverityLevel.ERROR)",
+        "public final class MinimalBugChecker extends BugChecker {}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-MinimalBugChecker.json",
+        "bugpattern-documentation-minimal.json");
+  }
+
+  @Test
+  void completeBugPattern(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "CompleteBugChecker.java",
+        "package pkg;",
+        "",
+        "import com.google.errorprone.BugPattern;",
+        "import com.google.errorprone.BugPattern.SeverityLevel;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import org.junit.jupiter.api.Test;",
+        "",
+        "@BugPattern(",
+        "    name = \"OtherName\",",
+        "    summary = \"CompleteBugChecker summary\",",
+        "    linkType = BugPattern.LinkType.CUSTOM,",
+        "    link = \"https://error-prone.picnic.tech\",",
+        "    explanation = \"Example explanation\",",
+        "    severity = SeverityLevel.SUGGESTION,",
+        "    altNames = \"Check\",",
+        "    tags = BugPattern.StandardTags.SIMPLIFICATION,",
+        "    disableable = false,",
+        "    suppressionAnnotations = {BugPattern.class, Test.class})",
+        "public final class CompleteBugChecker extends BugChecker {}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-CompleteBugChecker.json",
+        "bugpattern-documentation-complete.json");
+  }
+
+  @Test
+  void undocumentedSuppressionBugPattern(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "UndocumentedSuppressionBugPattern.java",
+        "package pkg;",
+        "",
+        "import com.google.errorprone.BugPattern;",
+        "import com.google.errorprone.BugPattern.SeverityLevel;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "@BugPattern(",
+        "    summary = \"UndocumentedSuppressionBugPattern summary\",",
+        "    severity = SeverityLevel.WARNING,",
+        "    documentSuppression = false)",
+        "public final class UndocumentedSuppressionBugPattern extends BugChecker {}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-UndocumentedSuppressionBugPattern.json",
+        "bugpattern-documentation-undocumented-suppression.json");
+  }
+
+  @Test
+  void bugPatternAnnotationIsAbsent() {
+    CompilationTestHelper.newInstance(TestChecker.class, getClass())
+        .addSourceLines(
+            "TestChecker.java",
+            "import com.google.errorprone.bugpatterns.BugChecker;",
+            "",
+            "// BUG: Diagnostic contains: Can extract: false",
+            "public final class TestChecker extends BugChecker {}")
+        .doTest();
+  }
+
+  private static void verifyFileMatchesResource(
+      Path outputDirectory, String fileName, String resourceName) throws IOException {
+    assertThat(outputDirectory.resolve(fileName))
+        .content(UTF_8)
+        .isEqualToIgnoringWhitespace(getResource(resourceName));
+  }
+
+  // XXX: Once we support only JDK 15+, drop this method in favour of including the resources as
+  // text blocks in this class. (This also requires renaming the `verifyFileMatchesResource`
+  // method.)
+  private static String getResource(String resourceName) throws IOException {
+    return Resources.toString(
+        Resources.getResource(BugPatternExtractorTest.class, resourceName), UTF_8);
+  }
+
+  /** A {@link BugChecker} that validates the {@link BugPatternExtractor}. */
+  @BugPattern(summary = "Validates `BugPatternExtractor` extraction", severity = ERROR)
+  public static final class TestChecker extends BugChecker implements ClassTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchClass(ClassTree tree, VisitorState state) {
+      return buildDescription(tree)
+          .setMessage(
+              String.format(
+                  "Can extract: %s", new BugPatternExtractor().tryExtract(tree, state).isPresent()))
+          .build();
+    }
+  }
+}

documentation-support/src/test/java/tech/picnic/errorprone/documentation/BugPatternTestExtractorTest.java

@@ -0,0 +1,352 @@
+package tech.picnic.errorprone.documentation;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.io.Resources;
+import java.io.IOException;
+import java.nio.file.Path;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+final class BugPatternTestExtractorTest {
+  @Test
+  void noBugPatternTest(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerWithoutAnnotation.java",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "public final class TestCheckerWithoutAnnotation extends BugChecker {}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void bugPatternTestFileWithoutTestSuffix(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerWithWrongSuffix.java",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "",
+        "final class TestCheckerWithoutTestSuffix {",
+        "  private static class TestCheckerWithout extends BugChecker {}",
+        "",
+        "  CompilationTestHelper compilationTestHelper = CompilationTestHelper.newInstance(TestCheckerWithout.class, getClass());",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void minimalBugPatternTest(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  CompilationTestHelper compilationTestHelper = CompilationTestHelper.newInstance(TestChecker.class, getClass());",
+        "}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-test-TestCheckerTest.json",
+        "bugpattern-test-documentation-minimal.json");
+  }
+
+  @Test
+  void differentBugPatternAsClassVariableTest(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class DifferentChecker extends BugChecker {}",
+        "",
+        "  CompilationTestHelper compilationTestHelper = CompilationTestHelper.newInstance(DifferentChecker.class, getClass());",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void differentBugPatternAsLocalVariable(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import org.junit.jupiter.api.Test;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class DifferentChecker extends BugChecker {}",
+        "",
+        "  @Test",
+        "  void identification() {",
+        "    CompilationTestHelper.newInstance(DifferentChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"class A {}\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void bugPatternTestSingleIdentification(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import org.junit.jupiter.api.Test;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  @Test",
+        "  void identification() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"class A {}\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-test-TestCheckerTest.json",
+        "bugpattern-test-documentation-identification.json");
+  }
+
+  @Test
+  void bugPatternTestIdentificationMultipleSourceLines(@TempDir Path outputDirectory)
+      throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "package pkg;",
+        "",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import org.junit.jupiter.api.Test;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  @Test",
+        "  void identification() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"class A {}\")",
+        "        .addSourceLines(\"B.java\", \"class B {}\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-test-TestCheckerTest.json",
+        "bugpattern-test-documentation-identification-two-sources.json");
+  }
+
+  @Test
+  void bugPatternTestSingleReplacement(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import org.junit.jupiter.api.Test;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  @Test",
+        "  void replacement() {",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A {}\")",
+        "        .doTest(TestMode.TEXT_MATCH);",
+        "  }",
+        "}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-test-TestCheckerTest.json",
+        "bugpattern-test-documentation-replacement.json");
+  }
+
+  @Test
+  void bugPatternTestMultipleReplacementSources(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import org.junit.jupiter.api.Test;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  @Test",
+        "  void replacement() {",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A {}\")",
+        "        .addInputLines(\"B.java\", \"class B {}\")",
+        "        .addOutputLines(\"B.java\", \"class B {}\")",
+        "        .doTest(TestMode.TEXT_MATCH);",
+        "  }",
+        "}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-test-TestCheckerTest.json",
+        "bugpattern-test-documentation-replacement-two-sources.json");
+  }
+
+  @Test
+  void bugPatternReplacementExpectUnchanged(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import org.junit.jupiter.api.Test;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  @Test",
+        "  void replacement() {",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .expectUnchanged()",
+        "        .doTest(TestMode.TEXT_MATCH);",
+        "  }",
+        "}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-test-TestCheckerTest.json",
+        "bugpattern-test-documentation-replacement-expect-unchanged.json");
+  }
+
+  @Test
+  void bugPatternTestIdentificationAndReplacement(@TempDir Path outputDirectory)
+      throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import org.junit.jupiter.api.Test;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  @Test",
+        "  void identification() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"class A {}\")",
+        "        .doTest();",
+        "  }",
+        "",
+        "  @Test",
+        "  void replacement() {",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A {}\")",
+        "        .doTest(TestMode.TEXT_MATCH);",
+        "  }",
+        "}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-test-TestCheckerTest.json",
+        "bugpattern-test-documentation-identification-and-replacement.json");
+  }
+
+  @Test
+  void bugPatternTestMultipleIdentificationAndReplacement(@TempDir Path outputDirectory)
+      throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "package pkg;",
+        "",
+        "import static com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers.SECOND;",
+        "",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import org.junit.jupiter.api.Test;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  @Test",
+        "  void identification() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"class A {}\")",
+        "        .doTest();",
+        "  }",
+        "",
+        "  @Test",
+        "  void identification2() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(\"B.java\", \"class B {}\")",
+        "        .doTest();",
+        "  }",
+        "",
+        "  @Test",
+        "  void replacementFirstSuggestedFix() {",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A {}\")",
+        "        .doTest(TestMode.TEXT_MATCH);",
+        "  }",
+        "",
+        "  @Test",
+        "  void replacementSecondSuggestedFix() {",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .setFixChooser(SECOND)",
+        "        .addInputLines(\"B.java\", \"class B {}\")",
+        "        .addOutputLines(\"B.java\", \"class B {}\")",
+        "        .doTest(TestMode.TEXT_MATCH);",
+        "  }",
+        "}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-test-TestCheckerTest.json",
+        "bugpattern-test-documentation-multiple-identification-and-replacement.json");
+  }
+
+  private static void verifyFileMatchesResource(
+      Path outputDirectory, String fileName, String resourceName) throws IOException {
+    assertThat(outputDirectory.resolve(fileName))
+        .content(UTF_8)
+        .isEqualToIgnoringWhitespace(getResource(resourceName));
+  }
+
+  // XXX: Once we support only JDK 15+, drop this method in favour of including the resources as
+  // text blocks in this class. (This also requires renaming the `verifyFileMatchesResource`
+  // method.)
+  private static String getResource(String resourceName) throws IOException {
+    return Resources.toString(
+        Resources.getResource(BugPatternTestExtractorTest.class, resourceName), UTF_8);
+  }
+}

documentation-support/src/test/java/tech/picnic/errorprone/documentation/Compilation.java

@@ -0,0 +1,45 @@
+package tech.picnic.errorprone.documentation;
+
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.FileManagers;
+import com.google.errorprone.FileObjects;
+import com.sun.tools.javac.api.JavacTaskImpl;
+import com.sun.tools.javac.api.JavacTool;
+import com.sun.tools.javac.file.JavacFileManager;
+import java.nio.file.Path;
+import javax.tools.JavaCompiler;
+import javax.tools.JavaFileObject;
+
+// XXX: Generalize and move this class so that it can also be used by `refaster-compiler`.
+// XXX: Add support for this class to the `ErrorProneTestHelperSourceFormat` check.
+public final class Compilation {
+  private Compilation() {}
+
+  public static void compileWithDocumentationGenerator(
+      Path outputDirectory, String fileName, String... lines) {
+    compileWithDocumentationGenerator(outputDirectory.toAbsolutePath().toString(), fileName, lines);
+  }
+
+  public static void compileWithDocumentationGenerator(
+      String outputDirectory, String fileName, String... lines) {
+    compile(
+        ImmutableList.of("-Xplugin:DocumentationGenerator -XoutputDirectory=" + outputDirectory),
+        FileObjects.forSourceLines(fileName, lines));
+  }
+
+  private static void compile(ImmutableList<String> options, JavaFileObject javaFileObject) {
+    JavacFileManager javacFileManager = FileManagers.testFileManager();
+    JavaCompiler compiler = JavacTool.create();
+    JavacTaskImpl task =
+        (JavacTaskImpl)
+            compiler.getTask(
+                null,
+                javacFileManager,
+                null,
+                options,
+                ImmutableList.of(),
+                ImmutableList.of(javaFileObject));
+
+    task.call();
+  }
+}

documentation-support/src/test/java/tech/picnic/errorprone/documentation/DocumentationGeneratorTaskListenerTest.java

@@ -0,0 +1,138 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static java.nio.file.attribute.AclEntryPermission.ADD_SUBDIRECTORY;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.junit.jupiter.api.condition.OS.WINDOWS;
+
+import com.google.auto.service.AutoService;
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Sets;
+import com.google.common.collect.Streams;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.annotations.Immutable;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.Tree;
+import java.io.IOException;
+import java.nio.file.FileSystemException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.attribute.AclEntry;
+import java.nio.file.attribute.AclFileAttributeView;
+import java.util.Optional;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.DisabledOnOs;
+import org.junit.jupiter.api.condition.EnabledOnOs;
+import org.junit.jupiter.api.io.TempDir;
+
+final class DocumentationGeneratorTaskListenerTest {
+  @EnabledOnOs(WINDOWS)
+  @Test
+  void readOnlyFileSystemWindows(@TempDir Path outputDirectory) throws IOException {
+    AclFileAttributeView view =
+        Files.getFileAttributeView(outputDirectory, AclFileAttributeView.class);
+    view.setAcl(
+        view.getAcl().stream()
+            .map(
+                entry ->
+                    AclEntry.newBuilder(entry)
+                        .setPermissions(
+                            Sets.difference(entry.permissions(), ImmutableSet.of(ADD_SUBDIRECTORY)))
+                        .build())
+            .collect(toImmutableList()));
+
+    readOnlyFileSystemFailsToWrite(outputDirectory.resolve("nonexistent"));
+  }
+
+  @DisabledOnOs(WINDOWS)
+  @Test
+  void readOnlyFileSystemNonWindows(@TempDir Path outputDirectory) {
+    assertThat(outputDirectory.toFile().setWritable(false))
+        .describedAs("Failed to make test directory unwritable")
+        .isTrue();
+
+    readOnlyFileSystemFailsToWrite(outputDirectory.resolve("nonexistent"));
+  }
+
+  private static void readOnlyFileSystemFailsToWrite(Path outputDirectory) {
+    assertThatThrownBy(
+            () ->
+                Compilation.compileWithDocumentationGenerator(
+                    outputDirectory, "A.java", "class A {}"))
+        .hasRootCauseInstanceOf(FileSystemException.class)
+        .hasCauseInstanceOf(IllegalStateException.class)
+        .hasMessageEndingWith("Error while creating directory with path '%s'", outputDirectory);
+  }
+
+  @Test
+  void noClassNoOutput(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(outputDirectory, "A.java", "package pkg;");
+
+    assertThat(outputDirectory).isEmptyDirectory();
+  }
+
+  @Test
+  void excessArguments(@TempDir Path outputDirectory) {
+    assertThatThrownBy(
+            () ->
+                Compilation.compileWithDocumentationGenerator(
+                    outputDirectory.toAbsolutePath() + " extra-arg", "A.java", "package pkg;"))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessage("Precisely one path must be provided");
+  }
+
+  @Test
+  void extraction(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "DocumentationGeneratorTaskListenerTestClass.java",
+        "class DocumentationGeneratorTaskListenerTestClass {}");
+
+    // XXX: Once we support only JDK 15+, use a text block for the `expected` string.
+    assertThat(
+            outputDirectory.resolve(
+                "documentation-generator-task-listener-test-DocumentationGeneratorTaskListenerTestClass.json"))
+        .content(UTF_8)
+        .isEqualToIgnoringWhitespace(
+            "{\"className\":\"DocumentationGeneratorTaskListenerTestClass\",\"path\":[\"CLASS: DocumentationGeneratorTaskListenerTestClass\",\"COMPILATION_UNIT\"]}");
+  }
+
+  @Immutable
+  @AutoService(Extractor.class)
+  public static final class TestExtractor implements Extractor<ExtractionParameters> {
+    @Override
+    public String identifier() {
+      return "documentation-generator-task-listener-test";
+    }
+
+    @Override
+    public Optional<ExtractionParameters> tryExtract(ClassTree tree, VisitorState state) {
+      return Optional.of(tree.getSimpleName().toString())
+          .filter(n -> n.contains(DocumentationGeneratorTaskListenerTest.class.getSimpleName()))
+          .map(
+              className ->
+                  new AutoValue_DocumentationGeneratorTaskListenerTest_ExtractionParameters(
+                      className,
+                      Streams.stream(state.getPath())
+                          .map(TestExtractor::describeTree)
+                          .collect(toImmutableList())));
+    }
+
+    private static String describeTree(Tree tree) {
+      return (tree instanceof ClassTree)
+          ? String.join(": ", String.valueOf(tree.getKind()), ((ClassTree) tree).getSimpleName())
+          : tree.getKind().toString();
+    }
+  }
+
+  @AutoValue
+  abstract static class ExtractionParameters {
+    abstract String className();
+
+    abstract ImmutableList<String> path();
+  }
+}

documentation-support/src/test/java/tech/picnic/errorprone/documentation/DocumentationGeneratorTest.java

@@ -0,0 +1,38 @@
+package tech.picnic.errorprone.documentation;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static tech.picnic.errorprone.documentation.DocumentationGenerator.OUTPUT_DIRECTORY_FLAG;
+
+import java.nio.file.InvalidPathException;
+import java.nio.file.Path;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+final class DocumentationGeneratorTest {
+  @ParameterizedTest
+  @ValueSource(strings = {"bar", "foo"})
+  void getOutputPath(String path) {
+    assertThat(DocumentationGenerator.getOutputPath(OUTPUT_DIRECTORY_FLAG + '=' + path))
+        .isEqualTo(Path.of(path));
+  }
+
+  @ParameterizedTest
+  @ValueSource(strings = {"", "-XoutputDirectory", "invalidOption=Test", "nothing"})
+  void getOutputPathWithInvalidArgument(String pathArg) {
+    assertThatThrownBy(() -> DocumentationGenerator.getOutputPath(pathArg))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessage("'%s' must be of the form '%s=<value>'", pathArg, OUTPUT_DIRECTORY_FLAG);
+  }
+
+  @Test
+  void getOutputPathWithInvalidPath() {
+    String basePath = "path-with-null-char-\0";
+    assertThatThrownBy(
+            () -> DocumentationGenerator.getOutputPath(OUTPUT_DIRECTORY_FLAG + '=' + basePath))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasCauseInstanceOf(InvalidPathException.class)
+        .hasMessageEndingWith("Invalid path '%s'", basePath);
+  }
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-documentation-complete.json

@@ -0,0 +1,19 @@
+{
+  "fullyQualifiedName": "pkg.CompleteBugChecker",
+  "name": "OtherName",
+  "altNames": [
+    "Check"
+  ],
+  "link": "https://error-prone.picnic.tech",
+  "tags": [
+    "Simplification"
+  ],
+  "summary": "CompleteBugChecker summary",
+  "explanation": "Example explanation",
+  "severityLevel": "SUGGESTION",
+  "canDisable": false,
+  "suppressionAnnotations": [
+    "com.google.errorprone.BugPattern",
+    "org.junit.jupiter.api.Test"
+  ]
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-documentation-minimal.json

@@ -0,0 +1,14 @@
+{
+  "fullyQualifiedName": "pkg.MinimalBugChecker",
+  "name": "MinimalBugChecker",
+  "altNames": [],
+  "link": "",
+  "tags": [],
+  "summary": "MinimalBugChecker summary",
+  "explanation": "",
+  "severityLevel": "ERROR",
+  "canDisable": true,
+  "suppressionAnnotations": [
+    "java.lang.SuppressWarnings"
+  ]
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-documentation-undocumented-suppression.json

@@ -0,0 +1,12 @@
+{
+  "fullyQualifiedName": "pkg.UndocumentedSuppressionBugPattern",
+  "name": "UndocumentedSuppressionBugPattern",
+  "altNames": [],
+  "link": "",
+  "tags": [],
+  "summary": "UndocumentedSuppressionBugPattern summary",
+  "explanation": "",
+  "severityLevel": "WARNING",
+  "canDisable": true,
+  "suppressionAnnotations": []
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-test-documentation-identification-and-replacement.json

@@ -0,0 +1,12 @@
+{
+  "name": "TestChecker",
+  "identificationTests": [
+    "class A {}\n"
+  ],
+  "replacementTests": [
+    {
+      "inputLines": "class A {}\n",
+      "outputLines": "class A {}\n"
+    }
+  ]
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-test-documentation-identification-two-sources.json

@@ -0,0 +1,8 @@
+{
+  "name": "TestChecker",
+  "identificationTests": [
+    "class B {}\n",
+    "class A {}\n"
+  ],
+  "replacementTests": []
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-test-documentation-identification.json

@@ -0,0 +1,7 @@
+{
+  "name": "TestChecker",
+  "identificationTests": [
+    "class A {}\n"
+  ],
+  "replacementTests": []
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-test-documentation-minimal.json

@@ -0,0 +1,5 @@
+{
+  "name": "TestChecker",
+  "identificationTests": [],
+  "replacementTests": []
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-test-documentation-multiple-identification-and-replacement.json

@@ -0,0 +1,17 @@
+{
+  "name": "TestChecker",
+  "identificationTests": [
+    "class A {}\n",
+    "class B {}\n"
+  ],
+  "replacementTests": [
+    {
+      "inputLines": "class A {}\n",
+      "outputLines": "class A {}\n"
+    },
+    {
+      "inputLines": "class B {}\n",
+      "outputLines": "class B {}\n"
+    }
+  ]
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-test-documentation-replacement-expect-unchanged.json

@@ -0,0 +1,5 @@
+{
+  "name": "TestChecker",
+  "identificationTests": [],
+  "replacementTests": []
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-test-documentation-replacement-two-sources.json

@@ -0,0 +1,14 @@
+{
+  "name": "TestChecker",
+  "identificationTests": [],
+  "replacementTests": [
+    {
+      "inputLines": "class B {}\n",
+      "outputLines": "class B {}\n"
+    },
+    {
+      "inputLines": "class A {}\n",
+      "outputLines": "class A {}\n"
+    }
+  ]
+}

documentation-support/src/test/resources/tech/picnic/errorprone/documentation/bugpattern-test-documentation-replacement.json

@@ -0,0 +1,10 @@
+{
+  "name": "TestChecker",
+  "identificationTests": [],
+  "replacementTests": [
+    {
+      "inputLines": "class A {}\n",
+      "outputLines": "class A {}\n"
+    }
+  ]
+}

error-prone-contrib/README.md

@@ -11,71 +11,22 @@ request.
 
 ### Building
 
-This is a [Maven][maven] project, so running `mvn clean install` performs a
-full clean build. Some relevant flags:
-- `-Dverification.warn` makes the warnings and errors emitted by various
-  plugins and the Java compiler non-fatal, where possible.
-- `-Dverification.skip` disables various non-essential plugins and compiles the
-  code with minimal checks (i.e. without linting, Error Prone checks, etc.)
-- `-Dversion.error-prone=some-version` runs the build using the specified
-  version of Error Prone. This is useful e.g. when testing a locally built
-  Error Prone SNAPSHOT.
-- `-Perror-prone-fork` run the build using Picnic's [Error Prone
-  fork][error-prone-fork-repo], hosted on [Jitpack][error-prone-fork-jitpack].
-  This fork generally contains a few changes on top of the latest Error Prone
-  release.
-
-Two other goals that one may find relevant:
-- `mvn fmt:format` formats the code using
-  [`google-java-format`][google-java-format].
-- `mvn pitest:mutationCoverage` runs mutation tests using [PIT][pitest]. The
-  results can be reviewed by opening the respective
-  `target/pit-reports/index.html` files. For more information check the [PIT
-  Maven plugin][pitest-maven].
-
-When loading the project in IntelliJ IDEA (and perhaps other IDEs) errors about
-the inaccessibility of `com.sun.tools.javac.*` classes may be reported. If this
-happens, configure your IDE to enable the `add-exports` profile.
+See the main [readme][main-readme].
 
 ### Contribution guidelines
 
-To the extend possible, the pull request process guards our coding guidelines.
-Some pointers:
-- Checks should we _topical_: Ideally they address a single concern.
-- Where possible checks should provide _fixes_, and ideally these are
-  completely behavior preserving. In order for a check to be adopted by users
-  it must not "get in the way". So for a check which addresses a relatively
-  trivial stylistic concern it is doubly important that the violations it
-  detects can be auto-patched.
-- Make sure you have read Error Prone's [criteria for new
-  checks][error-prone-criteria]. Most guidelines described there apply to this
-  project as well, except that this project _does_ focus quite heavy on style
-  enforcement. But that just makes the previous point doubly important.
-- Make sure that a check's (mutation) coverage is or remains about as high as
-  it can be. Not only does this lead to better tests, it also points out
-  opportunities to simplify the code.
-- Please restrict the scope of a pull request to a single feature or fix. Don't
-  sneak in unrelated changes.
-- When in doubt about whether a pull request will be accepted, please first
-  file an issue to discuss it.
+See our [contributing guidelines][main-contributing].
 
 ### Our wishlist
 
 We expect the following tasks to help improve the quality of this open source
 project:
 
-- Publish the artifact to Maven Central, then document the coordinates in this
-  `README.md`.
-- Document how to enable the checks.
 - Document how to apply patches.
 - Document each of the checks.
-- Add Travis CI, [SonarQube][sonarcloud] and [Codecov][codecov]
-  integrations.
-- Investigate whether it makes sense to include license headers in each file.
-  If so, set that up and enforce it.
+- Add [SonarQube][sonarcloud] and [Codecov][codecov] integrations.
 - Add non-Java file formatting support, like we have internally at Picnic.
   (I.e., somehow open-source that stuff.)
-- Add relevant "badges" at the top of this `README.md`.
 - Auto-generate a website listing each of the checks, just like the Error Prone
   [bug patterns page][error-prone-bug-patterns]. The [Error Prone
   repository][error-prone-repo] contains code for this.
@@ -93,7 +44,7 @@ project:
 - Improve an existing check (see `XXX`-marked comments in the code) or write a
   new one (see the list of suggestions below).
 
