Introduce MonoSingle Refaster rule

For first build, run with `-Dversion.error-prone-orig=2.20.0`.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -42,9 +42,9 @@ Please replace this sentence with log output, if applicable.
 <!-- Please complete the following information: -->
 
 - Operating system (e.g. MacOS Monterey).
-- Java version (i.e. `java --version`, e.g. `17.0.6`).
+- Java version (i.e. `java --version`, e.g. `17.0.7`).
 - Error Prone version (e.g. `2.18.0`).
-- Error Prone Support version (e.g. `0.8.0`).
+- Error Prone Support version (e.g. `0.9.0`).
 
 ### Additional context
 

.github/workflows/build.yaml

@@ -10,34 +10,32 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-22.04 ]
-        jdk: [ 11.0.18, 17.0.6, 19.0.2 ]
+        jdk: [ 11.0.19, 17.0.7, 20.0.1 ]
         distribution: [ temurin ]
         experimental: [ false ]
         include:
           - os: macos-12
-            jdk: 17.0.6
+            jdk: 17.0.7
             distribution: temurin
             experimental: false
           - os: windows-2022
-            jdk: 17.0.6
+            jdk: 17.0.7
             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.
+      # 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
+        uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
+        with:
+          persist-credentials: false
       - name: Set up JDK
-        uses: actions/setup-java@v3.8.0
+        uses: actions/setup-java@5ffc13f4174014e2d4d4572b3d74c3fa61aeb2c2 # v3.11.0
         with:
           java-version: ${{ matrix.jdk }}
           distribution: ${{ matrix.distribution }}
@@ -52,4 +50,3 @@ jobs:
         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@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
+        with:
+          persist-credentials: false
+      - name: Set up JDK
+        uses: actions/setup-java@5ffc13f4174014e2d4d4572b3d74c3fa61aeb2c2 # v3.11.0
+        with:
+          java-version: 17.0.7
+          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

@@ -3,22 +3,24 @@ on:
   pull_request:
   push:
     branches: [ master, website ]
+permissions:
+  contents: read
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
 jobs:
   build:
-    permissions:
-      contents: read
     runs-on: ubuntu-22.04
     steps:
       - name: Check out code
-        uses: actions/checkout@v3.1.0
+        uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
+        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
+        uses: actions/configure-pages@f156874f8191504dae5b037505266ed5dda6c382 # v3.0.6
       - name: Generate documentation
         run: ./generate-docs.sh
       - name: Build website with Jekyll
@@ -30,7 +32,7 @@ jobs:
         # "Refaster rules" terminology on our website and in the code.
         run: bundle exec htmlproofer --disable_external true --check-external-hash false ./_site
       - name: Upload website as artifact
-        uses: actions/upload-pages-artifact@v1.0.5
+        uses: actions/upload-pages-artifact@66b63f4a7de003f4f00cc8e9af4b83b8f2abdb96 # v1.0.9
         with:
           path: ./website/_site
   deploy:
@@ -46,4 +48,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v1.2.3
+        uses: actions/deploy-pages@ee48c7b82e077d7b8ef30b50a719e6a792a50c9a # v2.0.2

.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@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
+        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

@@ -12,13 +12,14 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Check out code
-        uses: actions/checkout@v3.1.0
+        uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
         with:
           fetch-depth: 2
+          persist-credentials: false
       - name: Set up JDK
-        uses: actions/setup-java@v3.8.0
+        uses: actions/setup-java@5ffc13f4174014e2d4d4572b3d74c3fa61aeb2c2 # v3.11.0
         with:
-          java-version: 17.0.6
+          java-version: 17.0.7
           distribution: temurin
           cache: maven
       - name: Run Pitest
@@ -31,7 +32,7 @@ jobs:
       - 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
+        uses: actions/upload-artifact@0b7f8abb1508181956e8e162db84b466c27e18ce # v3.1.2
         with:
           name: pitest-reports
           path: ./target/pit-reports-ci

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

@@ -9,24 +9,28 @@ on:
       - completed
 permissions:
   actions: read
-  checks: write
-  contents: read
-  pull-requests: write
 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
-      - name: Set up JDK
-        uses: actions/setup-java@v3.8.0
+        uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
         with:
-          java-version: 17.0.6
+          persist-credentials: false
+      - name: Set up JDK
+        uses: actions/setup-java@5ffc13f4174014e2d4d4572b3d74c3fa61aeb2c2 # v3.11.0
+        with:
+          java-version: 17.0.7
           distribution: temurin
           cache: maven
       - name: Download Pitest analysis artifact
-        uses: dawidd6/action-download-artifact@v2.24.2
+        uses: dawidd6/action-download-artifact@246dbf436b23d7c49e21a7ab8204ca9ecd1fe615 # v2.27.0
         with:
           workflow: ${{ github.event.workflow_run.workflow_id }}
           name: pitest-reports

.github/workflows/sonarcloud.yml

@@ -0,0 +1,36 @@
+# Analyzes the code base using SonarCloud. See
+# https://sonarcloud.io/project/overview?id=PicnicSupermarket_error-prone-support.
+name: SonarCloud analysis
+on:
+  pull_request:
+  push:
+    branches: [ master ]
+  schedule:
+    - cron: '0 4 * * 1'
+permissions:
+  contents: read
+jobs:
+  analyze:
+    permissions:
+      contents: read
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Check out code
+        uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
+        with:
+          fetch-depth: 0
+          persist-credentials: false
+      - name: Set up JDK
+        uses: actions/setup-java@5ffc13f4174014e2d4d4572b3d74c3fa61aeb2c2 # v3.11.0
+        with:
+          java-version: 17.0.7
+          distribution: temurin
+          cache: maven
+      - name: Create missing `test` directory
+        # XXX: Drop this step in favour of actually having a test.
+        run: mkdir refaster-compiler/src/test
+      - name: Perform SonarCloud analysis
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}
+        run: mvn -T1C jacoco:prepare-agent verify jacoco:report sonar:sonar -Dverification.skip -Dsonar.projectKey=PicnicSupermarket_error-prone-support

.renovaterc.json

@@ -1,5 +1,8 @@
 {
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "helpers:pinGitHubActionDigests"
+  ],
   "packageRules": [
     {
       "matchPackagePatterns": [

CONTRIBUTING.md

@@ -48,6 +48,17 @@ be accepted. When in doubt, make sure to first raise an
 
 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
@@ -66,6 +77,9 @@ Some pointers:
   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

README.md

@@ -21,7 +21,18 @@ code_][picnic-blog-ep-post].
 
 [![Maven Central][maven-central-badge]][maven-central-search]
 [![Reproducible Builds][reproducible-builds-badge]][reproducible-builds-report]
+[![OpenSSF Best Practices][openssf-best-practices-badge]][openssf-best-practices-checklist]
+[![OpenSSF Scorecard][openssf-scorecard-badge]][openssf-scorecard-report]
+[![CodeQL Analysis][codeql-badge]][codeql-master]
 [![GitHub Actions][github-actions-build-badge]][github-actions-build-master]
+[![Mutation tested with PIT][pitest-badge]][pitest]
+[![Quality Gate Status][sonarcloud-quality-badge]][sonarcloud-quality-master]
+[![Maintainability Rating][sonarcloud-maintainability-badge]][sonarcloud-maintainability-master]
+[![Reliability Rating][sonarcloud-reliability-badge]][sonarcloud-reliability-master]
+[![Security Rating][sonarcloud-security-badge]][sonarcloud-security-master]
+[![Coverage][sonarcloud-coverage-badge]][sonarcloud-coverage-master]
+[![Duplicated Lines (%)][sonarcloud-duplication-badge]][sonarcloud-duplication-master]
+[![Technical Debt][sonarcloud-technical-debt-badge]][sonarcloud-technical-debt-master]
 [![License][license-badge]][license]
 [![PRs Welcome][pr-badge]][contributing]
 
@@ -98,8 +109,9 @@ definition. -->
 
 #### Gradle
 
-1. First, follow the [installation guide]
-   [error-prone-gradle-installation-guide] of the `gradle-errorprone-plugin`.
+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:
 
@@ -171,8 +183,15 @@ 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. Some
-relevant flags:
+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.
@@ -189,19 +208,25 @@ relevant flags:
   Pending a release of [google/error-prone#3301][error-prone-pull-3301], this
   flag must currently be used in combination with `-Perror-prone-fork`.
 
-Some other commands one may find relevant:
+Other highly relevant commands:
 
 - `mvn fmt:format` formats the code using
   [`google-java-format`][google-java-format].
-- `./run-mutation-tests.sh` runs mutation tests using [Pitest][pitest]. The
-  results can be reviewed by opening the respective
+- [`./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].
-- `./apply-error-prone-suggestions.sh` 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.
 
 When running the project's tests in IntelliJ IDEA, you might see the following
 error:
@@ -228,9 +253,17 @@ 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 vulnerability, 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
+[codeql-badge]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/codeql.yml/badge.svg?branch=master&event=push
+[codeql-master]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/codeql.yml?query=branch:master+event:push
 [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
@@ -239,7 +272,7 @@ guidelines][contributing].
 [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
+[github-actions-build-master]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/build.yaml?query=branch:master&event=push
 [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
@@ -247,8 +280,13 @@ guidelines][contributing].
 [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]: https://blog.picnic.nl
+[openssf-best-practices-badge]: https://bestpractices.coreinfrastructure.org/projects/7199/badge
+[openssf-best-practices-checklist]: https://bestpractices.coreinfrastructure.org/projects/7199
+[openssf-scorecard-badge]: https://img.shields.io/ossf-scorecard/github.com/PicnicSupermarket/error-prone-support?label=openssf%20scorecard
+[openssf-scorecard-report]: https://api.securityscorecards.dev/projects/github.com/PicnicSupermarket/error-prone-support
 [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-badge]: https://img.shields.io/badge/-Mutation%20tested%20with%20PIT-blue.svg
 [pitest]: https://pitest.org
 [pitest-maven]: https://pitest.org/quickstart/maven
 [pr-badge]: https://img.shields.io/badge/PRs-welcome-brightgreen.svg
@@ -257,3 +295,21 @@ guidelines][contributing].
 [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
+[sonarcloud-coverage-badge]: https://sonarcloud.io/api/project_badges/measure?project=PicnicSupermarket_error-prone-support&metric=coverage
+[sonarcloud-coverage-master]: https://sonarcloud.io/component_measures?id=PicnicSupermarket_error-prone-support&metric=coverage
+[sonarcloud-duplication-badge]: https://sonarcloud.io/api/project_badges/measure?project=PicnicSupermarket_error-prone-support&metric=duplicated_lines_density
+[sonarcloud-duplication-master]: https://sonarcloud.io/component_measures?id=PicnicSupermarket_error-prone-support&metric=duplicated_lines_density
+[sonarcloud-maintainability-badge]: https://sonarcloud.io/api/project_badges/measure?project=PicnicSupermarket_error-prone-support&metric=sqale_rating
+[sonarcloud-maintainability-master]: https://sonarcloud.io/component_measures?id=PicnicSupermarket_error-prone-support&metric=sqale_rating
+[sonarcloud-quality-badge]: https://sonarcloud.io/api/project_badges/measure?project=PicnicSupermarket_error-prone-support&metric=alert_status
+[sonarcloud-quality-master]: https://sonarcloud.io/summary/new_code?id=PicnicSupermarket_error-prone-support
+[sonarcloud-reliability-badge]: https://sonarcloud.io/api/project_badges/measure?project=PicnicSupermarket_error-prone-support&metric=reliability_rating
+[sonarcloud-reliability-master]: https://sonarcloud.io/component_measures?id=PicnicSupermarket_error-prone-support&metric=reliability_rating
+[sonarcloud-security-badge]: https://sonarcloud.io/api/project_badges/measure?project=PicnicSupermarket_error-prone-support&metric=security_rating
+[sonarcloud-security-master]: https://sonarcloud.io/component_measures?id=PicnicSupermarket_error-prone-support&metric=security_rating
+[sonarcloud-technical-debt-badge]: https://sonarcloud.io/api/project_badges/measure?project=PicnicSupermarket_error-prone-support&metric=sqale_index
+[sonarcloud-technical-debt-master]: https://sonarcloud.io/component_measures?id=PicnicSupermarket_error-prone-support&metric=sqale_index

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

documentation-support/pom.xml

@@ -5,7 +5,7 @@
     <parent>
         <groupId>tech.picnic.error-prone-support</groupId>
         <artifactId>error-prone-support</artifactId>
-        <version>0.9.0</version>
+        <version>0.12.1-SNAPSHOT</version>
     </parent>
 
     <artifactId>documentation-support</artifactId>

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

@@ -25,6 +25,7 @@ enum ExtractorType {
     return identifier;
   }
 
+  @SuppressWarnings("java:S1452" /* The extractor returns data of an unspecified type. */)
   Extractor<?> getExtractor() {
     return extractor;
   }

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

@@ -67,10 +67,11 @@ final class DocumentationGeneratorTaskListenerTest {
 
   @Test
   void excessArguments(@TempDir Path outputDirectory) {
+    String actualOutputDirectory = outputDirectory.toAbsolutePath() + " extra-arg";
     assertThatThrownBy(
             () ->
                 Compilation.compileWithDocumentationGenerator(
-                    outputDirectory.toAbsolutePath() + " extra-arg", "A.java", "package pkg;"))
+                    actualOutputDirectory, "A.java", "package pkg;"))
         .isInstanceOf(IllegalArgumentException.class)
         .hasMessage("Precisely one path must be provided");
   }

error-prone-contrib/README.md

@@ -24,7 +24,6 @@ project:
 
 - Document how to apply patches.
 - Document each of the checks.
-- 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.)
 - Auto-generate a website listing each of the checks, just like the Error Prone
@@ -273,7 +272,6 @@ Refaster's expressiveness:
 [autorefactor]: https://autorefactor.org
 [bettercodehub]: https://bettercodehub.com
 [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]: https://errorprone.info
 [error-prone-repo]: https://github.com/google/error-prone
@@ -283,4 +281,3 @@ Refaster's expressiveness:
 [main-contributing]: ../CONTRIBUTING.md
 [main-readme]: ../README.md
 [modernizer-maven-plugin]: https://github.com/gaul/modernizer-maven-plugin
-[sonarcloud]: https://sonarcloud.io

error-prone-contrib/pom.xml

@@ -5,7 +5,7 @@
     <parent>
         <groupId>tech.picnic.error-prone-support</groupId>
         <artifactId>error-prone-support</artifactId>
-        <version>0.9.0</version>
+        <version>0.12.1-SNAPSHOT</version>
     </parent>
 
     <artifactId>error-prone-contrib</artifactId>
@@ -49,9 +49,22 @@
         </dependency>
         <dependency>
             <groupId>${project.groupId}</groupId>
-            <artifactId>refaster-support</artifactId>
+            <artifactId>migration-util</artifactId>
+            <scope>compile</scope>
+        </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>refaster-compiler</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. -->
             <scope>provided</scope>
         </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>refaster-support</artifactId>
+            <scope>compile</scope>
+        </dependency>
         <dependency>
             <groupId>${project.groupId}</groupId>
             <artifactId>refaster-test-support</artifactId>
@@ -126,6 +139,11 @@
             <artifactId>jakarta.servlet-api</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>javax.inject</groupId>
+            <artifactId>javax.inject</artifactId>
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>javax.xml.bind</groupId>
             <artifactId>jaxb-api</artifactId>
@@ -236,6 +254,11 @@
                                 <artifactId>refaster-support</artifactId>
                                 <version>${project.version}</version>
                             </path>
+                            <path>
+                                <groupId>${project.groupId}</groupId>
+                                <artifactId>migration-util</artifactId>
+                                <version>${project.version}</version>
+                            </path>
                         </annotationProcessorPaths>
                         <compilerArgs combine.children="append">
                             <arg>-Xplugin:RefasterRuleCompiler</arg>

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

@@ -0,0 +1,103 @@
+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 =
+        "This method implements 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 fix = processMatchingArguments(tree, matcher, state);
+        return fix.isEmpty() ? Description.NO_MATCH : describeMatch(tree, fix);
+      }
+    }
+
+    return Description.NO_MATCH;
+  }
+
+  private static SuggestedFix processMatchingArguments(
+      MethodInvocationTree tree, Matcher<ExpressionTree> matcher, VisitorState 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(invocation, tree.getArguments(), state)
+                : SourceCode.unwrapMethodInvocation(invocation, state));
+      }
+    }
+
+    return fix.build();
+  }
+
+  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

@@ -58,8 +58,8 @@ public final class AutowiredConstructor extends BugChecker implements ClassTreeM
 
     /*
      * This is the only `@Autowired` constructor: suggest that it be removed. Note that this likely
-     * means that the associated import can be removed as well. Rather than adding code for this case we
-     * leave flagging the unused import to Error Prone's `RemoveUnusedImports` check.
+     * means that the associated import can be removed as well. Rather than adding code for this
+     * case we leave flagging the unused import to Error Prone's `RemoveUnusedImports` check.
      */
     AnnotationTree annotation = Iterables.getOnlyElement(annotations);
     return describeMatch(annotation, SourceCode.deleteWithTrailingWhitespace(annotation, state));

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

@@ -30,7 +30,7 @@ import tech.picnic.errorprone.bugpatterns.util.ThirdPartyLibrary;
 @AutoService(BugChecker.class)
 @BugPattern(
     summary =
-        "Avoid `Collectors.to{List,Map,Set}` in favour of alternatives that emphasize (im)mutability",
+        "Avoid `Collectors.to{List,Map,Set}` in favor of collectors that emphasize (im)mutability",
     link = BUG_PATTERNS_BASE_URL + "CollectorMutability",
     linkType = CUSTOM,
     severity = WARNING,

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

@@ -14,6 +14,7 @@ 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;
@@ -26,14 +27,18 @@ 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;
 
@@ -75,7 +80,10 @@ public final class DirectReturn extends BugChecker implements BlockTreeMatcher {
     StatementTree precedingStatement = statements.get(statements.size() - 2);
 
     return tryMatchAssignment(variableSymbol, precedingStatement)
-        .filter(resultExpr -> canInlineToReturnStatement(resultExpr, state))
+        .filter(
+            resultExpr ->
+                canInlineToReturnStatement(resultExpr, state)
+                    && !isIdentifierSymbolReferencedInAssociatedFinallyBlock(variableSymbol, state))
         .map(
             resultExpr ->
                 describeMatch(
@@ -113,13 +121,13 @@ public final class DirectReturn extends BugChecker implements BlockTreeMatcher {
   }
 
   /**
-   * Tells whether inlining the given expression to the associated return statement can be done
-   * safely.
+   * Tells whether inlining the given expression to the associated return statement can likely be
+   * done without changing the expression's return type.
    *
-   * <p>Inlining is generally safe, 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.
+   * <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) {
@@ -128,4 +136,40 @@ public final class DirectReturn extends BugChecker implements BlockTreeMatcher {
             .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

@@ -42,6 +42,7 @@ public final class EmptyMethod extends BugChecker implements MethodTreeMatcher {
   public EmptyMethod() {}
 
   @Override
+  @SuppressWarnings("java:S1067" /* Chaining disjunctions like this does not impact readability. */)
   public Description matchMethod(MethodTree tree, VisitorState state) {
     if (tree.getBody() == null
         || !tree.getBody().getStatements().isEmpty()