-### Ideas for new checks
+### BugChecker extension ideas
 
 The following is a list of checks we'd like to see implemented:
 
@@ -103,7 +54,7 @@ The following is a list of checks we'd like to see implemented:
   signature groups. Using Error Prone's method matchers forbidden method calls
   can easily be identified. But Error Prone can go one step further by
   auto-patching violations. For each violation two fixes can be proposed: a
-  purely behavior-preserving fix which makes the platform-dependent behavior
+  purely behavior-preserving fix, which makes the platform-dependent behavior
   explicit, and another which replaces the platform-dependent behavior with the
   preferred alternative. (Such as using `UTF-8` instead of the system default
   charset.)
@@ -113,128 +64,128 @@ The following is a list of checks we'd like to see implemented:
   functionality.
 - A subset of the refactor operations provided by the Eclipse-specific
   [AutoRefactor][autorefactor] plugin.
-- A check which replaces fully qualified types with simple types in contexts
+- A check that replaces fully qualified types with simple types in contexts
   where this does not introduce ambiguity. Should consider both actual Java
   code and Javadoc `@link` references.
-- A check which simplifies array expressions. It would replace empty array
+- A check that simplifies array expressions. It would replace empty array
   expressions of the form `new int[] {}` with `new int[0]`. Statements of the
   form `byte[] arr = new byte[] {'c'};` would be shortened to `byte[] arr =
   {'c'};`.
-- A check which replaces expressions of the form `String.format("some prefix
+- A check that replaces expressions of the form `String.format("some prefix
   %s", arg)` with `"some prefix " + arg`, and similar for simple suffixes. Can
   perhaps be generalized further, though it's unclear how far. (Well, a
   `String.format` call without arguments can certainly be simplified, too.)
-- A check which replaces single-character strings with `char`s where possible.
+- A check that replaces single-character strings with `char`s where possible.
   For example as argument to `StringBuilder.append` and in string
   concatenations.
-- A check which adds or removes the first `Locale` argument to `String.format`
+- A check that adds or removes the first `Locale` argument to `String.format`
   and similar calls as necessary. (For example, a format string containing only
   `%s` placeholders is locale-insensitive unless any of the arguments is a
   `Formattable`, while `%f` placeholders _are_ locale-sensitive.)
-- A check which replaces `String.replaceAll` with `String.replace` if the first
+- A check that replaces `String.replaceAll` with `String.replace` if the first
   argument is certainly not a regular expression. And if both arguments are
   single-character strings then the `(char, char)` overload can be invoked
   instead.
-- A check which flags (and ideally, replaces) `try-finally` constructs with
+- A check that flags (and ideally, replaces) `try-finally` constructs with
   equivalent `try-with-resources` constructs.
-- A check which drops exceptions declared in `throws` clauses if they are (a)
+- A check that drops exceptions declared in `throws` clauses if they are (a)
   not actually thrown and (b) the associated method cannot be overridden.
-- A check which tries to statically import certain methods whenever used, if
+- A check that tries to statically import certain methods whenever used, if
   possible. The set of targeted methods should be configurable, but may default
   to e.g. `java.util.Function.identity()`, the static methods exposed by
   `java.util.stream.Collectors` and the various Guava collector factory
   methods.
-- A check which replaces `new Random().someMethod()` calls with
-  `ThreadLocalRandom.current().someMethod()` calls, so as to avoid unnecessary
+- A check that replaces `new Random().someMethod()` calls with
+  `ThreadLocalRandom.current().someMethod()` calls, to avoid unnecessary
   synchronization.
-- A check which drops `this.` from `this.someMethod()` calls and which
+- A check that drops `this.` from `this.someMethod()` calls and which
   optionally does the same for fields, if no ambiguity arises.
-- A check which replaces `Integer.valueOf` calls with `Integer.parseInt` or
-  vice versa in order to prevent auto (un)boxing, and likewise for other number
+- A check that replaces `Integer.valueOf` calls with `Integer.parseInt` or vice
+  versa in order to prevent auto (un)boxing, and likewise for other number
   types.
-- A check which flags nullable collections.
-- A check which flags `AutoCloseable` resources not managed by a
+- A check that flags nullable collections.
+- A check that flags `AutoCloseable` resources not managed by a
   `try-with-resources` construct. Certain subtypes, such as jOOQ's `DSLContext`
   should be excluded.
-- A check which flags `java.time` methods which implicitly consult the system
+- A check that flags `java.time` methods which implicitly consult the system
   clock, suggesting that a passed-in `Clock` is used instead.
-- A check which flags public methods on public classes which reference
+- A check that flags public methods on public classes which reference
   non-public types. This can cause `IllegalAccessError`s and
   `BootstrapMethodError`s at runtime.
-- A check which swaps the LHS and RHS in expressions of the form
+- A check that swaps the LHS and RHS in expressions of the form
   `nonConstant.equals(someNonNullConstant)`.
-- A check which annotates methods which only throw an exception with
+- A check that annotates methods which only throw an exception with
   `@Deprecated` or ` @DoNotCall`.
-- A check which flags imports from other test classes.
-- A Guava-specific check which replaces `Joiner.join` calls with `String.join`
+- A check that flags imports from other test classes.
+- A Guava-specific check that replaces `Joiner.join` calls with `String.join`
   calls in those cases where the latter is a proper substitute for the former.
-- A Guava-specific check which flags `{Immutable,}Multimap` type usages
-  where `{Immutable,}{List,Set}Multimap` would be more appropriate.
-- A Guava-specific check which rewrites `if (conditional) { throw new
+- A Guava-specific check that flags `{Immutable,}Multimap` type usages where
+  `{Immutable,}{List,Set}Multimap` would be more appropriate.
+- A Guava-specific check that rewrites `if (conditional) { throw new
   IllegalArgumentException(); }` and variants to an equivalent `checkArgument`
   statement. Idem for other exception types.
-- A Guava-specific check which replaces simple anonymous `CacheLoader` subclass
+- A Guava-specific check that replaces simple anonymous `CacheLoader` subclass
   declarations with `CacheLoader.from(someLambda)`.
-- A Spring-specific check which enforces that methods with the `@Scheduled`
+- A Spring-specific check that enforces that methods with the `@Scheduled`
   annotation are also annotated with New Relic's `@Trace` annotation. Such
   methods should ideally not also represent Spring MVC endpoints.
-- A Spring-specific check which enforces that `@RequestMapping` annotations,
+- A Spring-specific check that enforces that `@RequestMapping` annotations,
   when applied to a method, explicitly specify one or more target HTTP methods.
-- A Spring-specific check which looks for classes in which all
-  `@RequestMapping` annotations (and the various aliases) specify the same
-  `path`/`value` property and then moves that path to the class level.
-- A Spring-specific check which flags `@Value("some.property")` annotations, as
+- A Spring-specific check that looks for classes in which all `@RequestMapping`
+  annotations (and the various aliases) specify the same `path`/`value`
+  property and then moves that path to the class level.
+- A Spring-specific check that flags `@Value("some.property")` annotations, as
   these almost certainly should be `@Value("${some.property}")`.
-- A Spring-specific check which drops the `required` attribute from
+- A Spring-specific check that drops the `required` attribute from
   `@RequestParam` annotations when the `defaultValue` attribute is also
   specified.
-- A Spring-specific check which rewrites a class which uses field injection to
+- A Spring-specific check that rewrites a class which uses field injection to
   one which uses constructor injection. This check wouldn't be strictly
   behavior preserving, but could be used for a one-off code base migration.
-- A Spring-specific check which disallows field injection, except in
+- A Spring-specific check that disallows field injection, except in
   `AbstractTestNGSpringContextTests` subclasses. (One known edge case:
   self-injections so that a bean can call itself through an implicit proxy.)
-- A Spring-specific check which verifies that public methods on all classes
+- A Spring-specific check that verifies that public methods on all classes
   whose name matches a certain pattern, e.g. `.*Service`, are annotated
   `@Secured`.
-- A Spring-specific check which verifies that annotations such as
+- A Spring-specific check that verifies that annotations such as
   `@RequestParam` are only present in `@RestController` classes.
-- A Spring-specific check which disallows `@ResponseStatus` on MVC endpoint
+- A Spring-specific check that disallows `@ResponseStatus` on MVC endpoint
   methods, as this prevents communication of error status codes.
-- A Hibernate Validator-specific check which looks for `@UnwrapValidatedValue`
+- A Hibernate Validator-specific check that looks for `@UnwrapValidatedValue`
   usages and migrates the associated constraint annotations to the generic type
   argument to which they (are presumed to) apply.
-- A TestNG-specific check which drops method-level `@Test` annotations if a
+- A TestNG-specific check that drops method-level `@Test` annotations if a
   matching/more specific annotation is already present at the class level.
-- A TestNG-specific check which enforces that all tests are in a group.
-- A TestNG-specific check which flags field assignments in
+- A TestNG-specific check that enforces that all tests are in a group.
+- A TestNG-specific check that flags field assignments in
   `@BeforeMethod`-annotated methods unless the class is annotated
   `@Test(singleThreaded = true)`.
-- A TestNG-specific check which flags usages of the `expectedExceptions`
+- A TestNG-specific check that flags usages of the `expectedExceptions`
   attribute of the `@Test` annotation, pointing to `assertThrows`.
-- A Jongo-specific check which disallows the creation of sparse indices, in
+- A Jongo-specific check that disallows the creation of sparse indices, in
   favour of partial indices.
-- An Immutables-specific check which replaces
+- An Immutables-specific check that replaces
   `checkState`/`IllegalStateException` usages inside a `@Value.Check`-annotated
   method with `checkArgument`/`IllegalArgument`, since the method is invoked
   when a caller attempts to create an immutable instance.
-- An Immutables-specific check which disallows references to collection types
+- An Immutables-specific check that disallows references to collection types
   other than the Guava immutable collections, including inside generic type
   arguments.
-- An SLF4J-specific check which drops or adds a trailing dot from log messages,
+- An SLF4J-specific check that drops or adds a trailing dot from log messages,
   as applicable.
-- A Mockito-specific check which identifies sequences of statements which mock
-  a significant number of methods on a single object with "default data"; such
+- A Mockito-specific check that identifies sequences of statements which mock a
+  significant number of methods on a single object with "default data"; such
   constructions can often benefit from a different type of default answer, such
   as `Answers.RETURNS_MOCKS`.
-- An RxJava-specific check which flags `.toCompletable()` calls on expressions
+- An RxJava-specific check that flags `.toCompletable()` calls on expressions
   of type `Single<Completable>` etc., as most likely
   `.flatMapCompletable(Functions.identity())` was meant instead. Idem for other
   variations.
-- An RxJava-specific check which flags `expr.firstOrError()` calls and suggests
+- An RxJava-specific check that flags `expr.firstOrError()` calls and suggests
   `expr.switchIfEmpty(Single.error(...))`, so that an application-specific
   exception is thrown instead of `NoSuchElementException`.
-- An RxJava-specific check which flags use of `#assertValueSet` without
+- An RxJava-specific check that flags use of `#assertValueSet` without
   `#assertValueCount`, as the former method doesn't do what one may intuitively
   expect it to do. See ReactiveX/RxJava#6151.
 
@@ -247,6 +198,7 @@ but on the flip side Refaster is much less expressive. While this gap can never
 be fully closed, there are some ways in which Refaster's scope of utility could
 be extended. The following is a non-exhaustive list of ideas on how to extend
 Refaster's expressiveness:
+
 - Allow more control over _which_ methods are statically imported by
   `@UseImportPolicy`. Sometimes the `@AfterTemplate` contains more than one
   static method invocation, and only a subset should be statically imported.
@@ -261,9 +213,9 @@ Refaster's expressiveness:
   pure expression. Introduce a way to express such a constraint. For example,
   rewriting `optional1.map(Optional::of).orElse(optional2)` to `optional1.or(()
   -> optional2)` is not behavior preserving if evaluation of `optional2` has
-  side-effects.
+  side effects.
 - Similarly, certain refactoring operations are only valid if one of the
-  matches expressions is not `@Nullable`. It'd be nice to be able to express
+  matched expressions is not `@Nullable`. It'd be nice to be able to express
   this.
 - Generalize `@Placeholder` support such that rules can reference e.g. "any
   concrete unary method". This would allow refactorings such as
@@ -276,10 +228,6 @@ Refaster's expressiveness:
   to be lost. In such a case don't statically import the method, so that the
   generic type information can be retained. (There may be cases where generic
   type information should even be _added_. Find an example.)
-- Upon application of a template Refaster can throw a _No binding for
-  Key{identifier=someAfterTemplateParam}_ exception. When this happens the
-  template is invalid. Instead perform this check at compile time, such that
-  such malformed templates cannot be defined in the first place.
 - Provide a way to express "match if (not) annotated (with _X_)". See #1 for a
   motivating example.
 - Provide a way to place match constraints on compile time constants. For
@@ -288,42 +236,38 @@ Refaster's expressiveness:
 - Provide a way to express transformations of compile-time constants. This
   would allow one to e.g. rewrite single-character strings to chars or vice
   versa, thereby accommodating a target API. Another example would be to
-  replace SLF4J's `{}` place holders with `%s` or vice versa. Yet another
+  replace SLF4J's `{}` placeholders with `%s` or vice versa. Yet another
   example would be to rewrite `BigDecimal.valueOf("<some-long-value>")` to
   `BigDecimal.valueOf(theParsedLongValue)`.
-- More generally, investigate ways to plug in in fully dynamic behavior, e.g.
-  by providing hooks using which arbitrary predicates/transformations can be
-  plugged in. The result would be a Refaster/`BugChecker` hybrid. A feature
-  such as this could form the basis for many other features listed here. (As a
-  concrete example, consider the ability to reference
+- More generally, investigate ways to plug in fully dynamic behavior, e.g.  by
+  providing hooks which enable plugging in arbitrary
+  predicates/transformations. The result would be a Refaster/`BugChecker`
+  hybrid. A feature like this could form the basis for many other features
+  listed here. (As a concrete example, consider the ability to reference
   `com.google.errorprone.matchers.Matcher` implementations.)
-- Provide a way to match lambda expressions and method references which match a
-  specified functional interface. This would allow rewrites such as
-  `Mono.fromCallable(this::doesNotThrowCheckException)` ->
-  `Mono.fromSupplier(this::doesNotThrowCheckException)`.
-- Provide an extension API using which methods or expressions can be defined
-  based on functional properties. A motivating example is the Java Collections
+- Provide an extension API that enables defining methods or expressions based
+  on functional properties. A motivating example is the Java Collections
   framework, which allows many ways to define (im)mutable (un)ordered
   collections with(out) duplicates. One could then express things like "match
-  any method call with collects its inputs into an immutable ordered list". An
+  any method call that collects its inputs into an immutable ordered list". An
   enum analogous to `java.util.stream.Collector.Characteristics` could be used.
   Out of the box JDK and Guava collection factory methods could be classified,
   with the user having the option to extend the classification.
 - Refaster currently unconditionally ignores expressions containing comments.
   Provide two additional modes: (a) match and drop the comments or (b)
   transport the comments to before/after the replaced expression.
-- Extend Refaster to drop imports that come become unnecessary as a result of a
-  refactoring. This e.g. allows one to replace a statically import TestNG
+- Extend Refaster to drop imports that become unnecessary as a result of a
+  refactoring. This e.g. allows one to replace a statically imported TestNG
   `fail(...)` invocation with a statically imported equivalent AssertJ
-  `fail(...)` invocation. (Observe that without an impor cleanup this
+  `fail(...)` invocation. (Observe that without an import cleanup this
   replacement would cause a compilation error.)
 - Extend the `@Repeated` match semantics such that it also covers non-varargs
   methods. For a motivating example see google/error-prone#568.
 - When matching explicit type references, also match super types. For a
-  motivating example, see the two subtly difference loop definitions in
-  `CollectionRemoveAllFromCollectionBlock`.
+  motivating example, see the two subtly different loop definitions in
+  `CollectionRemoveAllFromCollectionExpression`.
 - Figure out why Refaster sometimes doesn't match the correct generic overload.
-  See the `AssertThatIterableHasOneComparableElementEqualTo` template for an
+  See the `AssertThatIterableHasOneComparableElementEqualTo` rule for an
   example.
 
 [autorefactor]: https://autorefactor.org
@@ -331,16 +275,12 @@ Refaster's expressiveness:
 [checkstyle-external-project-tests]: https://github.com/checkstyle/checkstyle/blob/master/wercker.yml
 [codecov]: https://codecov.io
 [error-prone-bug-patterns]: https://errorprone.info/bugpatterns
-[error-prone-criteria]: https://errorprone.info/docs/criteria
-[error-prone-fork-jitpack]: https://jitpack.io/#PicnicSupermarket/error-prone
-[error-prone-fork-repo]: https://github.com/PicnicSupermarket/error-prone
 [error-prone]: https://errorprone.info
 [error-prone-repo]: https://github.com/google/error-prone
 [forbidden-apis]: https://github.com/policeman-tools/forbidden-apis
 [fossa]: https://fossa.io
 [google-java-format]: https://github.com/google/google-java-format
-[maven]: https://maven.apache.org
+[main-contributing]: ../CONTRIBUTING.md
+[main-readme]: ../README.md
 [modernizer-maven-plugin]: https://github.com/gaul/modernizer-maven-plugin
 [sonarcloud]: https://sonarcloud.io
-[pitest]: https://pitest.org
-[pitest-maven]: https://pitest.org/quickstart/maven

error-prone-contrib/pom.xml

@@ -5,7 +5,7 @@
     <parent>
         <groupId>tech.picnic.error-prone-support</groupId>
         <artifactId>error-prone-support</artifactId>
-        <version>0.0.1-SNAPSHOT</version>
+        <version>0.9.1-SNAPSHOT</version>
     </parent>
 
     <artifactId>error-prone-contrib</artifactId>
@@ -37,11 +37,11 @@
         <dependency>
             <groupId>${groupId.error-prone}</groupId>
             <artifactId>error_prone_test_helpers</artifactId>
-            <scope>test</scope>
+            <scope>provided</scope>
         </dependency>
         <dependency>
             <groupId>${project.groupId}</groupId>
-            <artifactId>refaster-resource-compiler</artifactId>
+            <artifactId>documentation-support</artifactId>
             <!-- This dependency is declared only as a hint to Maven that
             compilation depends on it; see the `maven-compiler-plugin`'s
             `annotationProcessorPaths` configuration below. -->
@@ -50,32 +50,42 @@
         <dependency>
             <groupId>${project.groupId}</groupId>
             <artifactId>refaster-support</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>refaster-test-support</artifactId>
+            <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>com.fasterxml.jackson.core</groupId>
             <artifactId>jackson-annotations</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.google.auto</groupId>
+            <artifactId>auto-common</artifactId>
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>com.google.auto.service</groupId>
             <artifactId>auto-service-annotations</artifactId>
             <scope>provided</scope>
         </dependency>
         <dependency>
-            <groupId>com.google.code.findbugs</groupId>
-            <artifactId>jsr305</artifactId>
-            <scope>provided</scope>
-        </dependency>
-        <dependency>
-            <groupId>com.google.errorprone</groupId>
-            <artifactId>javac</artifactId>
-            <scope>provided</scope>
+            <groupId>com.google.googlejavaformat</groupId>
+            <artifactId>google-java-format</artifactId>
         </dependency>
         <dependency>
             <groupId>com.google.guava</groupId>
             <artifactId>guava</artifactId>
             <scope>provided</scope>
         </dependency>
+        <dependency>
+            <groupId>com.newrelic.agent.java</groupId>
+            <artifactId>newrelic-api</artifactId>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>io.projectreactor</groupId>
             <artifactId>reactor-core</artifactId>
@@ -91,6 +101,11 @@
             <artifactId>reactor-adapter</artifactId>
             <scope>provided</scope>
         </dependency>
+        <dependency>
+            <groupId>io.projectreactor.addons</groupId>
+            <artifactId>reactor-extra</artifactId>
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>io.reactivex.rxjava2</groupId>
             <artifactId>rxjava</artifactId>
@@ -127,14 +142,19 @@
             <scope>provided</scope>
         </dependency>
         <dependency>
-            <groupId>org.hamcrest</groupId>
-            <artifactId>hamcrest-library</artifactId>
+            <groupId>org.immutables</groupId>
+            <artifactId>value-annotations</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.jspecify</groupId>
+            <artifactId>jspecify</artifactId>
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-api</artifactId>
-            <scope>test</scope>
+            <scope>provided</scope>
         </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>
@@ -161,11 +181,6 @@
             <artifactId>slf4j-api</artifactId>
             <scope>test</scope>
         </dependency>
-        <dependency>
-            <groupId>org.springframework</groupId>
-            <artifactId>spring-beans</artifactId>
-            <scope>test</scope>
-        </dependency>
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-context</artifactId>
@@ -186,6 +201,11 @@
             <artifactId>spring-webflux</artifactId>
             <scope>provided</scope>
         </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-test</artifactId>
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>org.testng</groupId>
             <artifactId>testng</artifactId>
@@ -196,15 +216,6 @@
     <build>
         <pluginManagement>
             <plugins>
-                <plugin>
-                    <groupId>com.coveo</groupId>
-                    <artifactId>fmt-maven-plugin</artifactId>
-                    <configuration>
-                        <additionalSourceDirectories>
-                            <additionalSourceDirectory>${basedir}/src/test/resources</additionalSourceDirectory>
-                        </additionalSourceDirectories>
-                    </configuration>
-                </plugin>
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-compiler-plugin</artifactId>
@@ -212,7 +223,12 @@
                         <annotationProcessorPaths combine.children="append">
                             <path>
                                 <groupId>${project.groupId}</groupId>
-                                <artifactId>refaster-resource-compiler</artifactId>
+                                <artifactId>documentation-support</artifactId>
+                                <version>${project.version}</version>
+                            </path>
+                            <path>
+                                <groupId>${project.groupId}</groupId>
+                                <artifactId>refaster-compiler</artifactId>
                                 <version>${project.version}</version>
                             </path>
                             <path>
@@ -222,7 +238,8 @@
                             </path>
                         </annotationProcessorPaths>
                         <compilerArgs combine.children="append">
-                            <arg>-Xplugin:RefasterRuleResourceCompiler</arg>
+                            <arg>-Xplugin:RefasterRuleCompiler</arg>
+                            <arg>-Xplugin:DocumentationGenerator -XoutputDirectory=${project.build.directory}/docs</arg>
                         </compilerArgs>
                     </configuration>
                 </plugin>
@@ -240,4 +257,33 @@
             </plugins>
         </pluginManagement>
     </build>
+
+    <profiles>
+        <profile>
+            <id>docgen</id>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.codehaus.mojo</groupId>
+                        <artifactId>build-helper-maven-plugin</artifactId>
+                        <version>3.3.0</version>
+                        <executions>
+                            <execution>
+                                <id>add-test-source</id>
+                                <goals>
+                                    <goal>add-test-source</goal>
+                                </goals>
+                                <phase>generate-test-sources</phase>
+                                <configuration>
+                                    <sources>
+                                        <source>src/test/resources</source>
+                                    </sources>
+                                </configuration>
+                            </execution>
+                        </executions>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
+    </profiles>
 </project>

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/AmbiguousJsonCreator.java

@@ -1,12 +1,13 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.LIKELY_ERROR;
 import static com.google.errorprone.matchers.Matchers.isType;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.AnnotationTreeMatcher;
@@ -22,19 +23,22 @@ import com.sun.tools.javac.code.Symbol;
 import java.util.Map;
 import javax.lang.model.element.AnnotationValue;
 
-/** A {@link BugChecker} which flags ambiguous {@code @JsonCreator}s in enums. */
+/** A {@link BugChecker} that flags ambiguous {@code @JsonCreator}s in enums. */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "AmbiguousJsonCreator",
     summary = "`JsonCreator.Mode` should be set for single-argument creators",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.WARNING,
-    tags = StandardTags.LIKELY_ERROR)
-public final class AmbiguousJsonCreatorCheck extends BugChecker implements AnnotationTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "AmbiguousJsonCreator",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = LIKELY_ERROR)
+public final class AmbiguousJsonCreator extends BugChecker implements AnnotationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Matcher<AnnotationTree> IS_JSON_CREATOR_ANNOTATION =
       isType("com.fasterxml.jackson.annotation.JsonCreator");
 
+  /** Instantiates a new {@link AmbiguousJsonCreator} instance. */
+  public AmbiguousJsonCreator() {}
+
   @Override
   public Description matchAnnotation(AnnotationTree tree, VisitorState state) {
     if (!IS_JSON_CREATOR_ANNOTATION.matches(tree, state)) {

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/AssertJIsNull.java

@@ -0,0 +1,62 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.argument;
+import static com.google.errorprone.matchers.Matchers.argumentCount;
+import static com.google.errorprone.matchers.Matchers.instanceMethod;
+import static com.google.errorprone.matchers.Matchers.nullLiteral;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.sun.source.tree.MethodInvocationTree;
+
+/**
+ * A {@link BugChecker} that flags AssertJ {@code isEqualTo(null)} checks for simplification.
+ *
+ * <p>This bug checker cannot be replaced with a simple Refaster rule, as the Refaster approach
+ * would require that all overloads of {@link org.assertj.core.api.Assert#isEqualTo(Object)} (such
+ * as {@link org.assertj.core.api.AbstractStringAssert#isEqualTo(String)}) are explicitly
+ * enumerated. This bug checker generically matches all such current and future overloads.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Prefer `.isNull()` over `.isEqualTo(null)`",
+    link = BUG_PATTERNS_BASE_URL + "AssertJIsNull",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class AssertJIsNull extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<MethodInvocationTree> ASSERT_IS_EQUAL_TO_NULL =
+      allOf(
+          instanceMethod().onDescendantOf("org.assertj.core.api.Assert").named("isEqualTo"),
+          argumentCount(1),
+          argument(0, nullLiteral()));
+
+  /** Instantiates a new {@link AssertJIsNull} instance. */
+  public AssertJIsNull() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (!ASSERT_IS_EQUAL_TO_NULL.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    SuggestedFix.Builder fix =
+        SuggestedFix.builder().merge(SuggestedFixes.renameMethodInvocation(tree, "isNull", state));
+    tree.getArguments().forEach(arg -> fix.merge(SuggestedFix.delete(arg)));
+
+    return describeMatch(tree, fix.build());
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/AssociativeMethodInvocation.java

@@ -0,0 +1,96 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.not;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static com.google.errorprone.matchers.Matchers.toType;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.matchers.Matchers;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.suppliers.Supplier;
+import com.google.errorprone.suppliers.Suppliers;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.tools.javac.code.Type;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags unnecessarily nested usage of methods that implement an
+ * associative operation.
+ *
+ * <p>The arguments to such methods can be flattened without affecting semantics, while making the
+ * code more readable.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary =
+        "These methods implement an associative operation, so the list of operands can be flattened",
+    link = BUG_PATTERNS_BASE_URL + "AssociativeMethodInvocation",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class AssociativeMethodInvocation extends BugChecker
+    implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Supplier<Type> ITERABLE = Suppliers.typeFromClass(Iterable.class);
+  private static final ImmutableSet<Matcher<ExpressionTree>> ASSOCIATIVE_OPERATIONS =
+      ImmutableSet.of(
+          allOf(
+              staticMethod().onClass(Suppliers.typeFromClass(Matchers.class)).named("allOf"),
+              toType(MethodInvocationTree.class, not(hasArgumentOfType(ITERABLE)))),
+          allOf(
+              staticMethod().onClass(Suppliers.typeFromClass(Matchers.class)).named("anyOf"),
+              toType(MethodInvocationTree.class, not(hasArgumentOfType(ITERABLE)))),
+          staticMethod().onClass(Suppliers.typeFromClass(Refaster.class)).named("anyOf"));
+
+  /** Instantiates a new {@link AssociativeMethodInvocation} instance. */
+  public AssociativeMethodInvocation() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (tree.getArguments().isEmpty()) {
+      /* Absent any arguments, there is nothing to simplify. */
+      return Description.NO_MATCH;
+    }
+
+    for (Matcher<ExpressionTree> matcher : ASSOCIATIVE_OPERATIONS) {
+      if (matcher.matches(tree, state)) {
+        SuggestedFix.Builder fix = SuggestedFix.builder();
+        for (ExpressionTree arg : tree.getArguments()) {
+          if (matcher.matches(arg, state)) {
+            MethodInvocationTree invocation = (MethodInvocationTree) arg;
+            fix.merge(
+                invocation.getArguments().isEmpty()
+                    ? SuggestedFixes.removeElement(arg, tree.getArguments(), state)
+                    : SourceCode.unwrapMethodInvocation(invocation, state));
+          }
+        }
+
+        return fix.isEmpty() ? Description.NO_MATCH : describeMatch(tree, fix.build());
+      }
+    }
+
+    return Description.NO_MATCH;
+  }
+
+  private static Matcher<MethodInvocationTree> hasArgumentOfType(Supplier<Type> type) {
+    return (tree, state) ->
+        tree.getArguments().stream()
+            .anyMatch(arg -> ASTHelpers.isSubtype(ASTHelpers.getType(arg), type.get(state), state));
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/AutowiredConstructor.java

@@ -1,19 +1,20 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
 import static com.google.errorprone.matchers.Matchers.annotations;
 import static com.google.errorprone.matchers.Matchers.isType;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
-import com.google.errorprone.fixes.SuggestedFix;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.matchers.MultiMatcher;
 import com.google.errorprone.util.ASTHelpers;
@@ -22,20 +23,24 @@ import com.sun.source.tree.ClassTree;
 import com.sun.source.tree.MethodTree;
 import com.sun.source.tree.Tree;
 import java.util.List;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
-/** A {@link BugChecker} which flags redundant {@code @Autowired} constructor annotations. */
+/** A {@link BugChecker} that flags redundant {@code @Autowired} constructor annotations. */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "AutowiredConstructor",
     summary = "Omit `@Autowired` on a class' sole constructor, as it is redundant",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.SIMPLIFICATION)
-public final class AutowiredConstructorCheck extends BugChecker implements ClassTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "AutowiredConstructor",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class AutowiredConstructor extends BugChecker implements ClassTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final MultiMatcher<Tree, AnnotationTree> AUTOWIRED_ANNOTATION =
       annotations(AT_LEAST_ONE, isType("org.springframework.beans.factory.annotation.Autowired"));
 
+  /** Instantiates a new {@link AutowiredConstructor} instance. */
+  public AutowiredConstructor() {}
+
   @Override
   public Description matchClass(ClassTree tree, VisitorState state) {
     List<MethodTree> constructors = ASTHelpers.getConstructors(tree);
@@ -43,7 +48,7 @@ public final class AutowiredConstructorCheck extends BugChecker implements Class
       return Description.NO_MATCH;
     }
 
-    List<AnnotationTree> annotations =
+    ImmutableList<AnnotationTree> annotations =
         AUTOWIRED_ANNOTATION
             .multiMatchResult(Iterables.getOnlyElement(constructors), state)
             .matchingNodes();
@@ -57,6 +62,6 @@ public final class AutowiredConstructorCheck extends BugChecker implements Class
      * leave flagging the unused import to Error Prone's `RemoveUnusedImports` check.
      */
     AnnotationTree annotation = Iterables.getOnlyElement(annotations);
-    return describeMatch(annotation, SuggestedFix.delete(annotation));
+    return describeMatch(annotation, SourceCode.deleteWithTrailingWhitespace(annotation, state));
   }
 }

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/CanonicalAnnotationSyntax.java

@@ -1,11 +1,13 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
 import com.google.auto.service.AutoService;
 import com.google.common.collect.ImmutableSet;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.AnnotationTreeMatcher;
@@ -24,25 +26,28 @@ import java.util.Optional;
 import java.util.function.BiFunction;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
-/** A {@link BugChecker} which flags annotations that could be written more concisely. */
+/** A {@link BugChecker} that flags annotations that could be written more concisely. */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "CanonicalAnnotationSyntax",
     summary = "Omit redundant syntax from annotation declarations",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.SIMPLIFICATION)
-public final class CanonicalAnnotationSyntaxCheck extends BugChecker
-    implements AnnotationTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "CanonicalAnnotationSyntax",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class CanonicalAnnotationSyntax extends BugChecker implements AnnotationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Pattern TRAILING_ARRAY_COMMA = Pattern.compile(",\\s*}$");
   private static final ImmutableSet<BiFunction<AnnotationTree, VisitorState, Optional<Fix>>>
       FIX_FACTORIES =
           ImmutableSet.of(
-              CanonicalAnnotationSyntaxCheck::dropRedundantParentheses,
-              CanonicalAnnotationSyntaxCheck::dropRedundantValueAttribute,
-              CanonicalAnnotationSyntaxCheck::dropRedundantCurlies);
+              CanonicalAnnotationSyntax::dropRedundantParentheses,
+              CanonicalAnnotationSyntax::dropRedundantValueAttribute,
+              CanonicalAnnotationSyntax::dropRedundantCurlies);
+
+  /** Instantiates a new {@link CanonicalAnnotationSyntax} instance. */
+  public CanonicalAnnotationSyntax() {}
 
   @Override
   public Description matchAnnotation(AnnotationTree tree, VisitorState state) {
@@ -102,7 +107,8 @@ public final class CanonicalAnnotationSyntaxCheck extends BugChecker
     return Optional.of(
         SuggestedFix.replace(
             arg,
-            simplifyAttributeValue(expr, state).orElseGet(() -> Util.treeToString(expr, state))));
+            simplifyAttributeValue(expr, state)
+                .orElseGet(() -> SourceCode.treeToString(expr, state))));
   }
 
   private static Optional<Fix> dropRedundantCurlies(AnnotationTree tree, VisitorState state) {
@@ -137,11 +143,11 @@ public final class CanonicalAnnotationSyntaxCheck extends BugChecker
   private static Optional<String> simplifySingletonArray(NewArrayTree array, VisitorState state) {
     return Optional.of(array.getInitializers())
         .filter(initializers -> initializers.size() == 1)
-        .map(initializers -> Util.treeToString(initializers.get(0), state));
+        .map(initializers -> SourceCode.treeToString(initializers.get(0), state));
   }
 
   private static Optional<String> dropTrailingComma(NewArrayTree array, VisitorState state) {
-    String src = Util.treeToString(array, state);
+    String src = SourceCode.treeToString(array, state);
     return Optional.of(TRAILING_ARRAY_COMMA.matcher(src))
         .filter(Matcher::find)
         .map(m -> src.substring(0, m.start()) + '}');

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/CollectorMutability.java

@@ -0,0 +1,124 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.FRAGILE_CODE;
+import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import java.util.stream.Collector;
+import tech.picnic.errorprone.bugpatterns.util.ThirdPartyLibrary;
+
+/**
+ * A {@link BugChecker} that flags {@link Collector Collectors} that don't clearly express
+ * (im)mutability.
+ *
+ * <p>Replacing such collectors with alternatives that produce immutable collections is preferred.
+ * Do note that Guava's immutable collections are null-hostile.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary =
+        "Avoid `Collectors.to{List,Map,Set}` in favour of alternatives that emphasize (im)mutability",
+    link = BUG_PATTERNS_BASE_URL + "CollectorMutability",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = FRAGILE_CODE)
+public final class CollectorMutability extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> COLLECTOR_METHOD =
+      staticMethod().onClass("java.util.stream.Collectors");
+  private static final Matcher<ExpressionTree> LIST_COLLECTOR =
+      staticMethod().anyClass().named("toList");
+  private static final Matcher<ExpressionTree> MAP_COLLECTOR =
+      staticMethod().anyClass().named("toMap");
+  private static final Matcher<ExpressionTree> SET_COLLECTOR =
+      staticMethod().anyClass().named("toSet");
+
+  /** Instantiates a new {@link CollectorMutability} instance. */
+  public CollectorMutability() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (!ThirdPartyLibrary.GUAVA.isIntroductionAllowed(state)
+        || !COLLECTOR_METHOD.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    if (LIST_COLLECTOR.matches(tree, state)) {
+      return suggestToCollectionAlternatives(
+          tree, "com.google.common.collect.ImmutableList.toImmutableList", "ArrayList", state);
+    }
+
+    if (MAP_COLLECTOR.matches(tree, state)) {
+      return suggestToMapAlternatives(tree, state);
+    }
+
+    if (SET_COLLECTOR.matches(tree, state)) {
+      return suggestToCollectionAlternatives(
+          tree, "com.google.common.collect.ImmutableSet.toImmutableSet", "HashSet", state);
+    }
+
+    return Description.NO_MATCH;
+  }
+
+  private Description suggestToCollectionAlternatives(
+      MethodInvocationTree tree,
+      String fullyQualifiedImmutableReplacement,
+      String mutableReplacement,
+      VisitorState state) {
+    SuggestedFix.Builder mutableFix = SuggestedFix.builder();
+    String toCollectionSelect =
+        SuggestedFixes.qualifyStaticImport(
+            "java.util.stream.Collectors.toCollection", mutableFix, state);
+
+    return buildDescription(tree)
+        .addFix(replaceMethodInvocation(tree, fullyQualifiedImmutableReplacement, state))
+        .addFix(
+            mutableFix
+                .addImport(String.format("java.util.%s", mutableReplacement))
+                .replace(tree, String.format("%s(%s::new)", toCollectionSelect, mutableReplacement))
+                .build())
+        .build();
+  }
+
+  private Description suggestToMapAlternatives(MethodInvocationTree tree, VisitorState state) {
+    int argCount = tree.getArguments().size();
+    if (argCount > 3) {
+      return Description.NO_MATCH;
+    }
+
+    return buildDescription(tree)
+        .addFix(
+            replaceMethodInvocation(
+                tree, "com.google.common.collect.ImmutableMap.toImmutableMap", state))
+        .addFix(
+            SuggestedFix.builder()
+                .addImport("java.util.HashMap")
+                .postfixWith(
+                    tree.getArguments().get(argCount - 1),
+                    (argCount == 2 ? ", (a, b) -> { throw new IllegalStateException(); }" : "")
+                        + ", HashMap::new")
+                .build())
+        .build();
+  }
+
+  private static SuggestedFix replaceMethodInvocation(
+      MethodInvocationTree tree, String fullyQualifiedReplacement, VisitorState state) {
+    SuggestedFix.Builder fix = SuggestedFix.builder();
+    String replacement = SuggestedFixes.qualifyStaticImport(fullyQualifiedReplacement, fix, state);
+    fix.merge(SuggestedFix.replace(tree.getMethodSelect(), replacement));
+    return fix.build();
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/DirectReturn.java

@@ -0,0 +1,175 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.argument;
+import static com.google.errorprone.matchers.Matchers.isSameType;
+import static com.google.errorprone.matchers.Matchers.isVariable;
+import static com.google.errorprone.matchers.Matchers.not;
+import static com.google.errorprone.matchers.Matchers.returnStatement;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static com.google.errorprone.matchers.Matchers.toType;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.Streams;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.BlockTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.AssignmentTree;
+import com.sun.source.tree.BlockTree;
+import com.sun.source.tree.ExpressionStatementTree;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.IdentifierTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.source.tree.ReturnTree;
+import com.sun.source.tree.StatementTree;
+import com.sun.source.tree.Tree;
+import com.sun.source.tree.TryTree;
+import com.sun.source.tree.VariableTree;
+import com.sun.source.util.TreeScanner;
+import com.sun.tools.javac.code.Symbol;
+import java.util.List;
+import java.util.Optional;
+import org.jspecify.annotations.Nullable;
+import tech.picnic.errorprone.bugpatterns.util.MoreASTHelpers;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags unnecessary local variable assignments preceding a return
+ * statement.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Variable assignment is redundant; value can be returned directly",
+    link = BUG_PATTERNS_BASE_URL + "DirectReturn",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class DirectReturn extends BugChecker implements BlockTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<StatementTree> VARIABLE_RETURN = returnStatement(isVariable());
+  private static final Matcher<ExpressionTree> MOCKITO_MOCK_OR_SPY_WITH_IMPLICIT_TYPE =
+      allOf(
+          not(toType(MethodInvocationTree.class, argument(0, isSameType(Class.class.getName())))),
+          staticMethod().onClass("org.mockito.Mockito").namedAnyOf("mock", "spy"));
+
+  /** Instantiates a new {@link DirectReturn} instance. */
+  public DirectReturn() {}
+
+  @Override
+  public Description matchBlock(BlockTree tree, VisitorState state) {
+    List<? extends StatementTree> statements = tree.getStatements();
+    if (statements.size() < 2) {
+      return Description.NO_MATCH;
+    }
+
+    StatementTree finalStatement = statements.get(statements.size() - 1);
+    if (!VARIABLE_RETURN.matches(finalStatement, state)) {
+      return Description.NO_MATCH;
+    }
+
+    Symbol variableSymbol = ASTHelpers.getSymbol(((ReturnTree) finalStatement).getExpression());
+    StatementTree precedingStatement = statements.get(statements.size() - 2);
+
+    return tryMatchAssignment(variableSymbol, precedingStatement)
+        .filter(
+            resultExpr ->
+                canInlineToReturnStatement(resultExpr, state)
+                    && !isIdentifierSymbolReferencedInAssociatedFinallyBlock(variableSymbol, state))
+        .map(
+            resultExpr ->
+                describeMatch(
+                    precedingStatement,
+                    SuggestedFix.builder()
+                        .replace(
+                            precedingStatement,
+                            String.format("return %s;", SourceCode.treeToString(resultExpr, state)))
+                        .delete(finalStatement)
+                        .build()))
+        .orElse(Description.NO_MATCH);
+  }
+
+  private static Optional<ExpressionTree> tryMatchAssignment(Symbol targetSymbol, Tree tree) {
+    if (tree instanceof ExpressionStatementTree) {
+      return tryMatchAssignment(targetSymbol, ((ExpressionStatementTree) tree).getExpression());
+    }
+
+    if (tree instanceof AssignmentTree) {
+      AssignmentTree assignment = (AssignmentTree) tree;
+      return targetSymbol.equals(ASTHelpers.getSymbol(assignment.getVariable()))
+          ? Optional.of(assignment.getExpression())
+          : Optional.empty();
+    }
+
+    if (tree instanceof VariableTree) {
+      VariableTree declaration = (VariableTree) tree;
+      return declaration.getModifiers().getAnnotations().isEmpty()
+              && targetSymbol.equals(ASTHelpers.getSymbol(declaration))
+          ? Optional.ofNullable(declaration.getInitializer())
+          : Optional.empty();
+    }
+
+    return Optional.empty();
+  }
+
+  /**
+   * Tells whether inlining the given expression to the associated return statement can likely be
+   * done without changing the expression's return type.
+   *
+   * <p>Inlining an expression generally does not change its return type, but in rare cases the
+   * operation may have a functional impact. The sole case considered here is the inlining of a
+   * Mockito mock or spy construction without an explicit type. In such a case the type created
+   * depends on context, such as the method's return type.
+   */
+  private static boolean canInlineToReturnStatement(
+      ExpressionTree expressionTree, VisitorState state) {
+    return !MOCKITO_MOCK_OR_SPY_WITH_IMPLICIT_TYPE.matches(expressionTree, state)
+        || MoreASTHelpers.findMethodExitedOnReturn(state)
+            .filter(m -> MoreASTHelpers.areSameType(expressionTree, m.getReturnType(), state))
+            .isPresent();
+  }
+
+  /**
+   * Tells whether the given identifier {@link Symbol} is referenced in a {@code finally} block that
+   * is executed <em>after</em> control flow returns from the {@link VisitorState#getPath() current
+   * location}.
+   */
+  private static boolean isIdentifierSymbolReferencedInAssociatedFinallyBlock(
+      Symbol symbol, VisitorState state) {
+    return Streams.zip(
+            Streams.stream(state.getPath()).skip(1),
+            Streams.stream(state.getPath()),
+            (tree, child) -> {
+              if (!(tree instanceof TryTree)) {
+                return null;
+              }
+
+              BlockTree finallyBlock = ((TryTree) tree).getFinallyBlock();
+              return !child.equals(finallyBlock) ? finallyBlock : null;
+            })
+        .anyMatch(finallyBlock -> referencesIdentifierSymbol(symbol, finallyBlock));
+  }
+
+  private static boolean referencesIdentifierSymbol(Symbol symbol, @Nullable BlockTree tree) {
+    return Boolean.TRUE.equals(
+        new TreeScanner<Boolean, @Nullable Void>() {
+          @Override
+          public Boolean visitIdentifier(IdentifierTree node, @Nullable Void unused) {
+            return symbol.equals(ASTHelpers.getSymbol(node));
+          }
+
+          @Override
+          public Boolean reduce(Boolean r1, Boolean r2) {
+            return Boolean.TRUE.equals(r1) || Boolean.TRUE.equals(r2);
+          }
+        }.scan(tree, null));
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/EmptyMethod.java

@@ -1,43 +1,46 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
 import static com.google.errorprone.matchers.Matchers.annotations;
 import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.Matchers.isType;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
-import com.google.errorprone.fixes.SuggestedFix;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.matchers.Matcher;
 import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.ClassTree;
 import com.sun.source.tree.MethodTree;
 import com.sun.source.tree.Tree;
-import com.sun.tools.javac.code.Symbol.MethodSymbol;
 import java.util.Optional;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
-/** A {@link BugChecker} which flags empty methods that seemingly can simply be deleted. */
+/** A {@link BugChecker} that flags empty methods that seemingly can simply be deleted. */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "EmptyMethod",
     summary = "Empty method can likely be deleted",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.SIMPLIFICATION)
-public final class EmptyMethodCheck extends BugChecker implements MethodTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "EmptyMethod",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class EmptyMethod extends BugChecker implements MethodTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Matcher<Tree> PERMITTED_ANNOTATION =
       annotations(
           AT_LEAST_ONE,
           anyOf(isType("java.lang.Override"), isType("org.aspectj.lang.annotation.Pointcut")));
 
+  /** Instantiates a new {@link EmptyMethod} instance. */
+  public EmptyMethod() {}
+
   @Override
   public Description matchMethod(MethodTree tree, VisitorState state) {
     if (tree.getBody() == null
@@ -48,12 +51,11 @@ public final class EmptyMethodCheck extends BugChecker implements MethodTreeMatc
       return Description.NO_MATCH;
     }
 
-    MethodSymbol sym = ASTHelpers.getSymbol(tree);
-    if (sym == null || ASTHelpers.methodCanBeOverridden(sym)) {
+    if (ASTHelpers.methodCanBeOverridden(ASTHelpers.getSymbol(tree))) {
       return Description.NO_MATCH;
     }
 
-    return describeMatch(tree, SuggestedFix.delete(tree));
+    return describeMatch(tree, SourceCode.deleteWithTrailingWhitespace(tree, state));
   }
 
   private static boolean isInPossibleTestHelperClass(VisitorState state) {

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/ErrorProneTestHelperSourceFormat.java

@@ -0,0 +1,165 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.STYLE;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.instanceMethod;
+import static java.util.stream.Collectors.joining;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.common.base.Splitter;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.google.googlejavaformat.java.Formatter;
+import com.google.googlejavaformat.java.FormatterException;
+import com.google.googlejavaformat.java.ImportOrderer;
+import com.google.googlejavaformat.java.JavaFormatterOptions.Style;
+import com.google.googlejavaformat.java.RemoveUnusedImports;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.source.tree.Tree;
+import com.sun.tools.javac.util.Position;
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * A {@link BugChecker} that flags improperly formatted Error Prone test code.
+ *
+ * <p>All test code should be formatted in accordance with Google Java Format's {@link Formatter}
+ * output, and imports should be ordered according to the {@link Style#GOOGLE Google} style.
+ *
+ * <p>This checker inspects inline code passed to {@code
+ * com.google.errorprone.CompilationTestHelper} and {@code
+ * com.google.errorprone.BugCheckerRefactoringTestHelper}. It requires that this code is properly
+ * formatted and that its imports are organized. Only code that represents the expected output of a
+ * refactoring operation is allowed to have unused imports, as most {@link BugChecker}s do not (and
+ * are not able to) remove imports that become obsolete as a result of applying their suggested
+ * fix(es).
+ */
+// XXX: Once we target JDK 17 (optionally?) suggest text block fixes.
+// XXX: GJF guesses the line separator to be used by inspecting the source. When using text blocks
+// this may cause the current unconditional use of `\n` not to be sufficient when building on
+// Windows; TBD.
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Test code should follow the Google Java style",
+    link = BUG_PATTERNS_BASE_URL + "ErrorProneTestHelperSourceFormat",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = STYLE)
+public final class ErrorProneTestHelperSourceFormat extends BugChecker
+    implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Formatter FORMATTER = new Formatter();
+  private static final Matcher<ExpressionTree> INPUT_SOURCE_ACCEPTING_METHOD =
+      anyOf(
+          instanceMethod()
+              .onDescendantOf("com.google.errorprone.CompilationTestHelper")
+              .named("addSourceLines"),
+          instanceMethod()
+              .onDescendantOf("com.google.errorprone.BugCheckerRefactoringTestHelper")
+              .named("addInputLines"));
+  private static final Matcher<ExpressionTree> OUTPUT_SOURCE_ACCEPTING_METHOD =
+      instanceMethod()
+          .onDescendantOf("com.google.errorprone.BugCheckerRefactoringTestHelper.ExpectOutput")
+          .named("addOutputLines");
+
+  /** Instantiates a new {@link ErrorProneTestHelperSourceFormat} instance. */
+  public ErrorProneTestHelperSourceFormat() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    boolean isOutputSource = OUTPUT_SOURCE_ACCEPTING_METHOD.matches(tree, state);
+    if (!isOutputSource && !INPUT_SOURCE_ACCEPTING_METHOD.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    List<? extends ExpressionTree> sourceLines =
+        tree.getArguments().subList(1, tree.getArguments().size());
+    if (sourceLines.isEmpty()) {
+      return buildDescription(tree).setMessage("No source code provided").build();
+    }
+
+    int startPos = ASTHelpers.getStartPosition(sourceLines.get(0));
+    int endPos = state.getEndPosition(sourceLines.get(sourceLines.size() - 1));
+
+    /* Attempt to format the source code only if it fully consists of constant expressions. */
+    return getConstantSourceCode(sourceLines)
+        .map(source -> flagFormattingIssues(startPos, endPos, source, isOutputSource, state))
+        .orElse(Description.NO_MATCH);
+  }
+
+  private Description flagFormattingIssues(
+      int startPos, int endPos, String source, boolean retainUnusedImports, VisitorState state) {
+    Tree methodInvocation = state.getPath().getLeaf();
+
+    String formatted;
+    try {
+      formatted = formatSourceCode(source, retainUnusedImports).trim();
+    } catch (FormatterException e) {
+      return buildDescription(methodInvocation)
+          .setMessage(String.format("Source code is malformed: %s", e.getMessage()))
+          .build();
+    }
+
+    if (source.trim().equals(formatted)) {
+      return Description.NO_MATCH;
+    }
+
+    if (startPos == Position.NOPOS || endPos == Position.NOPOS) {
+      /*
+       * We have insufficient source information to emit a fix, so we only flag the fact that the
+       * code isn't properly formatted.
+       */
+      return describeMatch(methodInvocation);
+    }
+
+    /*
+     * The code isn't properly formatted; replace all lines with the properly formatted
+     * alternatives.
+     */
+    return describeMatch(
+        methodInvocation,
+        SuggestedFix.replace(
+            startPos,
+            endPos,
+            Splitter.on('\n')
+                .splitToStream(formatted)
+                .map(state::getConstantExpression)
+                .collect(joining(", "))));
+  }
+
+  private static String formatSourceCode(String source, boolean retainUnusedImports)
+      throws FormatterException {
+    String withReorderedImports = ImportOrderer.reorderImports(source, Style.GOOGLE);
+    String withOptionallyRemovedImports =
+        retainUnusedImports
+            ? withReorderedImports
+            : RemoveUnusedImports.removeUnusedImports(withReorderedImports);
+    return FORMATTER.formatSource(withOptionallyRemovedImports);
+  }
+
+  private static Optional<String> getConstantSourceCode(
+      List<? extends ExpressionTree> sourceLines) {
+    StringBuilder source = new StringBuilder();
+
+    for (ExpressionTree sourceLine : sourceLines) {
+      String value = ASTHelpers.constValue(sourceLine, String.class);
+      if (value == null) {
+        return Optional.empty();
+      }
+
+      source.append(value).append('\n');
+    }
+
+    return Optional.of(source.toString());
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/ExplicitEnumOrdering.java

@@ -2,8 +2,12 @@ package tech.picnic.errorprone.bugpatterns;
 
 import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.common.collect.ImmutableSetMultimap.toImmutableSetMultimap;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.FRAGILE_CODE;
 import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
 import static java.util.stream.Collectors.collectingAndThen;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.common.collect.ImmutableSet;
@@ -12,9 +16,6 @@ import com.google.common.collect.Multimaps;
 import com.google.common.collect.Ordering;
 import com.google.common.collect.Sets;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
@@ -30,22 +31,24 @@ import java.util.Set;
 import java.util.stream.Stream;
 
 /**
- * A {@link BugChecker} which flags {@link Ordering#explicit(Object, Object[])}} invocations listing
+ * A {@link BugChecker} that flags {@link Ordering#explicit(Object, Object[])}} invocations listing
  * a subset of an enum type's values.
  */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "ExplicitEnumOrdering",
     summary = "Make sure `Ordering#explicit` lists all of an enum's values",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.WARNING,
-    tags = StandardTags.FRAGILE_CODE)
-public final class ExplicitEnumOrderingCheck extends BugChecker
-    implements MethodInvocationTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "ExplicitEnumOrdering",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = FRAGILE_CODE)
+public final class ExplicitEnumOrdering extends BugChecker implements MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Matcher<ExpressionTree> EXPLICIT_ORDERING =
       staticMethod().onClass(Ordering.class.getName()).named("explicit");
 
+  /** Instantiates a new {@link ExplicitEnumOrdering} instance. */
+  public ExplicitEnumOrdering() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (!EXPLICIT_ORDERING.matches(tree, state)) {
@@ -73,7 +76,7 @@ public final class ExplicitEnumOrderingCheck extends BugChecker
         .collect(
             collectingAndThen(
                 toImmutableSetMultimap(Symbol::asType, Symbol::toString),
-                ExplicitEnumOrderingCheck::getMissingEnumValues));
+                ExplicitEnumOrdering::getMissingEnumValues));
   }
 
   private static ImmutableSet<String> getMissingEnumValues(
@@ -86,6 +89,6 @@ public final class ExplicitEnumOrderingCheck extends BugChecker
   private static Stream<String> getMissingEnumValues(Type enumType, Set<String> values) {
     Symbol.TypeSymbol typeSymbol = enumType.asElement();
     return Sets.difference(ASTHelpers.enumValues(typeSymbol), values).stream()
-        .map(v -> String.format("%s.%s", typeSymbol.getSimpleName(), v));
+        .map(v -> String.join(".", typeSymbol.getSimpleName(), v));
   }
 }

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/FluxFlatMapUsage.java

@@ -0,0 +1,114 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+import static com.google.errorprone.BugPattern.StandardTags.LIKELY_ERROR;
+import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.generic;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.subOf;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.type;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.unbound;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.Iterables;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MemberReferenceTreeMatcher;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.suppliers.Supplier;
+import com.google.errorprone.suppliers.Suppliers;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MemberReferenceTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.tools.javac.code.Type;
+import java.util.function.Function;
+import reactor.core.publisher.Flux;
+
+/**
+ * A {@link BugChecker} that flags usages of {@link Flux#flatMap(Function)} and {@link
+ * Flux#flatMapSequential(Function)}.
+ *
+ * <p>{@link Flux#flatMap(Function)} and {@link Flux#flatMapSequential(Function)} eagerly perform up
+ * to {@link reactor.util.concurrent.Queues#SMALL_BUFFER_SIZE} subscriptions. Additionally, the
+ * former interleaves values as they are emitted, yielding nondeterministic results. In most cases
+ * {@link Flux#concatMap(Function)} should be preferred, as it produces consistent results and
+ * avoids potentially saturating the thread pool on which subscription happens. If {@code
+ * concatMap}'s sequential-subscription semantics are undesirable one should invoke a {@code
+ * flatMap} or {@code flatMapSequential} overload with an explicit concurrency level.
+ *
+ * <p>NB: The rarely-used overload {@link Flux#flatMap(Function, Function,
+ * java.util.function.Supplier)} is not flagged by this check because there is no clear alternative
+ * to point to.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary =
+        "`Flux#flatMap` and `Flux#flatMapSequential` have subtle semantics; "
+            + "please use `Flux#concatMap` or explicitly specify the desired amount of concurrency",
+    link = BUG_PATTERNS_BASE_URL + "FluxFlatMapUsage",
+    linkType = CUSTOM,
+    severity = ERROR,
+    tags = LIKELY_ERROR)
+public final class FluxFlatMapUsage extends BugChecker
+    implements MethodInvocationTreeMatcher, MemberReferenceTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final String MAX_CONCURRENCY_ARG_NAME = "MAX_CONCURRENCY";
+  private static final Supplier<Type> FLUX =
+      Suppliers.typeFromString("reactor.core.publisher.Flux");
+  private static final Matcher<ExpressionTree> FLUX_FLATMAP =
+      instanceMethod()
+          .onDescendantOf(FLUX)
+          .namedAnyOf("flatMap", "flatMapSequential")
+          .withParameters(Function.class.getName());
+  private static final Supplier<Type> FLUX_OF_PUBLISHERS =
+      VisitorState.memoize(
+          generic(FLUX, subOf(generic(type("org.reactivestreams.Publisher"), unbound()))));
+
+  /** Instantiates a new {@link FluxFlatMapUsage} instance. */
+  public FluxFlatMapUsage() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (!FLUX_FLATMAP.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    SuggestedFix serializationFix = SuggestedFixes.renameMethodInvocation(tree, "concatMap", state);
+    SuggestedFix concurrencyCapFix =
+        SuggestedFix.postfixWith(
+            Iterables.getOnlyElement(tree.getArguments()), ", " + MAX_CONCURRENCY_ARG_NAME);
+
+    Description.Builder description = buildDescription(tree);
+
+    if (state.getTypes().isSubtype(ASTHelpers.getType(tree), FLUX_OF_PUBLISHERS.get(state))) {
+      /*
+       * Nested publishers may need to be subscribed to eagerly in order to avoid a deadlock, e.g.
+       * if they are produced by `Flux#groupBy`. In this case we suggest specifying an explicit
+       * concurrently bound, in favour of sequential subscriptions using `Flux#concatMap`.
+       */
+      description.addFix(concurrencyCapFix).addFix(serializationFix);
+    } else {
+      description.addFix(serializationFix).addFix(concurrencyCapFix);
+    }
+
+    return description.build();
+  }
+
+  @Override
+  public Description matchMemberReference(MemberReferenceTree tree, VisitorState state) {
+    if (!FLUX_FLATMAP.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    // Method references are expected to occur very infrequently; generating both variants of
+    // suggested fixes is not worth the trouble.
+    return describeMatch(tree);
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/FluxImplicitBlock.java