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

@@ -104,7 +104,9 @@ public final class ErrorProneTestHelperSourceFormat extends BugChecker
     String formatted;
     try {
       formatted = formatSourceCode(source, retainUnusedImports).trim();
-    } catch (FormatterException e) {
+    } catch (
+        @SuppressWarnings("java:S1166" /* Stack trace not relevant. */)
+        FormatterException e) {
       return buildDescription(methodInvocation)
           .setMessage(String.format("Source code is malformed: %s", e.getMessage()))
           .build();
@@ -131,7 +133,7 @@ public final class ErrorProneTestHelperSourceFormat extends BugChecker
         SuggestedFix.replace(
             startPos,
             endPos,
-            Splitter.on('\n')
+            Splitter.on(System.lineSeparator())
                 .splitToStream(formatted)
                 .map(state::getConstantExpression)
                 .collect(joining(", "))));
@@ -157,7 +159,7 @@ public final class ErrorProneTestHelperSourceFormat extends BugChecker
         return Optional.empty();
       }
 
-      source.append(value).append('\n');
+      source.append(value).append(System.lineSeparator());
     }
 
     return Optional.of(source.toString());

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

@@ -82,10 +82,8 @@ public final class FluxFlatMapUsage extends BugChecker
 
     SuggestedFix serializationFix = SuggestedFixes.renameMethodInvocation(tree, "concatMap", state);
     SuggestedFix concurrencyCapFix =
-        SuggestedFix.builder()
-            .postfixWith(
-                Iterables.getOnlyElement(tree.getArguments()), ", " + MAX_CONCURRENCY_ARG_NAME)
-            .build();
+        SuggestedFix.postfixWith(
+            Iterables.getOnlyElement(tree.getArguments()), ", " + MAX_CONCURRENCY_ARG_NAME);
 
     Description.Builder description = buildDescription(tree);
 

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

@@ -35,6 +35,8 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 // 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",

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

@@ -40,6 +40,7 @@ import java.util.List;
 import java.util.Optional;
 import java.util.Set;
 import java.util.stream.Stream;
+import javax.inject.Inject;
 import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.bugpatterns.util.AnnotationAttributeMatcher;
 import tech.picnic.errorprone.bugpatterns.util.Flags;
@@ -58,6 +59,7 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
     linkType = CUSTOM,
     severity = SUGGESTION,
     tags = STYLE)
+@SuppressWarnings("java:S2160" /* Super class equality definition suffices. */)
 public final class LexicographicalAnnotationAttributeListing extends BugChecker
     implements AnnotationTreeMatcher {
   private static final long serialVersionUID = 1L;
@@ -93,7 +95,8 @@ public final class LexicographicalAnnotationAttributeListing extends BugChecker
    *
    * @param flags Any provided command line flags.
    */
-  public LexicographicalAnnotationAttributeListing(ErrorProneFlags flags) {
+  @Inject
+  LexicographicalAnnotationAttributeListing(ErrorProneFlags flags) {
     matcher = createAnnotationAttributeMatcher(flags);
   }
 

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

@@ -46,9 +46,19 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 public final class LexicographicalAnnotationListing extends BugChecker
     implements MethodTreeMatcher {
   private static final long serialVersionUID = 1L;
+  /**
+   * A comparator that minimally reorders {@link AnnotationType}s, such that declaration annotations
+   * are placed before type annotations.
+   */
+  @SuppressWarnings({
+    "java:S1067",
+    "java:S3358"
+  } /* Avoiding the nested ternary operator hurts readability. */)
   private static final Comparator<@Nullable AnnotationType> BY_ANNOTATION_TYPE =
       (a, b) ->
-          (a == null || a == DECLARATION) && b == TYPE ? -1 : a == TYPE && b == DECLARATION ? 1 : 0;
+          (a == null || a == DECLARATION) && b == TYPE
+              ? -1
+              : (a == TYPE && b == DECLARATION ? 1 : 0);
 
   /** Instantiates a new {@link LexicographicalAnnotationListing} instance. */
   public LexicographicalAnnotationListing() {}

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

@@ -118,6 +118,8 @@ public final class MethodReferenceUsage extends BugChecker implements LambdaExpr
         .flatMap(expectedInstance -> constructMethodRef(lambdaExpr, subTree, expectedInstance));
   }
 
+  @SuppressWarnings(
+      "java:S1151" /* Extracting `IDENTIFIER` case block to separate method does not improve readability. */)
   private static Optional<SuggestedFix.Builder> constructMethodRef(
       LambdaExpressionTree lambdaExpr,
       MethodInvocationTree subTree,
@@ -130,10 +132,9 @@ public final class MethodReferenceUsage extends BugChecker implements LambdaExpr
           return Optional.empty();
         }
         Symbol sym = ASTHelpers.getSymbol(methodSelect);
-        if (!ASTHelpers.isStatic(sym)) {
-          return constructFix(lambdaExpr, "this", methodSelect);
-        }
-        return constructFix(lambdaExpr, sym.owner, methodSelect);
+        return ASTHelpers.isStatic(sym)
+            ? constructFix(lambdaExpr, sym.owner, methodSelect)
+            : constructFix(lambdaExpr, "this", methodSelect);
       case MEMBER_SELECT:
         return constructMethodRef(lambdaExpr, (MemberSelectTree) methodSelect, expectedInstance);
       default:

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

@@ -1,59 +0,0 @@
-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.VisitorState;
-import com.google.errorprone.bugpatterns.BugChecker;
-import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
-import com.google.errorprone.matchers.Description;
-import com.google.errorprone.matchers.MultiMatcher;
-import com.google.errorprone.util.ASTHelpers;
-import com.sun.source.tree.AnnotationTree;
-import com.sun.source.tree.ClassTree;
-import com.sun.source.tree.MethodTree;
-import com.sun.source.tree.Tree;
-
-/** A {@link BugChecker} that flags likely missing Refaster annotations. */
-@AutoService(BugChecker.class)
-@BugPattern(
-    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(
-          AT_LEAST_ONE,
-          anyOf(
-              isType("com.google.errorprone.refaster.annotation.Placeholder"),
-              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 =
-        tree.getMembers().stream()
-            .filter(member -> member.getKind() == Tree.Kind.METHOD)
-            .map(MethodTree.class::cast)
-            .filter(method -> !ASTHelpers.isGeneratedConstructor(method))
-            .map(method -> REFASTER_ANNOTATION.matches(method, state))
-            .distinct()
-            .count();
-
-    return methodTypes < 2 ? Description.NO_MATCH : buildDescription(tree).build();
-  }
-}

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

@@ -43,6 +43,7 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 // 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.
+@SuppressWarnings("java:S1192" /* Factoring out repeated method names impacts readability. */)
 public final class NonEmptyMono extends BugChecker implements MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Matcher<ExpressionTree> MONO_SIZE_CHECK =

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

@@ -49,6 +49,7 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
     linkType = CUSTOM,
     severity = WARNING,
     tags = PERFORMANCE)
+@SuppressWarnings("java:S1192" /* Factoring out repeated method names impacts readability. */)
 public final class PrimitiveComparison extends BugChecker implements MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Matcher<ExpressionTree> STATIC_COMPARISON_METHOD =

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

@@ -50,6 +50,7 @@ import java.util.Locale;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.stream.Stream;
+import javax.inject.Inject;
 import tech.picnic.errorprone.bugpatterns.util.Flags;
 import tech.picnic.errorprone.bugpatterns.util.MethodMatcherFactory;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
@@ -62,6 +63,11 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
     linkType = CUSTOM,
     severity = SUGGESTION,
     tags = SIMPLIFICATION)
+@SuppressWarnings({
+  "java:S1192" /* Factoring out repeated method names impacts readability. */,
+  "java:S2160" /* Super class equality definition suffices. */,
+  "key-to-resolve-AnnotationUseStyle-and-TrailingComment-check-conflict"
+})
 public final class RedundantStringConversion extends BugChecker
     implements BinaryTreeMatcher, CompoundAssignmentTreeMatcher, MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
@@ -150,7 +156,8 @@ public final class RedundantStringConversion extends BugChecker
    *
    * @param flags Any provided command line flags.
    */
-  public RedundantStringConversion(ErrorProneFlags flags) {
+  @Inject
+  RedundantStringConversion(ErrorProneFlags flags) {
     conversionMethodMatcher = createConversionMethodMatcher(flags);
   }
 
@@ -163,7 +170,7 @@ public final class RedundantStringConversion extends BugChecker
     ExpressionTree lhs = tree.getLeftOperand();
     ExpressionTree rhs = tree.getRightOperand();
     if (!STRING.matches(lhs, state)) {
-      return finalize(tree, tryFix(rhs, state, STRING));
+      return createDescription(tree, tryFix(rhs, state, STRING));
     }
 
     List<SuggestedFix.Builder> fixes = new ArrayList<>();
@@ -177,7 +184,7 @@ public final class RedundantStringConversion extends BugChecker
     }
     tryFix(rhs, state, ANY_EXPR).ifPresent(fixes::add);
 
-    return finalize(tree, fixes.stream().reduce(SuggestedFix.Builder::merge));
+    return createDescription(tree, fixes.stream().reduce(SuggestedFix.Builder::merge));
   }
 
   @Override
@@ -186,36 +193,36 @@ public final class RedundantStringConversion extends BugChecker
       return Description.NO_MATCH;
     }
 
-    return finalize(tree, tryFix(tree.getExpression(), state, ANY_EXPR));
+    return createDescription(tree, tryFix(tree.getExpression(), state, ANY_EXPR));
   }
 
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (STRINGBUILDER_APPEND_INVOCATION.matches(tree, state)) {
-      return finalize(tree, tryFixPositionalConverter(tree.getArguments(), state, 0));
+      return createDescription(tree, tryFixPositionalConverter(tree.getArguments(), state, 0));
     }
 
     if (STRINGBUILDER_INSERT_INVOCATION.matches(tree, state)) {
-      return finalize(tree, tryFixPositionalConverter(tree.getArguments(), state, 1));
+      return createDescription(tree, tryFixPositionalConverter(tree.getArguments(), state, 1));
     }
 
     if (FORMATTER_INVOCATION.matches(tree, state)) {
-      return finalize(tree, tryFixFormatter(tree.getArguments(), state));
+      return createDescription(tree, tryFixFormatter(tree.getArguments(), state));
     }
 
     if (GUAVA_GUARD_INVOCATION.matches(tree, state)) {
-      return finalize(tree, tryFixGuavaGuard(tree.getArguments(), state));
+      return createDescription(tree, tryFixGuavaGuard(tree.getArguments(), state));
     }
 
     if (SLF4J_LOGGER_INVOCATION.matches(tree, state)) {
-      return finalize(tree, tryFixSlf4jLogger(tree.getArguments(), state));
+      return createDescription(tree, tryFixSlf4jLogger(tree.getArguments(), state));
     }
 
     if (instanceMethod().matches(tree, state)) {
-      return finalize(tree, tryFix(tree, state, STRING));
+      return createDescription(tree, tryFix(tree, state, STRING));
     }
 
-    return finalize(tree, tryFix(tree, state, NON_NULL_STRING));
+    return createDescription(tree, tryFix(tree, state, NON_NULL_STRING));
   }
 
   private Optional<SuggestedFix.Builder> tryFixPositionalConverter(
@@ -298,7 +305,7 @@ public final class RedundantStringConversion extends BugChecker
 
     /* Simplify the values to be plugged into the format pattern, if possible. */
     return arguments.stream()
-        .skip(patternIndex + 1)
+        .skip(patternIndex + 1L)
         .map(arg -> tryFix(arg, state, remainingArgFilter))
         .flatMap(Optional::stream)
         .reduce(SuggestedFix.Builder::merge);
@@ -362,7 +369,7 @@ public final class RedundantStringConversion extends BugChecker
     return Optional.of(Iterables.getOnlyElement(methodInvocation.getArguments()));
   }
 
-  private Description finalize(Tree tree, Optional<SuggestedFix.Builder> fixes) {
+  private Description createDescription(Tree tree, Optional<SuggestedFix.Builder> fixes) {
     return fixes
         .map(SuggestedFix.Builder::build)
         .map(fix -> describeMatch(tree, fix))

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

@@ -99,8 +99,9 @@ public final class RequestMappingAnnotation extends BugChecker implements Method
             && LACKS_PARAMETER_ANNOTATION.matches(tree, state)
         ? buildDescription(tree)
             .setMessage(
-                "Not all parameters of this request mapping method are annotated; this may be a mistake. "
-                    + "If the unannotated parameters represent query string parameters, annotate them with `@RequestParam`.")
+                "Not all parameters of this request mapping method are annotated; this may be a "
+                    + "mistake. If the unannotated parameters represent query string parameters, "
+                    + "annotate them with `@RequestParam`.")
             .build()
         : Description.NO_MATCH;
   }

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

@@ -27,6 +27,7 @@ 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 javax.inject.Inject;
 import tech.picnic.errorprone.bugpatterns.util.Flags;
 
 /** A {@link BugChecker} that flags {@code @RequestParam} parameters with an unsupported type. */
@@ -38,6 +39,7 @@ import tech.picnic.errorprone.bugpatterns.util.Flags;
     linkType = CUSTOM,
     severity = ERROR,
     tags = LIKELY_ERROR)
+@SuppressWarnings("java:S2160" /* Super class equality definition suffices. */)
 public final class RequestParamType extends BugChecker implements VariableTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final String SUPPORTED_CUSTOM_TYPES_FLAG = "RequestParamType:SupportedCustomTypes";
@@ -54,7 +56,8 @@ public final class RequestParamType extends BugChecker implements VariableTreeMa
    *
    * @param flags Any provided command line flags.
    */
-  public RequestParamType(ErrorProneFlags flags) {
+  @Inject
+  RequestParamType(ErrorProneFlags flags) {
     hasUnsupportedRequestParamType = hasUnsupportedRequestParamType(flags);
   }
 

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

@@ -1,89 +0,0 @@
-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/util/AnnotationAttributeMatcher.java

@@ -103,7 +103,7 @@ public final class AnnotationAttributeMatcher implements Serializable {
    * @param tree The annotation AST node to be inspected.
    * @return Any matching annotation arguments.
    */
-  public Stream<? extends ExpressionTree> extractMatchingArguments(AnnotationTree tree) {
+  public Stream<ExpressionTree> extractMatchingArguments(AnnotationTree tree) {
     Type type = ASTHelpers.getType(tree.getAnnotationType());
     if (type == null) {
       return Stream.empty();
@@ -111,6 +111,7 @@ public final class AnnotationAttributeMatcher implements Serializable {
 
     String annotationType = type.toString();
     return tree.getArguments().stream()
+        .map(ExpressionTree.class::cast)
         .filter(a -> matches(annotationType, extractAttributeName(a)));
   }
 

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

@@ -114,6 +114,7 @@ public final class JavaKeywords {
    * @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>
    */
+  @SuppressWarnings("java:S1067" /* Chaining conjunctions like this does not impact readability. */)
   public static boolean isValidIdentifier(String str) {
     return !str.isEmpty()
         && !isReservedKeyword(str)

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

@@ -18,6 +18,9 @@ import java.util.regex.Pattern;
 public final class MethodMatcherFactory {
   private static final Splitter ARGUMENT_TYPE_SPLITTER =
       Splitter.on(',').trimResults().omitEmptyStrings();
+  // XXX: Check whether we can use a parser for "standard" Java signatures here. Maybe
+  // `sun.reflect.generics.parser.SignatureParser`?
+  @SuppressWarnings("java:S5998" /* In practice there will be only modest recursion. */)
   private static final Pattern METHOD_SIGNATURE =
       Pattern.compile("([^\\s#(,)]+)#([^\\s#(,)]+)\\(((?:[^\\s#(,)]+(?:,[^\\s#(,)]+)*)?)\\)");
 

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

@@ -1,12 +1,22 @@
 package tech.picnic.errorprone.bugpatterns.util;
 
+import static com.sun.tools.javac.parser.Tokens.TokenKind.RPAREN;
 import static com.sun.tools.javac.util.Position.NOPOS;
+import static java.util.stream.Collectors.joining;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.CharMatcher;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Streams;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.util.ErrorProneToken;
+import com.google.errorprone.util.ErrorProneTokens;
+import com.sun.source.tree.MethodInvocationTree;
 import com.sun.source.tree.Tree;
 import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
+import com.sun.tools.javac.util.Position;
+import java.util.Optional;
 
 /**
  * A collection of Error Prone utility methods for dealing with the source code representation of
@@ -59,4 +69,57 @@ public final class SourceCode {
         whitespaceEndPos == -1 ? sourceCode.length() : whitespaceEndPos,
         "");
   }
+
+  /**
+   * Creates a {@link SuggestedFix} for the replacement of the given {@link MethodInvocationTree}
+   * with just the arguments to the method invocation, effectively "unwrapping" the method
+   * invocation.
+   *
+   * <p>For example, given the method invocation {@code foo.bar(1, 2, 3)}, this method will return a
+   * {@link SuggestedFix} that replaces the method invocation with {@code 1, 2, 3}.
+   *
+   * <p>This method aims to preserve the original formatting of the method invocation, including
+   * whitespace and comments.
+   *
+   * @param tree The AST node to be unwrapped.
+   * @param state A {@link VisitorState} describing the context in which the given {@link
+   *     MethodInvocationTree} is found.
+   * @return A non-{@code null} {@link SuggestedFix}.
+   */
+  public static SuggestedFix unwrapMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    CharSequence sourceCode = state.getSourceCode();
+    int startPosition = state.getEndPosition(tree.getMethodSelect());
+    int endPosition = state.getEndPosition(tree);
+
+    if (sourceCode == null || startPosition == Position.NOPOS || endPosition == Position.NOPOS) {
+      return unwrapMethodInvocationDroppingWhitespaceAndComments(tree, state);
+    }
+
+    ImmutableList<ErrorProneToken> tokens =
+        ErrorProneTokens.getTokens(
+            sourceCode.subSequence(startPosition, endPosition).toString(), state.context);
+
+    Optional<Integer> leftParenPosition =
+        tokens.stream().findFirst().map(t -> startPosition + t.endPos());
+    Optional<Integer> rightParenPosition =
+        Streams.findLast(tokens.stream().filter(t -> t.kind() == RPAREN))
+            .map(t -> startPosition + t.pos());
+    if (leftParenPosition.isEmpty() || rightParenPosition.isEmpty()) {
+      return unwrapMethodInvocationDroppingWhitespaceAndComments(tree, state);
+    }
+
+    return SuggestedFix.replace(
+        tree,
+        sourceCode
+            .subSequence(leftParenPosition.orElseThrow(), rightParenPosition.orElseThrow())
+            .toString());
+  }
+
+  @VisibleForTesting
+  static SuggestedFix unwrapMethodInvocationDroppingWhitespaceAndComments(
+      MethodInvocationTree tree, VisitorState state) {
+    return SuggestedFix.replace(
+        tree,
+        tree.getArguments().stream().map(arg -> treeToString(arg, state)).collect(joining(", ")));
+  }
 }

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

@@ -4,7 +4,10 @@ import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.suppliers.Supplier;
 import com.sun.tools.javac.code.ClassFinder;
+import com.sun.tools.javac.code.Source;
 import com.sun.tools.javac.code.Symbol.CompletionFailure;
+import com.sun.tools.javac.code.Symbol.ModuleSymbol;
+import com.sun.tools.javac.code.Symtab;
 import com.sun.tools.javac.util.Name;
 
 /**
@@ -86,11 +89,19 @@ public enum ThirdPartyLibrary {
 
   private static boolean canLoadClass(String className, VisitorState state) {
     ClassFinder classFinder = ClassFinder.instance(state.context);
+    Symtab symtab = state.getSymtab();
+    // XXX: Drop support for targeting Java 8 once the oldest supported JDK drops such support.
+    ModuleSymbol module =
+        Source.instance(state.context).compareTo(Source.JDK9) < 0
+            ? symtab.noModule
+            : symtab.unnamedModule;
     Name binaryName = state.binaryNameFromClassname(className);
     try {
-      classFinder.loadClass(state.getSymtab().unnamedModule, binaryName);
+      classFinder.loadClass(module, binaryName);
       return true;
-    } catch (CompletionFailure e) {
+    } catch (
+        @SuppressWarnings("java:S1166" /* Not exceptional. */)
+        CompletionFailure e) {
       return false;
     }
   }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/AssertJMapRules.java

@@ -16,15 +16,18 @@ import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.Map;
+import java.util.Set;
 import java.util.TreeMap;
 import java.util.TreeSet;
 import org.assertj.core.api.AbstractAssert;
 import org.assertj.core.api.AbstractBooleanAssert;
+import org.assertj.core.api.AbstractCollectionAssert;
 import org.assertj.core.api.AbstractMapAssert;
 import org.assertj.core.api.MapAssert;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
@@ -220,6 +223,19 @@ final class AssertJMapRules {
     }
   }
 
+  static final class AssertThatMapContainsOnlyKeys<K, V> {
+    @BeforeTemplate
+    AbstractCollectionAssert<?, Collection<? extends K>, K, ?> before(Map<K, V> map, Set<K> keys) {
+      return assertThat(map.keySet()).hasSameElementsAs(keys);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    MapAssert<K, V> after(Map<K, V> map, Set<K> keys) {
+      return assertThat(map).containsOnlyKeys(keys);
+    }
+  }
+
   static final class AssertThatMapContainsValue<K, V> {
     @BeforeTemplate
     AbstractBooleanAssert<?> before(Map<K, V> map, V value) {

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/AssertJPrimitiveRules.java

@@ -23,6 +23,8 @@ final class AssertJPrimitiveRules {
     }
 
     @BeforeTemplate
+    @SuppressWarnings(
+        "java:S1244" /* The (in)equality checks are fragile, but may be seen in the wild. */)
     AbstractBooleanAssert<?> before(double actual, double expected) {
       return Refaster.anyOf(
           assertThat(actual == expected).isTrue(), assertThat(actual != expected).isFalse());
@@ -43,6 +45,8 @@ final class AssertJPrimitiveRules {
     }
 
     @BeforeTemplate
+    @SuppressWarnings(
+        "java:S1244" /* The (in)equality checks are fragile, but may be seen in the wild. */)
     AbstractBooleanAssert<?> before(double actual, double expected) {
       return Refaster.anyOf(
           assertThat(actual != expected).isTrue(), assertThat(actual == expected).isFalse());

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/AssertJRules.java

@@ -2024,8 +2024,8 @@ final class AssertJRules {
   ////////////////////////////////////////////////////////////////////////////
   // Above: Generated code.
 