@@ -0,0 +1,100 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.common.base.Preconditions.checkState;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.CONCURRENCY;
+import static com.google.errorprone.BugPattern.StandardTags.PERFORMANCE;
+import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.suppliers.Supplier;
+import com.google.errorprone.suppliers.Suppliers;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.tools.javac.code.Type;
+import com.sun.tools.javac.util.Position;
+import java.util.stream.Stream;
+import tech.picnic.errorprone.bugpatterns.util.ThirdPartyLibrary;
+
+/**
+ * A {@link BugChecker} that flags {@link reactor.core.publisher.Flux} operator usages that may
+ * implicitly cause the calling thread to be blocked.
+ *
+ * <p>Note that the methods flagged here are not themselves blocking, but iterating over the
+ * resulting {@link Iterable} or {@link Stream} may be.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Avoid iterating over `Flux`es in an implicitly blocking manner",
+    link = BUG_PATTERNS_BASE_URL + "FluxImplicitBlock",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = {CONCURRENCY, PERFORMANCE})
+public final class FluxImplicitBlock extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> FLUX_WITH_IMPLICIT_BLOCK =
+      instanceMethod()
+          .onDescendantOf("reactor.core.publisher.Flux")
+          .namedAnyOf("toIterable", "toStream")
+          .withNoParameters();
+  private static final Supplier<Type> STREAM = Suppliers.typeFromString(Stream.class.getName());
+
+  /** Instantiates a new {@link FluxImplicitBlock} instance. */
+  public FluxImplicitBlock() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (!FLUX_WITH_IMPLICIT_BLOCK.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    Description.Builder description =
+        buildDescription(tree).addFix(SuggestedFixes.addSuppressWarnings(state, canonicalName()));
+    if (ThirdPartyLibrary.GUAVA.isIntroductionAllowed(state)) {
+      description.addFix(
+          suggestBlockingElementCollection(
+              tree, "com.google.common.collect.ImmutableList.toImmutableList", state));
+    }
+    description.addFix(
+        suggestBlockingElementCollection(tree, "java.util.stream.Collectors.toList", state));
+
+    return description.build();
+  }
+
+  private static SuggestedFix suggestBlockingElementCollection(
+      MethodInvocationTree tree, String fullyQualifiedCollectorMethod, VisitorState state) {
+    SuggestedFix.Builder importSuggestion = SuggestedFix.builder();
+    String replacementMethodInvocation =
+        SuggestedFixes.qualifyStaticImport(fullyQualifiedCollectorMethod, importSuggestion, state);
+
+    boolean isStream =
+        ASTHelpers.isSubtype(ASTHelpers.getResultType(tree), STREAM.get(state), state);
+    String replacement =
+        String.format(
+            ".collect(%s()).block()%s", replacementMethodInvocation, isStream ? ".stream()" : "");
+    return importSuggestion.merge(replaceMethodInvocation(tree, replacement, state)).build();
+  }
+
+  private static SuggestedFix.Builder replaceMethodInvocation(
+      MethodInvocationTree tree, String replacement, VisitorState state) {
+    int startPosition = state.getEndPosition(ASTHelpers.getReceiver(tree));
+    int endPosition = state.getEndPosition(tree);
+
+    checkState(
+        startPosition != Position.NOPOS && endPosition != Position.NOPOS,
+        "Cannot locate method to be replaced in source code");
+
+    return SuggestedFix.builder().replace(startPosition, endPosition, replacement);
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/FormatStringConcatenation.java

@@ -1,5 +1,8 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static com.google.errorprone.matchers.Matchers.allOf;
 import static com.google.errorprone.matchers.Matchers.anyMethod;
 import static com.google.errorprone.matchers.Matchers.anyOf;
@@ -7,12 +10,10 @@ import static com.google.errorprone.matchers.Matchers.instanceMethod;
 import static com.google.errorprone.matchers.Matchers.not;
 import static com.google.errorprone.matchers.Matchers.staticMethod;
 import static java.util.stream.Collectors.joining;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
@@ -31,10 +32,12 @@ import com.sun.source.util.SimpleTreeVisitor;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
+import org.jspecify.annotations.Nullable;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
- * A {@link BugChecker} which flags string concatenations that produce a format string; in such
- * cases the string concatenation should instead be deferred to the invoked method.
+ * A {@link BugChecker} that flags string concatenations that produce a format string; in such cases
+ * the string concatenation should instead be deferred to the invoked method.
  *
  * @implNote This checker is based on the implementation of {@link
  *     com.google.errorprone.bugpatterns.flogger.FloggerStringConcatenation}.
@@ -44,16 +47,16 @@ import java.util.Optional;
 // should introduce special handling of `Formattable` arguments, as this check would replace a
 // `Formattable#toString` invocation with a `Formattable#formatTo` invocation. But likely that
 // should be considered a bug fix, too.
-// XXX: Introduce a separate check which adds/removes the `Locale` parameter to `String.format`
-// invocations, as necessary.
+// XXX: Introduce a separate check that adds/removes the `Locale` parameter to `String.format`
+// invocations, as necessary. See also a comment in the `StringJoin` check.
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "FormatStringConcatenation",
     summary = "Defer string concatenation to the invoked method",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.WARNING,
-    tags = StandardTags.SIMPLIFICATION)
-public final class FormatStringConcatenationCheck extends BugChecker
+    link = BUG_PATTERNS_BASE_URL + "FormatStringConcatenation",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = SIMPLIFICATION)
+public final class FormatStringConcatenation extends BugChecker
     implements MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
   /**
@@ -126,6 +129,9 @@ public final class FormatStringConcatenationCheck extends BugChecker
           .onDescendantOf("org.slf4j.Logger")
           .namedAnyOf("debug", "error", "info", "trace", "warn");
 
+  /** Instantiates a new {@link FormatStringConcatenation} instance. */
+  public FormatStringConcatenation() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (hasNonConstantStringConcatenationArgument(tree, 0, state)) {
@@ -201,7 +207,7 @@ public final class FormatStringConcatenationCheck extends BugChecker
   }
 
   private static class ReplacementArgumentsConstructor
-      extends SimpleTreeVisitor<Void, VisitorState> {
+      extends SimpleTreeVisitor<@Nullable Void, VisitorState> {
     private final StringBuilder formatString = new StringBuilder();
     private final List<Tree> formatArguments = new ArrayList<>();
     private final String formatSpecifier;
@@ -211,7 +217,7 @@ public final class FormatStringConcatenationCheck extends BugChecker
     }
 
     @Override
-    public Void visitBinary(BinaryTree tree, VisitorState state) {
+    public @Nullable Void visitBinary(BinaryTree tree, VisitorState state) {
       if (tree.getKind() == Kind.PLUS && isStringTyped(tree, state)) {
         tree.getLeftOperand().accept(this, state);
         tree.getRightOperand().accept(this, state);
@@ -223,12 +229,12 @@ public final class FormatStringConcatenationCheck extends BugChecker
     }
 
     @Override
-    public Void visitParenthesized(ParenthesizedTree tree, VisitorState state) {
+    public @Nullable Void visitParenthesized(ParenthesizedTree tree, VisitorState state) {
       return tree.getExpression().accept(this, state);
     }
 
     @Override
-    protected Void defaultAction(Tree tree, VisitorState state) {
+    protected @Nullable Void defaultAction(Tree tree, VisitorState state) {
       appendExpression(tree);
       return null;
     }
@@ -246,7 +252,7 @@ public final class FormatStringConcatenationCheck extends BugChecker
       return state.getConstantExpression(formatString.toString())
           + ", "
           + formatArguments.stream()
-              .map(tree -> Util.treeToString(tree, state))
+              .map(tree -> SourceCode.treeToString(tree, state))
               .collect(joining(", "));
     }
   }

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/IdentityConversion.java

@@ -0,0 +1,130 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static com.google.errorprone.suppliers.Suppliers.OBJECT_TYPE;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.common.primitives.Primitives;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.bugpatterns.TypesWithUndefinedEquality;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.google.errorprone.util.ASTHelpers.TargetType;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MemberSelectTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.tools.javac.code.Type;
+import com.sun.tools.javac.code.Types;
+import java.util.Arrays;
+import java.util.List;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/** A {@link BugChecker} that flags redundant identity conversions. */
+// XXX: Consider detecting cases where a flagged expression is passed to a method, and where removal
+// of the identity conversion would cause a different method overload to be selected. Depending on
+// the target method such a modification may change the code's semantics or performance.
+// XXX: Also flag `Stream#map`, `Mono#map` and `Flux#map` invocations where the given transformation
+// is effectively the identity operation.
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Avoid or clarify identity conversions",
+    link = BUG_PATTERNS_BASE_URL + "IdentityConversion",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = SIMPLIFICATION)
+public final class IdentityConversion extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> IS_CONVERSION_METHOD =
+      anyOf(
+          staticMethod()
+              .onClassAny(
+                  Primitives.allWrapperTypes().stream()
+                      .map(Class::getName)
+                      .collect(toImmutableSet()))
+              .named("valueOf"),
+          staticMethod().onClass(String.class.getName()).named("valueOf"),
+          staticMethod()
+              .onClassAny(
+                  "com.google.common.collect.ImmutableBiMap",
+                  "com.google.common.collect.ImmutableList",
+                  "com.google.common.collect.ImmutableListMultimap",
+                  "com.google.common.collect.ImmutableMap",
+                  "com.google.common.collect.ImmutableMultimap",
+                  "com.google.common.collect.ImmutableMultiset",
+                  "com.google.common.collect.ImmutableRangeMap",
+                  "com.google.common.collect.ImmutableRangeSet",
+                  "com.google.common.collect.ImmutableSet",
+                  "com.google.common.collect.ImmutableSetMultimap",
+                  "com.google.common.collect.ImmutableTable")
+              .named("copyOf"),
+          staticMethod()
+              .onClass("com.google.errorprone.matchers.Matchers")
+              .namedAnyOf("allOf", "anyOf"),
+          staticMethod().onClass("reactor.adapter.rxjava.RxJava2Adapter"),
+          staticMethod()
+              .onClass("reactor.core.publisher.Flux")
+              .namedAnyOf("concat", "firstWithSignal", "from", "merge"),
+          staticMethod().onClass("reactor.core.publisher.Mono").namedAnyOf("from", "fromDirect"));
+
+  /** Instantiates a new {@link IdentityConversion} instance. */
+  public IdentityConversion() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    List<? extends ExpressionTree> arguments = tree.getArguments();
+    if (arguments.size() != 1 || !IS_CONVERSION_METHOD.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    ExpressionTree sourceTree = arguments.get(0);
+    Type sourceType = ASTHelpers.getType(sourceTree);
+    Type resultType = ASTHelpers.getType(tree);
+    TargetType targetType = ASTHelpers.targetType(state);
+    if (sourceType == null || resultType == null || targetType == null) {
+      return Description.NO_MATCH;
+    }
+
+    if (!state.getTypes().isSameType(sourceType, resultType)
+        && !isConvertibleWithWellDefinedEquality(sourceType, targetType.type(), state)) {
+      return Description.NO_MATCH;
+    }
+
+    if (sourceType.isPrimitive()
+        && state.getPath().getParentPath().getLeaf() instanceof MemberSelectTree) {
+      /*
+       * The result of the conversion method is dereferenced, while the source type is a primitive:
+       * dropping the conversion would yield uncompilable code.
+       */
+      return Description.NO_MATCH;
+    }
+
+    return buildDescription(tree)
+        .setMessage(
+            "This method invocation appears redundant; remove it or suppress this warning and "
+                + "add a comment explaining its purpose")
+        .addFix(SuggestedFix.replace(tree, SourceCode.treeToString(sourceTree, state)))
+        .addFix(SuggestedFixes.addSuppressWarnings(state, canonicalName()))
+        .build();
+  }
+
+  private static boolean isConvertibleWithWellDefinedEquality(
+      Type sourceType, Type targetType, VisitorState state) {
+    Types types = state.getTypes();
+    return !types.isSameType(targetType, OBJECT_TYPE.get(state))
+        && types.isConvertible(sourceType, targetType)
+        && Arrays.stream(TypesWithUndefinedEquality.values())
+            .noneMatch(b -> b.matchesType(sourceType, state) || b.matchesType(targetType, state));
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/ImmutablesSortedSetComparator.java

@@ -0,0 +1,86 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+import static com.google.errorprone.BugPattern.StandardTags.LIKELY_ERROR;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.enclosingClass;
+import static com.google.errorprone.matchers.Matchers.hasAnnotation;
+import static com.google.errorprone.matchers.Matchers.hasModifier;
+import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
+import static com.google.errorprone.matchers.Matchers.methodReturns;
+import static com.google.errorprone.matchers.Matchers.not;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.sun.source.tree.MethodTree;
+import java.util.SortedSet;
+import javax.lang.model.element.Modifier;
+
+/**
+ * A {@link BugChecker} that flags {@link SortedSet} property declarations inside
+ * {@code @Value.Immutable}- and {@code @Value.Modifiable}-annotated types that lack a
+ * {@code @Value.NaturalOrder} or {@code @Value.ReverseOrder} annotation.
+ *
+ * <p>Without such an annotation:
+ *
+ * <ul>
+ *   <li>deserialization of the enclosing type requires that the associated JSON property is
+ *       present, contrary to the way in which Immutables handles other collection properties; and
+ *   <li>different instances may use different comparator implementations (e.g. deserialization
+ *       would default to natural order sorting), potentially leading to subtle bugs.
+ * </ul>
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary =
+        "`SortedSet` properties of a `@Value.Immutable` or `@Value.Modifiable` type must be "
+            + "annotated with `@Value.NaturalOrder` or `@Value.ReverseOrder`",
+    link = BUG_PATTERNS_BASE_URL + "ImmutablesSortedSetComparator",
+    linkType = CUSTOM,
+    severity = ERROR,
+    tags = LIKELY_ERROR)
+public final class ImmutablesSortedSetComparator extends BugChecker implements MethodTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<MethodTree> METHOD_LACKS_ANNOTATION =
+      allOf(
+          methodReturns(isSubtypeOf(SortedSet.class)),
+          anyOf(
+              allOf(
+                  hasModifier(Modifier.ABSTRACT),
+                  enclosingClass(
+                      anyOf(
+                          hasAnnotation("org.immutables.value.Value.Immutable"),
+                          hasAnnotation("org.immutables.value.Value.Modifiable")))),
+              hasAnnotation("org.immutables.value.Value.Default")),
+          not(
+              anyOf(
+                  hasAnnotation("org.immutables.value.Value.NaturalOrder"),
+                  hasAnnotation("org.immutables.value.Value.ReverseOrder"))));
+
+  /** Instantiates a new {@link ImmutablesSortedSetComparator} instance. */
+  public ImmutablesSortedSetComparator() {}
+
+  @Override
+  public Description matchMethod(MethodTree tree, VisitorState state) {
+    if (!METHOD_LACKS_ANNOTATION.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    SuggestedFix.Builder builder = SuggestedFix.builder();
+    String valueTypeIdentifier =
+        SuggestedFixes.qualifyType(state, builder, "org.immutables.value.Value");
+    return describeMatch(
+        tree,
+        builder.prefixWith(tree, String.format("@%s.NaturalOrder ", valueTypeIdentifier)).build());
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/IsInstanceLambdaUsage.java

@@ -0,0 +1,60 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.Iterables;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.LambdaExpressionTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.InstanceOfTree;
+import com.sun.source.tree.LambdaExpressionTree;
+import com.sun.source.tree.Tree.Kind;
+import com.sun.source.tree.VariableTree;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags lambda expressions that can be replaced with a method reference
+ * of the form {@code T.class::isInstance}.
+ *
+ * @see MethodReferenceUsage
+ */
+// XXX: Consider folding this logic into the `MethodReferenceUsage` check.
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Prefer `Class::isInstance` method reference over equivalent lambda expression",
+    link = BUG_PATTERNS_BASE_URL + "IsInstanceLambdaUsage",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class IsInstanceLambdaUsage extends BugChecker implements LambdaExpressionTreeMatcher {
+  private static final long serialVersionUID = 1L;
+
+  /** Instantiates a new {@link IsInstanceLambdaUsage} instance. */
+  public IsInstanceLambdaUsage() {}
+
+  @Override
+  public Description matchLambdaExpression(LambdaExpressionTree tree, VisitorState state) {
+    if (tree.getParameters().size() != 1 || tree.getBody().getKind() != Kind.INSTANCE_OF) {
+      return Description.NO_MATCH;
+    }
+
+    VariableTree param = Iterables.getOnlyElement(tree.getParameters());
+    InstanceOfTree instanceOf = (InstanceOfTree) tree.getBody();
+    if (!ASTHelpers.getSymbol(param).equals(ASTHelpers.getSymbol(instanceOf.getExpression()))) {
+      return Description.NO_MATCH;
+    }
+
+    return describeMatch(
+        tree,
+        SuggestedFix.replace(
+            tree, SourceCode.treeToString(instanceOf.getType(), state) + ".class::isInstance"));
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/JUnitClassModifiers.java

@@ -0,0 +1,82 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.STYLE;
+import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.annotations;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.hasMethod;
+import static com.google.errorprone.matchers.Matchers.hasModifier;
+import static com.google.errorprone.matchers.Matchers.isType;
+import static com.google.errorprone.matchers.Matchers.not;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+import static tech.picnic.errorprone.bugpatterns.util.MoreJUnitMatchers.TEST_METHOD;
+import static tech.picnic.errorprone.bugpatterns.util.MoreMatchers.hasMetaAnnotation;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.sun.source.tree.ClassTree;
+import javax.lang.model.element.Modifier;
+
+/**
+ * A {@link BugChecker} that flags non-final and non package-private JUnit test class declarations,
+ * unless abstract.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Non-abstract JUnit test classes should be declared package-private and final",
+    linkType = CUSTOM,
+    link = BUG_PATTERNS_BASE_URL + "JUnitClassModifiers",
+    severity = SUGGESTION,
+    tags = STYLE)
+public final class JUnitClassModifiers extends BugChecker implements ClassTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ClassTree> HAS_SPRING_CONFIGURATION_ANNOTATION =
+      annotations(
+          AT_LEAST_ONE,
+          anyOf(
+              isType("org.springframework.context.annotation.Configuration"),
+              hasMetaAnnotation("org.springframework.context.annotation.Configuration")));
+  private static final Matcher<ClassTree> TEST_CLASS_WITH_INCORRECT_MODIFIERS =
+      allOf(
+          hasMethod(TEST_METHOD),
+          not(hasModifier(Modifier.ABSTRACT)),
+          anyOf(
+              hasModifier(Modifier.PRIVATE),
+              hasModifier(Modifier.PROTECTED),
+              hasModifier(Modifier.PUBLIC),
+              allOf(not(hasModifier(Modifier.FINAL)), not(HAS_SPRING_CONFIGURATION_ANNOTATION))));
+
+  /** Instantiates a new {@link JUnitClassModifiers} instance. */
+  public JUnitClassModifiers() {}
+
+  @Override
+  public Description matchClass(ClassTree tree, VisitorState state) {
+    if (!TEST_CLASS_WITH_INCORRECT_MODIFIERS.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    SuggestedFix.Builder fixBuilder = SuggestedFix.builder();
+    SuggestedFixes.removeModifiers(
+            tree.getModifiers(),
+            state,
+            ImmutableSet.of(Modifier.PRIVATE, Modifier.PROTECTED, Modifier.PUBLIC))
+        .ifPresent(fixBuilder::merge);
+
+    if (!HAS_SPRING_CONFIGURATION_ANNOTATION.matches(tree, state)) {
+      SuggestedFixes.addModifiers(tree, state, Modifier.FINAL).ifPresent(fixBuilder::merge);
+    }
+
+    return describeMatch(tree, fixBuilder.build());
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/JUnitMethodDeclaration.java

@@ -0,0 +1,118 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.enclosingClass;
+import static com.google.errorprone.matchers.Matchers.hasModifier;
+import static com.google.errorprone.matchers.Matchers.not;
+import static java.util.function.Predicate.not;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+import static tech.picnic.errorprone.bugpatterns.util.MoreJUnitMatchers.SETUP_OR_TEARDOWN_METHOD;
+import static tech.picnic.errorprone.bugpatterns.util.MoreJUnitMatchers.TEST_METHOD;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Sets;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.MethodTree;
+import com.sun.tools.javac.code.Symbol.MethodSymbol;
+import java.util.Optional;
+import javax.lang.model.element.Modifier;
+import tech.picnic.errorprone.bugpatterns.util.ConflictDetection;
+
+/** A {@link BugChecker} that flags non-canonical JUnit method declarations. */
+// XXX: Consider introducing a class-level check that enforces that test classes:
+// 1. Are named `*Test` or `Abstract*TestCase`.
+// 2. If not `abstract`, are package-private and don't have public methods and subclasses.
+// 3. Only have private fields.
+// XXX: If implemented, the current logic could flag only `private` JUnit methods.
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "JUnit method declaration can likely be improved",
+    link = BUG_PATTERNS_BASE_URL + "JUnitMethodDeclaration",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class JUnitMethodDeclaration extends BugChecker implements MethodTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final String TEST_PREFIX = "test";
+  private static final ImmutableSet<Modifier> ILLEGAL_MODIFIERS =
+      Sets.immutableEnumSet(Modifier.PRIVATE, Modifier.PROTECTED, Modifier.PUBLIC);
+  private static final Matcher<MethodTree> IS_LIKELY_OVERRIDDEN =
+      allOf(
+          not(hasModifier(Modifier.FINAL)),
+          not(hasModifier(Modifier.PRIVATE)),
+          enclosingClass(hasModifier(Modifier.ABSTRACT)));
+
+  /** Instantiates a new {@link JUnitMethodDeclaration} instance. */
+  public JUnitMethodDeclaration() {}
+
+  @Override
+  public Description matchMethod(MethodTree tree, VisitorState state) {
+    if (IS_LIKELY_OVERRIDDEN.matches(tree, state) || isOverride(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    boolean isTestMethod = TEST_METHOD.matches(tree, state);
+    if (!isTestMethod && !SETUP_OR_TEARDOWN_METHOD.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    SuggestedFix.Builder fixBuilder = SuggestedFix.builder();
+    SuggestedFixes.removeModifiers(tree.getModifiers(), state, ILLEGAL_MODIFIERS)
+        .ifPresent(fixBuilder::merge);
+
+    if (isTestMethod) {
+      suggestTestMethodRenameIfApplicable(tree, fixBuilder, state);
+    }
+
+    return fixBuilder.isEmpty() ? Description.NO_MATCH : describeMatch(tree, fixBuilder.build());
+  }
+
+  private void suggestTestMethodRenameIfApplicable(
+      MethodTree tree, SuggestedFix.Builder fixBuilder, VisitorState state) {
+    MethodSymbol symbol = ASTHelpers.getSymbol(tree);
+    tryCanonicalizeMethodName(symbol)
+        .ifPresent(
+            newName ->
+                ConflictDetection.findMethodRenameBlocker(symbol, newName, state)
+                    .ifPresentOrElse(
+                        blocker -> reportMethodRenameBlocker(tree, blocker, state),
+                        () -> fixBuilder.merge(SuggestedFixes.renameMethod(tree, newName, state))));
+  }
+
+  private void reportMethodRenameBlocker(MethodTree tree, String reason, VisitorState state) {
+    state.reportMatch(
+        buildDescription(tree)
+            .setMessage(
+                String.format(
+                    "This method's name should not redundantly start with `%s` (but note that %s)",
+                    TEST_PREFIX, reason))
+            .build());
+  }
+
+  private static Optional<String> tryCanonicalizeMethodName(MethodSymbol symbol) {
+    return Optional.of(symbol.getQualifiedName().toString())
+        .filter(name -> name.startsWith(TEST_PREFIX))
+        .map(name -> name.substring(TEST_PREFIX.length()))
+        .filter(not(String::isEmpty))
+        .map(name -> Character.toLowerCase(name.charAt(0)) + name.substring(1))
+        .filter(name -> !Character.isDigit(name.charAt(0)));
+  }
+
+  private static boolean isOverride(MethodTree tree, VisitorState state) {
+    return ASTHelpers.streamSuperMethods(ASTHelpers.getSymbol(tree), state.getTypes())
+        .findAny()
+        .isPresent();
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/JUnitMethodDeclarationCheck.java

@@ -1,114 +0,0 @@
-package tech.picnic.errorprone.bugpatterns;
-
-import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
-import static com.google.errorprone.matchers.Matchers.annotations;
-import static com.google.errorprone.matchers.Matchers.anyOf;
-import static com.google.errorprone.matchers.Matchers.isType;
-import static java.util.function.Predicate.not;
-
-import com.google.auto.service.AutoService;
-import com.google.common.collect.ImmutableSet;
-import com.google.errorprone.BugPattern;
-import com.google.errorprone.VisitorState;
-import com.google.errorprone.bugpatterns.BugChecker;
-import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
-import com.google.errorprone.fixes.SuggestedFix;
-import com.google.errorprone.fixes.SuggestedFixes;
-import com.google.errorprone.matchers.Description;
-import com.google.errorprone.matchers.Matcher;
-import com.google.errorprone.matchers.MultiMatcher;
-import com.google.errorprone.predicates.TypePredicate;
-import com.google.errorprone.util.ASTHelpers;
-import com.sun.source.tree.AnnotationTree;
-import com.sun.source.tree.MethodTree;
-import com.sun.tools.javac.code.Symbol;
-import java.util.Optional;
-import javax.lang.model.element.Modifier;
-
-/** A {@link BugChecker} which flags non-canonical JUnit method declarations. */
-// XXX: Consider introducing a class-level check which enforces that test classes:
-// 1. Are named `*Test` or `Abstract*TestCase`.
-// 2. If not `abstract`, don't have public methods and subclasses.
-// 3. Only have private fields.
-// XXX: If implemented, the current logic could flag only `private` JUnit methods.
-@AutoService(BugChecker.class)
-@BugPattern(
-    name = "JUnitMethodDeclaration",
-    summary = "JUnit method declaration can likely be improved",
-    linkType = BugPattern.LinkType.NONE,
-    severity = BugPattern.SeverityLevel.SUGGESTION,
-    tags = BugPattern.StandardTags.SIMPLIFICATION)
-public final class JUnitMethodDeclarationCheck extends BugChecker implements MethodTreeMatcher {
-  private static final long serialVersionUID = 1L;
-  private static final String TEST_PREFIX = "test";
-  private static final ImmutableSet<Modifier> ILLEGAL_MODIFIERS =
-      ImmutableSet.of(Modifier.PRIVATE, Modifier.PROTECTED, Modifier.PUBLIC);
-  private static final MultiMatcher<MethodTree, AnnotationTree> OVERRIDE_METHOD =
-      annotations(AT_LEAST_ONE, isType("java.lang.Override"));
-  private static final MultiMatcher<MethodTree, AnnotationTree> TEST_METHOD =
-      annotations(
-          AT_LEAST_ONE,
-          anyOf(
-              isType("org.junit.jupiter.api.Test"),
-              hasMetaAnnotation("org.junit.jupiter.api.TestTemplate")));
-  private static final MultiMatcher<MethodTree, AnnotationTree> SETUP_OR_TEARDOWN_METHOD =
-      annotations(
-          AT_LEAST_ONE,
-          anyOf(
-              isType("org.junit.jupiter.api.AfterAll"),
-              isType("org.junit.jupiter.api.AfterEach"),
-              isType("org.junit.jupiter.api.BeforeAll"),
-              isType("org.junit.jupiter.api.BeforeEach")));
-
-  @Override
-  public Description matchMethod(MethodTree tree, VisitorState state) {
-    // XXX: Perhaps we should also skip analysis of non-`private` non-`final` methods in abstract
-    // classes?
-    if (OVERRIDE_METHOD.matches(tree, state)) {
-      return Description.NO_MATCH;
-    }
-
-    boolean isTestMethod = TEST_METHOD.matches(tree, state);
-    if (!isTestMethod && !SETUP_OR_TEARDOWN_METHOD.matches(tree, state)) {
-      return Description.NO_MATCH;
-    }
-
-    SuggestedFix.Builder builder = SuggestedFix.builder();
-    SuggestedFixes.removeModifiers(tree.getModifiers(), state, ILLEGAL_MODIFIERS)
-        .ifPresent(builder::merge);
-
-    if (isTestMethod) {
-      // XXX: In theory this rename could clash with an existing method or static import. In that
-      // case we should emit a warning without a suggested replacement.
-      tryCanonicalizeMethodName(tree, state).ifPresent(builder::merge);
-    }
-
-    return builder.isEmpty() ? Description.NO_MATCH : describeMatch(tree, builder.build());
-  }
-
-  private static Optional<SuggestedFix> tryCanonicalizeMethodName(
-      MethodTree tree, VisitorState state) {
-    return Optional.ofNullable(ASTHelpers.getSymbol(tree))
-        .map(sym -> sym.getQualifiedName().toString())
-        .filter(name -> name.startsWith(TEST_PREFIX))
-        .map(name -> name.substring(TEST_PREFIX.length()))
-        .filter(not(String::isEmpty))
-        .map(name -> Character.toLowerCase(name.charAt(0)) + name.substring(1))
-        .filter(name -> !Character.isDigit(name.charAt(0)))
-        .map(name -> SuggestedFixes.renameMethod(tree, name, state));
-  }
-
-  // XXX: Move to a `MoreMatchers` utility class.
-  private static Matcher<AnnotationTree> hasMetaAnnotation(String annotationClassName) {
-    TypePredicate typePredicate = hasAnnotation(annotationClassName);
-    return (tree, state) -> {
-      Symbol sym = ASTHelpers.getSymbol(tree);
-      return sym != null && typePredicate.apply(sym.type, state);
-    };
-  }
-
-  // XXX: Move to a `MoreTypePredicates` utility class.
-  private static TypePredicate hasAnnotation(String annotationClassName) {
-    return (type, state) -> ASTHelpers.hasAnnotation(type.tsym, annotationClassName, state);
-  }
-}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/JUnitValueSource.java