-  ///////////////////////////////////////////////////////////////////////////////////////////////////////
-  ///////////////////////////////////////////////////////////////////////////////////////////////////////
+  ////////////////////////////////////////////////////////////////////////////
+  ////////////////////////////////////////////////////////////////////////////
   // Organize the code below.
 
   // XXX: Do the "single Comparable" match shown below.

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/AssertJThrowingCallableRules.java

@@ -47,7 +47,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByIllegalArgumentExceptionHasMessage {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByIllegalArgumentException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByIllegalArgumentException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
       return assertThatIllegalArgumentException().isThrownBy(throwingCallable).withMessage(message);
     }
@@ -64,7 +64,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByIllegalArgumentExceptionHasMessageParameters {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByIllegalArgumentException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByIllegalArgumentException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(
         ThrowingCallable throwingCallable, String message, @Repeated Object parameters) {
       return assertThatIllegalArgumentException()
@@ -85,7 +85,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByIllegalArgumentExceptionHasMessageStartingWith {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByIllegalArgumentException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByIllegalArgumentException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
       return assertThatIllegalArgumentException()
           .isThrownBy(throwingCallable)
@@ -104,7 +104,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByIllegalArgumentExceptionHasMessageContaining {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByIllegalArgumentException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByIllegalArgumentException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
       return assertThatIllegalArgumentException()
           .isThrownBy(throwingCallable)
@@ -123,7 +123,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByIllegalArgumentExceptionHasMessageNotContainingAny {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByIllegalArgumentException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByIllegalArgumentException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(
         ThrowingCallable throwingCallable, @Repeated CharSequence values) {
       return assertThatIllegalArgumentException()
@@ -157,7 +157,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByIllegalStateExceptionHasMessage {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByIllegalStateException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByIllegalStateException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
       return assertThatIllegalStateException().isThrownBy(throwingCallable).withMessage(message);
     }
@@ -174,7 +174,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByIllegalStateExceptionHasMessageParameters {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByIllegalStateException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByIllegalStateException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(
         ThrowingCallable throwingCallable, String message, @Repeated Object parameters) {
       return assertThatIllegalStateException()
@@ -195,7 +195,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByIllegalStateExceptionHasMessageStartingWith {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByIllegalStateException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByIllegalStateException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
       return assertThatIllegalStateException()
           .isThrownBy(throwingCallable)
@@ -214,7 +214,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByIllegalStateExceptionHasMessageContaining {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByIllegalStateException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByIllegalStateException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
       return assertThatIllegalStateException()
           .isThrownBy(throwingCallable)
@@ -233,7 +233,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByIllegalStateExceptionHasMessageNotContaining {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByIllegalStateException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByIllegalStateException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
       return assertThatIllegalStateException()
           .isThrownBy(throwingCallable)
@@ -265,7 +265,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByNullPointerExceptionHasMessage {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByNullPointerException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByNullPointerException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
       return assertThatNullPointerException().isThrownBy(throwingCallable).withMessage(message);
     }
@@ -282,7 +282,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByNullPointerExceptionHasMessageParameters {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByNullPointerException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByNullPointerException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(
         ThrowingCallable throwingCallable, String message, @Repeated Object parameters) {
       return assertThatNullPointerException()
@@ -303,7 +303,7 @@ final class AssertJThrowingCallableRules {
   static final class AssertThatThrownByNullPointerExceptionHasMessageStartingWith {
     @BeforeTemplate
     @SuppressWarnings(
-        "AssertThatThrownByNullPointerException" /* Matches strictly more specific expressions. */)
+        "AssertThatThrownByNullPointerException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
       return assertThatNullPointerException()
           .isThrownBy(throwingCallable)
@@ -319,6 +319,44 @@ final class AssertJThrowingCallableRules {
     }
   }
 
+  static final class AssertThatThrownByNullPointerExceptionHasMessageContaining {
+    @BeforeTemplate
+    @SuppressWarnings(
+        "AssertThatThrownByNullPointerException" /* This is a more specific template. */)
+    AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
+      return assertThatNullPointerException()
+          .isThrownBy(throwingCallable)
+          .withMessageContaining(message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    AbstractObjectAssert<?, ?> after(ThrowingCallable throwingCallable, String message) {
+      return assertThatThrownBy(throwingCallable)
+          .isInstanceOf(NullPointerException.class)
+          .hasMessageContaining(message);
+    }
+  }
+
+  static final class AssertThatThrownByNullPointerExceptionHasMessageNotContaining {
+    @BeforeTemplate
+    @SuppressWarnings(
+        "AssertThatThrownByNullPointerException" /* This is a more specific template. */)
+    AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
+      return assertThatNullPointerException()
+          .isThrownBy(throwingCallable)
+          .withMessageNotContaining(message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    AbstractObjectAssert<?, ?> after(ThrowingCallable throwingCallable, String message) {
+      return assertThatThrownBy(throwingCallable)
+          .isInstanceOf(NullPointerException.class)
+          .hasMessageNotContaining(message);
+    }
+  }
+
   static final class AssertThatThrownByIOException {
     @BeforeTemplate
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable) {
@@ -334,8 +372,7 @@ final class AssertJThrowingCallableRules {
 
   static final class AssertThatThrownByIOExceptionHasMessage {
     @BeforeTemplate
-    @SuppressWarnings(
-        "AssertThatThrownByIOException" /* Matches strictly more specific expressions. */)
+    @SuppressWarnings("AssertThatThrownByIOException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
       return assertThatIOException().isThrownBy(throwingCallable).withMessage(message);
     }
@@ -351,8 +388,7 @@ final class AssertJThrowingCallableRules {
 
   static final class AssertThatThrownByIOExceptionHasMessageParameters {
     @BeforeTemplate
-    @SuppressWarnings(
-        "AssertThatThrownByIOException" /* Matches strictly more specific expressions. */)
+    @SuppressWarnings("AssertThatThrownByIOException" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(
         ThrowingCallable throwingCallable, String message, @Repeated Object parameters) {
       return assertThatIOException().isThrownBy(throwingCallable).withMessage(message, parameters);
@@ -368,6 +404,54 @@ final class AssertJThrowingCallableRules {
     }
   }
 
+  static final class AssertThatThrownByIOExceptionHasMessageStartingWith {
+    @BeforeTemplate
+    @SuppressWarnings("AssertThatThrownByIOException" /* This is a more specific template. */)
+    AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
+      return assertThatIOException().isThrownBy(throwingCallable).withMessageStartingWith(message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    AbstractObjectAssert<?, ?> after(ThrowingCallable throwingCallable, String message) {
+      return assertThatThrownBy(throwingCallable)
+          .isInstanceOf(IOException.class)
+          .hasMessageStartingWith(message);
+    }
+  }
+
+  static final class AssertThatThrownByIOExceptionHasMessageContaining {
+    @BeforeTemplate
+    @SuppressWarnings("AssertThatThrownByIOException" /* This is a more specific template. */)
+    AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
+      return assertThatIOException().isThrownBy(throwingCallable).withMessageContaining(message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    AbstractObjectAssert<?, ?> after(ThrowingCallable throwingCallable, String message) {
+      return assertThatThrownBy(throwingCallable)
+          .isInstanceOf(IOException.class)
+          .hasMessageContaining(message);
+    }
+  }
+
+  static final class AssertThatThrownByIOExceptionHasMessageNotContaining {
+    @BeforeTemplate
+    @SuppressWarnings("AssertThatThrownByIOException" /* This is a more specific template. */)
+    AbstractObjectAssert<?, ?> before(ThrowingCallable throwingCallable, String message) {
+      return assertThatIOException().isThrownBy(throwingCallable).withMessageNotContaining(message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    AbstractObjectAssert<?, ?> after(ThrowingCallable throwingCallable, String message) {
+      return assertThatThrownBy(throwingCallable)
+          .isInstanceOf(IOException.class)
+          .hasMessageNotContaining(message);
+    }
+  }
+
   static final class AssertThatThrownBy {
     @BeforeTemplate
     AbstractObjectAssert<?, ?> before(
@@ -385,7 +469,7 @@ final class AssertJThrowingCallableRules {
 
   static final class AssertThatThrownByHasMessage {
     @BeforeTemplate
-    @SuppressWarnings("AssertThatThrownBy" /* Matches strictly more specific expressions. */)
+    @SuppressWarnings("AssertThatThrownBy" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(
         Class<? extends Throwable> exceptionType,
         ThrowingCallable throwingCallable,
@@ -407,7 +491,7 @@ final class AssertJThrowingCallableRules {
 
   static final class AssertThatThrownByHasMessageParameters {
     @BeforeTemplate
-    @SuppressWarnings("AssertThatThrownBy" /* Matches strictly more specific expressions. */)
+    @SuppressWarnings("AssertThatThrownBy" /* This is a more specific template. */)
     AbstractObjectAssert<?, ?> before(
         Class<? extends Throwable> exceptionType,
         ThrowingCallable throwingCallable,
@@ -431,6 +515,78 @@ final class AssertJThrowingCallableRules {
     }
   }
 
+  static final class AssertThatThrownByHasMessageStartingWith {
+    @BeforeTemplate
+    @SuppressWarnings("AssertThatThrownBy" /* This is a more specific template. */)
+    AbstractObjectAssert<?, ?> before(
+        Class<? extends Throwable> exceptionType,
+        ThrowingCallable throwingCallable,
+        String message) {
+      return assertThatExceptionOfType(exceptionType)
+          .isThrownBy(throwingCallable)
+          .withMessageStartingWith(message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    AbstractObjectAssert<?, ?> after(
+        Class<? extends Throwable> exceptionType,
+        ThrowingCallable throwingCallable,
+        String message) {
+      return assertThatThrownBy(throwingCallable)
+          .isInstanceOf(exceptionType)
+          .hasMessageStartingWith(message);
+    }
+  }
+
+  static final class AssertThatThrownByHasMessageContaining {
+    @BeforeTemplate
+    @SuppressWarnings("AssertThatThrownBy" /* This is a more specific template. */)
+    AbstractObjectAssert<?, ?> before(
+        Class<? extends Throwable> exceptionType,
+        ThrowingCallable throwingCallable,
+        String message) {
+      return assertThatExceptionOfType(exceptionType)
+          .isThrownBy(throwingCallable)
+          .withMessageContaining(message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    AbstractObjectAssert<?, ?> after(
+        Class<? extends Throwable> exceptionType,
+        ThrowingCallable throwingCallable,
+        String message) {
+      return assertThatThrownBy(throwingCallable)
+          .isInstanceOf(exceptionType)
+          .hasMessageContaining(message);
+    }
+  }
+
+  static final class AssertThatThrownByHasMessageNotContaining {
+    @BeforeTemplate
+    @SuppressWarnings("AssertThatThrownBy" /* This is a more specific template. */)
+    AbstractObjectAssert<?, ?> before(
+        Class<? extends Throwable> exceptionType,
+        ThrowingCallable throwingCallable,
+        String message) {
+      return assertThatExceptionOfType(exceptionType)
+          .isThrownBy(throwingCallable)
+          .withMessageNotContaining(message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    AbstractObjectAssert<?, ?> after(
+        Class<? extends Throwable> exceptionType,
+        ThrowingCallable throwingCallable,
+        String message) {
+      return assertThatThrownBy(throwingCallable)
+          .isInstanceOf(exceptionType)
+          .hasMessageNotContaining(message);
+    }
+  }
+
   // XXX: Drop this rule in favour of a generic Error Prone check that flags `String.format(...)`
   // arguments to a wide range of format methods.
   static final class AbstractThrowableAssertHasMessage {

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/AssortedRules.java

@@ -115,6 +115,7 @@ final class AssortedRules {
   // intelligently.
   static final class LogicalImplication {
     @BeforeTemplate
+    @SuppressWarnings("java:S2589" /* This violation will be rewritten. */)
     boolean before(boolean firstTest, boolean secondTest) {
       return firstTest || (!firstTest && secondTest);
     }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/BigDecimalRules.java

@@ -56,6 +56,7 @@ final class BigDecimalRules {
   // `BugChecker`.
   static final class BigDecimalValueOf {
     @BeforeTemplate
+    @SuppressWarnings("java:S2111" /* This violation will be rewritten. */)
     BigDecimal before(double value) {
       return new BigDecimal(value);
     }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/BugCheckerRules.java

@@ -3,6 +3,7 @@ package tech.picnic.errorprone.refasterrules;
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.FixChooser;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
@@ -25,6 +26,7 @@ final class BugCheckerRules {
     }
 
     @AfterTemplate
+    @CanIgnoreReturnValue
     BugCheckerRefactoringTestHelper after(BugCheckerRefactoringTestHelper helper) {
       return helper;
     }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/CollectionRules.java

@@ -35,6 +35,7 @@ final class CollectionRules {
    */
   static final class CollectionIsEmpty<T> {
     @BeforeTemplate
+    @SuppressWarnings("java:S1155" /* This violation will be rewritten. */)
     boolean before(Collection<T> collection) {
       return Refaster.anyOf(
           collection.size() == 0,
@@ -163,6 +164,8 @@ final class CollectionRules {
   }
 
   /** Prefer {@link ArrayList#ArrayList(Collection)} over the Guava alternative. */
+  @SuppressWarnings(
+      "NonApiType" /* Matching against `List` would unnecessarily constrain the rule. */)
   static final class NewArrayListFromCollection<T> {
     @BeforeTemplate
     ArrayList<T> before(Collection<T> collection) {

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ComparatorRules.java

@@ -12,6 +12,7 @@ import static java.util.function.Function.identity;
 import com.google.common.collect.Comparators;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
@@ -78,6 +79,7 @@ final class ComparatorRules {
     }
 
     @AfterTemplate
+    @CanIgnoreReturnValue
     @UseImportPolicy(STATIC_IMPORT_ALWAYS)
     Comparator<T> after(Comparator<T> cmp) {
       return cmp;
@@ -219,7 +221,6 @@ final class ComparatorRules {
    */
   static final class MinOfVarargs<T> {
     @BeforeTemplate
-    @SuppressWarnings("StreamOfArray" /* In practice individual values are provided. */)
     T before(@Repeated T value, Comparator<T> cmp) {
       return Stream.of(Refaster.asVarargs(value)).min(cmp).orElseThrow();
     }
@@ -233,6 +234,7 @@ final class ComparatorRules {
   /** Prefer {@link Comparators#min(Comparable, Comparable)}} over more verbose alternatives. */
   static final class MinOfPairNaturalOrder<T extends Comparable<? super T>> {
     @BeforeTemplate
+    @SuppressWarnings("java:S1067" /* The conditional operators are independent. */)
     T before(T value1, T value2) {
       return Refaster.anyOf(
           value1.compareTo(value2) <= 0 ? value1 : value2,
@@ -259,6 +261,7 @@ final class ComparatorRules {
    */
   static final class MinOfPairCustomOrder<T> {
     @BeforeTemplate
+    @SuppressWarnings("java:S1067" /* The conditional operators are independent. */)
     T before(T value1, T value2, Comparator<T> cmp) {
       return Refaster.anyOf(
           cmp.compare(value1, value2) <= 0 ? value1 : value2,
@@ -285,7 +288,6 @@ final class ComparatorRules {
    */
   static final class MaxOfVarargs<T> {
     @BeforeTemplate
-    @SuppressWarnings("StreamOfArray" /* In practice individual values are provided. */)
     T before(@Repeated T value, Comparator<T> cmp) {
       return Stream.of(Refaster.asVarargs(value)).max(cmp).orElseThrow();
     }
@@ -299,6 +301,7 @@ final class ComparatorRules {
   /** Prefer {@link Comparators#max(Comparable, Comparable)}} over more verbose alternatives. */
   static final class MaxOfPairNaturalOrder<T extends Comparable<? super T>> {
     @BeforeTemplate
+    @SuppressWarnings("java:S1067" /* The conditional operators are independent. */)
     T before(T value1, T value2) {
       return Refaster.anyOf(
           value1.compareTo(value2) >= 0 ? value1 : value2,
@@ -325,6 +328,7 @@ final class ComparatorRules {
    */
   static final class MaxOfPairCustomOrder<T> {
     @BeforeTemplate
+    @SuppressWarnings("java:S1067" /* The conditional operators are independent. */)
     T before(T value1, T value2, Comparator<T> cmp) {
       return Refaster.anyOf(
           cmp.compare(value1, value2) >= 0 ? value1 : value2,

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/DoubleStreamRules.java

@@ -1,6 +1,7 @@
 package tech.picnic.errorprone.refasterrules;
 
 import com.google.common.collect.Streams;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
@@ -27,6 +28,7 @@ final class DoubleStreamRules {
     }
 
     @AfterTemplate
+    @CanIgnoreReturnValue
     DoubleStream after(DoubleStream stream) {
       return stream;
     }
@@ -237,6 +239,7 @@ final class DoubleStreamRules {
   /** Prefer {@link DoubleStream#anyMatch(DoublePredicate)} over more contrived alternatives. */
   static final class DoubleStreamAnyMatch {
     @BeforeTemplate
+    @SuppressWarnings("java:S4034" /* This violation will be rewritten. */)
     boolean before(DoubleStream stream, DoublePredicate predicate) {
       return Refaster.anyOf(
           !stream.noneMatch(predicate), stream.filter(predicate).findAny().isPresent());

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/EqualityRules.java

@@ -1,5 +1,6 @@
 package tech.picnic.errorprone.refasterrules;
 
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.AlsoNegation;
@@ -30,6 +31,7 @@ final class EqualityRules {
 
     @AfterTemplate
     @AlsoNegation
+    @SuppressWarnings("java:S1698" /* Reference comparison is valid for enums. */)
     boolean after(T a, T b) {
       return a == b;
     }
@@ -56,11 +58,13 @@ final class EqualityRules {
   /** Avoid double negations; this is not Javascript. */
   static final class DoubleNegation {
     @BeforeTemplate
+    @SuppressWarnings("java:S2761" /* This violation will be rewritten. */)
     boolean before(boolean b) {
       return !!b;
     }
 
     @AfterTemplate
+    @CanIgnoreReturnValue
     boolean after(boolean b) {
       return b;
     }
@@ -72,6 +76,7 @@ final class EqualityRules {
    */
   // XXX: Replacing `a ? !b : b` with `a != b` changes semantics if both `a` and `b` are boxed
   // booleans.
+  @SuppressWarnings("java:S1940" /* This violation will be rewritten. */)
   static final class Negation {
     @BeforeTemplate
     boolean before(boolean a, boolean b) {
@@ -79,6 +84,8 @@ final class EqualityRules {
     }
 
     @BeforeTemplate
+    @SuppressWarnings(
+        "java:S1244" /* The equality check is fragile, but may be seen in the wild. */)
     boolean before(double a, double b) {
       return !(a == b);
     }
@@ -100,6 +107,7 @@ final class EqualityRules {
    */
   // XXX: Replacing `a ? b : !b` with `a == b` changes semantics if both `a` and `b` are boxed
   // booleans.
+  @SuppressWarnings("java:S1940" /* This violation will be rewritten. */)
   static final class IndirectDoubleNegation {
     @BeforeTemplate
     boolean before(boolean a, boolean b) {
@@ -107,6 +115,8 @@ final class EqualityRules {
     }
 
     @BeforeTemplate
+    @SuppressWarnings(
+        "java:S1244" /* The inequality check is fragile, but may be seen in the wild. */)
     boolean before(double a, double b) {
       return !(a != b);
     }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ImmutableMapRules.java

@@ -188,6 +188,8 @@ final class ImmutableMapRules {
   /**
    * Prefer creating an immutable copy of the result of {@link Maps#transformValues(Map,
    * com.google.common.base.Function)} over more contrived alternatives.
+   *
+   * <p>Additionally, this way it is easier to see that only values are being transformed.
    */
   abstract static class TransformMapValuesToImmutableMap<K, V1, V2> {
     @Placeholder(allowsIdentity = true)
@@ -250,7 +252,8 @@ final class ImmutableMapRules {
    * Prefer {@link ImmutableMap#of(Object, Object, Object, Object)} over alternatives that don't
    * communicate the immutability of the resulting map at the type level.
    */
-  // XXX: Also rewrite the `ImmutableMap.builder()` variant?
+  // XXX: Consider introducing a `BugChecker` to replace these `ImmutableMapOfX` rules. That will
+  // also make it easier to rewrite various `ImmutableMap.builder()` variants.
   static final class ImmutableMapOf2<K, V> {
     @BeforeTemplate
     Map<K, V> before(K k1, V v1, K k2, V v2) {
@@ -267,7 +270,8 @@ final class ImmutableMapRules {
    * Prefer {@link ImmutableMap#of(Object, Object, Object, Object, Object, Object)} over
    * alternatives that don't communicate the immutability of the resulting map at the type level.
    */
-  // XXX: Also rewrite the `ImmutableMap.builder()` variant?
+  // XXX: Consider introducing a `BugChecker` to replace these `ImmutableMapOfX` rules. That will
+  // also make it easier to rewrite various `ImmutableMap.builder()` variants.
   static final class ImmutableMapOf3<K, V> {
     @BeforeTemplate
     Map<K, V> before(K k1, V v1, K k2, V v2, K k3, V v3) {
@@ -285,7 +289,9 @@ final class ImmutableMapRules {
    * over alternatives that don't communicate the immutability of the resulting map at the type
    * level.
    */
-  // XXX: Also rewrite the `ImmutableMap.builder()` variant?
+  // XXX: Consider introducing a `BugChecker` to replace these `ImmutableMapOfX` rules. That will
+  // also make it easier to rewrite various `ImmutableMap.builder()` variants.
+  @SuppressWarnings("java:S107" /* Can't avoid many method parameters here. */)
   static final class ImmutableMapOf4<K, V> {
     @BeforeTemplate
     Map<K, V> before(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
@@ -303,7 +309,9 @@ final class ImmutableMapRules {
    * Object, Object)} over alternatives that don't communicate the immutability of the resulting map
    * at the type level.
    */
-  // XXX: Also rewrite the `ImmutableMap.builder()` variant?
+  // XXX: Consider introducing a `BugChecker` to replace these `ImmutableMapOfX` rules. That will
+  // also make it easier to rewrite various `ImmutableMap.builder()` variants.
+  @SuppressWarnings("java:S107" /* Can't avoid many method parameters here. */)
   static final class ImmutableMapOf5<K, V> {
     @BeforeTemplate
     Map<K, V> before(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ImmutableSetRules.java

@@ -4,8 +4,11 @@ import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 import static java.util.Collections.emptySet;
 import static java.util.Collections.singleton;
+import static java.util.function.Predicate.not;
 
 import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Multimap;
+import com.google.common.collect.Sets;
 import com.google.common.collect.Sets.SetView;
 import com.google.common.collect.Streams;
 import com.google.errorprone.refaster.Refaster;
@@ -15,6 +18,7 @@ import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Iterator;
+import java.util.Map;
 import java.util.Set;
 import java.util.stream.Stream;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
@@ -211,4 +215,116 @@ final class ImmutableSetRules {
       return ImmutableSet.of(e1, e2, e3, e4, e5);
     }
   }
+
+  /**
+   * Prefer an immutable copy of {@link Sets#difference(Set, Set)} over more contrived alternatives.
+   */
+  static final class SetsDifference<S, T> {
+    @BeforeTemplate
+    ImmutableSet<S> before(Set<S> set1, Set<T> set2) {
+      return set1.stream()
+          .filter(Refaster.anyOf(not(set2::contains), e -> !set2.contains(e)))
+          .collect(toImmutableSet());
+    }
+
+    @AfterTemplate
+    ImmutableSet<S> after(Set<S> set1, Set<T> set2) {
+      return Sets.difference(set1, set2).immutableCopy();
+    }
+  }
+
+  /**
+   * Prefer an immutable copy of {@link Sets#difference(Set, Set)} over more contrived alternatives.
+   */
+  static final class SetsDifferenceMap<T, K, V> {
+    @BeforeTemplate
+    ImmutableSet<T> before(Set<T> set, Map<K, V> map) {
+      return set.stream()
+          .filter(Refaster.anyOf(not(map::containsKey), e -> !map.containsKey(e)))
+          .collect(toImmutableSet());
+    }
+
+    @AfterTemplate
+    ImmutableSet<K> after(Set<K> set, Map<K, V> map) {
+      return Sets.difference(set, map.keySet()).immutableCopy();
+    }
+  }
+
+  /**
+   * Prefer an immutable copy of {@link Sets#difference(Set, Set)} over more contrived alternatives.
+   */
+  static final class SetsDifferenceMultimap<T, K, V> {
+    @BeforeTemplate
+    ImmutableSet<T> before(Set<T> set, Multimap<K, V> multimap) {
+      return set.stream()
+          .filter(Refaster.anyOf(not(multimap::containsKey), e -> !multimap.containsKey(e)))
+          .collect(toImmutableSet());
+    }
+
+    @AfterTemplate
+    ImmutableSet<T> after(Set<T> set, Multimap<K, V> multimap) {
+      return Sets.difference(set, multimap.keySet()).immutableCopy();
+    }
+  }
+
+  /**
+   * Prefer an immutable copy of {@link Sets#intersection(Set, Set)} over more contrived
+   * alternatives.
+   */
+  static final class SetsIntersection<S, T> {
+    @BeforeTemplate
+    ImmutableSet<S> before(Set<S> set1, Set<T> set2) {
+      return set1.stream().filter(set2::contains).collect(toImmutableSet());
+    }
+
+    @AfterTemplate
+    ImmutableSet<S> after(Set<S> set1, Set<T> set2) {
+      return Sets.intersection(set1, set2).immutableCopy();
+    }
+  }
+
+  /**
+   * Prefer an immutable copy of {@link Sets#intersection(Set, Set)} over more contrived
+   * alternatives.
+   */
+  static final class SetsIntersectionMap<T, K, V> {
+    @BeforeTemplate
+    ImmutableSet<T> before(Set<T> set, Map<K, V> map) {
+      return set.stream().filter(map::containsKey).collect(toImmutableSet());
+    }
+
+    @AfterTemplate
+    ImmutableSet<T> after(Set<T> set, Map<K, V> map) {
+      return Sets.intersection(set, map.keySet()).immutableCopy();
+    }
+  }
+
+  /**
+   * Prefer an immutable copy of {@link Sets#intersection(Set, Set)} over more contrived
+   * alternatives.
+   */
+  static final class SetsIntersectionMultimap<T, K, V> {
+    @BeforeTemplate
+    ImmutableSet<T> before(Set<T> set, Multimap<K, V> multimap) {
+      return set.stream().filter(multimap::containsKey).collect(toImmutableSet());
+    }
+
+    @AfterTemplate
+    ImmutableSet<T> after(Set<T> set, Multimap<K, V> multimap) {
+      return Sets.intersection(set, multimap.keySet()).immutableCopy();
+    }
+  }
+
+  /** Prefer an immutable copy of {@link Sets#union(Set, Set)} over more contrived alternatives. */
+  static final class SetsUnion<S, T extends S, U extends S> {
+    @BeforeTemplate
+    ImmutableSet<S> before(Set<T> set1, Set<U> set2) {
+      return Stream.concat(set1.stream(), set2.stream()).collect(toImmutableSet());
+    }
+
+    @AfterTemplate
+    ImmutableSet<S> after(Set<T> set1, Set<U> set2) {
+      return Sets.union(set1, set2).immutableCopy();
+    }
+  }
 }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/IntStreamRules.java

@@ -1,6 +1,7 @@
 package tech.picnic.errorprone.refasterrules;
 
 import com.google.common.collect.Streams;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
@@ -40,6 +41,7 @@ final class IntStreamRules {
     }
 
     @AfterTemplate
+    @CanIgnoreReturnValue
     IntStream after(IntStream stream) {
       return stream;
     }
@@ -250,6 +252,7 @@ final class IntStreamRules {
   /** Prefer {@link IntStream#anyMatch(IntPredicate)} over more contrived alternatives. */
   static final class IntStreamAnyMatch {
     @BeforeTemplate
+    @SuppressWarnings("java:S4034" /* This violation will be rewritten. */)
     boolean before(IntStream stream, IntPredicate predicate) {
       return Refaster.anyOf(
           !stream.noneMatch(predicate), stream.filter(predicate).findAny().isPresent());

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/JUnitToAssertJRules.java

@@ -34,8 +34,7 @@ import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
  * <p>Note that, while both libraries throw an {@link AssertionError} in case of an assertion
  * failure, the exact subtype used generally differs.
  */
-// XXX: Not all `org.assertj.core.api.Assertions` methods have an associated Refaster rule yet;
-// expand this class.
+// XXX: Not all JUnit `Assertions` methods have an associated Refaster rule yet; expand this class.
 // XXX: Introduce a `@Matcher` on `Executable` and `ThrowingSupplier` expressions, such that they
 // are only matched if they are also compatible with the `ThrowingCallable` functional interface.
 // When implementing such a matcher, note that expressions with a non-void return type such as
@@ -45,7 +44,7 @@ import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 final class JUnitToAssertJRules {
   private JUnitToAssertJRules() {}
 
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(
         Assertions.class,
         assertDoesNotThrow(() -> null),

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/LongStreamRules.java

@@ -1,6 +1,7 @@
 package tech.picnic.errorprone.refasterrules;
 
 import com.google.common.collect.Streams;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
@@ -40,6 +41,7 @@ final class LongStreamRules {
     }
 
     @AfterTemplate
+    @CanIgnoreReturnValue
     LongStream after(LongStream stream) {
       return stream;
     }
@@ -250,6 +252,7 @@ final class LongStreamRules {
   /** Prefer {@link LongStream#anyMatch(LongPredicate)} over more contrived alternatives. */
   static final class LongStreamAnyMatch {
     @BeforeTemplate
+    @SuppressWarnings("java:S4034" /* This violation will be rewritten. */)
     boolean before(LongStream stream, LongPredicate predicate) {
       return Refaster.anyOf(
           !stream.noneMatch(predicate), stream.filter(predicate).findAny().isPresent());

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/OptionalRules.java

@@ -3,10 +3,12 @@ package tech.picnic.errorprone.refasterrules;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 
 import com.google.common.collect.Streams;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import com.google.errorprone.refaster.annotation.MayOptionallyUse;
+import com.google.errorprone.refaster.annotation.NotMatches;
 import com.google.errorprone.refaster.annotation.Placeholder;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.Comparator;
@@ -18,6 +20,7 @@ import java.util.function.Supplier;
 import java.util.stream.Stream;
 import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+import tech.picnic.errorprone.refaster.matchers.IsLikelyTrivialComputation;
 
 /** Refaster rules related to expressions dealing with {@link Optional}s. */
 @OnlineDocumentation
@@ -68,7 +71,10 @@ final class OptionalRules {
   /** Prefer {@link Optional#orElseThrow()} over the less explicit {@link Optional#get()}. */
   static final class OptionalOrElseThrow<T> {
     @BeforeTemplate
-    @SuppressWarnings("NullAway")
+    @SuppressWarnings({
+      "java:S3655" /* Matched expressions are in practice embedded in a larger context. */,
+      "NullAway"
+    })
     T before(Optional<T> optional) {
       return optional.get();
     }
@@ -114,7 +120,7 @@ final class OptionalRules {
   /** Prefer {@link Optional#filter(Predicate)} over usage of the ternary operator. */
   // XXX: This rule may introduce a compilation error: the `test` expression may reference a
   // non-effectively final variable, which is not allowed in the replacement lambda expression.
-  // Maybe our `Refaster` checker should test `compilesWithFix`?
+  // Review whether a `@Matcher` can be used to avoid this.
   abstract static class TernaryOperatorOptionalPositiveFiltering<T> {
     @Placeholder
     abstract boolean test(T value);
@@ -134,7 +140,7 @@ final class OptionalRules {
   /** Prefer {@link Optional#filter(Predicate)} over usage of the ternary operator. */
   // XXX: This rule may introduce a compilation error: the `test` expression may reference a
   // non-effectively final variable, which is not allowed in the replacement lambda expression.
-  // Maybe our `Refaster` checker should test `compilesWithFix`?
+  // Review whether a `@Matcher` can be used to avoid this.
   abstract static class TernaryOperatorOptionalNegativeFiltering<T> {
     @Placeholder
     abstract boolean test(T value);
@@ -157,6 +163,7 @@ final class OptionalRules {
    */
   static final class MapOptionalToBoolean<T> {
     @BeforeTemplate
+    @SuppressWarnings("OptionalOrElseGet" /* Rule is confused by `Refaster#anyOf` usage. */)
     boolean before(Optional<T> optional, Function<? super T, Boolean> predicate) {
       return optional.map(predicate).orElse(Refaster.anyOf(false, Boolean.FALSE));
     }
@@ -220,6 +227,28 @@ final class OptionalRules {
     }
   }
 
+  /**
+   * Prefer {@link Optional#orElseGet(Supplier)} over {@link Optional#orElse(Object)} if the
+   * fallback value is not the result of a trivial computation.
+   */
+  // XXX: This rule may introduce a compilation error: the `value` expression may reference a
+  // non-effectively final variable, which is not allowed in the replacement lambda expression.
+  // Review whether a `@Matcher` can be used to avoid this.
+  // XXX: Once `MethodReferenceUsage` is "production ready", replace
+  // `@NotMatches(IsLikelyTrivialComputation.class)` with `@Matches(RequiresComputation.class)` (and
+  // reimplement the matcher accordingly).
+  static final class OptionalOrElseGet<T> {
+    @BeforeTemplate
+    T before(Optional<T> optional, @NotMatches(IsLikelyTrivialComputation.class) T value) {
+      return optional.orElse(value);
+    }
+
+    @AfterTemplate
+    T after(Optional<T> optional, T value) {
+      return optional.orElseGet(() -> value);
+    }
+  }
+
   /**
    * Flatten a stream of {@link Optional}s using {@link Optional#stream()}, rather than using one of
    * the more verbose alternatives.
@@ -304,14 +333,12 @@ final class OptionalRules {
     abstract Optional<S> toOptionalFunction(@MayOptionallyUse T element);
 
     @BeforeTemplate
-    Optional<R> before(
-        Optional<T> optional, Function<? super S, ? extends Optional<? extends R>> function) {
+    Optional<R> before(Optional<T> optional, Function<? super S, Optional<? extends R>> function) {
       return optional.flatMap(v -> toOptionalFunction(v).flatMap(function));
     }
 
     @AfterTemplate
-    Optional<R> after(
-        Optional<T> optional, Function<? super S, ? extends Optional<? extends R>> function) {
+    Optional<R> after(Optional<T> optional, Function<? super S, Optional<? extends R>> function) {
       return optional.flatMap(v -> toOptionalFunction(v)).flatMap(function);
     }
   }
@@ -323,6 +350,9 @@ final class OptionalRules {
     Optional<T> before(Optional<T> optional1, Optional<T> optional2) {
       // XXX: Note that rewriting the first and third variant will change the code's behavior if
       // `optional2` has side-effects.
+      // XXX: Note that rewriting the first and third variant will introduce a compilation error if
+      // `optional2` is not effectively final. Review whether a `@Matcher` can be used to avoid
+      // this.
       return Refaster.anyOf(
           optional1.map(Optional::of).orElse(optional2),
           optional1.map(Optional::of).orElseGet(() -> optional2),
@@ -350,6 +380,7 @@ final class OptionalRules {
     }
 
     @AfterTemplate
+    @CanIgnoreReturnValue
     Optional<T> after(Optional<T> optional) {
       return optional;
     }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/PreconditionsRules.java

@@ -91,6 +91,7 @@ final class PreconditionsRules {
   /** Prefer {@link Objects#requireNonNull(Object)} over more verbose alternatives. */
   static final class RequireNonNullStatement<T> {
     @BeforeTemplate
+    @SuppressWarnings("java:S1695" /* This violation will be rewritten. */)
     void before(T object) {
       if (object == null) {
         throw new NullPointerException();
@@ -121,6 +122,7 @@ final class PreconditionsRules {
   /** Prefer {@link Objects#requireNonNull(Object, String)} over more verbose alternatives. */
   static final class RequireNonNullWithMessageStatement<T> {
     @BeforeTemplate
+    @SuppressWarnings("java:S1695" /* This violation will be rewritten. */)
     void before(T object, String message) {
       if (object == null) {
         throw new NullPointerException(message);

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/PrimitiveRules.java

@@ -1,6 +1,13 @@
 package tech.picnic.errorprone.refasterrules;
 