@@ -0,0 +1,307 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.ALL;
+import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.anything;
+import static com.google.errorprone.matchers.Matchers.argument;
+import static com.google.errorprone.matchers.Matchers.argumentCount;
+import static com.google.errorprone.matchers.Matchers.classLiteral;
+import static com.google.errorprone.matchers.Matchers.hasArguments;
+import static com.google.errorprone.matchers.Matchers.isPrimitiveOrBoxedPrimitiveType;
+import static com.google.errorprone.matchers.Matchers.isSameType;
+import static com.google.errorprone.matchers.Matchers.methodHasParameters;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static com.google.errorprone.matchers.Matchers.toType;
+import static java.util.function.Predicate.not;
+import static java.util.stream.Collectors.joining;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+import static tech.picnic.errorprone.bugpatterns.util.MoreJUnitMatchers.HAS_METHOD_SOURCE;
+import static tech.picnic.errorprone.bugpatterns.util.MoreJUnitMatchers.getMethodSourceFactoryNames;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.Iterables;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.LambdaExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.source.tree.MethodTree;
+import com.sun.source.tree.NewArrayTree;
+import com.sun.source.tree.ReturnTree;
+import com.sun.source.util.TreeScanner;
+import com.sun.tools.javac.code.Type;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.Locale;
+import java.util.Optional;
+import java.util.Set;
+import java.util.function.Predicate;
+import java.util.stream.DoubleStream;
+import java.util.stream.IntStream;
+import java.util.stream.LongStream;
+import java.util.stream.Stream;
+import org.jspecify.annotations.Nullable;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags JUnit tests with a {@link
+ * org.junit.jupiter.params.provider.MethodSource} annotation that can be replaced with an
+ * equivalent {@link org.junit.jupiter.params.provider.ValueSource} annotation.
+ */
+// XXX: Where applicable, also flag `@MethodSource` annotations that reference multiple value
+// factory methods (or that repeat the same value factory method multiple times).
+// XXX: Support inlining of overloaded value factory methods.
+// XXX: Support inlining of value factory methods referenced by multiple `@MethodSource`
+// annotations.
+// XXX: Support value factory return expressions of the form `Stream.of(a, b,
+// c).map(Arguments::argument)`.
+// XXX: Support simplification of test methods that accept additional injected parameters such as
+// `TestInfo`; such parameters should be ignored for the purpose of this check.
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Prefer `@ValueSource` over a `@MethodSource` where possible and reasonable",
+    linkType = CUSTOM,
+    link = BUG_PATTERNS_BASE_URL + "JUnitValueSource",
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class JUnitValueSource extends BugChecker implements MethodTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> SUPPORTED_VALUE_FACTORY_VALUES =
+      anyOf(
+          isArrayArgumentValueCandidate(),
+          toType(
+              MethodInvocationTree.class,
+              allOf(
+                  staticMethod()
+                      .onClass("org.junit.jupiter.params.provider.Arguments")
+                      .namedAnyOf("arguments", "of"),
+                  argumentCount(1),
+                  argument(0, isArrayArgumentValueCandidate()))));
+  private static final Matcher<ExpressionTree> ARRAY_OF_SUPPORTED_SINGLE_VALUE_ARGUMENTS =
+      isSingleDimensionArrayCreationWithAllElementsMatching(SUPPORTED_VALUE_FACTORY_VALUES);
+  private static final Matcher<ExpressionTree> ENUMERATION_OF_SUPPORTED_SINGLE_VALUE_ARGUMENTS =
+      toType(
+          MethodInvocationTree.class,
+          allOf(
+              staticMethod()
+                  .onClassAny(
+                      Stream.class.getName(),
+                      IntStream.class.getName(),
+                      LongStream.class.getName(),
+                      DoubleStream.class.getName(),
+                      List.class.getName(),
+                      Set.class.getName(),
+                      "com.google.common.collect.ImmutableList",
+                      "com.google.common.collect.ImmutableSet")
+                  .named("of"),
+              hasArguments(AT_LEAST_ONE, anything()),
+              hasArguments(ALL, SUPPORTED_VALUE_FACTORY_VALUES)));
+  private static final Matcher<MethodTree> IS_UNARY_METHOD_WITH_SUPPORTED_PARAMETER =
+      methodHasParameters(
+          anyOf(
+              isPrimitiveOrBoxedPrimitiveType(),
+              isSameType(String.class),
+              isSameType(state -> state.getSymtab().classType)));
+
+  /** Instantiates a new {@link JUnitValueSource} instance. */
+  public JUnitValueSource() {}
+
+  @Override
+  public Description matchMethod(MethodTree tree, VisitorState state) {
+    if (!IS_UNARY_METHOD_WITH_SUPPORTED_PARAMETER.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    Type parameterType = ASTHelpers.getType(Iterables.getOnlyElement(tree.getParameters()));
+
+    return findMethodSourceAnnotation(tree, state)
+        .flatMap(
+            methodSourceAnnotation ->
+                getSoleLocalFactoryName(methodSourceAnnotation, tree)
+                    .filter(factory -> !hasSiblingReferencingValueFactory(tree, factory, state))
+                    .flatMap(factory -> findSiblingWithName(tree, factory, state))
+                    .flatMap(
+                        factoryMethod ->
+                            tryConstructValueSourceFix(
+                                parameterType, methodSourceAnnotation, factoryMethod, state))
+                    .map(fix -> describeMatch(methodSourceAnnotation, fix)))
+        .orElse(Description.NO_MATCH);
+  }
+
+  /**
+   * Returns the name of the value factory method pointed to by the given {@code @MethodSource}
+   * annotation, if it (a) is the only one and (b) is a method in the same class as the annotated
+   * method.
+   */
+  private static Optional<String> getSoleLocalFactoryName(
+      AnnotationTree methodSourceAnnotation, MethodTree method) {
+    return getElementIfSingleton(getMethodSourceFactoryNames(methodSourceAnnotation, method))
+        .filter(name -> name.indexOf('#') < 0);
+  }
+
+  /**
+   * Tells whether the given method has a sibling method in the same class that depends on the
+   * specified value factory method.
+   */
+  private static boolean hasSiblingReferencingValueFactory(
+      MethodTree tree, String valueFactory, VisitorState state) {
+    return findMatchingSibling(tree, m -> hasValueFactory(m, valueFactory, state), state)
+        .isPresent();
+  }
+
+  private static Optional<MethodTree> findSiblingWithName(
+      MethodTree tree, String methodName, VisitorState state) {
+    return findMatchingSibling(tree, m -> m.getName().contentEquals(methodName), state);
+  }
+
+  private static Optional<MethodTree> findMatchingSibling(
+      MethodTree tree, Predicate<? super MethodTree> predicate, VisitorState state) {
+    return state.findEnclosing(ClassTree.class).getMembers().stream()
+        .filter(MethodTree.class::isInstance)
+        .map(MethodTree.class::cast)
+        .filter(not(tree::equals))
+        .filter(predicate)
+        .findFirst();
+  }
+
+  private static boolean hasValueFactory(
+      MethodTree tree, String valueFactoryMethodName, VisitorState state) {
+    return findMethodSourceAnnotation(tree, state).stream()
+        .anyMatch(
+            annotation ->
+                getMethodSourceFactoryNames(annotation, tree).contains(valueFactoryMethodName));
+  }
+
+  private static Optional<AnnotationTree> findMethodSourceAnnotation(
+      MethodTree tree, VisitorState state) {
+    return HAS_METHOD_SOURCE.multiMatchResult(tree, state).matchingNodes().stream().findFirst();
+  }
+
+  private static Optional<SuggestedFix> tryConstructValueSourceFix(
+      Type parameterType,
+      AnnotationTree methodSourceAnnotation,
+      MethodTree valueFactoryMethod,
+      VisitorState state) {
+    return getSingleReturnExpression(valueFactoryMethod)
+        .flatMap(expression -> tryExtractValueSourceAttributeValue(expression, state))
+        .map(
+            valueSourceAttributeValue ->
+                SuggestedFix.builder()
+                    .addImport("org.junit.jupiter.params.provider.ValueSource")
+                    .replace(
+                        methodSourceAnnotation,
+                        String.format(
+                            "@ValueSource(%s = %s)",
+                            toValueSourceAttributeName(parameterType), valueSourceAttributeValue))
+                    .delete(valueFactoryMethod)
+                    .build());
+  }
+
+  // XXX: This pattern also occurs a few times inside Error Prone; contribute upstream.
+  private static Optional<ExpressionTree> getSingleReturnExpression(MethodTree methodTree) {
+    List<ExpressionTree> returnExpressions = new ArrayList<>();
+    new TreeScanner<@Nullable Void, @Nullable Void>() {
+      @Override
+      public @Nullable Void visitClass(ClassTree node, @Nullable Void unused) {
+        /* Ignore `return` statements inside anonymous/local classes. */
+        return null;
+      }
+
+      @Override
+      public @Nullable Void visitReturn(ReturnTree node, @Nullable Void unused) {
+        returnExpressions.add(node.getExpression());
+        return super.visitReturn(node, unused);
+      }
+
+      @Override
+      public @Nullable Void visitLambdaExpression(
+          LambdaExpressionTree node, @Nullable Void unused) {
+        /* Ignore `return` statements inside lambda expressions. */
+        return null;
+      }
+    }.scan(methodTree, null);
+
+    return getElementIfSingleton(returnExpressions);
+  }
+
+  private static Optional<String> tryExtractValueSourceAttributeValue(
+      ExpressionTree tree, VisitorState state) {
+    List<? extends ExpressionTree> arguments;
+    if (ENUMERATION_OF_SUPPORTED_SINGLE_VALUE_ARGUMENTS.matches(tree, state)) {
+      arguments = ((MethodInvocationTree) tree).getArguments();
+    } else if (ARRAY_OF_SUPPORTED_SINGLE_VALUE_ARGUMENTS.matches(tree, state)) {
+      arguments = ((NewArrayTree) tree).getInitializers();
+    } else {
+      return Optional.empty();
+    }
+
+    /*
+     * Join the values into a comma-separated string, unwrapping `Arguments` factory method
+     * invocations if applicable.
+     */
+    return Optional.of(
+            arguments.stream()
+                .map(
+                    arg ->
+                        arg instanceof MethodInvocationTree
+                            ? Iterables.getOnlyElement(((MethodInvocationTree) arg).getArguments())
+                            : arg)
+                .map(argument -> SourceCode.treeToString(argument, state))
+                .collect(joining(", ")))
+        .map(value -> arguments.size() > 1 ? String.format("{%s}", value) : value);
+  }
+
+  private static String toValueSourceAttributeName(Type type) {
+    String typeString = type.tsym.name.toString();
+
+    switch (typeString) {
+      case "Class":
+        return "classes";
+      case "Character":
+        return "chars";
+      case "Integer":
+        return "ints";
+      default:
+        return typeString.toLowerCase(Locale.ROOT) + 's';
+    }
+  }
+
+  private static <T> Optional<T> getElementIfSingleton(Collection<T> collection) {
+    return Optional.of(collection)
+        .filter(elements -> elements.size() == 1)
+        .map(Iterables::getOnlyElement);
+  }
+
+  private static Matcher<ExpressionTree> isSingleDimensionArrayCreationWithAllElementsMatching(
+      Matcher<? super ExpressionTree> elementMatcher) {
+    return (tree, state) -> {
+      if (!(tree instanceof NewArrayTree)) {
+        return false;
+      }
+
+      NewArrayTree newArray = (NewArrayTree) tree;
+      return newArray.getDimensions().isEmpty()
+          && !newArray.getInitializers().isEmpty()
+          && newArray.getInitializers().stream()
+              .allMatch(element -> elementMatcher.matches(element, state));
+    };
+  }
+
+  private static Matcher<ExpressionTree> isArrayArgumentValueCandidate() {
+    return anyOf(classLiteral(anything()), (tree, state) -> ASTHelpers.constValue(tree) != null);
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/LexicographicalAnnotationAttributeListing.java

@@ -1,17 +1,20 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.STYLE;
 import static java.util.Comparator.comparing;
 import static java.util.Comparator.naturalOrder;
 import static java.util.stream.Collectors.joining;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
+import com.google.common.base.Splitter;
 import com.google.common.collect.Comparators;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.ErrorProneFlags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
@@ -37,21 +40,25 @@ import java.util.List;
 import java.util.Optional;
 import java.util.Set;
 import java.util.stream.Stream;
+import org.jspecify.annotations.Nullable;
+import tech.picnic.errorprone.bugpatterns.util.AnnotationAttributeMatcher;
+import tech.picnic.errorprone.bugpatterns.util.Flags;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
- * A {@link BugChecker} which flags annotation array listings which aren't sorted lexicographically.
+ * A {@link BugChecker} that flags annotation array listings which aren't sorted lexicographically.
  *
  * <p>The idea behind this checker is that maintaining a sorted sequence simplifies conflict
  * resolution, and can even avoid it if two branches add the same entry.
  */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "LexicographicalAnnotationAttributeListing",
     summary = "Where possible, sort annotation array attributes lexicographically",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.STYLE)
-public final class LexicographicalAnnotationAttributeListingCheck extends BugChecker
+    link = BUG_PATTERNS_BASE_URL + "LexicographicalAnnotationAttributeListing",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = STYLE)
+public final class LexicographicalAnnotationAttributeListing extends BugChecker
     implements AnnotationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final ImmutableSet<String> BLACKLISTED_ANNOTATIONS =
@@ -60,24 +67,33 @@ public final class LexicographicalAnnotationAttributeListingCheck extends BugChe
           "com.fasterxml.jackson.annotation.JsonPropertyOrder#value",
           "io.swagger.annotations.ApiImplicitParams#value",
           "io.swagger.v3.oas.annotations.Parameters#value",
-          "javax.xml.bind.annotation.XmlType#propOrder");
+          "javax.xml.bind.annotation.XmlType#propOrder",
+          "org.springframework.context.annotation.PropertySource#value",
+          "org.springframework.test.context.TestPropertySource#locations",
+          "org.springframework.test.context.TestPropertySource#value");
   private static final String FLAG_PREFIX = "LexicographicalAnnotationAttributeListing:";
   private static final String INCLUDED_ANNOTATIONS_FLAG = FLAG_PREFIX + "Includes";
   private static final String EXCLUDED_ANNOTATIONS_FLAG = FLAG_PREFIX + "Excludes";
+  /**
+   * The splitter applied to string-typed annotation arguments prior to lexicographical sorting. By
+   * splitting on {@code =}, strings that represent e.g. inline Spring property declarations are
+   * properly sorted by key, then value.
+   */
+  private static final Splitter STRING_ARGUMENT_SPLITTER = Splitter.on('=');
 
   private final AnnotationAttributeMatcher matcher;
 
-  /** Instantiates the default {@link LexicographicalAnnotationAttributeListingCheck}. */
-  public LexicographicalAnnotationAttributeListingCheck() {
+  /** Instantiates a default {@link LexicographicalAnnotationAttributeListing} instance. */
+  public LexicographicalAnnotationAttributeListing() {
     this(ErrorProneFlags.empty());
   }
 
   /**
-   * Instantiates a customized {@link LexicographicalAnnotationAttributeListingCheck}.
+   * Instantiates a customized {@link LexicographicalAnnotationAttributeListing}.
    *
    * @param flags Any provided command line flags.
    */
-  public LexicographicalAnnotationAttributeListingCheck(ErrorProneFlags flags) {
+  public LexicographicalAnnotationAttributeListing(ErrorProneFlags flags) {
     matcher = createAnnotationAttributeMatcher(flags);
   }
 
@@ -119,7 +135,7 @@ public final class LexicographicalAnnotationAttributeListingCheck extends BugChe
     }
 
     List<? extends ExpressionTree> actualOrdering = array.getInitializers();
-    ImmutableList<? extends ExpressionTree> desiredOrdering = doSort(actualOrdering, state);
+    ImmutableList<? extends ExpressionTree> desiredOrdering = doSort(actualOrdering);
     if (actualOrdering.equals(desiredOrdering)) {
       /* In the (presumably) common case the elements are already sorted. */
       return Optional.empty();
@@ -128,7 +144,7 @@ public final class LexicographicalAnnotationAttributeListingCheck extends BugChe
     /* The elements aren't sorted. Suggest the sorted alternative. */
     String suggestion =
         desiredOrdering.stream()
-            .map(expr -> Util.treeToString(expr, state))
+            .map(expr -> SourceCode.treeToString(expr, state))
             .collect(joining(", ", "{", "}"));
     return Optional.of(SuggestedFix.builder().replace(array, suggestion));
   }
@@ -149,12 +165,12 @@ public final class LexicographicalAnnotationAttributeListingCheck extends BugChe
   }
 
   private static ImmutableList<? extends ExpressionTree> doSort(
-      Iterable<? extends ExpressionTree> elements, VisitorState state) {
+      Iterable<? extends ExpressionTree> elements) {
     // XXX: Perhaps we should use `Collator` with `.setStrength(Collator.PRIMARY)` and
     // `getCollationKey`. Not clear whether that's worth the hassle at this point.
     return ImmutableList.sortedCopyOf(
         comparing(
-            e -> getStructure(e, state),
+            LexicographicalAnnotationAttributeListing::getStructure,
             Comparators.lexicographical(
                 Comparators.lexicographical(
                     String.CASE_INSENSITIVE_ORDER.thenComparing(naturalOrder())))),
@@ -166,35 +182,31 @@ public final class LexicographicalAnnotationAttributeListingCheck extends BugChe
    * performed. This approach disregards e.g. irrelevant whitespace. It also allows special
    * structure within string literals to be respected.
    */
-  private static ImmutableList<ImmutableList<String>> getStructure(
-      ExpressionTree array, VisitorState state) {
+  private static ImmutableList<ImmutableList<String>> getStructure(ExpressionTree array) {
     ImmutableList.Builder<ImmutableList<String>> nodes = ImmutableList.builder();
 
-    new TreeScanner<Void, Void>() {
+    new TreeScanner<@Nullable Void, @Nullable Void>() {
       @Override
-      public Void visitIdentifier(IdentifierTree node, Void ctx) {
-        nodes.add(tokenize(node));
-        return super.visitIdentifier(node, ctx);
+      public @Nullable Void visitIdentifier(IdentifierTree node, @Nullable Void unused) {
+        nodes.add(ImmutableList.of(node.getName().toString()));
+        return super.visitIdentifier(node, unused);
       }
 
       @Override
-      public Void visitLiteral(LiteralTree node, Void ctx) {
-        nodes.add(tokenize(node));
-        return super.visitLiteral(node, ctx);
+      public @Nullable Void visitLiteral(LiteralTree node, @Nullable Void unused) {
+        Object value = ASTHelpers.constValue(node);
+        nodes.add(
+            value instanceof String
+                ? STRING_ARGUMENT_SPLITTER.splitToStream((String) value).collect(toImmutableList())
+                : ImmutableList.of(String.valueOf(value)));
+
+        return super.visitLiteral(node, unused);
       }
 
       @Override
-      public Void visitPrimitiveType(PrimitiveTypeTree node, Void ctx) {
-        nodes.add(tokenize(node));
-        return super.visitPrimitiveType(node, ctx);
-      }
-
-      private ImmutableList<String> tokenize(Tree node) {
-        /*
-         * Tokens are split on `=` so that e.g. inline Spring property declarations are properly
-         * sorted by key, then value.
-         */
-        return ImmutableList.copyOf(Util.treeToString(node, state).split("=", -1));
+      public @Nullable Void visitPrimitiveType(PrimitiveTypeTree node, @Nullable Void unused) {
+        nodes.add(ImmutableList.of(node.getPrimitiveTypeKind().toString()));
+        return super.visitPrimitiveType(node, unused);
       }
     }.scan(array, null);
 
@@ -209,7 +221,7 @@ public final class LexicographicalAnnotationAttributeListingCheck extends BugChe
 
   private static ImmutableList<String> excludedAnnotations(ErrorProneFlags flags) {
     Set<String> exclusions = new HashSet<>();
-    flags.getList(EXCLUDED_ANNOTATIONS_FLAG).ifPresent(exclusions::addAll);
+    exclusions.addAll(Flags.getList(flags, EXCLUDED_ANNOTATIONS_FLAG));
     exclusions.addAll(BLACKLISTED_ANNOTATIONS);
     return ImmutableList.copyOf(exclusions);
   }

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/LexicographicalAnnotationListing.java

@@ -0,0 +1,99 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.STYLE;
+import static com.sun.tools.javac.code.TypeAnnotations.AnnotationType.DECLARATION;
+import static com.sun.tools.javac.code.TypeAnnotations.AnnotationType.TYPE;
+import static java.util.Comparator.comparing;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.common.base.VerifyException;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Streams;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
+import com.google.errorprone.fixes.Fix;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.MethodTree;
+import com.sun.tools.javac.code.Symbol;
+import com.sun.tools.javac.code.TypeAnnotations.AnnotationType;
+import java.util.Comparator;
+import java.util.List;
+import org.jspecify.annotations.Nullable;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags annotations that are not lexicographically sorted.
+ *
+ * <p>The idea behind this checker is that maintaining a sorted sequence simplifies conflict
+ * resolution, and can even avoid it if two branches add the same annotation.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Sort annotations lexicographically where possible",
+    link = BUG_PATTERNS_BASE_URL + "LexicographicalAnnotationListing",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = STYLE)
+public final class LexicographicalAnnotationListing extends BugChecker
+    implements MethodTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Comparator<@Nullable AnnotationType> BY_ANNOTATION_TYPE =
+      (a, b) ->
+          (a == null || a == DECLARATION) && b == TYPE ? -1 : a == TYPE && b == DECLARATION ? 1 : 0;
+
+  /** Instantiates a new {@link LexicographicalAnnotationListing} instance. */
+  public LexicographicalAnnotationListing() {}
+
+  @Override
+  public Description matchMethod(MethodTree tree, VisitorState state) {
+    List<? extends AnnotationTree> originalOrdering = tree.getModifiers().getAnnotations();
+    if (originalOrdering.size() < 2) {
+      return Description.NO_MATCH;
+    }
+
+    ImmutableList<? extends AnnotationTree> sortedAnnotations =
+        sort(originalOrdering, ASTHelpers.getSymbol(tree), state);
+    if (originalOrdering.equals(sortedAnnotations)) {
+      return Description.NO_MATCH;
+    }
+
+    return describeMatch(
+        originalOrdering.get(0), fixOrdering(originalOrdering, sortedAnnotations, state));
+  }
+
+  private static ImmutableList<? extends AnnotationTree> sort(
+      List<? extends AnnotationTree> annotations, Symbol symbol, VisitorState state) {
+    return annotations.stream()
+        .sorted(
+            comparing(
+                    (AnnotationTree annotation) ->
+                        ASTHelpers.getAnnotationType(annotation, symbol, state),
+                    BY_ANNOTATION_TYPE)
+                .thenComparing(annotation -> SourceCode.treeToString(annotation, state)))
+        .collect(toImmutableList());
+  }
+
+  private static Fix fixOrdering(
+      List<? extends AnnotationTree> originalAnnotations,
+      ImmutableList<? extends AnnotationTree> sortedAnnotations,
+      VisitorState state) {
+    return Streams.zip(
+            originalAnnotations.stream(),
+            sortedAnnotations.stream(),
+            (original, replacement) ->
+                SuggestedFix.builder()
+                    .replace(original, SourceCode.treeToString(replacement, state)))
+        .reduce(SuggestedFix.Builder::merge)
+        .map(SuggestedFix.Builder::build)
+        .orElseThrow(() -> new VerifyException("No annotations were provided"));
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/LexicographicalAnnotationListingCheck.java

@@ -1,79 +0,0 @@
-package tech.picnic.errorprone.bugpatterns;
-
-import static com.google.common.collect.ImmutableList.toImmutableList;
-import static java.util.Comparator.comparing;
-
-import com.google.auto.service.AutoService;
-import com.google.common.collect.ImmutableList;
-import com.google.common.collect.Streams;
-import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
-import com.google.errorprone.VisitorState;
-import com.google.errorprone.bugpatterns.BugChecker;
-import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
-import com.google.errorprone.fixes.Fix;
-import com.google.errorprone.fixes.SuggestedFix;
-import com.google.errorprone.matchers.Description;
-import com.sun.source.tree.AnnotationTree;
-import com.sun.source.tree.MethodTree;
-import java.util.List;
-import java.util.Optional;
-
-/**
- * A {@link BugChecker} that flags annotations that are not lexicographically sorted.
- *
- * <p>The idea behind this checker is that maintaining a sorted sequence simplifies conflict
- * resolution, and can even avoid it if two branches add the same annotation.
- */
-@AutoService(BugChecker.class)
-@BugPattern(
-    name = "LexicographicalAnnotationListing",
-    summary = "Sort annotations lexicographically where possible",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.STYLE)
-public final class LexicographicalAnnotationListingCheck extends BugChecker
-    implements MethodTreeMatcher {
-  private static final long serialVersionUID = 1L;
-
-  @Override
-  public Description matchMethod(MethodTree tree, VisitorState state) {
-    List<? extends AnnotationTree> originalOrdering = tree.getModifiers().getAnnotations();
-    if (originalOrdering.size() < 2) {
-      return Description.NO_MATCH;
-    }
-
-    ImmutableList<? extends AnnotationTree> sortedAnnotations = sort(originalOrdering, state);
-    if (originalOrdering.equals(sortedAnnotations)) {
-      return Description.NO_MATCH;
-    }
-
-    Optional<Fix> fix = tryFixOrdering(originalOrdering, sortedAnnotations, state);
-
-    Description.Builder description = buildDescription(tree);
-    fix.ifPresent(description::addFix);
-    return description.build();
-  }
-
-  private static ImmutableList<? extends AnnotationTree> sort(
-      List<? extends AnnotationTree> annotations, VisitorState state) {
-    return annotations.stream()
-        .sorted(comparing(annotation -> Util.treeToString(annotation, state)))
-        .collect(toImmutableList());
-  }
-
-  private static Optional<Fix> tryFixOrdering(
-      List<? extends AnnotationTree> originalAnnotations,
-      ImmutableList<? extends AnnotationTree> sortedAnnotations,
-      VisitorState state) {
-    return Streams.zip(
-            originalAnnotations.stream(),
-            sortedAnnotations.stream(),
-            (original, replacement) ->
-                SuggestedFix.builder().replace(original, Util.treeToString(replacement, state)))
-        .reduce(SuggestedFix.Builder::merge)
-        .map(SuggestedFix.Builder::build);
-  }
-}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/MethodReferenceUsage.java

@@ -1,14 +1,15 @@
 package tech.picnic.errorprone.bugpatterns;
 
 import static com.google.common.collect.ImmutableList.toImmutableList;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.STYLE;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.common.base.VerifyException;
 import com.google.common.collect.ImmutableList;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.LambdaExpressionTreeMatcher;
@@ -35,7 +36,9 @@ import java.util.Optional;
 import javax.lang.model.element.Name;
 
 /**
- * A {@link BugChecker} which flags lambda expressions that can be replaced with method references.
+ * A {@link BugChecker} that flags lambda expressions that can be replaced with method references.
+ *
+ * @see IsInstanceLambdaUsage
  */
 // XXX: Other custom expressions we could rewrite:
 // - `a -> "str" + a` to `"str"::concat`. But only if `str` is provably non-null.
@@ -49,17 +52,22 @@ import javax.lang.model.element.Name;
 // `not(some::reference)`.
 // XXX: This check is extremely inefficient due to its reliance on `SuggestedFixes.compilesWithFix`.
 // Palantir's `LambdaMethodReference` check seems to suffer a similar issue at this time.
+// XXX: Expressions of the form `i -> SomeType.class.isInstance(i)` are not replaced; fix that using
+// a suitable generalization.
+// XXX: Consider folding the `IsInstanceLambdaUsage` check into this class.
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "MethodReferenceUsage",
     summary = "Prefer method references over lambda expressions",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.STYLE)
-public final class MethodReferenceUsageCheck extends BugChecker
-    implements LambdaExpressionTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "MethodReferenceUsage",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = STYLE)
+public final class MethodReferenceUsage extends BugChecker implements LambdaExpressionTreeMatcher {
   private static final long serialVersionUID = 1L;
 