+import com.google.common.primitives.Booleans;
+import com.google.common.primitives.Bytes;
+import com.google.common.primitives.Chars;
+import com.google.common.primitives.Doubles;
+import com.google.common.primitives.Floats;
 import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+import com.google.common.primitives.Shorts;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
@@ -13,12 +20,13 @@ final class PrimitiveRules {
   /** Avoid contrived ways of expressing the "less than" relationship. */
   static final class LessThan {
     @BeforeTemplate
+    @SuppressWarnings("java:S1940" /* This violation will be rewritten. */)
     boolean before(double a, double b) {
       return !(a >= b);
     }
 
     @AfterTemplate
-    boolean after(long a, long b) {
+    boolean after(double a, double b) {
       return a < b;
     }
   }
@@ -26,12 +34,13 @@ final class PrimitiveRules {
   /** Avoid contrived ways of expressing the "less than or equal to" relationship. */
   static final class LessThanOrEqualTo {
     @BeforeTemplate
+    @SuppressWarnings("java:S1940" /* This violation will be rewritten. */)
     boolean before(double a, double b) {
       return !(a > b);
     }
 
     @AfterTemplate
-    boolean after(long a, long b) {
+    boolean after(double a, double b) {
       return a <= b;
     }
   }
@@ -39,12 +48,13 @@ final class PrimitiveRules {
   /** Avoid contrived ways of expressing the "greater than" relationship. */
   static final class GreaterThan {
     @BeforeTemplate
+    @SuppressWarnings("java:S1940" /* This violation will be rewritten. */)
     boolean before(double a, double b) {
       return !(a <= b);
     }
 
     @AfterTemplate
-    boolean after(long a, long b) {
+    boolean after(double a, double b) {
       return a > b;
     }
   }
@@ -52,12 +62,13 @@ final class PrimitiveRules {
   /** Avoid contrived ways of expressing the "greater than or equal to" relationship. */
   static final class GreaterThanOrEqualTo {
     @BeforeTemplate
+    @SuppressWarnings("java:S1940" /* This violation will be rewritten. */)
     boolean before(double a, double b) {
       return !(a < b);
     }
 
     @AfterTemplate
-    boolean after(long a, long b) {
+    boolean after(double a, double b) {
       return a >= b;
     }
   }
@@ -65,13 +76,312 @@ final class PrimitiveRules {
   /** Prefer {@link Math#toIntExact(long)} over the Guava alternative. */
   static final class LongToIntExact {
     @BeforeTemplate
-    int before(long a) {
-      return Ints.checkedCast(a);
+    int before(long l) {
+      return Ints.checkedCast(l);
     }
 
     @AfterTemplate
-    int after(long a) {
-      return Math.toIntExact(a);
+    int after(long l) {
+      return Math.toIntExact(l);
+    }
+  }
+
+  /** Prefer {@link Boolean#hashCode(boolean)} over the Guava alternative. */
+  static final class BooleanHashCode {
+    @BeforeTemplate
+    int before(boolean b) {
+      return Booleans.hashCode(b);
+    }
+
+    @AfterTemplate
+    int after(boolean b) {
+      return Boolean.hashCode(b);
+    }
+  }
+
+  /** Prefer {@link Byte#hashCode(byte)} over the Guava alternative. */
+  static final class ByteHashCode {
+    @BeforeTemplate
+    int before(byte b) {
+      return Bytes.hashCode(b);
+    }
+
+    @AfterTemplate
+    int after(byte b) {
+      return Byte.hashCode(b);
+    }
+  }
+
+  /** Prefer {@link Character#hashCode(char)} over the Guava alternative. */
+  static final class CharacterHashCode {
+    @BeforeTemplate
+    int before(char c) {
+      return Chars.hashCode(c);
+    }
+
+    @AfterTemplate
+    int after(char c) {
+      return Character.hashCode(c);
+    }
+  }
+
+  /** Prefer {@link Short#hashCode(short)} over the Guava alternative. */
+  static final class ShortHashCode {
+    @BeforeTemplate
+    int before(short s) {
+      return Shorts.hashCode(s);
+    }
+
+    @AfterTemplate
+    int after(short s) {
+      return Short.hashCode(s);
+    }
+  }
+
+  /** Prefer {@link Integer#hashCode(int)} over the Guava alternative. */
+  static final class IntegerHashCode {
+    @BeforeTemplate
+    int before(int i) {
+      return Ints.hashCode(i);
+    }
+
+    @AfterTemplate
+    int after(int i) {
+      return Integer.hashCode(i);
+    }
+  }
+
+  /** Prefer {@link Long#hashCode(long)} over the Guava alternative. */
+  static final class LongHashCode {
+    @BeforeTemplate
+    int before(long l) {
+      return Longs.hashCode(l);
+    }
+
+    @AfterTemplate
+    int after(long l) {
+      return Long.hashCode(l);
+    }
+  }
+
+  /** Prefer {@link Float#hashCode(float)} over the Guava alternative. */
+  static final class FloatHashCode {
+    @BeforeTemplate
+    int before(float f) {
+      return Floats.hashCode(f);
+    }
+
+    @AfterTemplate
+    int after(float f) {
+      return Float.hashCode(f);
+    }
+  }
+
+  /** Prefer {@link Double#hashCode(double)} over the Guava alternative. */
+  static final class DoubleHashCode {
+    @BeforeTemplate
+    int before(double d) {
+      return Doubles.hashCode(d);
+    }
+
+    @AfterTemplate
+    int after(double d) {
+      return Double.hashCode(d);
+    }
+  }
+
+  /** Prefer {@link Boolean#compare(boolean, boolean)} over the Guava alternative. */
+  static final class BooleanCompare {
+    @BeforeTemplate
+    int before(boolean a, boolean b) {
+      return Booleans.compare(a, b);
+    }
+
+    @AfterTemplate
+    int after(boolean a, boolean b) {
+      return Boolean.compare(a, b);
+    }
+  }
+
+  /** Prefer {@link Character#compare(char, char)} over the Guava alternative. */
+  static final class CharacterCompare {
+    @BeforeTemplate
+    int before(char a, char b) {
+      return Chars.compare(a, b);
+    }
+
+    @AfterTemplate
+    int after(char a, char b) {
+      return Character.compare(a, b);
+    }
+  }
+
+  /** Prefer {@link Short#compare(short, short)} over the Guava alternative. */
+  static final class ShortCompare {
+    @BeforeTemplate
+    int before(short a, short b) {
+      return Shorts.compare(a, b);
+    }
+
+    @AfterTemplate
+    int after(short a, short b) {
+      return Short.compare(a, b);
+    }
+  }
+
+  /** Prefer {@link Integer#compare(int, int)} over the Guava alternative. */
+  static final class IntegerCompare {
+    @BeforeTemplate
+    int before(int a, int b) {
+      return Ints.compare(a, b);
+    }
+
+    @AfterTemplate
+    int after(int a, int b) {
+      return Integer.compare(a, b);
+    }
+  }
+
+  /** Prefer {@link Long#compare(long, long)} over the Guava alternative. */
+  static final class LongCompare {
+    @BeforeTemplate
+    int before(long a, long b) {
+      return Longs.compare(a, b);
+    }
+
+    @AfterTemplate
+    int after(long a, long b) {
+      return Long.compare(a, b);
+    }
+  }
+
+  /** Prefer {@link Float#compare(float, float)} over the Guava alternative. */
+  static final class FloatCompare {
+    @BeforeTemplate
+    int before(float a, float b) {
+      return Floats.compare(a, b);
+    }
+
+    @AfterTemplate
+    int after(float a, float b) {
+      return Float.compare(a, b);
+    }
+  }
+
+  /** Prefer {@link Double#compare(double, double)} over the Guava alternative. */
+  static final class DoubleCompare {
+    @BeforeTemplate
+    int before(double a, double b) {
+      return Doubles.compare(a, b);
+    }
+
+    @AfterTemplate
+    int after(double a, double b) {
+      return Double.compare(a, b);
+    }
+  }
+
+  /** Prefer {@link Character#BYTES} over the Guava alternative. */
+  static final class CharacterBytes {
+    @BeforeTemplate
+    int before() {
+      return Chars.BYTES;
+    }
+
+    @AfterTemplate
+    int after() {
+      return Character.BYTES;
+    }
+  }
+
+  /** Prefer {@link Short#BYTES} over the Guava alternative. */
+  static final class ShortBytes {
+    @BeforeTemplate
+    int before() {
+      return Shorts.BYTES;
+    }
+
+    @AfterTemplate
+    int after() {
+      return Short.BYTES;
+    }
+  }
+
+  /** Prefer {@link Integer#BYTES} over the Guava alternative. */
+  static final class IntegerBytes {
+    @BeforeTemplate
+    int before() {
+      return Ints.BYTES;
+    }
+
+    @AfterTemplate
+    int after() {
+      return Integer.BYTES;
+    }
+  }
+
+  /** Prefer {@link Long#BYTES} over the Guava alternative. */
+  static final class LongBytes {
+    @BeforeTemplate
+    int before() {
+      return Longs.BYTES;
+    }
+
+    @AfterTemplate
+    int after() {
+      return Long.BYTES;
+    }
+  }
+
+  /** Prefer {@link Float#BYTES} over the Guava alternative. */
+  static final class FloatBytes {
+    @BeforeTemplate
+    int before() {
+      return Floats.BYTES;
+    }
+
+    @AfterTemplate
+    int after() {
+      return Float.BYTES;
+    }
+  }
+
+  /** Prefer {@link Double#BYTES} over the Guava alternative. */
+  static final class DoubleBytes {
+    @BeforeTemplate
+    int before() {
+      return Doubles.BYTES;
+    }
+
+    @AfterTemplate
+    int after() {
+      return Double.BYTES;
+    }
+  }
+
+  /** Prefer {@link Float#isFinite(float)} over the Guava alternative. */
+  static final class FloatIsFinite {
+    @BeforeTemplate
+    boolean before(float f) {
+      return Floats.isFinite(f);
+    }
+
+    @AfterTemplate
+    boolean after(float f) {
+      return Float.isFinite(f);
+    }
+  }
+
+  /** Prefer {@link Double#isFinite(double)} over the Guava alternative. */
+  static final class DoubleIsFinite {
+    @BeforeTemplate
+    boolean before(double d) {
+      return Doubles.isFinite(d);
+    }
+
+    @AfterTemplate
+    boolean after(double d) {
+      return Double.isFinite(d);
     }
   }
 }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ReactorRules.java

@@ -1,6 +1,7 @@
 package tech.picnic.errorprone.refasterrules;
 
 import static com.google.common.collect.ImmutableList.toImmutableList;
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.common.collect.MoreCollectors.toOptional;
 import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
@@ -12,6 +13,8 @@ import static reactor.function.TupleUtils.function;
 import com.google.common.collect.ImmutableCollection;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
@@ -33,6 +36,7 @@ import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
+import java.util.stream.Collector;
 import org.jspecify.annotations.Nullable;
 import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
@@ -94,7 +98,7 @@ final class ReactorRules {
   }
 
   /** Prefer {@link Mono#justOrEmpty(Object)} over more contrived alternatives. */
-  static final class MonoJustOrEmpty<@Nullable T> {
+  static final class MonoJustOrEmptyObject<@Nullable T> {
     @BeforeTemplate
     Mono<T> before(T value) {
       return Mono.justOrEmpty(Optional.ofNullable(value));
@@ -107,9 +111,25 @@ final class ReactorRules {
   }
 
   /** Prefer {@link Mono#justOrEmpty(Optional)} over more verbose alternatives. */
+  static final class MonoJustOrEmptyOptional<T> {
+    @BeforeTemplate
+    Mono<T> before(Optional<T> optional) {
+      return Mono.just(optional).filter(Optional::isPresent).map(Optional::orElseThrow);
+    }
+
+    @AfterTemplate
+    Mono<T> after(Optional<T> optional) {
+      return Mono.justOrEmpty(optional);
+    }
+  }
+
+  /**
+   * Prefer {@link Mono#defer(Supplier) deferring} {@link Mono#justOrEmpty(Optional)} over more
+   * verbose alternatives.
+   */
   // XXX: If `optional` is a constant and effectively-final expression then the `Mono.defer` can be
   // dropped. Should look into Refaster support for identifying this.
-  static final class MonoFromOptional<T> {
+  static final class MonoDeferMonoJustOrEmpty<T> {
     @BeforeTemplate
     @SuppressWarnings(
         "MonoFromSupplier" /* `optional` may match a checked exception-throwing expression. */)
@@ -384,12 +404,36 @@ final class ReactorRules {
       return mono.then();
     }
 
+    // XXX: Replace this rule with an extension of the `IdentityConversion` rule, supporting
+    // `Stream#map`, `Mono#map` and `Flux#map`.
+    @BeforeTemplate
+    Mono<ImmutableList<T>> before3(Mono<ImmutableList<T>> mono) {
+      return mono.map(ImmutableList::copyOf);
+    }
+
     @AfterTemplate
+    @CanIgnoreReturnValue
     Mono<T> after(Mono<T> mono) {
       return mono;
     }
   }
 
+  /**
+   * Don't unnecessarily transform a {@link Mono} to a {@link Flux} before calling {@link
+   * Mono#single()}.
+   */
+  static final class MonoSingle<T> {
+    @BeforeTemplate
+    Mono<T> before(Mono<T> mono) {
+      return mono.flux().single();
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<T> mono) {
+      return mono.single();
+    }
+  }
+
   /** Don't unnecessarily pass an empty publisher to {@link Flux#switchIfEmpty(Publisher)}. */
   static final class FluxSwitchIfEmptyOfEmptyPublisher<T> {
     @BeforeTemplate
@@ -398,6 +442,7 @@ final class ReactorRules {
     }
 
     @AfterTemplate
+    @CanIgnoreReturnValue
     Flux<T> after(Flux<T> flux) {
       return flux;
     }
@@ -594,6 +639,7 @@ final class ReactorRules {
     abstract S transformation(@MayOptionallyUse T value);
 
     @BeforeTemplate
+    @SuppressWarnings("java:S138" /* Method is long, but not complex. */)
     Publisher<S> before(Flux<T> flux, boolean delayUntilEnd, int maxConcurrency, int prefetch) {
       return Refaster.anyOf(
           flux.concatMap(
@@ -1150,6 +1196,40 @@ final class ReactorRules {
     }
   }
 
+  /**
+   * Prefer {@link Flux#collect(Collector)} with {@link ImmutableList#toImmutableList()} over
+   * alternatives that do not explicitly return an immutable collection.
+   */
+  static final class FluxCollectToImmutableList<T> {
+    @BeforeTemplate
+    Mono<List<T>> before(Flux<T> flux) {
+      return flux.collectList();
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    Mono<ImmutableList<T>> after(Flux<T> flux) {
+      return flux.collect(toImmutableList());
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#collect(Collector)} with {@link ImmutableSet#toImmutableSet()} over more
+   * contrived alternatives.
+   */
+  static final class FluxCollectToImmutableSet<T> {
+    @BeforeTemplate
+    Mono<ImmutableSet<T>> before(Flux<T> flux) {
+      return flux.collect(toImmutableList()).map(ImmutableSet::copyOf);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    Mono<ImmutableSet<T>> after(Flux<T> flux) {
+      return flux.collect(toImmutableSet());
+    }
+  }
+
   /** Prefer {@link reactor.util.context.Context#empty()}} over more verbose alternatives. */
   // XXX: Consider introducing an `IsEmpty` matcher that identifies a wide range of guaranteed-empty
   // `Collection` and `Map` expressions.
@@ -1215,6 +1295,7 @@ final class ReactorRules {
     }
 
     @AfterTemplate
+    @CanIgnoreReturnValue
     StepVerifier.Step<T> after(StepVerifier.Step<T> step) {
       return step;
     }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/ReactorTemplates.java