+  /** Instantiates a new {@link MethodReferenceUsage} instance. */
+  public MethodReferenceUsage() {}
+
   @Override
   public Description matchLambdaExpression(LambdaExpressionTree tree, VisitorState state) {
     /*
@@ -102,6 +110,8 @@ public final class MethodReferenceUsageCheck extends BugChecker
         .flatMap(statements -> constructMethodRef(lambdaExpr, statements.get(0)));
   }
 
+  // XXX: Replace nested `Optional` usage.
+  @SuppressWarnings("NestedOptionals")
   private static Optional<SuggestedFix.Builder> constructMethodRef(
       LambdaExpressionTree lambdaExpr, MethodInvocationTree subTree) {
     return matchArguments(lambdaExpr, subTree)
@@ -120,7 +130,7 @@ public final class MethodReferenceUsageCheck extends BugChecker
           return Optional.empty();
         }
         Symbol sym = ASTHelpers.getSymbol(methodSelect);
-        if (!sym.isStatic()) {
+        if (!ASTHelpers.isStatic(sym)) {
           return constructFix(lambdaExpr, "this", methodSelect);
         }
         return constructFix(lambdaExpr, sym.owner, methodSelect);
@@ -158,6 +168,8 @@ public final class MethodReferenceUsageCheck extends BugChecker
     return constructFix(lambdaExpr, lhsType.tsym, subTree.getIdentifier());
   }
 
+  // XXX: Refactor or replace inner `Optional` with a custom type.
+  @SuppressWarnings("NestedOptionals")
   private static Optional<Optional<Name>> matchArguments(
       LambdaExpressionTree lambdaExpr, MethodInvocationTree subTree) {
     ImmutableList<Name> expectedArguments = getVariables(lambdaExpr);
@@ -188,7 +200,7 @@ public final class MethodReferenceUsageCheck extends BugChecker
     Name sName = target.getSimpleName();
     Optional<SuggestedFix.Builder> fix = constructFix(lambdaExpr, sName, methodName);
 
-    if (!"java.lang".equals(target.packge().toString())) {
+    if (!"java.lang".equals(ASTHelpers.enclosingPackage(target).toString())) {
       Name fqName = target.getQualifiedName();
       if (!sName.equals(fqName)) {
         return fix.map(b -> b.addImport(fqName.toString()));

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/MissingRefasterAnnotation.java

@@ -1,15 +1,16 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.LIKELY_ERROR;
 import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
 import static com.google.errorprone.matchers.Matchers.annotations;
 import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.Matchers.isType;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
@@ -24,12 +25,12 @@ import com.sun.source.tree.Tree;
 /** A {@link BugChecker} that flags likely missing Refaster annotations. */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "MissingRefasterAnnotation",
-    summary = "The Refaster template contains a method without any Refaster annotations",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.WARNING,
-    tags = StandardTags.LIKELY_ERROR)
-public final class MissingRefasterAnnotationCheck extends BugChecker implements ClassTreeMatcher {
+    summary = "The Refaster rule contains a method without any Refaster annotations",
+    link = BUG_PATTERNS_BASE_URL + "MissingRefasterAnnotation",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = LIKELY_ERROR)
+public final class MissingRefasterAnnotation extends BugChecker implements ClassTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final MultiMatcher<Tree, AnnotationTree> REFASTER_ANNOTATION =
       annotations(
@@ -39,6 +40,9 @@ public final class MissingRefasterAnnotationCheck extends BugChecker implements
               isType("com.google.errorprone.refaster.annotation.BeforeTemplate"),
               isType("com.google.errorprone.refaster.annotation.AfterTemplate")));
 
+  /** Instantiates a new {@link MissingRefasterAnnotation} instance. */
+  public MissingRefasterAnnotation() {}
+
   @Override
   public Description matchClass(ClassTree tree, VisitorState state) {
     long methodTypes =

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/MockitoMockClassReference.java

@@ -0,0 +1,86 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.argument;
+import static com.google.errorprone.matchers.Matchers.isSameType;
+import static com.google.errorprone.matchers.Matchers.isVariable;
+import static com.google.errorprone.matchers.Matchers.not;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.source.tree.Tree;
+import com.sun.source.tree.VariableTree;
+import java.util.List;
+import tech.picnic.errorprone.bugpatterns.util.MoreASTHelpers;
+
+/**
+ * A {@link BugChecker} that flags the use of {@link org.mockito.Mockito#mock(Class)} and {@link
+ * org.mockito.Mockito#spy(Class)} where instead the type to be mocked or spied can be derived from
+ * context.
+ */
+// XXX: This check currently does not flag method invocation arguments. When adding support for
+// this, consider that in some cases the type to be mocked or spied must be specified explicitly so
+// as to disambiguate between method overloads.
+// XXX: This check currently does not flag (implicit or explicit) lambda return expressions.
+// XXX: This check currently does not drop suppressions that become obsolete after the
+// suggested fix is applied; consider adding support for this.
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Don't unnecessarily pass a type to Mockito's `mock(Class)` and `spy(Class)` methods",
+    link = BUG_PATTERNS_BASE_URL + "MockitoMockClassReference",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class MockitoMockClassReference extends BugChecker
+    implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<MethodInvocationTree> MOCKITO_MOCK_OR_SPY_WITH_HARDCODED_TYPE =
+      allOf(
+          argument(0, allOf(isSameType(Class.class.getName()), not(isVariable()))),
+          staticMethod().onClass("org.mockito.Mockito").namedAnyOf("mock", "spy"));
+
+  /** Instantiates a new {@link MockitoMockClassReference} instance. */
+  public MockitoMockClassReference() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (!MOCKITO_MOCK_OR_SPY_WITH_HARDCODED_TYPE.matches(tree, state)
+        || !isTypeDerivableFromContext(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    List<? extends ExpressionTree> arguments = tree.getArguments();
+    return describeMatch(tree, SuggestedFixes.removeElement(arguments.get(0), arguments, state));
+  }
+
+  private static boolean isTypeDerivableFromContext(MethodInvocationTree tree, VisitorState state) {
+    Tree parent = state.getPath().getParentPath().getLeaf();
+    switch (parent.getKind()) {
+      case VARIABLE:
+        return !ASTHelpers.hasNoExplicitType((VariableTree) parent, state)
+            && MoreASTHelpers.areSameType(tree, parent, state);
+      case ASSIGNMENT:
+        return MoreASTHelpers.areSameType(tree, parent, state);
+      case RETURN:
+        return MoreASTHelpers.findMethodExitedOnReturn(state)
+            .filter(m -> MoreASTHelpers.areSameType(tree, m.getReturnType(), state))
+            .isPresent();
+      default:
+        return false;
+    }
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/MockitoStubbing.java

@@ -1,13 +1,14 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.common.collect.Iterables;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
@@ -17,23 +18,27 @@ import com.google.errorprone.matchers.Matcher;
 import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.MethodInvocationTree;
 import java.util.List;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
- * A {@link BugChecker} which flags method invocations for which all arguments are wrapped using
+ * A {@link BugChecker} that flags method invocations for which all arguments are wrapped using
  * {@link org.mockito.Mockito#eq}; this is redundant.
  */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "MockitoStubbing",
     summary = "Don't unnecessarily use Mockito's `eq(...)`",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.SIMPLIFICATION)
-public final class MockitoStubbingCheck extends BugChecker implements MethodInvocationTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "MockitoStubbing",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class MockitoStubbing extends BugChecker implements MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Matcher<ExpressionTree> MOCKITO_EQ_METHOD =
       staticMethod().onClass("org.mockito.ArgumentMatchers").named("eq");
 
+  /** Instantiates a new {@link MockitoStubbing} instance. */
+  public MockitoStubbing() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     List<? extends ExpressionTree> arguments = tree.getArguments();
@@ -45,7 +50,7 @@ public final class MockitoStubbingCheck extends BugChecker implements MethodInvo
     for (ExpressionTree arg : arguments) {
       suggestedFix.replace(
           arg,
-          Util.treeToString(
+          SourceCode.treeToString(
               Iterables.getOnlyElement(((MethodInvocationTree) arg).getArguments()), state));
     }
 

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/NestedOptionals.java

@@ -0,0 +1,51 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.FRAGILE_CODE;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.generic;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.raw;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.subOf;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.suppliers.Supplier;
+import com.google.errorprone.suppliers.Suppliers;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.tools.javac.code.Type;
+import java.util.Optional;
+
+/** A {@link BugChecker} that flags nesting of {@link Optional Optionals}. */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary =
+        "Avoid nesting `Optional`s inside `Optional`s; the resultant code is hard to reason about",
+    link = BUG_PATTERNS_BASE_URL + "NestedOptionals",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = FRAGILE_CODE)
+public final class NestedOptionals extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Supplier<Type> OPTIONAL = Suppliers.typeFromClass(Optional.class);
+  private static final Supplier<Type> OPTIONAL_OF_OPTIONAL =
+      VisitorState.memoize(generic(OPTIONAL, subOf(raw(OPTIONAL))));
+
+  /** Instantiates a new {@link NestedOptionals} instance. */
+  public NestedOptionals() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    Type type = OPTIONAL_OF_OPTIONAL.get(state);
+    if (type == null || !state.getTypes().isSubtype(ASTHelpers.getType(tree), type)) {
+      return Description.NO_MATCH;
+    }
+
+    return describeMatch(tree);
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/NonEmptyMono.java

@@ -0,0 +1,96 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.instanceMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import java.util.function.BiFunction;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags {@link Mono} operations that are known to be vacuous, given that
+ * they are invoked on a {@link Mono} that is known not to complete empty.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Avoid vacuous operations on known non-empty `Mono`s",
+    link = BUG_PATTERNS_BASE_URL + "NonEmptyMono",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = SIMPLIFICATION)
+// XXX: This check does not simplify `someFlux.defaultIfEmpty(T).{defaultIfEmpty(T),hasElements()}`,
+// as `someFlux.defaultIfEmpty(T)` yields a `Flux` rather than a `Mono`. Consider adding support for
+// these cases.
+// XXX: Given more advanced analysis many more expressions could be flagged. Consider
+// `Mono.just(someValue)`, `Flux.just(someNonEmptySequence)`,
+// `someMono.switchIfEmpty(someProvablyNonEmptyMono)` and many other variants.
+// XXX: Consider implementing a similar check for `Publisher`s that are known to complete without
+// emitting a value (e.g. `Mono.empty()`, `someFlux.then()`, ...), or known not to complete normally
+// (`Mono.never()`, `someFlux.repeat()`, `Mono.error(...)`, ...). The latter category could
+// potentially be split out further.
+public final class NonEmptyMono extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> MONO_SIZE_CHECK =
+      instanceMethod()
+          .onDescendantOf("reactor.core.publisher.Mono")
+          .namedAnyOf("defaultIfEmpty", "single", "switchIfEmpty");
+  private static final Matcher<ExpressionTree> NON_EMPTY_MONO =
+      anyOf(
+          instanceMethod()
+              .onDescendantOf("reactor.core.publisher.Flux")
+              .namedAnyOf(
+                  "all",
+                  "any",
+                  "collect",
+                  "collectList",
+                  "collectMap",
+                  "collectMultimap",
+                  "collectSortedList",
+                  "count",
+                  "elementAt",
+                  "hasElement",
+                  "hasElements",
+                  "last",
+                  "reduceWith",
+                  "single"),
+          instanceMethod()
+              .onDescendantOf("reactor.core.publisher.Flux")
+              .named("reduce")
+              .withParameters(Object.class.getName(), BiFunction.class.getName()),
+          instanceMethod()
+              .onDescendantOf("reactor.core.publisher.Mono")
+              .namedAnyOf("defaultIfEmpty", "hasElement", "single"));
+
+  /** Instantiates a new {@link NonEmptyMono} instance. */
+  public NonEmptyMono() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (!MONO_SIZE_CHECK.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    ExpressionTree receiver = ASTHelpers.getReceiver(tree);
+    if (!NON_EMPTY_MONO.matches(receiver, state)) {
+      return Description.NO_MATCH;
+    }
+
+    return describeMatch(
+        tree, SuggestedFix.replace(tree, SourceCode.treeToString(receiver, state)));
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/PrimitiveComparison.java

@@ -1,16 +1,17 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.PERFORMANCE;
 import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
 import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
-import static java.util.function.Predicate.not;
+import static java.util.stream.Collectors.joining;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.common.base.VerifyException;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
@@ -30,25 +31,25 @@ import com.sun.tools.javac.tree.JCTree.JCMemberReference;
 import java.util.Comparator;
 import java.util.Optional;
 import java.util.function.Function;
+import java.util.stream.Stream;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
- * A {@link BugChecker} which flags {@code Comparator#comparing*} invocations that can be replaced
+ * A {@link BugChecker} that flags {@code Comparator#comparing*} invocations that can be replaced
  * with an equivalent alternative so as to avoid unnecessary (un)boxing.
  */
 // XXX: Add more documentation. Explain how this is useful in the face of refactoring to more
 // specific types.
-// XXX: Change this checker's name?
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "PrimitiveComparison",
     summary =
         "Ensure invocations of `Comparator#comparing{,Double,Int,Long}` match the return type"
             + " of the provided function",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.WARNING,
-    tags = StandardTags.PERFORMANCE)
-public final class PrimitiveComparisonCheck extends BugChecker
-    implements MethodInvocationTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "PrimitiveComparison",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = PERFORMANCE)
+public final class PrimitiveComparison extends BugChecker implements MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Matcher<ExpressionTree> STATIC_COMPARISON_METHOD =
       anyOf(
@@ -69,6 +70,9 @@ public final class PrimitiveComparisonCheck extends BugChecker
               .named("thenComparing")
               .withParameters(Function.class.getName()));
 
+  /** Instantiates a new {@link PrimitiveComparison} instance. */
+  public PrimitiveComparison() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     boolean isStatic = STATIC_COMPARISON_METHOD.matches(tree, state);
@@ -77,23 +81,52 @@ public final class PrimitiveComparisonCheck extends BugChecker
     }
 
     return getPotentiallyBoxedReturnType(tree.getArguments().get(0))
-        .flatMap(cmpType -> tryFix(tree, state, cmpType, isStatic))
+        .flatMap(cmpType -> attemptMethodInvocationReplacement(tree, cmpType, isStatic, state))
         .map(fix -> describeMatch(tree, fix))
         .orElse(Description.NO_MATCH);
   }
 
-  private static Optional<Fix> tryFix(
-      MethodInvocationTree tree, VisitorState state, Type cmpType, boolean isStatic) {
-    return Optional.ofNullable(ASTHelpers.getSymbol(tree))
-        .map(methodSymbol -> methodSymbol.getSimpleName().toString())
-        .flatMap(
-            actualMethodName ->
-                Optional.of(getPreferredMethod(state, cmpType, isStatic))
-                    .filter(not(actualMethodName::equals)))
-        .map(preferredMethodName -> suggestFix(tree, preferredMethodName, state));
+  private static Optional<Fix> attemptMethodInvocationReplacement(
+      MethodInvocationTree tree, Type cmpType, boolean isStatic, VisitorState state) {
+    String actualMethodName = ASTHelpers.getSymbol(tree).getSimpleName().toString();
+    String preferredMethodName = getPreferredMethod(cmpType, isStatic, state);
+    if (actualMethodName.equals(preferredMethodName)) {
+      return Optional.empty();
+    }
+
+    return Optional.of(
+        suggestFix(
+            tree, prefixTypeArgumentsIfRelevant(preferredMethodName, tree, cmpType, state), state));
   }
 
-  private static String getPreferredMethod(VisitorState state, Type cmpType, boolean isStatic) {
+  /**
+   * Prefixes the given method name with generic type parameters if it replaces a {@code
+   * Comparator#comparing{,Double,Long,Int}} method which also has generic type parameters.
+   *
+   * <p>Such type parameters are retained as they are likely required.
+   *
+   * <p>Note that any type parameter to {@code Comparator#thenComparing} is likely redundant, and in
+   * any case becomes obsolete once that method is replaced with {@code
+   * Comparator#thenComparing{Double,Long,Int}}. Conversion in the opposite direction does not
+   * require the introduction of a generic type parameter.
+   */
+  private static String prefixTypeArgumentsIfRelevant(
+      String preferredMethodName, MethodInvocationTree tree, Type cmpType, VisitorState state) {
+    if (tree.getTypeArguments().isEmpty() || preferredMethodName.startsWith("then")) {
+      return preferredMethodName;
+    }
+
+    String typeArguments =
+        Stream.concat(
+                Stream.of(SourceCode.treeToString(tree.getTypeArguments().get(0), state)),
+                Stream.of(cmpType.tsym.getSimpleName())
+                    .filter(u -> "comparing".equals(preferredMethodName)))
+            .collect(joining(", ", "<", ">"));
+
+    return typeArguments + preferredMethodName;
+  }
+
+  private static String getPreferredMethod(Type cmpType, boolean isStatic, VisitorState state) {
     Types types = state.getTypes();
     Symtab symtab = state.getSymtab();
 
@@ -128,9 +161,6 @@ public final class PrimitiveComparisonCheck extends BugChecker
     }
   }
 
-  // XXX: We drop explicitly specified generic type information. In case the number of type
-  // arguments before and after doesn't match, that's for the better. But if we e.g. replace
-  // `comparingLong` with `comparingInt`, then we should retain it.
   private static Fix suggestFix(
       MethodInvocationTree tree, String preferredMethodName, VisitorState state) {
     ExpressionTree expr = tree.getMethodSelect();
@@ -143,7 +173,7 @@ public final class PrimitiveComparisonCheck extends BugChecker
       case MEMBER_SELECT:
         MemberSelectTree ms = (MemberSelectTree) tree.getMethodSelect();
         return SuggestedFix.replace(
-            ms, Util.treeToString(ms.getExpression(), state) + '.' + preferredMethodName);
+            ms, SourceCode.treeToString(ms.getExpression(), state) + '.' + preferredMethodName);
       default:
         throw new VerifyException("Unexpected type of expression: " + expr.getKind());
     }

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/RedundantStringConversion.java

@@ -1,20 +1,27 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.anyMethod;
 import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.anything;
+import static com.google.errorprone.matchers.Matchers.argumentCount;
 import static com.google.errorprone.matchers.Matchers.isNonNullUsingDataflow;
 import static com.google.errorprone.matchers.Matchers.isSameType;
 import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
 import static com.google.errorprone.matchers.Matchers.not;
 import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
 import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
+import com.google.common.primitives.Primitives;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.ErrorProneFlags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
@@ -24,6 +31,7 @@ import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
 import com.google.errorprone.fixes.SuggestedFix;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.suppliers.Suppliers;
 import com.sun.source.tree.BinaryTree;
 import com.sun.source.tree.CompoundAssignmentTree;
 import com.sun.source.tree.ExpressionTree;
@@ -41,25 +49,26 @@ import java.util.List;
 import java.util.Locale;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.stream.Stream;
+import tech.picnic.errorprone.bugpatterns.util.Flags;
+import tech.picnic.errorprone.bugpatterns.util.MethodMatcherFactory;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
-/** A {@link BugChecker} which flags redundant explicit string conversions. */
+/** A {@link BugChecker} that flags redundant explicit string conversions. */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "RedundantStringConversion",
     summary = "Avoid redundant string conversions when possible",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.SIMPLIFICATION)
-public final class RedundantStringConversionCheck extends BugChecker
+    link = BUG_PATTERNS_BASE_URL + "RedundantStringConversion",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class RedundantStringConversion extends BugChecker
     implements BinaryTreeMatcher, CompoundAssignmentTreeMatcher, MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
-  private static final String FLAG_PREFIX = "RedundantStringConversion:";
   private static final String EXTRA_STRING_CONVERSION_METHODS_FLAG =
-      FLAG_PREFIX + "ExtraConversionMethods";
-
-  @SuppressWarnings("UnnecessaryLambda")
-  private static final Matcher<ExpressionTree> ANY_EXPR = (t, s) -> true;
+      "RedundantStringConversion:ExtraConversionMethods";
 
+  private static final Matcher<ExpressionTree> ANY_EXPR = anything();
   private static final Matcher<ExpressionTree> LOCALE = isSameType(Locale.class);
   private static final Matcher<ExpressionTree> MARKER = isSubtypeOf("org.slf4j.Marker");
   private static final Matcher<ExpressionTree> STRING = isSameType(String.class);
@@ -68,49 +77,30 @@ public final class RedundantStringConversionCheck extends BugChecker
       allOf(STRING, isNonNullUsingDataflow());
   private static final Matcher<ExpressionTree> NOT_FORMATTABLE =
       not(isSubtypeOf(Formattable.class));
-  private static final Matcher<ExpressionTree> WELL_KNOWN_STRING_CONVERSION_METHODS =
+  private static final Matcher<MethodInvocationTree> WELL_KNOWN_STRING_CONVERSION_METHODS =
       anyOf(
-          instanceMethod().onDescendantOfAny(Object.class.getName()).named("toString"),
-          staticMethod()
-              .onClass(Objects.class.getName())
+          instanceMethod()
+              .onDescendantOfAny(Object.class.getName())
               .named("toString")
-              .withParameters(Object.class.getName()),
-          staticMethod()
-              .onClass(String.class.getName())
-              .named("valueOf")
-              .withParameters(Object.class.getName()),
-          staticMethod()
-              .onClass(String.class.getName())
-              .named("valueOf")
-              .withParameters(String.class.getName()),
-          staticMethod()
-              .onClass(Byte.class.getName())
-              .named("toString")
-              .withParameters(byte.class.getName()),
-          staticMethod()
-              .onClass(Character.class.getName())
-              .named("toString")
-              .withParameters(char.class.getName()),
-          staticMethod()
-              .onClass(Short.class.getName())
-              .named("toString")
-              .withParameters(short.class.getName()),
-          staticMethod()
-              .onClass(Integer.class.getName())
-              .named("toString")
-              .withParameters(int.class.getName()),
-          staticMethod()
-              .onClass(Long.class.getName())
-              .named("toString")
-              .withParameters(long.class.getName()),
-          staticMethod()
-              .onClass(Float.class.getName())
-              .named("toString")
-              .withParameters(float.class.getName()),
-          staticMethod()
-              .onClass(Double.class.getName())
-              .named("toString")
-              .withParameters(double.class.getName()));
+              .withNoParameters(),
+          allOf(
+              argumentCount(1),
+              anyOf(
+                  staticMethod()
+                      .onClassAny(
+                          Stream.concat(
+                                  Primitives.allWrapperTypes().stream(), Stream.of(Objects.class))
+                              .map(Class::getName)
+                              .collect(toImmutableSet()))
+                      .named("toString"),
+                  allOf(
+                      staticMethod().onClass(String.class.getName()).named("valueOf"),
+                      not(
+                          anyMethod()
+                              .anyClass()
+                              .withAnyName()
+                              .withParametersOfType(
+                                  ImmutableList.of(Suppliers.arrayOf(Suppliers.CHAR_TYPE))))))));
   private static final Matcher<ExpressionTree> STRINGBUILDER_APPEND_INVOCATION =
       instanceMethod()
           .onDescendantOf(StringBuilder.class.getName())
@@ -126,17 +116,10 @@ public final class RedundantStringConversionCheck extends BugChecker
           staticMethod().onClass(String.class.getName()).named("format"),
           instanceMethod().onDescendantOf(Formatter.class.getName()).named("format"),
           instanceMethod()
-              .onDescendantOf(PrintStream.class.getName())
+              .onDescendantOfAny(PrintStream.class.getName(), PrintWriter.class.getName())
               .namedAnyOf("format", "printf"),
           instanceMethod()
-              .onDescendantOf(PrintStream.class.getName())
-              .namedAnyOf("print", "println")
-              .withParameters(Object.class.getName()),
-          instanceMethod()
-              .onDescendantOf(PrintWriter.class.getName())
-              .namedAnyOf("format", "printf"),
-          instanceMethod()
-              .onDescendantOf(PrintWriter.class.getName())
+              .onDescendantOfAny(PrintStream.class.getName(), PrintWriter.class.getName())
               .namedAnyOf("print", "println")
               .withParameters(Object.class.getName()),
           staticMethod()
@@ -155,19 +138,19 @@ public final class RedundantStringConversionCheck extends BugChecker
           .onDescendantOf("org.slf4j.Logger")
           .namedAnyOf("trace", "debug", "info", "warn", "error");
 
-  private final Matcher<ExpressionTree> conversionMethodMatcher;
+  private final Matcher<MethodInvocationTree> conversionMethodMatcher;
 
-  /** Instantiates the default {@link RedundantStringConversionCheck}. */
-  public RedundantStringConversionCheck() {
+  /** Instantiates a default {@link RedundantStringConversion} instance. */
+  public RedundantStringConversion() {
     this(ErrorProneFlags.empty());
   }
 
   /**
-   * Instantiates a customized {@link RedundantStringConversionCheck}.
+   * Instantiates a customized {@link RedundantStringConversion}.
    *
    * @param flags Any provided command line flags.
    */
-  public RedundantStringConversionCheck(ErrorProneFlags flags) {
+  public RedundantStringConversion(ErrorProneFlags flags) {
     conversionMethodMatcher = createConversionMethodMatcher(flags);
   }
 
@@ -185,7 +168,7 @@ public final class RedundantStringConversionCheck extends BugChecker
 
     List<SuggestedFix.Builder> fixes = new ArrayList<>();
 
-    // XXX: Not so nice: we try to simplify the RHS twice.
+    // XXX: Avoid trying to simplify the RHS twice.
     ExpressionTree preferredRhs = trySimplify(rhs, state).orElse(rhs);
     if (STRING.matches(preferredRhs, state)) {
       tryFix(lhs, state, ANY_EXPR).ifPresent(fixes::add);
@@ -242,7 +225,7 @@ public final class RedundantStringConversionCheck extends BugChecker
         .flatMap(args -> tryFix(args.get(index), state, ANY_EXPR));
   }
 
-  // XXX: Write another check which checks that Formatter patterns don't use `{}` and have a
+  // XXX: Write another check that checks that Formatter patterns don't use `{}` and have a
   // matching number of arguments of the appropriate type. Also flag explicit conversions from
   // `Formattable` to string.
   private Optional<SuggestedFix.Builder> tryFixFormatter(
@@ -273,17 +256,17 @@ public final class RedundantStringConversionCheck extends BugChecker
     return tryFixFormatterArguments(arguments, state, ANY_EXPR, ANY_EXPR);
   }
 
-  // XXX: Write another check which checks that SLF4J patterns don't use `%s` and have a matching
+  // XXX: Write another check that checks that SLF4J patterns don't use `%s` and have a matching
   // number of arguments of the appropriate type. Also flag explicit conversions from `Throwable` to
-  // string as the last logger argument. Suggests either dropping the converison or going with
+  // string as the last logger argument. Suggests either dropping the conversion or going with
   // `Throwable#getMessage()` instead.
   private Optional<SuggestedFix.Builder> tryFixSlf4jLogger(
       List<? extends ExpressionTree> arguments, VisitorState state) {
     /*
-     * SLF4J treats the final argument to a log statement specially if it is a `Throwabe`: it
+     * SLF4J treats the final argument to a log statement specially if it is a `Throwable`: it
      * will always choose to render the associated stacktrace, even if the argument has a
      * matching `{}` placeholder. (In this case the `{}` will simply be logged verbatim.) So if
-     * a log statement's final argument is the string representation of a `Throwble`, then we
+     * a log statement's final argument is the string representation of a `Throwable`, then we
      * must not strip this explicit string conversion, as that would change the statement's
      * semantics.
      */
@@ -326,7 +309,7 @@ public final class RedundantStringConversionCheck extends BugChecker
     return trySimplify(tree, state, filter)
         .map(
             replacement ->
-                SuggestedFix.builder().replace(tree, Util.treeToString(replacement, state)));
+                SuggestedFix.builder().replace(tree, SourceCode.treeToString(replacement, state)));
   }
 
   private Optional<ExpressionTree> trySimplify(
@@ -337,11 +320,15 @@ public final class RedundantStringConversionCheck extends BugChecker
   }
 
   private Optional<ExpressionTree> trySimplify(ExpressionTree tree, VisitorState state) {
-    if (tree.getKind() != Kind.METHOD_INVOCATION || !conversionMethodMatcher.matches(tree, state)) {
+    if (tree.getKind() != Kind.METHOD_INVOCATION) {
       return Optional.empty();
     }
 
     MethodInvocationTree methodInvocation = (MethodInvocationTree) tree;
+    if (!conversionMethodMatcher.matches(methodInvocation, state)) {
+      return Optional.empty();
+    }
+
     switch (methodInvocation.getArguments().size()) {
       case 0:
         return trySimplifyNullaryMethod(methodInvocation, state);
@@ -350,7 +337,7 @@ public final class RedundantStringConversionCheck extends BugChecker
       default:
         throw new IllegalStateException(
             "Cannot simplify method call with two or more arguments: "
-                + Util.treeToString(tree, state));
+                + SourceCode.treeToString(tree, state));
     }
   }
 