@@ -0,0 +1,435 @@
+package tech.picnic.errorprone.refasterrules;
+
+import static com.google.common.collect.MoreCollectors.toOptional;
+
+import com.google.common.collect.MoreCollectors;
+import com.google.errorprone.refaster.ImportPolicy;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.MayOptionallyUse;
+import com.google.errorprone.refaster.annotation.Placeholder;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import java.time.Duration;
+import java.util.Optional;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.function.Supplier;
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import reactor.test.publisher.PublisherProbe;
+
+/** Refaster templates related to Reactor expressions and statements. */
+final class ReactorTemplates {
+  private ReactorTemplates() {}
+
+  /** Prefer {@link Mono#justOrEmpty(Optional)} over more verbose alternatives. */
+  // XXX: If `optional` is a constant and effectively-final expression then the `Mono.defer` can be
+  // dropped. Should look into Refaster support for identifying this.
+  static final class MonoFromOptional<T> {
+    @BeforeTemplate
+    Mono<T> before(Optional<T> optional) {
+      return Refaster.anyOf(
+          Mono.fromCallable(() -> optional.orElse(null)),
+          Mono.fromSupplier(() -> optional.orElse(null)));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Optional<T> optional) {
+      return Mono.defer(() -> Mono.justOrEmpty(optional));
+    }
+  }
+  // XXX: Fix this after knowing how to add Matches for CanBeCoercedToRunnable.
+  //
+  //  abstract static class MonoFromRunnable<T> {
+  //    @Placeholder
+  //    abstract boolean test(); // Improve return type here and naming of method.
+  //
+  //    @BeforeTemplate
+  //    Mono<Void> before(Supplier<T> supplier) {
+  //      return Mono.fromSupplier(() -> test()).then();
+  //    }
+  //
+  //    @AfterTemplate
+  //    Mono<Void> after(Runnable supplier) {
+  //      return Mono.fromRunnable(supplier);
+  //    }
+  //  }
+
+  /** Don't unnecessarily defer {@link Mono#error(Throwable)}. */
+  static final class MonoDeferredError<T> {
+    @BeforeTemplate
+    Mono<T> before(Throwable throwable) {
+      return Mono.defer(() -> Mono.error(throwable));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Throwable throwable) {
+      return Mono.error(() -> throwable);
+    }
+  }
+
+  /** Don't unnecessarily defer {@link Flux#error(Throwable)}. */
+  static final class FluxDeferredError<T> {
+    @BeforeTemplate
+    Flux<T> before(Throwable throwable) {
+      return Flux.defer(() -> Flux.error(throwable));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Throwable throwable) {
+      return Flux.error(() -> throwable);
+    }
+  }
+
+  /**
+   * Don't unnecessarily pass {@link Mono#error(Supplier)} a method reference or lambda expression.
+   */
+  // XXX: Drop this rule once the more general rule `AssortedTemplates#SupplierAsSupplier` works
+  // reliably.
+  static final class MonoErrorSupplier<T, E extends Throwable> {
+    @BeforeTemplate
+    Mono<T> before(Supplier<E> supplier) {
+      return Mono.error(() -> supplier.get());
+    }
+
+    @AfterTemplate
+    Mono<T> after(Supplier<E> supplier) {
+      return Mono.error(supplier);
+    }
+  }
+
+  /**
+   * Don't unnecessarily pass {@link Flux#error(Supplier)} a method reference or lambda expression.
+   */
+  // XXX: Drop this rule once the more general rule `AssortedTemplates#SupplierAsSupplier` works
+  // reliably.
+  static final class FluxErrorSupplier<T, E extends Throwable> {
+    @BeforeTemplate
+    Flux<T> before(Supplier<E> supplier) {
+      return Flux.error(() -> supplier.get());
+    }
+
+    @AfterTemplate
+    Flux<T> after(Supplier<E> supplier) {
+      return Flux.error(supplier);
+    }
+  }
+
+  /** Prefer {@link Mono#thenReturn(Object)} over more verbose alternatives. */
+  static final class MonoThenReturn<T, S> {
+    @BeforeTemplate
+    Mono<S> before(Mono<T> mono, S object) {
+      return mono.then(Mono.just(object));
+    }
+
+    @AfterTemplate
+    Mono<S> after(Mono<T> mono, S object) {
+      return mono.thenReturn(object);
+    }
+  }
+
+  /** Don't unnecessarily pass an empty publisher to {@link Mono#switchIfEmpty(Mono)}. */
+  static final class MonoSwitchIfEmptyOfEmptyPublisher<T> {
+    @BeforeTemplate
+    Mono<T> before(Mono<T> mono) {
+      return mono.switchIfEmpty(Mono.empty());
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<T> mono) {
+      return mono;
+    }
+  }
+
+  /** Don't unnecessarily pass an empty publisher to {@link Flux#switchIfEmpty(Publisher)}. */
+  static final class FluxSwitchIfEmptyOfEmptyPublisher<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux) {
+      return flux.switchIfEmpty(Refaster.anyOf(Mono.empty(), Flux.empty()));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux) {
+      return flux;
+    }
+  }
+
+  /** Prefer {@link Flux#concatMap(Function)} over more contrived alternatives. */
+  static final class FluxConcatMap<T, S> {
+    @BeforeTemplate
+    Flux<S> before(Flux<T> flux, Function<? super T, ? extends Publisher<? extends S>> function) {
+      return Refaster.anyOf(flux.flatMap(function, 1), flux.flatMapSequential(function, 1));
+    }
+
+    @AfterTemplate
+    Flux<S> after(Flux<T> flux, Function<? super T, ? extends Publisher<? extends S>> function) {
+      return flux.concatMap(function);
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#concatMapIterable(Function)} over {@link Flux#concatMapIterable(Function)},
+   * as the former has equivalent semantics but a clearer name.
+   */
+  static final class FluxConcatMapIterable<T, S> {
+    @BeforeTemplate
+    Flux<S> before(Flux<T> flux, Function<? super T, ? extends Iterable<? extends S>> function) {
+      return flux.flatMapIterable(function);
+    }
+
+    @AfterTemplate
+    Flux<S> after(Flux<T> flux, Function<? super T, ? extends Iterable<? extends S>> function) {
+      return flux.concatMapIterable(function);
+    }
+  }
+
+  /** Don't unnecessarily call {@link Mono#flux()}. */
+  static final class MonoFlatMapIterable<T, R> {
+    @BeforeTemplate
+    Flux<R> before(Mono<T> mono, Function<? super T, ? extends Iterable<? extends R>> mapper) {
+      return mono.flux().concatMapIterable(mapper);
+    }
+
+    @AfterTemplate
+    Flux<R> after(Mono<T> mono, Function<? super T, ? extends Iterable<? extends R>> mapper) {
+      return mono.flatMapIterable(mapper);
+    }
+  }
+
+  /**
+   * Don't use {@link Mono#flatMapMany(Function)} to implicitly convert a {@link Mono} to a {@link
+   * Flux}.
+   */
+  abstract static class MonoFlatMapToFlux<T, S> {
+    @Placeholder(allowsIdentity = true)
+    abstract Mono<S> valueTransformation(@MayOptionallyUse T value);
+
+    @BeforeTemplate
+    Flux<S> before(Mono<T> mono) {
+      return mono.flatMapMany(v -> valueTransformation(v));
+    }
+
+    @AfterTemplate
+    Flux<S> after(Mono<T> mono) {
+      return mono.flatMap(v -> valueTransformation(v)).flux();
+    }
+  }
+
+  /** Prefer {@link Mono#flux()}} over more contrived alternatives. */
+  static final class MonoFlux<T> {
+    @BeforeTemplate
+    Flux<T> before(Mono<T> mono) {
+      return Flux.concat(mono);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Mono<T> mono) {
+      return mono.flux();
+    }
+  }
+
+  /** Don't unnecessarily invoke {@link Flux#concat(Publisher)}. */
+  static final class FluxIdentity<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux) {
+      return Flux.concat(flux);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux) {
+      return flux;
+    }
+  }
+
+  /**
+   * Prefer a collection using {@link MoreCollectors#toOptional()} over more contrived alternatives.
+   */
+  // XXX: Consider creating a plugin which flags/discourages `Mono<Optional<T>>` method return
+  // types, just as we discourage nullable `Boolean`s and `Optional`s.
+  static final class MonoCollectToOptional<T> {
+    @BeforeTemplate
+    Mono<Optional<T>> before(Mono<T> mono) {
+      return Refaster.anyOf(
+          mono.map(Optional::of).defaultIfEmpty(Optional.empty()),
+          mono.map(Optional::of).switchIfEmpty(Mono.just(Optional.empty())));
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.STATIC_IMPORT_ALWAYS)
+    Mono<Optional<T>> after(Mono<T> mono) {
+      return mono.flux().collect(toOptional());
+    }
+  }
+
+  /** Prefer {@link PublisherProbe#empty()}} over more verbose alternatives. */
+  static final class PublisherProbeEmpty<T> {
+    @BeforeTemplate
+    PublisherProbe<T> before() {
+      return Refaster.anyOf(PublisherProbe.of(Mono.empty()), PublisherProbe.of(Flux.empty()));
+    }
+
+    @AfterTemplate
+    PublisherProbe<T> after() {
+      return PublisherProbe.empty();
+    }
+  }
+
+  /** Prefer {@link Mono#as(Function)} when creating a {@link StepVerifier}. */
+  static final class StepVerifierFromMono<T> {
+    @BeforeTemplate
+    StepVerifier.FirstStep<? extends T> before(Mono<T> mono) {
+      return StepVerifier.create(mono);
+    }
+
+    @AfterTemplate
+    StepVerifier.FirstStep<? extends T> after(Mono<T> mono) {
+      return mono.as(StepVerifier::create);
+    }
+  }
+
+  /** Prefer {@link Flux#as(Function)} when creating a {@link StepVerifier}. */
+  static final class StepVerifierFromFlux<T> {
+    @BeforeTemplate
+    StepVerifier.FirstStep<? extends T> before(Flux<T> flux) {
+      return StepVerifier.create(flux);
+    }
+
+    @AfterTemplate
+    StepVerifier.FirstStep<? extends T> after(Flux<T> flux) {
+      return flux.as(StepVerifier::create);
+    }
+  }
+
+  /** Don't unnecessarily call {@link StepVerifier.Step#expectNext(Object[])}. */
+  static final class StepVerifierStepExpectNextEmpty<T> {
+    @BeforeTemplate
+    @SuppressWarnings("unchecked")
+    StepVerifier.Step<T> before(StepVerifier.Step<T> step) {
+      return step.expectNext();
+    }
+
+    @AfterTemplate
+    StepVerifier.Step<T> after(StepVerifier.Step<T> step) {
+      return step;
+    }
+  }
+
+  /** Prefer {@link StepVerifier.Step#expectNext(Object)} over more verbose alternatives. */
+  static final class StepVerifierStepExpectNext<T> {
+    @BeforeTemplate
+    StepVerifier.Step<T> before(StepVerifier.Step<T> step, T object) {
+      return Refaster.anyOf(
+          step.expectNextMatches(e -> e.equals(object)), step.expectNextMatches(object::equals));
+    }
+
+    @AfterTemplate
+    StepVerifier.Step<T> after(StepVerifier.Step<T> step, T object) {
+      return step.expectNext(object);
+    }
+  }
+
+  /** Prefer {@link StepVerifier.LastStep#verifyComplete()} over more verbose alternatives. */
+  static final class StepVerifierLastStepVerifyComplete {
+    @BeforeTemplate
+    Duration before(StepVerifier.LastStep step) {
+      return step.expectComplete().verify();
+    }
+
+    @AfterTemplate
+    Duration after(StepVerifier.LastStep step) {
+      return step.verifyComplete();
+    }
+  }
+
+  /** Prefer {@link StepVerifier.LastStep#verifyError()} over more verbose alternatives. */
+  static final class StepVerifierLastStepVerifyError {
+    @BeforeTemplate
+    Duration before(StepVerifier.LastStep step) {
+      return step.expectError().verify();
+    }
+
+    @AfterTemplate
+    Duration after(StepVerifier.LastStep step) {
+      return step.verifyError();
+    }
+  }
+
+  /** Prefer {@link StepVerifier.LastStep#verifyError(Class)} over more verbose alternatives. */
+  static final class StepVerifierLastStepVerifyErrorClass<T extends Throwable> {
+    @BeforeTemplate
+    Duration before(StepVerifier.LastStep step, Class<T> clazz) {
+      return step.expectError(clazz).verify();
+    }
+
+    @AfterTemplate
+    Duration after(StepVerifier.LastStep step, Class<T> clazz) {
+      return step.verifyError(clazz);
+    }
+  }
+
+  /**
+   * Prefer {@link StepVerifier.LastStep#verifyErrorMatches(Predicate)} over more verbose
+   * alternatives.
+   */
+  static final class StepVerifierLastStepVerifyErrorMatches {
+    @BeforeTemplate
+    Duration before(StepVerifier.LastStep step, Predicate<Throwable> predicate) {
+      return step.expectErrorMatches(predicate).verify();
+    }
+
+    @AfterTemplate
+    Duration after(StepVerifier.LastStep step, Predicate<Throwable> predicate) {
+      return step.verifyErrorMatches(predicate);
+    }
+  }
+
+  /**
+   * Prefer {@link StepVerifier.LastStep#verifyErrorSatisfies(Consumer)} over more verbose
+   * alternatives.
+   */
+  static final class StepVerifierLastStepVerifyErrorSatisfies {
+    @BeforeTemplate
+    Duration before(StepVerifier.LastStep step, Consumer<Throwable> consumer) {
+      return step.expectErrorSatisfies(consumer).verify();
+    }
+
+    @AfterTemplate
+    Duration after(StepVerifier.LastStep step, Consumer<Throwable> consumer) {
+      return step.verifyErrorSatisfies(consumer);
+    }
+  }
+
+  /**
+   * Prefer {@link StepVerifier.LastStep#verifyErrorMessage(String)} over more verbose alternatives.
+   */
+  static final class StepVerifierLastStepVerifyErrorMessage {
+    @BeforeTemplate
+    Duration before(StepVerifier.LastStep step, String message) {
+      return step.expectErrorMessage(message).verify();
+    }
+
+    @AfterTemplate
+    Duration after(StepVerifier.LastStep step, String message) {
+      return step.verifyErrorMessage(message);
+    }
+  }
+
+  /**
+   * Prefer {@link StepVerifier.LastStep#verifyTimeout(Duration)} over more verbose alternatives.
+   */
+  static final class StepVerifierLastStepVerifyTimeout {
+    @BeforeTemplate
+    Duration before(StepVerifier.LastStep step, Duration duration) {
+      return step.expectTimeout(duration).verify();
+    }
+
+    @AfterTemplate
+    Duration after(StepVerifier.LastStep step, Duration duration) {
+      return step.verifyTimeout(duration);
+    }
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/RxJava2AdapterRules.java

@@ -20,6 +20,19 @@ import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 final class RxJava2AdapterRules {
   private RxJava2AdapterRules() {}
 
+  /** Remove double conversion of ... */
+  static final class FluxToFlowableToFlux<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux) {
+      return RxJava2Adapter.flowableToFlux(RxJava2Adapter.fluxToFlowable(flux));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux) {
+      return flux;
+    }
+  }
+
   /** Use the fluent API style when using {@link RxJava2Adapter#completableToMono}. */
   static final class CompletableToMono {
     @BeforeTemplate

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/RxJavaCompletableToReactorTemplates.java

@@ -0,0 +1,525 @@
+package tech.picnic.errorprone.refasterrules;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.collect.Streams;
+import com.google.errorprone.refaster.ImportPolicy;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Single;
+import io.reactivex.SingleSource;
+import io.reactivex.functions.Action;
+import io.reactivex.functions.Consumer;
+import io.reactivex.functions.Predicate;
+import java.time.Duration;
+import java.util.concurrent.Callable;
+import java.util.concurrent.TimeUnit;
+import java.util.function.Supplier;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+/** The Refaster templates for the migration of the RxJava {@link Completable} to Reactor. */
+final class RxJavaCompletableToReactorTemplates {
+  private RxJavaCompletableToReactorTemplates() {}
+
+  static final class CompletableAmb {
+    @BeforeTemplate
+    Completable before(Iterable<? extends Completable> sources) {
+      return Completable.amb(sources);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    Completable after(Iterable<? extends Completable> sources) {
+      return RxJava2Adapter.monoToCompletable(
+          Mono.firstWithSignal(
+              Streams.stream(sources)
+                  .map(RxJava2Adapter::completableToMono)
+                  .collect(toImmutableList())));
+    }
+  }
+
+  // XXX: public static Completable ambArray(CompletableSource[])
+
+  static final class CompletableComplete {
+    @BeforeTemplate
+    Completable before() {
+      return Completable.complete();
+    }
+
+    @AfterTemplate
+    Completable after() {
+      return RxJava2Adapter.monoToCompletable(Mono.empty());
+    }
+  }
+
+  // XXX: public static Completable concat(Iterable)
+  // XXX: public static Completable concat(Publisher)
+  // XXX: public static Completable concat(Publisher,int)
+  // XXX: public static Completable concatArray(CompletableSource[])
+  // XXX: public static Completable create(CompletableOnSubscribe)
+
+  // XXX: The types of the @Before and @After are not matching
+  static final class CompletableDefer {
+    @BeforeTemplate
+    Completable before(Callable<? extends CompletableSource> supplier) {
+      return Completable.defer(supplier);
+    }
+
+    @AfterTemplate
+    Completable after(Callable<? extends Completable> supplier) {
+      return RxJava2Adapter.monoToCompletable(
+          Mono.defer(
+              () ->
+                  RxJava2Adapter.completableToMono(
+                      RxJavaReactorMigrationUtil.callableAsSupplier(supplier).get())));
+    }
+  }
+
+  static final class CompletableErrorCallable {
+    @BeforeTemplate
+    Completable before(Callable<? extends Throwable> throwable) {
+      return Completable.error(throwable);
+    }
+
+    @AfterTemplate
+    Completable after(Supplier<? extends Throwable> throwable) {
+      return RxJava2Adapter.monoToCompletable(Mono.error(throwable));
+    }
+  }
+
+  static final class CompletableErrorThrowable {
+    @BeforeTemplate
+    Completable before(Throwable throwable) {
+      return Completable.error(throwable);
+    }
+
+    @AfterTemplate
+    Completable after(Throwable throwable) {
+      return RxJava2Adapter.monoToCompletable(Mono.error(throwable));
+    }
+  }
+
+  static final class CompletableFromAction {
+    @BeforeTemplate
+    Completable before(Action action) {
+      return Completable.fromAction(action);
+    }
+
+    @AfterTemplate
+    Completable after(Action action) {
+      return RxJava2Adapter.monoToCompletable(
+          Mono.fromRunnable(RxJavaReactorMigrationUtil.toRunnable(action)));
+    }
+  }
+
+  static final class CompletableFromCallable {
+    @BeforeTemplate
+    Completable before(Callable<?> supplier) {
+      return Completable.fromCallable(supplier);
+    }
+
+    @AfterTemplate
+    Completable after(Callable<?> supplier) {
+      return RxJava2Adapter.monoToCompletable(Mono.fromCallable(supplier));
+    }
+  }
+
+  // XXX: public static Completable fromFuture(Future)
+  // XXX: public static Completable fromMaybe(MaybeSource)
+  // XXX: public static Completable fromObservable(ObservableSource)
+
+  static final class CompletableFromPublisher<T> {
+    @BeforeTemplate
+    Completable before(Publisher<T> source) {
+      return Completable.fromPublisher(source);
+    }
+
+    @AfterTemplate
+    Completable after(Publisher<T> source) {
+      return RxJava2Adapter.monoToCompletable(Mono.from(source));
+    }
+  }
+
+  static final class CompletableFromRunnable {
+    @BeforeTemplate
+    Completable before(Runnable runnable) {
+      return Completable.fromRunnable(runnable);
+    }
+
+    @AfterTemplate
+    Completable after(Runnable runnable) {
+      return RxJava2Adapter.monoToCompletable(Mono.fromRunnable(runnable));
+    }
+  }
+
+  // XXX: public static Completable fromSingle(SingleSource)
+  // XXX: public static Completable merge(Iterable)
+  // XXX: public static Completable merge(Publisher)
+  // XXX: public static Completable merge(Publisher,int)
+  // XXX: public static Completable mergeArray(CompletableSource[])
+  // XXX: public static Completable mergeArrayDelayError(CompletableSource[])
+  // XXX: public static Completable mergeDelayError(Iterable)
+  // XXX: public static Completable mergeDelayError(Publisher)
+  // XXX: public static Completable mergeDelayError(Publisher,int)
+  // XXX: public static Completable never()
+  // XXX: public static Completable timer(long,TimeUnit)
+  // XXX: public static Completable timer(long,TimeUnit,Scheduler)
+  // XXX: public static Completable unsafeCreate(CompletableSource)
+  // XXX: public static Completable using(Callable,Function,Consumer)
+  // XXX: public static Completable using(Callable,Function,Consumer,boolean)
+
+  static final class CompletableWrap {
+    @BeforeTemplate
+    Completable before(Completable source) {
+      return Completable.wrap(source);
+    }
+
+    @AfterTemplate
+    Completable after(Completable source) {
+      return source;
+    }
+  }
+
+  // XXX: public final Completable ambWith(CompletableSource)
+
+  static final class CompletableAndThenCompletable {
+    @BeforeTemplate
+    Completable before(Completable completable, CompletableSource source) {
+      return completable.andThen(source);
+    }
+
+    @AfterTemplate
+    Completable after(Completable completable, CompletableSource source) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.completableToMono(completable)
+              .then(RxJava2Adapter.completableToMono(Completable.wrap(source))));
+    }
+  }
+
+  static final class CompletableAndThenMaybe<T> {
+    @BeforeTemplate
+    Maybe<T> before(Completable completable, MaybeSource<T> source) {
+      return completable.andThen(source);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Completable completable, MaybeSource<T> source) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.completableToMono(completable)
+              .then(RxJava2Adapter.maybeToMono(Maybe.wrap(source))));
+    }
+  }
+
+  // XXX: public final Observable andThen(ObservableSource)
+
+  static final class CompletableAndThenPublisher<T> {
+    @BeforeTemplate
+    Flowable<T> before(Completable completable, Publisher<T> source) {
+      return completable.andThen(source);
+    }
+
+    @AfterTemplate
+    Flowable<T> after(Completable completable, Publisher<T> source) {
+      return RxJava2Adapter.fluxToFlowable(
+          RxJava2Adapter.completableToMono(completable).thenMany(source));
+    }
+  }
+
+  static final class CompletableAndThenSingle<T> {
+    @BeforeTemplate
+    Single<T> before(Completable completable, SingleSource<T> source) {
+      return completable.andThen(source);
+    }
+
+    @AfterTemplate
+    Single<T> after(Completable completable, SingleSource<T> source) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.completableToMono(completable)
+              .then(RxJava2Adapter.singleToMono(Single.wrap(source))));
+    }
+  }
+
+  // XXX: public final Object as(CompletableConverter)
+
+  static final class CompletableBlockingAwait {
+    @BeforeTemplate
+    void before(Completable completable) {
+      completable.blockingAwait();
+    }
+
+    @AfterTemplate
+    void after(Completable completable) {
+      RxJava2Adapter.completableToMono(completable).block();
+    }
+  }
+
+  // XXX: public final boolean blockingAwait(long,TimeUnit)
+  // XXX: public final Throwable blockingGet()
+  // XXX: public final Throwable blockingGet(long,TimeUnit)
+  // XXX: public final Completable cache()
+  // XXX: public final Completable compose(CompletableTransformer)
+  // XXX: public final Completable concatWith(CompletableSource)
+  // XXX: public final Completable delay(long,TimeUnit)
+  // XXX: public final Completable delay(long,TimeUnit,Scheduler)
+  // XXX: public final Completable delay(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Completable delaySubscription(long,TimeUnit)
+  // XXX: public final Completable delaySubscription(long,TimeUnit,Scheduler)
+  // XXX: public final Completable doAfterTerminate(Action)
+  // XXX: public final Completable doFinally(Action)
+  // XXX: public final Completable doOnComplete(Action)
+  // XXX: public final Completable doOnDispose(Action)
+  // XXX: public final Completable doOnError(Consumer)
+  // XXX: public final Completable doOnEvent(Consumer)
+  // XXX: public final Completable doOnSubscribe(Consumer)
+
+  static final class CompletableDoOnError {
+    @BeforeTemplate
+    Completable before(Completable completable, Consumer<? super Throwable> consumer) {
+      return completable.doOnError(consumer);
+    }
+
+    @AfterTemplate
+    Completable after(Completable completable, Consumer<? super Throwable> consumer) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.completableToMono(completable)
+              .doOnError(RxJavaReactorMigrationUtil.toJdkConsumer(consumer)));
+    }
+  }
+
+  // XXX: public final Completable doOnTerminate(Action)
+  // XXX: public final Completable hide()
+  // XXX: public final Completable lift(CompletableOperator)
+  // XXX: public final Single materialize()
+  // XXX: public final Completable mergeWith(CompletableSource)
+  // XXX: public final Completable observeOn(Scheduler)
+
+  // XXX: Verify whether this is the correct equivalent.
+  static final class CompletableOnErrorComplete {
+    @BeforeTemplate
+    Completable before(Completable completable) {
+      return completable.onErrorComplete();
+    }
+
+    @AfterTemplate
+    Completable after(Completable completable) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.completableToMono(completable).onErrorStop());
+    }
+  }
+
+  static final class CompletableOnErrorCompletePredicate {
+    @BeforeTemplate
+    Completable before(Completable completable, Predicate<? super Throwable> predicate) {
+      return completable.onErrorComplete(predicate);
+    }
+
+    @AfterTemplate
+    Completable after(Completable completable, Predicate<? super Throwable> predicate) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.completableToMono(completable)
+              .onErrorResume(
+                  RxJavaReactorMigrationUtil.toJdkPredicate(predicate), t -> Mono.empty()));
+    }
+  }
+
+  // XXX: public final Completable onErrorComplete(Predicate)
+  // XXX: public final Completable onErrorResumeNext(Function)
+  // XXX: public final Completable onTerminateDetach()
+  // XXX: public final Completable repeat()
+  // XXX: public final Completable repeat(long)
+  // XXX: public final Completable repeatUntil(BooleanSupplier)
+  // XXX: public final Completable repeatWhen(Function)
+  // XXX: public final Completable retry()
+  // XXX: public final Completable retry(BiPredicate)
+  // XXX: public final Completable retry(long)
+  // XXX: public final Completable retry(long,Predicate)
+  // XXX: public final Completable retry(Predicate)
+  // XXX: public final Completable retryWhen(Function)
+  // XXX: public final Completable startWith(CompletableSource)
+  // XXX: public final Observable startWith(Observable)
+  // XXX: public final Flowable startWith(Publisher)
+  // XXX: public final Disposable subscribe()
+  // XXX: public final Disposable subscribe(Action)
+  // XXX: public final Disposable subscribe(Action,Consumer)
+  // XXX: public final void subscribe(CompletableObserver)
+  // XXX: public final Completable subscribeOn(Scheduler)
+  // XXX: public final CompletableObserver subscribeWith(CompletableObserver)
+  // XXX: public final Completable takeUntil(CompletableSource)
+
+  static final class CompletableTimeoutLongTimeUnit {
+    @BeforeTemplate
+    Completable before(Completable completable, long timeout, TimeUnit unit) {
+      return completable.timeout(timeout, unit);
+    }
+
+    @AfterTemplate
+    Completable after(Completable completable, long timeout, TimeUnit unit) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.completableToMono(completable)
+              .timeout(Duration.of(timeout, unit.toChronoUnit())));
+    }
+  }
+
+  // XXX: public final Completable timeout(long,TimeUnit,CompletableSource)
+  // XXX: public final Completable timeout(long,TimeUnit,Scheduler)
+  // XXX: public final Completable timeout(long,TimeUnit,Scheduler,CompletableSource)
+  // XXX: public final Object to(Function)
+
+  static final class CompletableToFlowable {
+    @BeforeTemplate
+    Flowable<Void> before(Completable completable) {
+      return completable.toFlowable();
+    }
+
+    @AfterTemplate
+    Flowable<Void> after(Completable completable) {
+      return RxJava2Adapter.fluxToFlowable(RxJava2Adapter.completableToMono(completable).flux());
+    }
+  }
+
+  // XXX: Requires investigation. Should not be Void...
+  static final class CompletableToMaybe {
+    @BeforeTemplate
+    Maybe<Void> before(Completable completable) {
+      return completable.toMaybe();
+    }
+
+    @AfterTemplate
+    Maybe<Void> after(Completable completable) {
+      return RxJava2Adapter.monoToMaybe(RxJava2Adapter.completableToMono(completable));
+    }
+  }
+
+  // XXX: public final Observable toObservable()
+  // XXX: public final Single toSingle(Callable)
+  // XXX: public final Single toSingleDefault(Object)
+  // XXX: public final Completable unsubscribeOn(Scheduler)
+
+  static final class CompletableTestAssertResult {
+    @BeforeTemplate
+    void before(Completable completable) throws InterruptedException {
+      Refaster.anyOf(
+          completable.test().await().assertResult(),
+          completable.test().assertResult(),
+          completable.test().await());
+    }
+
+    @AfterTemplate
+    void after(Completable completable) {
+      RxJava2Adapter.completableToMono(completable).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class CompletableTestAssertComplete {
+    @BeforeTemplate
+    void before(Completable completable) throws InterruptedException {
+      Refaster.anyOf(
+          completable.test().await().assertComplete(), completable.test().assertComplete());
+    }
+
+    @AfterTemplate
+    void after(Completable completable) {
+      RxJava2Adapter.completableToMono(completable).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class CompletableTestAssertErrorClass {
+    @BeforeTemplate
+    void before(Completable completable, Class<? extends Throwable> errorClass)
+        throws InterruptedException {
+      Refaster.anyOf(
+          completable.test().await().assertError(errorClass),
+          completable.test().assertError(errorClass));
+    }
+
+    @AfterTemplate
+    void after(Completable completable, Class<? extends Throwable> errorClass) {
+      RxJava2Adapter.completableToMono(completable)
+          .as(StepVerifier::create)
+          .verifyError(errorClass);
+    }
+  }
+
+  static final class CompletableTestAssertNoErrors {
+    @BeforeTemplate
+    void before(Completable completable) throws InterruptedException {
+      completable.test().await().assertNoErrors();
+    }
+
+    @AfterTemplate
+    void after(Completable completable) {
+      RxJava2Adapter.completableToMono(completable).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class CompletableTestAssertValueCount {
+    @BeforeTemplate
+    void before(Completable completable, int count) throws InterruptedException {
+      completable.test().await().assertValueCount(count);
+    }
+
+    @AfterTemplate
+    void after(Completable completable, int count) {
+      RxJava2Adapter.completableToMono(completable)
+          .as(StepVerifier::create)
+          .expectNextCount(count)
+          .verifyComplete();
+    }
+  }
+
+  static final class CompletableTestAssertFailure {
+    @BeforeTemplate
+    void before(Completable completable, Class<? extends Throwable> error)
+        throws InterruptedException {
+      completable.test().await().assertFailure(error);
+    }
+
+    @AfterTemplate
+    void after(Completable completable, Class<? extends Throwable> error) {
+      RxJava2Adapter.completableToMono(completable).as(StepVerifier::create).verifyError(error);
+    }
+  }
+
+  static final class CompletableTestAssertNoValues {
+    @BeforeTemplate
+    void before(Completable completable) throws InterruptedException {
+      completable.test().await().assertNoValues();
+    }
+
+    @AfterTemplate
+    void after(Completable completable) {
+      RxJava2Adapter.completableToMono(completable).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class CompletableTestAssertFailureAndMessage {
+    @BeforeTemplate
+    void before(Completable completable, Class<? extends Throwable> error, String message)
+        throws InterruptedException {
+      completable.test().await().assertFailureAndMessage(error, message);
+    }
+
+    @AfterTemplate
+    void after(Completable completable, Class<? extends Throwable> error, String message) {
+      RxJava2Adapter.completableToMono(completable)
+          .as(StepVerifier::create)
+          .expectErrorSatisfies(
+              t -> assertThat(t).isInstanceOf(error).hasMessageContaining(message))
+          .verify();
+    }
+  }
+
+  // XXX: public final TestObserver test(boolean)
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/RxJavaObservableToReactorTemplates.java