@@ -363,7 +350,7 @@ public final class RedundantStringConversionCheck extends BugChecker
     return Optional.of(methodInvocation.getMethodSelect())
         .filter(methodSelect -> methodSelect.getKind() == Kind.MEMBER_SELECT)
         .map(methodSelect -> ((MemberSelectTree) methodSelect).getExpression())
-        .filter(expr -> !"super".equals(Util.treeToString(expr, state)));
+        .filter(expr -> !"super".equals(SourceCode.treeToString(expr, state)));
   }
 
   private static Optional<ExpressionTree> trySimplifyUnaryMethod(
@@ -382,13 +369,13 @@ public final class RedundantStringConversionCheck extends BugChecker
         .orElse(Description.NO_MATCH);
   }
 
-  private static Matcher<ExpressionTree> createConversionMethodMatcher(ErrorProneFlags flags) {
+  private static Matcher<MethodInvocationTree> createConversionMethodMatcher(
+      ErrorProneFlags flags) {
     // XXX: ErrorProneFlags#getList splits by comma, but method signatures may also contain commas.
     // For this class methods accepting more than one argument are not valid, but still: not nice.
-    return flags
-        .getList(EXTRA_STRING_CONVERSION_METHODS_FLAG)
-        .map(new MethodMatcherFactory()::create)
-        .map(m -> anyOf(WELL_KNOWN_STRING_CONVERSION_METHODS, m))
-        .orElse(WELL_KNOWN_STRING_CONVERSION_METHODS);
+    return anyOf(
+        WELL_KNOWN_STRING_CONVERSION_METHODS,
+        new MethodMatcherFactory()
+            .create(Flags.getList(flags, EXTRA_STRING_CONVERSION_METHODS_FLAG)));
   }
 }

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/RefasterAnyOfUsage.java

@@ -1,12 +1,13 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
@@ -16,26 +17,29 @@ import com.google.errorprone.matchers.Matcher;
 import com.google.errorprone.refaster.Refaster;
 import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.MethodInvocationTree;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
- * A {@link BugChecker} which flags unnecessary {@link Refaster#anyOf(Object[])} usages.
+ * A {@link BugChecker} that flags unnecessary {@link Refaster#anyOf(Object[])} usages.
  *
- * <p>Note that this logic can't be implemented as a Refaster template, as the {@link Refaster}
- * class is treated specially.
+ * <p>Note that this logic can't be implemented as a Refaster rule, as the {@link Refaster} class is
+ * treated specially.
  */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "RefasterAnyOfUsage",
     summary = "`Refaster#anyOf` should be passed at least two parameters",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.SIMPLIFICATION)
-public final class RefasterAnyOfUsageCheck extends BugChecker
-    implements MethodInvocationTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "RefasterAnyOfUsage",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class RefasterAnyOfUsage extends BugChecker implements MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Matcher<ExpressionTree> REFASTER_ANY_OF =
       staticMethod().onClass(Refaster.class.getName()).named("anyOf");
 
+  /** Instantiates a new {@link RefasterAnyOfUsage} instance. */
+  public RefasterAnyOfUsage() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (REFASTER_ANY_OF.matches(tree, state)) {
@@ -46,7 +50,8 @@ public final class RefasterAnyOfUsageCheck extends BugChecker
         case 1:
           return describeMatch(
               tree,
-              SuggestedFix.replace(tree, Util.treeToString(tree.getArguments().get(0), state)));
+              SuggestedFix.replace(
+                  tree, SourceCode.treeToString(tree.getArguments().get(0), state)));
         default:
           /* Handled below. */
       }

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/RefasterRuleModifiers.java

@@ -0,0 +1,116 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.STYLE;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.hasAnnotation;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
+import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.Placeholder;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.MethodTree;
+import com.sun.source.tree.Tree;
+import java.util.EnumSet;
+import java.util.Set;
+import javax.lang.model.element.Modifier;
+
+/**
+ * A {@link BugChecker} that suggests a canonical set of modifiers for Refaster class and method
+ * definitions.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Refaster class and method definitions should specify a canonical set of modifiers",
+    link = BUG_PATTERNS_BASE_URL + "RefasterRuleModifiers",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = STYLE)
+public final class RefasterRuleModifiers extends BugChecker
+    implements ClassTreeMatcher, MethodTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<Tree> BEFORE_TEMPLATE_METHOD = hasAnnotation(BeforeTemplate.class);
+  private static final Matcher<Tree> AFTER_TEMPLATE_METHOD = hasAnnotation(AfterTemplate.class);
+  private static final Matcher<Tree> PLACEHOLDER_METHOD = hasAnnotation(Placeholder.class);
+  private static final Matcher<Tree> REFASTER_METHOD =
+      anyOf(BEFORE_TEMPLATE_METHOD, AFTER_TEMPLATE_METHOD, PLACEHOLDER_METHOD);
+
+  /** Instantiates a new {@link RefasterRuleModifiers} instance. */
+  public RefasterRuleModifiers() {}
+
+  @Override
+  public Description matchClass(ClassTree tree, VisitorState state) {
+    if (!hasMatchingMember(tree, BEFORE_TEMPLATE_METHOD, state)) {
+      /* This class does not contain a Refaster template. */
+      return Description.NO_MATCH;
+    }
+
+    SuggestedFix fix = suggestCanonicalModifiers(tree, state);
+    return fix.isEmpty() ? Description.NO_MATCH : describeMatch(tree, fix);
+  }
+
+  @Override
+  public Description matchMethod(MethodTree tree, VisitorState state) {
+    if (!REFASTER_METHOD.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    return SuggestedFixes.removeModifiers(
+            tree,
+            state,
+            Modifier.FINAL,
+            Modifier.PRIVATE,
+            Modifier.PROTECTED,
+            Modifier.PUBLIC,
+            Modifier.STATIC,
+            Modifier.SYNCHRONIZED)
+        .map(fix -> describeMatch(tree, fix))
+        .orElse(Description.NO_MATCH);
+  }
+
+  private static SuggestedFix suggestCanonicalModifiers(ClassTree tree, VisitorState state) {
+    Set<Modifier> modifiersToAdd = EnumSet.noneOf(Modifier.class);
+    Set<Modifier> modifiersToRemove =
+        EnumSet.of(Modifier.PRIVATE, Modifier.PROTECTED, Modifier.PUBLIC, Modifier.SYNCHRONIZED);
+
+    if (!hasMatchingMember(tree, PLACEHOLDER_METHOD, state)) {
+      /*
+       * Rules without a `@Placeholder` method should be `final`. Note that Refaster enforces
+       * that `@Placeholder` methods are `abstract`, so rules _with_ such a method will
+       * naturally be `abstract` and non-`final`.
+       */
+      modifiersToAdd.add(Modifier.FINAL);
+      modifiersToRemove.add(Modifier.ABSTRACT);
+    }
+
+    if (ASTHelpers.findEnclosingNode(state.getPath(), ClassTree.class) != null) {
+      /* Nested classes should be `static`. */
+      modifiersToAdd.add(Modifier.STATIC);
+    }
+
+    SuggestedFix.Builder fix = SuggestedFix.builder();
+    SuggestedFixes.addModifiers(tree, tree.getModifiers(), state, modifiersToAdd)
+        .ifPresent(fix::merge);
+    SuggestedFixes.removeModifiers(tree.getModifiers(), state, modifiersToRemove)
+        .ifPresent(fix::merge);
+    return fix.build();
+  }
+
+  private static boolean hasMatchingMember(
+      ClassTree tree, Matcher<Tree> matcher, VisitorState state) {
+    return tree.getMembers().stream().anyMatch(member -> matcher.matches(member, state));
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/RequestMappingAnnotation.java

@@ -1,20 +1,20 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.LIKELY_ERROR;
 import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.ALL;
 import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
 import static com.google.errorprone.matchers.Matchers.annotations;
 import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.Matchers.isSameType;
-import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
 import static com.google.errorprone.matchers.Matchers.isType;
 import static com.google.errorprone.matchers.Matchers.methodHasParameters;
 import static com.google.errorprone.matchers.Matchers.not;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
@@ -24,19 +24,19 @@ import com.sun.source.tree.MethodTree;
 import com.sun.source.tree.Tree;
 
 /**
- * A {@link BugChecker} which flags {@code @RequestMapping} methods that have one or more parameters
+ * A {@link BugChecker} that flags {@code @RequestMapping} methods that have one or more parameters
  * that appear to lack a relevant annotation.
  *
  * <p>Matched mappings are {@code @{Delete,Get,Patch,Post,Put,Request}Mapping}.
  */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "RequestMappingAnnotation",
     summary = "Make sure all `@RequestMapping` method parameters are annotated",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.WARNING,
-    tags = StandardTags.LIKELY_ERROR)
-public final class RequestMappingAnnotationCheck extends BugChecker implements MethodTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "RequestMappingAnnotation",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = LIKELY_ERROR)
+public final class RequestMappingAnnotation extends BugChecker implements MethodTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final String ANN_PACKAGE_PREFIX = "org.springframework.web.bind.annotation.";
   // XXX: Generalize this logic to fully support Spring meta-annotations, then update the class
@@ -51,8 +51,11 @@ public final class RequestMappingAnnotationCheck extends BugChecker implements M
               isType(ANN_PACKAGE_PREFIX + "PostMapping"),
               isType(ANN_PACKAGE_PREFIX + "PutMapping"),
               isType(ANN_PACKAGE_PREFIX + "RequestMapping")));
-  // XXX: Add other parameters as necessary. See
-  // https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html#mvc-ann-arguments.
+  // XXX: Add other parameters as necessary. Also consider whether it makes sense to have WebMVC-
+  // and WebFlux-specific logic. See
+  // https://docs.spring.io/spring-framework/docs/current/reference/html/web.html#mvc-ann-arguments
+  // and
+  // https://docs.spring.io/spring-framework/docs/current/reference/html/web-reactive.html#webflux-ann-arguments.
   private static final Matcher<MethodTree> LACKS_PARAMETER_ANNOTATION =
       not(
           methodHasParameters(
@@ -62,14 +65,30 @@ public final class RequestMappingAnnotationCheck extends BugChecker implements M
                       AT_LEAST_ONE,
                       anyOf(
                           isType(ANN_PACKAGE_PREFIX + "PathVariable"),
+                          isType(ANN_PACKAGE_PREFIX + "RequestAttribute"),
                           isType(ANN_PACKAGE_PREFIX + "RequestBody"),
                           isType(ANN_PACKAGE_PREFIX + "RequestHeader"),
-                          isType(ANN_PACKAGE_PREFIX + "RequestParam"))),
+                          isType(ANN_PACKAGE_PREFIX + "RequestParam"),
+                          isType(ANN_PACKAGE_PREFIX + "RequestPart"))),
                   isSameType("java.io.InputStream"),
+                  isSameType("java.time.ZoneId"),
+                  isSameType("java.util.Locale"),
+                  isSameType("java.util.TimeZone"),
+                  isSameType("jakarta.servlet.http.HttpServletRequest"),
+                  isSameType("jakarta.servlet.http.HttpServletResponse"),
                   isSameType("javax.servlet.http.HttpServletRequest"),
                   isSameType("javax.servlet.http.HttpServletResponse"),
                   isSameType("org.springframework.http.HttpMethod"),
-                  isSubtypeOf("org.springframework.web.context.request.WebRequest"))));
+                  isSameType("org.springframework.ui.Model"),
+                  isSameType("org.springframework.validation.BindingResult"),
+                  isSameType("org.springframework.web.context.request.NativeWebRequest"),
+                  isSameType("org.springframework.web.context.request.WebRequest"),
+                  isSameType("org.springframework.web.server.ServerWebExchange"),
+                  isSameType("org.springframework.web.util.UriBuilder"),
+                  isSameType("org.springframework.web.util.UriComponentsBuilder"))));
+
+  /** Instantiates a new {@link RequestMappingAnnotation} instance. */
+  public RequestMappingAnnotation() {}
 
   @Override
   public Description matchMethod(MethodTree tree, VisitorState state) {

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/RequestParamType.java

@@ -0,0 +1,81 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+import static com.google.errorprone.BugPattern.StandardTags.LIKELY_ERROR;
+import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.annotations;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
+import static com.google.errorprone.matchers.Matchers.isType;
+import static com.google.errorprone.matchers.Matchers.not;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableCollection;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.ErrorProneFlags;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.VariableTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.suppliers.Suppliers;
+import com.sun.source.tree.Tree;
+import com.sun.source.tree.VariableTree;
+import tech.picnic.errorprone.bugpatterns.util.Flags;
+
+/** A {@link BugChecker} that flags {@code @RequestParam} parameters with an unsupported type. */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary =
+        "By default, `@RequestParam` does not support `ImmutableCollection` and `ImmutableMap` subtypes",
+    link = BUG_PATTERNS_BASE_URL + "RequestParamType",
+    linkType = CUSTOM,
+    severity = ERROR,
+    tags = LIKELY_ERROR)
+public final class RequestParamType extends BugChecker implements VariableTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final String SUPPORTED_CUSTOM_TYPES_FLAG = "RequestParamType:SupportedCustomTypes";
+
+  private final Matcher<VariableTree> hasUnsupportedRequestParamType;
+
+  /** Instantiates a default {@link RequestParamType} instance. */
+  public RequestParamType() {
+    this(ErrorProneFlags.empty());
+  }
+
+  /**
+   * Instantiates a customized {@link RequestParamType} instance.
+   *
+   * @param flags Any provided command line flags.
+   */
+  public RequestParamType(ErrorProneFlags flags) {
+    hasUnsupportedRequestParamType = hasUnsupportedRequestParamType(flags);
+  }
+
+  @Override
+  public Description matchVariable(VariableTree tree, VisitorState state) {
+    return hasUnsupportedRequestParamType.matches(tree, state)
+        ? describeMatch(tree)
+        : Description.NO_MATCH;
+  }
+
+  private static Matcher<VariableTree> hasUnsupportedRequestParamType(ErrorProneFlags flags) {
+    return allOf(
+        annotations(AT_LEAST_ONE, isType("org.springframework.web.bind.annotation.RequestParam")),
+        anyOf(isSubtypeOf(ImmutableCollection.class), isSubtypeOf(ImmutableMap.class)),
+        not(isSubtypeOfAny(Flags.getList(flags, SUPPORTED_CUSTOM_TYPES_FLAG))));
+  }
+
+  private static Matcher<Tree> isSubtypeOfAny(ImmutableList<String> inclusions) {
+    return anyOf(
+        inclusions.stream()
+            .map(inclusion -> isSubtypeOf(Suppliers.typeFromString(inclusion)))
+            .collect(toImmutableList()));
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/ScheduledTransactionTrace.java

@@ -0,0 +1,94 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+import static com.google.errorprone.BugPattern.StandardTags.LIKELY_ERROR;
+import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
+import static com.google.errorprone.matchers.Matchers.annotations;
+import static com.google.errorprone.matchers.Matchers.hasAnnotation;
+import static com.google.errorprone.matchers.Matchers.isType;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.common.AnnotationMirrors;
+import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Iterables;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.matchers.MultiMatcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.MethodTree;
+import com.sun.source.tree.Tree;
+import tech.picnic.errorprone.bugpatterns.util.ThirdPartyLibrary;
+
+/**
+ * A {@link BugChecker} that flags methods with Spring's {@code @Scheduled} annotation that lack New
+ * Relic Agent's {@code @Trace(dispatcher = true)}.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Scheduled operation must start a new New Relic transaction",
+    link = BUG_PATTERNS_BASE_URL + "ScheduledTransactionTrace",
+    linkType = CUSTOM,
+    severity = ERROR,
+    tags = LIKELY_ERROR)
+public final class ScheduledTransactionTrace extends BugChecker implements MethodTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final String TRACE_ANNOTATION_FQCN = "com.newrelic.api.agent.Trace";
+  private static final Matcher<Tree> IS_SCHEDULED =
+      hasAnnotation("org.springframework.scheduling.annotation.Scheduled");
+  private static final MultiMatcher<Tree, AnnotationTree> TRACE_ANNOTATION =
+      annotations(AT_LEAST_ONE, isType(TRACE_ANNOTATION_FQCN));
+
+  /** Instantiates a new {@link ScheduledTransactionTrace} instance. */
+  public ScheduledTransactionTrace() {}
+
+  @Override
+  public Description matchMethod(MethodTree tree, VisitorState state) {
+    if (!ThirdPartyLibrary.NEW_RELIC_AGENT_API.isIntroductionAllowed(state)
+        || !IS_SCHEDULED.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    ImmutableList<AnnotationTree> traceAnnotations =
+        TRACE_ANNOTATION.multiMatchResult(tree, state).matchingNodes();
+    if (traceAnnotations.isEmpty()) {
+      /* This method completely lacks the `@Trace` annotation; add it. */
+      return describeMatch(
+          tree,
+          SuggestedFix.builder()
+              .addImport(TRACE_ANNOTATION_FQCN)
+              .prefixWith(tree, "@Trace(dispatcher = true)")
+              .build());
+    }
+
+    AnnotationTree traceAnnotation = Iterables.getOnlyElement(traceAnnotations);
+    if (isCorrectAnnotation(traceAnnotation)) {
+      return Description.NO_MATCH;
+    }
+
+    /*
+     * The `@Trace` annotation is present but does not specify `dispatcher = true`. Add or update
+     * the `dispatcher` annotation element.
+     */
+    return describeMatch(
+        traceAnnotation,
+        SuggestedFixes.updateAnnotationArgumentValues(
+                traceAnnotation, state, "dispatcher", ImmutableList.of("true"))
+            .build());
+  }
+
+  private static boolean isCorrectAnnotation(AnnotationTree traceAnnotation) {
+    return Boolean.TRUE.equals(
+        AnnotationMirrors.getAnnotationValue(
+                ASTHelpers.getAnnotationMirror(traceAnnotation), "dispatcher")
+            .getValue());
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/Slf4jLogStatement.java

@@ -1,15 +1,16 @@
 package tech.picnic.errorprone.bugpatterns;
 
 import static com.google.common.base.Verify.verify;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.LIKELY_ERROR;
 import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
 import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.common.base.Splitter;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
@@ -22,22 +23,23 @@ import com.sun.source.tree.MethodInvocationTree;
 import com.sun.source.tree.Tree.Kind;
 import java.util.List;
 import java.util.Optional;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
-/** A {@link BugChecker} which flags SLF4J usages that are likely to be in error. */
+/** A {@link BugChecker} that flags SLF4J usages that are likely to be in error. */
 // XXX: The special-casing of Throwable applies only to SLF4J 1.6.0+; see
 // https://www.slf4j.org/faq.html#paramException. That should be documented.
 // XXX: Also simplify `LOG.error(String.format("Something %s", arg), throwable)`.
+// XXX: Also simplify `LOG.error(String.join("sep", arg1, arg2), throwable)`? Perhaps too obscure.
 // XXX: Write a similar checker for Spring RestTemplates, String.format and friends, Guava
 // preconditions, ...
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "Slf4jLogStatement",
     summary = "Make sure SLF4J log statements contain proper placeholders with matching arguments",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.WARNING,
-    tags = StandardTags.LIKELY_ERROR)
-public final class Slf4jLogStatementCheck extends BugChecker
-    implements MethodInvocationTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "Slf4jLogStatement",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = LIKELY_ERROR)
+public final class Slf4jLogStatement extends BugChecker implements MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Matcher<ExpressionTree> MARKER = isSubtypeOf("org.slf4j.Marker");
   private static final Matcher<ExpressionTree> THROWABLE = isSubtypeOf(Throwable.class);
@@ -46,6 +48,9 @@ public final class Slf4jLogStatementCheck extends BugChecker
           .onDescendantOf("org.slf4j.Logger")
           .namedAnyOf("trace", "debug", "info", "warn", "error");
 
+  /** Instantiates a new {@link Slf4jLogStatement} instance. */
+  public Slf4jLogStatement() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (!SLF4J_LOGGER_INVOCATION.matches(tree, state)) {
@@ -114,7 +119,7 @@ public final class Slf4jLogStatementCheck extends BugChecker
        * replaced at this usage site.
        */
       description.addFix(
-          SuggestedFix.replace(tree, Util.treeToString(tree, state).replace("%s", "{}")));
+          SuggestedFix.replace(tree, SourceCode.treeToString(tree, state).replace("%s", "{}")));
     }
 
     return false;

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/SpringMvcAnnotation.java

@@ -1,17 +1,18 @@
 package tech.picnic.errorprone.bugpatterns;
 
 import static com.google.common.base.Verify.verify;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static java.util.function.Predicate.not;
 import static java.util.stream.Collectors.joining;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.common.base.VerifyException;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.AnnotationTreeMatcher;
@@ -25,20 +26,22 @@ import com.sun.source.tree.MemberSelectTree;
 import com.sun.source.tree.NewArrayTree;
 import com.sun.source.tree.Tree.Kind;
 import java.util.Optional;
+import tech.picnic.errorprone.bugpatterns.util.AnnotationAttributeMatcher;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
- * A {@link BugChecker} which flags {@code @RequestMapping} annotations that can be written more
+ * A {@link BugChecker} that flags {@code @RequestMapping} annotations that can be written more
  * concisely.
  */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "SpringMvcAnnotation",
     summary =
         "Prefer the conciseness of `@{Get,Put,Post,Delete,Patch}Mapping` over `@RequestMapping`",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.SIMPLIFICATION)
-public final class SpringMvcAnnotationCheck extends BugChecker implements AnnotationTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "SpringMvcAnnotation",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class SpringMvcAnnotation extends BugChecker implements AnnotationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final String ANN_PACKAGE_PREFIX = "org.springframework.web.bind.annotation.";
   private static final AnnotationAttributeMatcher ARGUMENT_SELECTOR =
@@ -54,6 +57,9 @@ public final class SpringMvcAnnotationCheck extends BugChecker implements Annota
           .put("PUT", "PutMapping")
           .build();
 
+  /** Instantiates a new {@link SpringMvcAnnotation} instance. */
+  public SpringMvcAnnotation() {}
+
   @Override
   public Description matchAnnotation(AnnotationTree tree, VisitorState state) {
     // XXX: We could remove the `@RequestMapping` import if not other usages remain.
@@ -92,7 +98,7 @@ public final class SpringMvcAnnotationCheck extends BugChecker implements Annota
   private static String extractMethod(ExpressionTree expr, VisitorState state) {
     switch (expr.getKind()) {
       case IDENTIFIER:
-        return Util.treeToString(expr, state);
+        return SourceCode.treeToString(expr, state);
       case MEMBER_SELECT:
         return ((MemberSelectTree) expr).getIdentifier().toString();
       default:
@@ -105,7 +111,7 @@ public final class SpringMvcAnnotationCheck extends BugChecker implements Annota
     String newArguments =
         tree.getArguments().stream()
             .filter(not(argToRemove::equals))
-            .map(arg -> Util.treeToString(arg, state))
+            .map(arg -> SourceCode.treeToString(arg, state))
             .collect(joining(", "));
 
     return SuggestedFix.builder()

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/StaticImport.java

@@ -1,15 +1,16 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static java.util.Objects.requireNonNull;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSetMultimap;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MemberSelectTreeMatcher;
@@ -19,19 +20,22 @@ import com.google.errorprone.fixes.Fix;
 import com.google.errorprone.fixes.SuggestedFix;
 import com.google.errorprone.fixes.SuggestedFixes;
 import com.google.errorprone.matchers.Description;
+import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.MemberSelectTree;
 import com.sun.source.tree.MethodInvocationTree;
 import com.sun.source.tree.Tree;
+import com.sun.tools.javac.code.Type;
 import java.util.Optional;
 
-/** A {@link BugChecker} which flags methods that can and should be statically imported. */
+/**
+ * A {@link BugChecker} that flags methods and constants that can and should be statically imported.
+ */
 // XXX: Tricky cases:
-// - `org.springframework.http.MediaType` (do except for `ALL`?)
 // - `org.springframework.http.HttpStatus` (not always an improvement, and `valueOf` must
 //    certainly be excluded)
 // - `com.google.common.collect.Tables`
 // - `ch.qos.logback.classic.Level.{DEBUG, ERROR, INFO, TRACE, WARN"}`
-// XXX: Also introduce a check which disallows static imports of certain methods. Candidates:
+// XXX: Also introduce a check that disallows static imports of certain methods. Candidates:
 // - `com.google.common.base.Strings`
 // - `java.util.Optional.empty`
 // - `java.util.Locale.ROOT`
@@ -41,21 +45,30 @@ import java.util.Optional;
 // - Likely any of `*.{ZERO, ONE, MIX, MAX, MIN_VALUE, MAX_VALUE}`.
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "StaticImport",
-    summary = "Method should be statically imported",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.SUGGESTION,
-    tags = StandardTags.SIMPLIFICATION)
-public final class StaticImportCheck extends BugChecker implements MemberSelectTreeMatcher {
+    summary = "Identifier should be statically imported",
+    link = BUG_PATTERNS_BASE_URL + "StaticImport",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class StaticImport extends BugChecker implements MemberSelectTreeMatcher {
   private static final long serialVersionUID = 1L;
 
+  /**
+   * Types whose members should be statically imported, unless exempted by {@link
+   * #STATIC_IMPORT_EXEMPTED_MEMBERS} or {@link #STATIC_IMPORT_EXEMPTED_IDENTIFIERS}.
+   */
   @VisibleForTesting
-  static final ImmutableSet<String> STATIC_IMPORT_CANDIDATE_CLASSES =
+  static final ImmutableSet<String> STATIC_IMPORT_CANDIDATE_TYPES =
       ImmutableSet.of(
           "com.google.common.base.Preconditions",
           "com.google.common.base.Predicates",
           "com.google.common.base.Verify",
           "com.google.common.collect.MoreCollectors",
+          "com.google.errorprone.BugPattern.LinkType",
+          "com.google.errorprone.BugPattern.SeverityLevel",
+          "com.google.errorprone.BugPattern.StandardTags",
+          "com.google.errorprone.matchers.Matchers",
+          "com.google.errorprone.refaster.ImportPolicy",
           "com.mongodb.client.model.Accumulators",
           "com.mongodb.client.model.Aggregates",
           "com.mongodb.client.model.Filters",
@@ -64,8 +77,10 @@ public final class StaticImportCheck extends BugChecker implements MemberSelectT
           "com.mongodb.client.model.Sorts",
           "com.mongodb.client.model.Updates",
           "java.nio.charset.StandardCharsets",
+          "java.util.Collections",
           "java.util.Comparator",
           "java.util.Map.Entry",
+          "java.util.regex.Pattern",
           "java.util.stream.Collectors",
           "org.assertj.core.api.Assertions",
           "org.assertj.core.api.InstanceOfAssertFactories",
@@ -80,14 +95,18 @@ public final class StaticImportCheck extends BugChecker implements MemberSelectT
           "org.mockito.Answers",
           "org.mockito.ArgumentMatchers",
           "org.mockito.Mockito",
+          "org.springframework.boot.test.context.SpringBootTest.WebEnvironment",
           "org.springframework.format.annotation.DateTimeFormat.ISO",
           "org.springframework.http.HttpHeaders",
           "org.springframework.http.HttpMethod",
+          "org.springframework.http.MediaType",
           "org.testng.Assert",
-          "reactor.function.TupleUtils");
+          "reactor.function.TupleUtils",
+          "tech.picnic.errorprone.bugpatterns.util.MoreTypes");
 
+  /** Type members that should be statically imported. */
   @VisibleForTesting
-  static final ImmutableSetMultimap<String, String> STATIC_IMPORT_CANDIDATE_METHODS =
+  static final ImmutableSetMultimap<String, String> STATIC_IMPORT_CANDIDATE_MEMBERS =
       ImmutableSetMultimap.<String, String>builder()
           .putAll(
               "com.google.common.collect.ImmutableListMultimap",
@@ -108,8 +127,10 @@ public final class StaticImportCheck extends BugChecker implements MemberSelectT
           .put("com.google.common.collect.ImmutableTable", "toImmutableTable")
           .put("com.google.common.collect.Sets", "toImmutableEnumSet")
           .put("com.google.common.base.Functions", "identity")
+          .put("java.time.ZoneOffset", "UTC")
           .put("java.util.function.Function", "identity")
           .put("java.util.function.Predicate", "not")
+          .put("java.util.UUID", "randomUUID")
           .put("org.junit.jupiter.params.provider.Arguments", "arguments")
           .putAll(
               "java.util.Objects",
@@ -122,9 +143,60 @@ public final class StaticImportCheck extends BugChecker implements MemberSelectT
           .putAll("com.google.common.collect.Comparators", "emptiesFirst", "emptiesLast")
           .build();
 
+  /**
+   * Type members that should never be statically imported.
+   *
+   * <p>Identifiers listed by {@link #STATIC_IMPORT_EXEMPTED_IDENTIFIERS} should be omitted from
+   * this collection.
+   */
+  // XXX: Perhaps the set of exempted `java.util.Collections` methods is too strict. For now any
+  // method name that could be considered "too vague" or could conceivably mean something else in a
+  // specific context is left out.
+  @VisibleForTesting
+  static final ImmutableSetMultimap<String, String> STATIC_IMPORT_EXEMPTED_MEMBERS =
+      ImmutableSetMultimap.<String, String>builder()
+          .put("com.mongodb.client.model.Filters", "empty")
+          .putAll(
+              "java.util.Collections",
+              "addAll",
+              "copy",
+              "fill",
+              "list",
+              "max",
+              "min",
+              "nCopies",
+              "rotate",
+              "sort",
+              "swap")
+          .putAll("java.util.regex.Pattern", "compile", "matches", "quote")
+          .put("org.springframework.http.MediaType", "ALL")
+          .build();
+
+  /**
+   * Identifiers that should never be statically imported.
+   *
+   * <p>This should be a superset of the identifiers flagged by {@link
+   * com.google.errorprone.bugpatterns.BadImport}.
+   */
+  @VisibleForTesting
+  static final ImmutableSet<String> STATIC_IMPORT_EXEMPTED_IDENTIFIERS =
+      ImmutableSet.of(
+          "builder",
+          "create",
+          "copyOf",
+          "from",
+          "getDefaultInstance",
+          "INSTANCE",
+          "newBuilder",
+          "of",
+          "valueOf");
+
+  /** Instantiates a new {@link StaticImport} instance. */
+  public StaticImport() {}
+
   @Override
   public Description matchMemberSelect(MemberSelectTree tree, VisitorState state) {
-    if (!isCandidate(state)) {
+    if (!isCandidateContext(state) || !isCandidate(tree)) {
       return Description.NO_MATCH;
     }
 
@@ -139,7 +211,7 @@ public final class StaticImportCheck extends BugChecker implements MemberSelectT
         .orElse(Description.NO_MATCH);
   }
 
-  private static boolean isCandidate(VisitorState state) {
+  private static boolean isCandidateContext(VisitorState state) {
     Tree parentTree =
         requireNonNull(state.getPath().getParentPath(), "MemberSelectTree lacks enclosing node")
             .getLeaf();
@@ -154,6 +226,17 @@ public final class StaticImportCheck extends BugChecker implements MemberSelectT
     }
   }
 
+  private static boolean isCandidate(MemberSelectTree tree) {
+    String identifier = tree.getIdentifier().toString();
+    if (STATIC_IMPORT_EXEMPTED_IDENTIFIERS.contains(identifier)) {
+      return false;
+    }
+
+    Type type = ASTHelpers.getType(tree.getExpression());
+    return type != null
+        && !STATIC_IMPORT_EXEMPTED_MEMBERS.containsEntry(type.toString(), identifier);
+  }
+
   private static Optional<String> getCandidateSimpleName(StaticImportInfo importInfo) {
     String canonicalName = importInfo.canonicalName();
     return importInfo
@@ -161,8 +244,8 @@ public final class StaticImportCheck extends BugChecker implements MemberSelectT
         .toJavaUtil()
         .filter(
             name ->
-                STATIC_IMPORT_CANDIDATE_CLASSES.contains(canonicalName)
-                    || STATIC_IMPORT_CANDIDATE_METHODS.containsEntry(canonicalName, name));
+                STATIC_IMPORT_CANDIDATE_TYPES.contains(canonicalName)
+                    || STATIC_IMPORT_CANDIDATE_MEMBERS.containsEntry(canonicalName, name));
   }
 
   private static Optional<Fix> tryStaticImport(

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/StringCaseLocaleUsage.java

@@ -0,0 +1,89 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.FRAGILE_CODE;
+import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
+import static com.sun.tools.javac.parser.Tokens.TokenKind.RPAREN;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.Streams;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.Fix;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.google.errorprone.util.ErrorProneTokens;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.tools.javac.util.Position;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags calls to {@link String#toLowerCase()} and {@link
+ * String#toUpperCase()}, as these methods implicitly rely on the environment's default locale.
+ */
+// XXX: Also flag `String::toLowerCase` and `String::toUpperCase` method references. For these cases
+// the suggested fix should introduce a lambda expression with a parameter of which the name does
+// not coincide with the name of an existing variable name. Such functionality should likely be
+// introduced in a utility class.
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Specify a `Locale` when calling `String#to{Lower,Upper}Case`",
+    link = BUG_PATTERNS_BASE_URL + "StringCaseLocaleUsage",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = FRAGILE_CODE)
+public final class StringCaseLocaleUsage extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> DEFAULT_LOCALE_CASE_CONVERSION =
+      instanceMethod()
+          .onExactClass(String.class.getName())
+          .namedAnyOf("toLowerCase", "toUpperCase")
+          .withNoParameters();
+
+  /** Instantiates a new {@link StringCaseLocaleUsage} instance. */
+  public StringCaseLocaleUsage() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (!DEFAULT_LOCALE_CASE_CONVERSION.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    int closingParenPosition = getClosingParenPosition(tree, state);
+    if (closingParenPosition == Position.NOPOS) {
+      return describeMatch(tree);
+    }
+
+    return buildDescription(tree)
+        .addFix(suggestLocale(closingParenPosition, "Locale.ROOT"))
+        .addFix(suggestLocale(closingParenPosition, "Locale.getDefault()"))
+        .build();
+  }
+
+  private static Fix suggestLocale(int insertPosition, String locale) {
+    return SuggestedFix.builder()
+        .addImport("java.util.Locale")
+        .replace(insertPosition, insertPosition, locale)
+        .build();
+  }
+
+  private static int getClosingParenPosition(MethodInvocationTree tree, VisitorState state) {
+    int startPosition = ASTHelpers.getStartPosition(tree);
+    if (startPosition == Position.NOPOS) {
+      return Position.NOPOS;
+    }
+
+    return Streams.findLast(
+            ErrorProneTokens.getTokens(SourceCode.treeToString(tree, state), state.context).stream()
+                .filter(t -> t.kind() == RPAREN))
+        .map(token -> startPosition + token.pos())
+        .orElse(Position.NOPOS);
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/StringJoin.java

@@ -0,0 +1,187 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.common.base.Splitter;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Iterables;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.suppliers.Supplier;
+import com.google.errorprone.suppliers.Suppliers;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.tools.javac.code.Type;
+import com.sun.tools.javac.util.Convert;
+import java.util.Formattable;
+import java.util.Iterator;
+import java.util.List;
+import org.jspecify.annotations.Nullable;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags {@link String#format(String, Object...)} invocations which can be
+ * replaced with a {@link String#join(CharSequence, CharSequence...)} or even a {@link
+ * String#valueOf} invocation.
+ */
+// XXX: What about `v1 + "sep" + v2` and similar expressions? Do we want to rewrite those to
+// `String.join`, or should some `String.join` invocations be rewritten to use the `+` operator?
+// (The latter suggestion would conflict with the `FormatStringConcatenation` check.)
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Prefer `String#join` over `String#format`",
+    link = BUG_PATTERNS_BASE_URL + "StringJoin",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class StringJoin extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Splitter FORMAT_SPECIFIER_SPLITTER = Splitter.on("%s");
+  private static final Matcher<ExpressionTree> STRING_FORMAT_INVOCATION =
+      staticMethod().onClass(String.class.getName()).named("format");
+  private static final Supplier<Type> CHAR_SEQUENCE_TYPE =
+      Suppliers.typeFromClass(CharSequence.class);
+  private static final Supplier<Type> FORMATTABLE_TYPE = Suppliers.typeFromClass(Formattable.class);
+
+  /** Instantiates a new {@link StringJoin} instance. */
+  public StringJoin() {}
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (!STRING_FORMAT_INVOCATION.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    // XXX: This check assumes that if the first argument to `String#format` is a `Locale`, that
+    // this argument is not vacuous, and that as a result the expression cannot be simplified using
+    // `#valueOf` or `#join`. Implement a separate check that identifies and drops redundant
+    // `Locale` arguments. See also a related comment in `FormatStringConcatenation`.
+    String formatString = ASTHelpers.constValue(tree.getArguments().get(0), String.class);
+    if (formatString == null) {
+      return Description.NO_MATCH;
+    }
+
+    List<String> separators = FORMAT_SPECIFIER_SPLITTER.splitToList(formatString);
+    if (separators.size() < 2) {
+      /* The format string does not contain `%s` format specifiers. */
+      return Description.NO_MATCH;
+    }
+
+    if (separators.size() != tree.getArguments().size()) {
+      /* The number of arguments does not match the number of `%s` format specifiers. */
+      return Description.NO_MATCH;
+    }
+
+    int lastIndex = separators.size() - 1;
+    if (!separators.get(0).isEmpty() || !separators.get(lastIndex).isEmpty()) {
+      /* The format string contains leading or trailing characters. */
+      return Description.NO_MATCH;
+    }
+
+    ImmutableSet<String> innerSeparators = ImmutableSet.copyOf(separators.subList(1, lastIndex));
+    if (innerSeparators.size() > 1) {
+      /* The `%s` format specifiers are not uniformly separated. */
+      return Description.NO_MATCH;
+    }
+
+    if (innerSeparators.isEmpty()) {
+      /*
+       * This `String#format` invocation performs a straightforward string conversion; use
+       * `String#valueOf` instead.
+       */
+      return trySuggestExplicitStringConversion(tree, state);
+    }
+
+    String separator = Iterables.getOnlyElement(innerSeparators);
+    if (separator.indexOf('%') >= 0) {
+      /* The `%s` format specifiers are separated by another format specifier. */
+      // XXX: Strictly speaking we could support `%%` by mapping it to a literal `%`, but that
+      // doesn't seem worth the trouble.
+      return Description.NO_MATCH;
+    }
+
+    return trySuggestExplicitJoin(tree, separator, state);
+  }
+
+  /**
+   * If guaranteed to be behavior preserving, suggests replacing {@code String.format("%s", arg)}
+   * with {@code String.valueOf(arg)}.
+   *
+   * <p>If {@code arg} is already a string then the resultant conversion is vacuous. The {@link
+   * IdentityConversion} check will subsequently drop it.
+   */
+  private Description trySuggestExplicitStringConversion(
+      MethodInvocationTree tree, VisitorState state) {
+    ExpressionTree argument = tree.getArguments().get(1);
+    if (isSubtype(ASTHelpers.getType(argument), FORMATTABLE_TYPE, state)) {
+      /*
+       * `Formattable` arguments are handled specially; `String#valueOf` is not a suitable
+       * alternative.
+       */
+      return Description.NO_MATCH;
+    }
+
+    return buildDescription(tree)
+        .setMessage("Prefer `String#valueOf` over `String#format`")
+        .addFix(SuggestedFix.replace(tree, withStringConversionExpression(argument, state)))
+        .build();
+  }
+
+  /**
+   * Unless the given {@code String.format} expression includes {@link Formattable} arguments,
+   * suggests replacing it with a {@code String.join} expression using the specified argument
+   * separator.
+   */
+  private Description trySuggestExplicitJoin(
+      MethodInvocationTree tree, String separator, VisitorState state) {
+    Iterator<? extends ExpressionTree> arguments = tree.getArguments().iterator();
+
+    SuggestedFix.Builder fix =
+        SuggestedFix.builder()
+            .replace(tree.getMethodSelect(), "String.join")
+            .replace(arguments.next(), String.format("\"%s\"", Convert.quote(separator)));
+
+    while (arguments.hasNext()) {
+      ExpressionTree argument = arguments.next();
+      Type argumentType = ASTHelpers.getType(argument);
+      if (isSubtype(argumentType, FORMATTABLE_TYPE, state)) {
+        /*
+         * `Formattable` arguments are handled specially; `String#join` is not a suitable
+         * alternative.
+         */
+        return Description.NO_MATCH;
+      }
+
+      if (!isSubtype(argumentType, CHAR_SEQUENCE_TYPE, state)) {
+        /*
+         * The argument was previously implicitly converted to a string; now this must happen
+         * explicitly.
+         */
+        fix.replace(argument, withStringConversionExpression(argument, state));
+      }
+    }
+
+    return describeMatch(tree, fix.build());
+  }
+
+  private static boolean isSubtype(
+      @Nullable Type subType, Supplier<Type> superType, VisitorState state) {
+    return ASTHelpers.isSubtype(subType, superType.get(state), state);
+  }
+
+  private static String withStringConversionExpression(
+      ExpressionTree argument, VisitorState state) {
+    return String.format("String.valueOf(%s)", SourceCode.treeToString(argument, state));
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/TimeZoneUsage.java

@@ -1,5 +1,8 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.FRAGILE_CODE;
 import static com.google.errorprone.matchers.Matchers.allOf;
 import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.Matchers.enclosingClass;
@@ -7,12 +10,10 @@ import static com.google.errorprone.matchers.Matchers.instanceMethod;
 import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
 import static com.google.errorprone.matchers.Matchers.not;
 import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.errorprone.BugPattern;
-import com.google.errorprone.BugPattern.LinkType;
-import com.google.errorprone.BugPattern.SeverityLevel;
-import com.google.errorprone.BugPattern.StandardTags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
@@ -25,17 +26,20 @@ import java.time.Instant;
 import java.time.LocalDate;
 import java.time.LocalDateTime;
 import java.time.LocalTime;
+import java.time.OffsetDateTime;
+import java.time.OffsetTime;
+import java.time.ZonedDateTime;
 
-/** A {@link BugChecker} which flags illegal time-zone related operations. */
+/** A {@link BugChecker} that flags illegal time-zone related operations. */
 @AutoService(BugChecker.class)
 @BugPattern(
-    name = "TimeZoneUsage",
     summary =
         "Derive the current time from an existing `Clock` Spring bean, and don't rely on a `Clock`'s time zone",
-    linkType = LinkType.NONE,
-    severity = SeverityLevel.WARNING,
-    tags = StandardTags.FRAGILE_CODE)
-public final class TimeZoneUsageCheck extends BugChecker implements MethodInvocationTreeMatcher {
+    link = BUG_PATTERNS_BASE_URL + "TimeZoneUsage",
+    linkType = CUSTOM,
+    severity = WARNING,
+    tags = FRAGILE_CODE)
+public final class TimeZoneUsage extends BugChecker implements MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Matcher<ExpressionTree> BANNED_TIME_METHOD =
       anyOf(
@@ -57,9 +61,15 @@ public final class TimeZoneUsageCheck extends BugChecker implements MethodInvoca
               .onClassAny(
                   LocalDate.class.getName(),
                   LocalDateTime.class.getName(),
-                  LocalTime.class.getName())
+                  LocalTime.class.getName(),
+                  OffsetDateTime.class.getName(),
+                  OffsetTime.class.getName(),
+                  ZonedDateTime.class.getName())
               .named("now"),
-          staticMethod().onClassAny(Instant.class.getName()).named("now").withParameters());
+          staticMethod().onClassAny(Instant.class.getName()).named("now").withNoParameters());
+
+  /** Instantiates a new {@link TimeZoneUsage} instance. */
+  public TimeZoneUsage() {}
 
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/Util.java

@@ -1,20 +0,0 @@
-package tech.picnic.errorprone.bugpatterns;
-
-import com.google.errorprone.VisitorState;
-import com.sun.source.tree.Tree;
-
-// XXX: Can we locate this code in a better place? Maybe contribute it upstream?
-final class Util {
-  private Util() {}
-
-  /**
-   * Returns a string representation of the given {@link Tree}, preferring the original source code
-   * (if available) over its prettified representation.
-   *
-   * @return A non-{@code null} string.
-   */
-  static String treeToString(Tree tree, VisitorState state) {
-    String src = state.getSourceForNode(tree);
-    return src != null ? src : tree.toString();
-  }
-}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/package-info.java

@@ -1,4 +1,4 @@
 /** Picnic Error Prone Contrib checks. */
 @com.google.errorprone.annotations.CheckReturnValue
-@javax.annotation.ParametersAreNonnullByDefault
+@org.jspecify.annotations.NullMarked
 package tech.picnic.errorprone.bugpatterns;

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/util/AnnotationAttributeMatcher.java

@@ -1,4 +1,4 @@
-package tech.picnic.errorprone.bugpatterns;
+package tech.picnic.errorprone.bugpatterns.util;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.HashMultimap;
@@ -28,7 +28,7 @@ import java.util.stream.Stream;
  * <p>This class allows one to define a whitelist or blacklist of annotations or their attributes.
  * Annotations are identified by their fully qualified name.
  */
-final class AnnotationAttributeMatcher implements Serializable {
+public final class AnnotationAttributeMatcher implements Serializable {
   private static final long serialVersionUID = 1L;
 
   private final boolean complement;
@@ -59,7 +59,7 @@ final class AnnotationAttributeMatcher implements Serializable {
    * @param exclusions The listed annotations or annotation attributes are not matched.
    * @return A non-{@code null} {@link AnnotationAttributeMatcher}.
    */
-  static AnnotationAttributeMatcher create(
+  public static AnnotationAttributeMatcher create(
       Optional<? extends List<String>> inclusions, Iterable<String> exclusions) {
     Set<String> includedWholeTypes = new HashSet<>();
     Set<String> excludedWholeTypes = new HashSet<>();
@@ -97,7 +97,13 @@ final class AnnotationAttributeMatcher implements Serializable {
     }
   }
 
-  Stream<? extends ExpressionTree> extractMatchingArguments(AnnotationTree tree) {
+  /**
+   * Returns the subset of arguments of the given {@link AnnotationTree} matched by this instance.
+   *
+   * @param tree The annotation AST node to be inspected.
+   * @return Any matching annotation arguments.
+   */
+  public Stream<? extends ExpressionTree> extractMatchingArguments(AnnotationTree tree) {
     Type type = ASTHelpers.getType(tree.getAnnotationType());
     if (type == null) {
       return Stream.empty();

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/util/ConflictDetection.java

@@ -0,0 +1,75 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static tech.picnic.errorprone.bugpatterns.util.JavaKeywords.isValidIdentifier;
+
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ImportTree;
+import com.sun.source.tree.Tree;
+import com.sun.tools.javac.code.Symbol.MethodSymbol;
+import com.sun.tools.javac.code.Type;
+import java.util.Optional;
+
+/** A set of helper methods for detecting conflicts that would be caused when applying fixes. */
+public final class ConflictDetection {
+  private ConflictDetection() {}
+
+  /**
+   * If applicable, returns a human-readable argument against assigning the given name to an
+   * existing method.
+   *
+   * <p>This method implements imperfect heuristics. Things it currently does not consider include
+   * the following:
+   *
+   * <ul>
+   *   <li>Whether the rename would merely introduce a method overload, rather than clashing with an
+   *       existing method declaration in its class or a supertype.
+   *   <li>Whether the rename would in fact clash with a static import. (It could be that a static
+   *       import of the same name is only referenced from lexical scopes in which the method under
+   *       consideration cannot be referenced directly.)
+   * </ul>
+   *
+   * @param method The method considered for renaming.
+   * @param newName The newly proposed name for the method.
+   * @param state The {@link VisitorState} to use when searching for blockers.
+   * @return A human-readable argument against assigning the proposed name to the given method, or
+   *     {@link Optional#empty()} if no blocker was found.
+   */
+  public static Optional<String> findMethodRenameBlocker(
+      MethodSymbol method, String newName, VisitorState state) {
+    if (isExistingMethodName(method.owner.type, newName, state)) {
+      return Optional.of(
+          String.format(
+              "a method named `%s` is already defined in this class or a supertype", newName));
+    }
+
+    if (isSimpleNameStaticallyImported(newName, state)) {
+      return Optional.of(String.format("`%s` is already statically imported", newName));
+    }
+
+    if (!isValidIdentifier(newName)) {
+      return Optional.of(String.format("`%s` is not a valid identifier", newName));
+    }
+
+    return Optional.empty();
+  }
+
+  private static boolean isExistingMethodName(Type clazz, String name, VisitorState state) {
+    return ASTHelpers.matchingMethods(state.getName(name), method -> true, clazz, state.getTypes())
+        .findAny()
+        .isPresent();
+  }
+
+  private static boolean isSimpleNameStaticallyImported(String simpleName, VisitorState state) {
+    return state.getPath().getCompilationUnit().getImports().stream()
+        .filter(ImportTree::isStatic)
+        .map(ImportTree::getQualifiedIdentifier)
+        .map(tree -> getStaticImportSimpleName(tree, state))
+        .anyMatch(simpleName::contentEquals);
+  }
+
+  private static CharSequence getStaticImportSimpleName(Tree tree, VisitorState state) {
+    String source = SourceCode.treeToString(tree, state);
+    return source.subSequence(source.lastIndexOf('.') + 1, source.length());
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/util/Documentation.java

@@ -0,0 +1,9 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+/** Utility class providing documentation-related code. */
+public final class Documentation {
+  /** The base URL at which Error Prone Support bug patterns are hosted. */
+  public static final String BUG_PATTERNS_BASE_URL = "https://error-prone.picnic.tech/bugpatterns/";
+
+  private Documentation() {}
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/util/Flags.java

@@ -0,0 +1,25 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.ErrorProneFlags;
+
+/** Helper methods for working with {@link ErrorProneFlags}. */
+public final class Flags {
+  private Flags() {}
+
+  /**
+   * Returns the list of (comma-separated) arguments passed using the given Error Prone flag.
+   *
+   * @param errorProneFlags The full set of flags provided.
+   * @param name The name of the flag of interest.
+   * @return A non-{@code null} list of provided arguments; this list is empty if the flag was not
+   *     provided, or if the flag's value is the empty string.
+   */
+  public static ImmutableList<String> getList(ErrorProneFlags errorProneFlags, String name) {
+    return errorProneFlags
+        .getList(name)
+        .map(ImmutableList::copyOf)
+        .filter(flags -> !flags.equals(ImmutableList.of("")))
+        .orElseGet(ImmutableList::of);
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/util/JavaKeywords.java

@@ -0,0 +1,155 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Sets;
+
+/** Utility class that can be used to identify reserved keywords of the Java language. */
+// XXX: This class is no longer only about keywords. Consider changing its name and class-level
+// documentation.
+public final class JavaKeywords {
+  /**
+   * Enumeration of boolean and null literals.
+   *
+   * @see <a href="https://docs.oracle.com/javase/specs/jls/se17/html/jls-3.html#jls-3.10.3">JDK 17
+   *     JLS section 3.10.3: Boolean Literals</a>
+   * @see <a href="https://docs.oracle.com/javase/specs/jls/se17/html/jls-3.html#jls-3.10.8">JDK 17
+   *     JLS section 3.10.8: The Null Literal</a>
+   */
+  private static final ImmutableSet<String> BOOLEAN_AND_NULL_LITERALS =
+      ImmutableSet.of("true", "false", "null");
+  /**
+   * List of all reserved keywords in the Java language.
+   *
+   * @see <a href="https://docs.oracle.com/javase/specs/jls/se17/html/jls-3.html#jls-3.9">JDK 17 JLS
+   *     section 3.9: Keywords</a>
+   */
+  private static final ImmutableSet<String> RESERVED_KEYWORDS =
+      ImmutableSet.of(
+          "_",
+          "abstract",
+          "assert",
+          "boolean",
+          "break",
+          "byte",
+          "case",
+          "catch",
+          "char",
+          "class",
+          "const",
+          "continue",
+          "default",
+          "do",
+          "double",
+          "else",
+          "enum",
+          "extends",
+          "final",
+          "finally",
+          "float",
+          "for",
+          "goto",
+          "if",
+          "implements",
+          "import",
+          "instanceof",
+          "int",
+          "interface",
+          "long",
+          "native",
+          "new",
+          "package",
+          "private",
+          "protected",
+          "public",
+          "return",
+          "short",
+          "static",
+          "strictfp",
+          "super",
+          "switch",
+          "synchronized",
+          "this",
+          "throw",
+          "throws",
+          "transient",
+          "try",
+          "void",
+          "volatile",
+          "while");
+  /**
+   * List of all contextual keywords in the Java language.
+   *
+   * @see <a href="https://docs.oracle.com/javase/specs/jls/se17/html/jls-3.html#jls-3.9">JDK 17 JLS
+   *     section 3.9: Keywords</a>
+   */
+  private static final ImmutableSet<String> CONTEXTUAL_KEYWORDS =
+      ImmutableSet.of(
+          "exports",
+          "module",
+          "non-sealed",
+          "open",
+          "opens",
+          "permits",
+          "provides",
+          "record",
+          "requires",
+          "sealed",
+          "to",
+          "transitive",
+          "uses",
+          "var",
+          "with",
+          "yield");
+  /** List of all keywords in the Java language. */
+  private static final ImmutableSet<String> ALL_KEYWORDS =
+      Sets.union(RESERVED_KEYWORDS, CONTEXTUAL_KEYWORDS).immutableCopy();
+
+  private JavaKeywords() {}
+
+  /**
+   * Tells whether the given string is a valid identifier in the Java language.
+   *
+   * @param str The string of interest.
+   * @return {@code true} if the given string is a valid identifier in the Java language.
+   * @see <a href="https://docs.oracle.com/javase/specs/jls/se17/html/jls-3.html#jls-3.8">JDK 17 JLS
+   *     section 3.8: Identifiers</a>
+   */
+  public static boolean isValidIdentifier(String str) {
+    return !str.isEmpty()
+        && !isReservedKeyword(str)
+        && !BOOLEAN_AND_NULL_LITERALS.contains(str)
+        && Character.isJavaIdentifierStart(str.codePointAt(0))
+        && str.codePoints().skip(1).allMatch(Character::isUnicodeIdentifierPart);
+  }
+
+  /**
+   * Tells whether the given string is a reserved keyword in the Java language.
+   *
+   * @param str The string of interest.
+   * @return {@code true} if the given string is a reserved keyword in the Java language.
+   */
+  public static boolean isReservedKeyword(String str) {
+    return RESERVED_KEYWORDS.contains(str);
+  }
+
+  /**
+   * Tells whether the given string is a contextual keyword in the Java language.
+   *
+   * @param str The string of interest.
+   * @return {@code true} if the given string is a contextual keyword in the Java language.
+   */
+  public static boolean isContextualKeyword(String str) {
+    return CONTEXTUAL_KEYWORDS.contains(str);
+  }
+
+  /**
+   * Tells whether the given string is a reserved or contextual keyword in the Java language.
+   *
+   * @param str The string of interest.
+   * @return {@code true} if the given string is a reserved or contextual keyword in the Java
+   *     language.
+   */
+  public static boolean isKeyword(String str) {
+    return ALL_KEYWORDS.contains(str);
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/util/MethodMatcherFactory.java

@@ -1,4 +1,4 @@
-package tech.picnic.errorprone.bugpatterns;
+package tech.picnic.errorprone.bugpatterns.util;
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.collect.ImmutableSet.toImmutableSet;
@@ -15,13 +15,23 @@ import java.util.regex.Pattern;
 /** A method invocation expression {@link Matcher} factory. */
 // XXX: Document better. The expressions accepted here could also be defined using `MethodMatchers`.
 // So explain why this class is still useful.
-final class MethodMatcherFactory {
+public final class MethodMatcherFactory {
   private static final Splitter ARGUMENT_TYPE_SPLITTER =
       Splitter.on(',').trimResults().omitEmptyStrings();
   private static final Pattern METHOD_SIGNATURE =
       Pattern.compile("([^\\s#(,)]+)#([^\\s#(,)]+)\\(((?:[^\\s#(,)]+(?:,[^\\s#(,)]+)*)?)\\)");
 
-  Matcher<ExpressionTree> create(Collection<String> signatures) {
+  /** Instantiates a new {@link MethodMatcherFactory} instance. */
+  public MethodMatcherFactory() {}
+
+  /**
+   * Creates a {@link Matcher} of methods with any of the given signatures.
+   *
+   * @param signatures The method signatures of interest.
+   * @return A new {@link Matcher} which accepts invocation expressions of any method identified by
+   *     the given signatures.
+   */
+  public Matcher<ExpressionTree> create(Collection<String> signatures) {
     return anyOf(
         signatures.stream()
             .map(MethodMatcherFactory::createMethodMatcher)