@@ -0,0 +1,944 @@
+package tech.picnic.errorprone.refasterrules;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.collect.Streams;
+import com.google.errorprone.refaster.ImportPolicy;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.Repeated;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import io.reactivex.BackpressureStrategy;
+import io.reactivex.Completable;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Observable;
+import io.reactivex.ObservableSource;
+import io.reactivex.functions.Function;
+import io.reactivex.functions.Predicate;
+import java.time.Duration;
+import java.util.concurrent.Callable;
+import java.util.concurrent.TimeUnit;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+/** The Refaster templates for the migration of the RxJava {@link Observable} to Reactor. */
+final class RxJavaObservableToReactorTemplates {
+  private RxJavaObservableToReactorTemplates() {}
+
+  static final class ObservableAmb<T> {
+    @BeforeTemplate
+    Observable<T> before(Iterable<? extends Observable<T>> sources) {
+      return Observable.amb(sources);
+    }
+
+    @AfterTemplate
+    Observable<T> after(Iterable<? extends Observable<T>> sources) {
+      return RxJava2Adapter.fluxToObservable(
+          Flux.<T>firstWithSignal(
+              Streams.stream(sources)
+                  .map(e -> e.toFlowable(BackpressureStrategy.BUFFER))
+                  .map(RxJava2Adapter::flowableToFlux)
+                  .collect(toImmutableList())));
+    }
+  }
+
+  // XXX: public static Observable ambArray(ObservableSource[])
+  // XXX: public static int bufferSize()
+  // XXX: public static Observable combineLatest(Function,int,ObservableSource[])
+  // XXX: public static Observable combineLatest(Iterable,Function)
+  // XXX: public static Observable combineLatest(Iterable,Function,int)
+  // XXX: public static Observable combineLatest(ObservableSource[],Function)
+  // XXX: public static Observable combineLatest(ObservableSource[],Function,int)
+  // XXX: public static Observable combineLatest(ObservableSource,ObservableSource,BiFunction)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,Function3)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function4)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function5)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function6)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function7)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function8)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function9)
+  // XXX: public static Observable combineLatestDelayError(Function,int,ObservableSource[])
+  // XXX: public static Observable combineLatestDelayError(Iterable,Function)
+  // XXX: public static Observable combineLatestDelayError(Iterable,Function,int)
+  // XXX: public static Observable combineLatestDelayError(ObservableSource[],Function)
+  // XXX: public static Observable combineLatestDelayError(ObservableSource[],Function,int)
+  // XXX: public static Observable concat(Iterable)
+  // XXX: public static Observable concat(ObservableSource)
+  // XXX: public static Observable concat(ObservableSource,int)
+  // XXX: public static Observable concat(ObservableSource,ObservableSource)
+  // XXX: public static Observable concat(ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable
+  // concat(ObservableSource,ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable concatArray(ObservableSource[])
+  // XXX: public static Observable concatArrayDelayError(ObservableSource[])
+  // XXX: public static Observable concatArrayEager(int,int,ObservableSource[])
+  // XXX: public static Observable concatArrayEager(ObservableSource[])
+  // XXX: public static Observable concatArrayEagerDelayError(int,int,ObservableSource[])
+  // XXX: public static Observable concatArrayEagerDelayError(ObservableSource[])
+  // XXX: public static Observable concatDelayError(Iterable)
+  // XXX: public static Observable concatDelayError(ObservableSource)
+  // XXX: public static Observable concatDelayError(ObservableSource,int,boolean)
+  // XXX: public static Observable concatEager(Iterable)
+  // XXX: public static Observable concatEager(Iterable,int,int)
+  // XXX: public static Observable concatEager(ObservableSource)
+  // XXX: public static Observable concatEager(ObservableSource,int,int)
+  // XXX: public static Observable create(ObservableOnSubscribe)
+  // XXX: public static Observable defer(Callable)
+
+  static final class ObservableEmpty<T> {
+    @BeforeTemplate
+    Observable<T> before() {
+      return Observable.empty();
+    }
+
+    @AfterTemplate
+    Observable<T> after() {
+      return RxJava2Adapter.fluxToObservable(Flux.empty());
+    }
+  }
+
+  // XXX: public static Observable error(Callable)
+  // XXX: public static Observable error(Throwable)
+  // XXX: public static Observable fromArray(Object[])
+
+  static final class ObservableFromCallable<T> {
+    @BeforeTemplate
+    Observable<? extends T> before(Callable<? extends T> callable) {
+      return Observable.fromCallable(callable);
+    }
+
+    @AfterTemplate
+    Observable<? extends T> after(Callable<? extends T> callable) {
+      return RxJava2Adapter.fluxToObservable(
+          Mono.fromSupplier(RxJavaReactorMigrationUtil.callableAsSupplier(callable)).flux());
+    }
+  }
+
+  // XXX: public static Observable fromFuture(Future)
+  // XXX: public static Observable fromFuture(Future,long,TimeUnit)
+  // XXX: public static Observable fromFuture(Future,long,TimeUnit,Scheduler)
+  // XXX: public static Observable fromFuture(Future,Scheduler)
+  // XXX: public static Observable fromIterable(Iterable)
+
+  static final class ObservableFromPublisher<T> {
+    @BeforeTemplate
+    Observable<T> before(Publisher<? extends T> source) {
+      return Observable.fromPublisher(source);
+    }
+
+    @AfterTemplate
+    Observable<T> after(Publisher<? extends T> source) {
+      return RxJava2Adapter.fluxToObservable(Flux.from(source));
+    }
+  }
+
+  // XXX: public static Observable generate(Callable,BiConsumer)
+  // XXX: public static Observable generate(Callable,BiConsumer,Consumer)
+  // XXX: public static Observable generate(Callable,BiFunction)
+  // XXX: public static Observable generate(Callable,BiFunction,Consumer)
+  // XXX: public static Observable generate(Consumer)
+  // XXX: public static Observable interval(long,long,TimeUnit)
+  // XXX: public static Observable interval(long,long,TimeUnit,Scheduler)
+  // XXX: public static Observable interval(long,TimeUnit)
+  // XXX: public static Observable interval(long,TimeUnit,Scheduler)
+  // XXX: public static Observable intervalRange(long,long,long,long,TimeUnit)
+  // XXX: public static Observable intervalRange(long,long,long,long,TimeUnit,Scheduler)
+
+  static final class ObservableJust<T> {
+    @BeforeTemplate
+    Observable<T> before(T t) {
+      return Observable.just(t);
+    }
+
+    @AfterTemplate
+    Observable<T> after(T t) {
+      return RxJava2Adapter.fluxToObservable(Flux.just(t));
+    }
+  }
+
+  static final class ObservableJustTwo<T> {
+    @BeforeTemplate
+    Observable<T> before(T t, T t2) {
+      return Observable.just(t, t2);
+    }
+
+    @AfterTemplate
+    Observable<T> after(T t, T t2) {
+      return RxJava2Adapter.fluxToObservable(Flux.just(t, t2));
+    }
+  }
+
+  static final class ObservableJustThree<T> {
+    @BeforeTemplate
+    Observable<T> before(T t, T t2, T t3) {
+      return Observable.just(t, t2, t3);
+    }
+
+    @AfterTemplate
+    Observable<T> after(T t, T t2, T t3) {
+      return RxJava2Adapter.fluxToObservable(Flux.just(t, t2, t3));
+    }
+  }
+
+  // XXX: public static Observable just(Object,Object,Object,Object)
+  // XXX: public static Observable just(Object,Object,Object,Object,Object)
+  // XXX: public static Observable just(Object,Object,Object,Object,Object,Object)
+  // XXX: public static Observable just(Object,Object,Object,Object,Object,Object,Object)
+  // XXX: public static Observable just(Object,Object,Object,Object,Object,Object,Object,Object)
+  // XXX: public static Observable
+  // just(Object,Object,Object,Object,Object,Object,Object,Object,Object)
+  // XXX: public static Observable
+  // just(Object,Object,Object,Object,Object,Object,Object,Object,Object,Object)
+  // XXX: public static Observable merge(Iterable)
+  // XXX: public static Observable merge(Iterable,int)
+  // XXX: public static Observable merge(Iterable,int,int)
+  // XXX: public static Observable merge(ObservableSource)
+  // XXX: public static Observable merge(ObservableSource,int)
+  // XXX: public static Observable merge(ObservableSource,ObservableSource)
+  // XXX: public static Observable merge(ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable
+  // merge(ObservableSource,ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable mergeArray(int,int,ObservableSource[])
+  // XXX: public static Observable mergeArray(ObservableSource[])
+  // XXX: public static Observable mergeArrayDelayError(int,int,ObservableSource[])
+  // XXX: public static Observable mergeArrayDelayError(ObservableSource[])
+  // XXX: public static Observable mergeDelayError(Iterable)
+  // XXX: public static Observable mergeDelayError(Iterable,int)
+  // XXX: public static Observable mergeDelayError(Iterable,int,int)
+  // XXX: public static Observable mergeDelayError(ObservableSource)
+  // XXX: public static Observable mergeDelayError(ObservableSource,int)
+  // XXX: public static Observable mergeDelayError(ObservableSource,ObservableSource)
+  // XXX: public static Observable
+  // mergeDelayError(ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable
+  // mergeDelayError(ObservableSource,ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable never()
+  // XXX: public static Observable range(int,int)
+  // XXX: public static Observable rangeLong(long,long)
+  // XXX: public static Single sequenceEqual(ObservableSource,ObservableSource)
+  // XXX: public static Single sequenceEqual(ObservableSource,ObservableSource,BiPredicate)
+  // XXX: public static Single sequenceEqual(ObservableSource,ObservableSource,BiPredicate,int)
+  // XXX: public static Single sequenceEqual(ObservableSource,ObservableSource,int)
+  // XXX: public static Observable switchOnNext(ObservableSource)
+  // XXX: public static Observable switchOnNext(ObservableSource,int)
+  // XXX: public static Observable switchOnNextDelayError(ObservableSource)
+  // XXX: public static Observable switchOnNextDelayError(ObservableSource,int)
+  // XXX: public static Observable timer(long,TimeUnit)
+  // XXX: public static Observable timer(long,TimeUnit,Scheduler)
+  // XXX: public static Observable unsafeCreate(ObservableSource)
+  // XXX: public static Observable using(Callable,Function,Consumer)
+  // XXX: public static Observable using(Callable,Function,Consumer,boolean)
+  // XXX: public static Observable wrap(ObservableSource)
+  // XXX: public static Observable zip(Iterable,Function)
+  // XXX: public static Observable zip(ObservableSource,Function)
+  // XXX: public static Observable zip(ObservableSource,ObservableSource,BiFunction)
+  // XXX: public static Observable zip(ObservableSource,ObservableSource,BiFunction,boolean)
+  // XXX: public static Observable zip(ObservableSource,ObservableSource,BiFunction,boolean,int)
+  // XXX: public static Observable zip(ObservableSource,ObservableSource,ObservableSource,Function3)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function4)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function5)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function6)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function7)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function8)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function9)
+  // XXX: public static Observable zipArray(Function,boolean,int,ObservableSource[])
+  // XXX: public static Observable zipIterable(Iterable,Function,boolean,int)
+  // XXX: public final Single all(Predicate)
+  // XXX: public final Observable ambWith(ObservableSource)
+  // XXX: public final Single any(Predicate)
+  // XXX: public final Object as(ObservableConverter)
+  // XXX: public final Object blockingFirst()
+  // XXX: public final Object blockingFirst(Object)
+  // XXX: public final void blockingForEach(Consumer)
+  // XXX: public final Iterable blockingIterable()
+  // XXX: public final Iterable blockingIterable(int)
+  // XXX: public final Object blockingLast()
+  // XXX: public final Object blockingLast(Object)
+  // XXX: public final Iterable blockingLatest()
+  // XXX: public final Iterable blockingMostRecent(Object)
+  // XXX: public final Iterable blockingNext()
+  // XXX: public final Object blockingSingle()
+  // XXX: public final Object blockingSingle(Object)
+  // XXX: public final void blockingSubscribe()
+  // XXX: public final void blockingSubscribe(Consumer)
+  // XXX: public final void blockingSubscribe(Consumer,Consumer)
+  // XXX: public final void blockingSubscribe(Consumer,Consumer,Action)
+  // XXX: public final void blockingSubscribe(Observer)
+  // XXX: public final Observable buffer(Callable)
+  // XXX: public final Observable buffer(Callable,Callable)
+  // XXX: public final Observable buffer(int)
+  // XXX: public final Observable buffer(int,Callable)
+  // XXX: public final Observable buffer(int,int)
+  // XXX: public final Observable buffer(int,int,Callable)
+  // XXX: public final Observable buffer(long,long,TimeUnit)
+  // XXX: public final Observable buffer(long,long,TimeUnit,Scheduler)
+  // XXX: public final Observable buffer(long,long,TimeUnit,Scheduler,Callable)
+  // XXX: public final Observable buffer(long,TimeUnit)
+  // XXX: public final Observable buffer(long,TimeUnit,int)
+  // XXX: public final Observable buffer(long,TimeUnit,Scheduler)
+  // XXX: public final Observable buffer(long,TimeUnit,Scheduler,int)
+  // XXX: public final Observable buffer(long,TimeUnit,Scheduler,int,Callable,boolean)
+  // XXX: public final Observable buffer(ObservableSource)
+  // XXX: public final Observable buffer(ObservableSource,Callable)
+  // XXX: public final Observable buffer(ObservableSource,Function)
+  // XXX: public final Observable buffer(ObservableSource,Function,Callable)
+  // XXX: public final Observable buffer(ObservableSource,int)
+  // XXX: public final Observable cache()
+  // XXX: public final Observable cacheWithInitialCapacity(int)
+  // XXX: public final Observable cast(Class)
+  // XXX: public final Single collect(Callable,BiConsumer)
+  // XXX: public final Single collectInto(Object,BiConsumer)
+  // XXX: public final Observable compose(ObservableTransformer)
+  // XXX: public final Observable concatMap(Function)
+  // XXX: public final Observable concatMap(Function,int)
+  // XXX: public final Completable concatMapCompletable(Function)
+  // XXX: public final Completable concatMapCompletable(Function,int)
+  // XXX: public final Completable concatMapCompletableDelayError(Function)
+  // XXX: public final Completable concatMapCompletableDelayError(Function,boolean)
+  // XXX: public final Completable concatMapCompletableDelayError(Function,boolean,int)
+  // XXX: public final Observable concatMapDelayError(Function)
+  // XXX: public final Observable concatMapDelayError(Function,int,boolean)
+  // XXX: public final Observable concatMapEager(Function)
+  // XXX: public final Observable concatMapEager(Function,int,int)
+  // XXX: public final Observable concatMapEagerDelayError(Function,boolean)
+  // XXX: public final Observable concatMapEagerDelayError(Function,int,int,boolean)
+  // XXX: public final Observable concatMapIterable(Function)
+  // XXX: public final Observable concatMapIterable(Function,int)
+  // XXX: public final Observable concatMapMaybe(Function)
+  // XXX: public final Observable concatMapMaybe(Function,int)
+  // XXX: public final Observable concatMapMaybeDelayError(Function)
+  // XXX: public final Observable concatMapMaybeDelayError(Function,boolean)
+  // XXX: public final Observable concatMapMaybeDelayError(Function,boolean,int)
+  // XXX: public final Observable concatMapSingle(Function)
+  // XXX: public final Observable concatMapSingle(Function,int)
+  // XXX: public final Observable concatMapSingleDelayError(Function)
+  // XXX: public final Observable concatMapSingleDelayError(Function,boolean)
+  // XXX: public final Observable concatMapSingleDelayError(Function,boolean,int)
+  // XXX: public final Observable concatWith(CompletableSource)
+  // XXX: public final Observable concatWith(MaybeSource)
+  // XXX: public final Observable concatWith(ObservableSource)
+  // XXX: public final Observable concatWith(SingleSource)
+  // XXX: public final Single contains(Object)
+  // XXX: public final Single count()
+  // XXX: public final Observable debounce(Function)
+  // XXX: public final Observable debounce(long,TimeUnit)
+  // XXX: public final Observable debounce(long,TimeUnit,Scheduler)
+  // XXX: public final Observable defaultIfEmpty(Object)
+  // XXX: public final Observable delay(Function)
+  // XXX: public final Observable delay(long,TimeUnit)
+  // XXX: public final Observable delay(long,TimeUnit,boolean)
+  // XXX: public final Observable delay(long,TimeUnit,Scheduler)
+  // XXX: public final Observable delay(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Observable delay(ObservableSource,Function)
+  // XXX: public final Observable delaySubscription(long,TimeUnit)
+  // XXX: public final Observable delaySubscription(long,TimeUnit,Scheduler)
+  // XXX: public final Observable delaySubscription(ObservableSource)
+  // XXX: public final Observable dematerialize()
+  // XXX: public final Observable dematerialize(Function)
+  // XXX: public final Observable distinct()
+  // XXX: public final Observable distinct(Function)
+  // XXX: public final Observable distinct(Function,Callable)
+  // XXX: public final Observable distinctUntilChanged()
+  // XXX: public final Observable distinctUntilChanged(BiPredicate)
+  // XXX: public final Observable distinctUntilChanged(Function)
+  // XXX: public final Observable doAfterNext(Consumer)
+  // XXX: public final Observable doAfterTerminate(Action)
+  // XXX: public final Observable doFinally(Action)
+  // XXX: public final Observable doOnComplete(Action)
+  // XXX: public final Observable doOnDispose(Action)
+  // XXX: public final Observable doOnEach(Consumer)
+  // XXX: public final Observable doOnEach(Observer)
+  // XXX: public final Observable doOnError(Consumer)
+  // XXX: public final Observable doOnLifecycle(Consumer,Action)
+  // XXX: public final Observable doOnNext(Consumer)
+  // XXX: public final Observable doOnSubscribe(Consumer)
+  // XXX: public final Observable doOnTerminate(Action)
+  // XXX: public final Maybe elementAt(long)
+  // XXX: public final Single elementAt(long,Object)
+  // XXX: public final Single elementAtOrError(long)
+
+  // XXX: Default BackPressureStrategy.BUFFER is set.
+  static final class ObservableFilter<T> {
+    @BeforeTemplate
+    Observable<T> before(Observable<T> observable, Predicate<T> predicate) {
+      return observable.filter(predicate);
+    }
+
+    @AfterTemplate
+    Observable<T> after(Observable<T> observable, Predicate<T> predicate) {
+      return RxJava2Adapter.fluxToObservable(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+              .filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate)));
+    }
+  }
+
+  // XXX: public final Single first(Object)
+
+  // XXX: Default BUFFER is chosen here.
+  static final class MaybeFirstElement<T> {
+    @BeforeTemplate
+    Maybe<T> before(Observable<T> observable) {
+      return observable.firstElement();
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Observable<T> observable) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER).next());
+    }
+  }
+
+  // XXX: public final Single firstOrError()
+  // XXX: public final Observable flatMap(Function)
+
+  // XXX: Add test
+  // XXX: Default BUFFER is set here.
+  static final class ObservableFlatMap<I, T extends I, O, P extends ObservableSource<O>> {
+    @BeforeTemplate
+    Observable<O> before(
+        Observable<T> observable,
+        Function<? super T, ? extends ObservableSource<? extends O>> function) {
+      return observable.flatMap(function);
+    }
+
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    @AfterTemplate
+    Observable<O> after(Observable<T> observable, Function<I, P> function) {
+      return RxJava2Adapter.fluxToObservable(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+              .flatMap(
+                  z ->
+                      RxJava2Adapter.observableToFlux(
+                          Observable.wrap(
+                              RxJavaReactorMigrationUtil.<I, P>toJdkFunction(function).apply(z)),
+                          BackpressureStrategy.BUFFER)));
+    }
+  }
+
+  // XXX: public final Observable flatMap(Function,BiFunction)
+  // XXX: public final Observable flatMap(Function,BiFunction,boolean)
+  // XXX: public final Observable flatMap(Function,BiFunction,boolean,int)
+  // XXX: public final Observable flatMap(Function,BiFunction,boolean,int,int)
+  // XXX: public final Observable flatMap(Function,BiFunction,int)
+  // XXX: public final Observable flatMap(Function,boolean)
+  // XXX: public final Observable flatMap(Function,boolean,int)
+  // XXX: public final Observable flatMap(Function,boolean,int,int)
+  // XXX: public final Observable flatMap(Function,Function,Callable)
+  // XXX: public final Observable flatMap(Function,Function,Callable,int)
+  // XXX: public final Observable flatMap(Function,int)
+  // XXX: public final Completable flatMapCompletable(Function)
+  // XXX: public final Completable flatMapCompletable(Function,boolean)
+
+  static final class ObservableFromIterable<T> {
+    @BeforeTemplate
+    Observable<T> before(Iterable<? extends T> iterable) {
+      return Observable.fromIterable(iterable);
+    }
+
+    @AfterTemplate
+    Observable<T> after(Iterable<? extends T> iterable) {
+      return RxJava2Adapter.fluxToObservable(Flux.fromIterable(iterable));
+    }
+  }
+
+  // XXX: public final Observable flatMapIterable(Function,BiFunction)
+
+  static final class ObservableFlatMapMaybe<T, R, O extends R, M extends MaybeSource<O>> {
+    Observable<O> before(
+        Observable<T> observable, Function<? super T, ? extends MaybeSource<? extends O>> mapper) {
+      return observable.flatMapMaybe(mapper);
+    }
+
+    Observable<O> after(Observable<T> observable, Function<T, M> mapper) {
+      return RxJava2Adapter.fluxToObservable(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+              .flatMap(
+                  t ->
+                      RxJava2Adapter.maybeToMono(
+                          Maybe.wrap(
+                              RxJavaReactorMigrationUtil.<T, M>toJdkFunction(mapper).apply(t)))));
+    }
+  } // XXX: public final Observable flatMapMaybe(Function,boolean)
+  // XXX: public final Observable flatMapSingle(Function)
+  // XXX: public final Observable flatMapSingle(Function,boolean)
+  // XXX: public final Disposable forEach(Consumer)
+  // XXX: public final Disposable forEachWhile(Predicate)
+  // XXX: public final Disposable forEachWhile(Predicate,Consumer)
+  // XXX: public final Disposable forEachWhile(Predicate,Consumer,Action)
+  // XXX: public final Observable groupBy(Function)
+  // XXX: public final Observable groupBy(Function,boolean)
+  // XXX: public final Observable groupBy(Function,Function)
+  // XXX: public final Observable groupBy(Function,Function,boolean)
+  // XXX: public final Observable groupBy(Function,Function,boolean,int)
+  // XXX: public final Observable groupJoin(ObservableSource,Function,Function,BiFunction)
+  // XXX: public final Observable hide()
+
+  static final class ObservableIgnoreElements<T> {
+    @BeforeTemplate
+    Completable before(Observable<T> observable) {
+      return observable.ignoreElements();
+    }
+
+    @AfterTemplate
+    Completable after(Observable<T> observable) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+              .ignoreElements()
+              .then());
+    }
+  }
+
+  // XXX: public final Single isEmpty()
+  // XXX: public final Observable join(ObservableSource,Function,Function,BiFunction)
+  // XXX: public final Single last(Object)
+  // XXX: public final Maybe lastElement()
+  // XXX: public final Single lastOrError()
+  // XXX: public final Observable lift(ObservableOperator)
+  // XXX: public final Observable map(Function)
+  // XXX: public final Observable materialize()
+  // XXX: public final Observable mergeWith(CompletableSource)
+  // XXX: public final Observable mergeWith(MaybeSource)
+  // XXX: public final Observable mergeWith(ObservableSource)
+  // XXX: public final Observable mergeWith(SingleSource)
+  // XXX: public final Observable observeOn(Scheduler)
+  // XXX: public final Observable observeOn(Scheduler,boolean)
+  // XXX: public final Observable observeOn(Scheduler,boolean,int)
+  // XXX: public final Observable ofType(Class)
+  // XXX: public final Observable onErrorResumeNext(Function)
+  // XXX: public final Observable onErrorResumeNext(ObservableSource)
+  // XXX: public final Observable onErrorReturn(Function)
+  // XXX: public final Observable onErrorReturnItem(Object)
+  // XXX: public final Observable onExceptionResumeNext(ObservableSource)
+  // XXX: public final Observable onTerminateDetach()
+  // XXX: public final ConnectableObservable publish()
+  // XXX: public final Observable publish(Function)
+  // XXX: public final Maybe reduce(BiFunction)
+  // XXX: public final Single reduce(Object,BiFunction)
+  // XXX: public final Single reduceWith(Callable,BiFunction)
+  // XXX: public final Observable repeat()
+  // XXX: public final Observable repeat(long)
+  // XXX: public final Observable repeatUntil(BooleanSupplier)
+  // XXX: public final Observable repeatWhen(Function)
+  // XXX: public final ConnectableObservable replay()
+  // XXX: public final Observable replay(Function)
+  // XXX: public final Observable replay(Function,int)
+  // XXX: public final Observable replay(Function,int,long,TimeUnit)
+  // XXX: public final Observable replay(Function,int,long,TimeUnit,Scheduler)
+  // XXX: public final Observable replay(Function,int,Scheduler)
+  // XXX: public final Observable replay(Function,long,TimeUnit)
+  // XXX: public final Observable replay(Function,long,TimeUnit,Scheduler)
+  // XXX: public final Observable replay(Function,Scheduler)
+  // XXX: public final ConnectableObservable replay(int)
+  // XXX: public final ConnectableObservable replay(int,long,TimeUnit)
+  // XXX: public final ConnectableObservable replay(int,long,TimeUnit,Scheduler)
+  // XXX: public final ConnectableObservable replay(int,Scheduler)
+  // XXX: public final ConnectableObservable replay(long,TimeUnit)
+  // XXX: public final ConnectableObservable replay(long,TimeUnit,Scheduler)
+  // XXX: public final ConnectableObservable replay(Scheduler)
+  // XXX: public final Observable retry()
+  // XXX: public final Observable retry(BiPredicate)
+  // XXX: public final Observable retry(long)
+  // XXX: public final Observable retry(long,Predicate)
+  // XXX: public final Observable retry(Predicate)
+  // XXX: public final Observable retryUntil(BooleanSupplier)
+  // XXX: public final Observable retryWhen(Function)
+  // XXX: public final void safeSubscribe(Observer)
+  // XXX: public final Observable sample(long,TimeUnit)
+  // XXX: public final Observable sample(long,TimeUnit,boolean)
+  // XXX: public final Observable sample(long,TimeUnit,Scheduler)
+  // XXX: public final Observable sample(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Observable sample(ObservableSource)
+  // XXX: public final Observable sample(ObservableSource,boolean)
+  // XXX: public final Observable scan(BiFunction)
+  // XXX: public final Observable scan(Object,BiFunction)
+  // XXX: public final Observable scanWith(Callable,BiFunction)
+  // XXX: public final Observable serialize()
+  // XXX: public final Observable share()
+  // XXX: public final Single single(Object)
+  // XXX: public final Maybe singleElement()
+  // XXX: public final Single singleOrError()
+  // XXX: public final Observable skip(long)
+  // XXX: public final Observable skip(long,TimeUnit)
+  // XXX: public final Observable skip(long,TimeUnit,Scheduler)
+  // XXX: public final Observable skipLast(int)
+  // XXX: public final Observable skipLast(long,TimeUnit)
+  // XXX: public final Observable skipLast(long,TimeUnit,boolean)
+  // XXX: public final Observable skipLast(long,TimeUnit,Scheduler)
+  // XXX: public final Observable skipLast(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Observable skipLast(long,TimeUnit,Scheduler,boolean,int)
+  // XXX: public final Observable skipUntil(ObservableSource)
+  // XXX: public final Observable skipWhile(Predicate)
+  // XXX: public final Observable sorted()
+  // XXX: public final Observable sorted(Comparator)
+  // XXX: public final Observable startWith(Iterable)
+  // XXX: public final Observable startWith(Object)
+  // XXX: public final Observable startWith(ObservableSource)
+  // XXX: public final Observable startWithArray(Object[])
+  // XXX: public final Disposable subscribe()
+  // XXX: public final Disposable subscribe(Consumer)
+  // XXX: public final Disposable subscribe(Consumer,Consumer)
+  // XXX: public final Disposable subscribe(Consumer,Consumer,Action)
+  // XXX: public final Disposable subscribe(Consumer,Consumer,Action,Consumer)
+  // XXX: public final void subscribe(Observer)
+  // XXX: public final Observable subscribeOn(Scheduler)
+  // XXX: public final Observer subscribeWith(Observer)
+  // XXX: public final Observable switchIfEmpty(ObservableSource)
+  // XXX: public final Observable switchMap(Function)
+  // XXX: public final Observable switchMap(Function,int)
+  // XXX: public final Completable switchMapCompletable(Function)
+  // XXX: public final Completable switchMapCompletableDelayError(Function)
+  // XXX: public final Observable switchMapDelayError(Function)
+  // XXX: public final Observable switchMapDelayError(Function,int)
+  // XXX: public final Observable switchMapMaybe(Function)
+  // XXX: public final Observable switchMapMaybeDelayError(Function)
+  // XXX: public final Observable switchMapSingle(Function)
+  // XXX: public final Observable switchMapSingleDelayError(Function)
+  // XXX: public final Observable take(long)
+  // XXX: public final Observable take(long,TimeUnit)
+  // XXX: public final Observable take(long,TimeUnit,Scheduler)
+  // XXX: public final Observable takeLast(int)
+  // XXX: public final Observable takeLast(long,long,TimeUnit)
+  // XXX: public final Observable takeLast(long,long,TimeUnit,Scheduler)
+  // XXX: public final Observable takeLast(long,long,TimeUnit,Scheduler,boolean,int)
+  // XXX: public final Observable takeLast(long,TimeUnit)
+  // XXX: public final Observable takeLast(long,TimeUnit,boolean)
+  // XXX: public final Observable takeLast(long,TimeUnit,Scheduler)
+  // XXX: public final Observable takeLast(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Observable takeLast(long,TimeUnit,Scheduler,boolean,int)
+  // XXX: public final Observable takeUntil(ObservableSource)
+  // XXX: public final Observable takeUntil(Predicate)
+  // XXX: public final Observable takeWhile(Predicate)
+  // XXX: public final Observable throttleFirst(long,TimeUnit)
+  // XXX: public final Observable throttleFirst(long,TimeUnit,Scheduler)
+  // XXX: public final Observable throttleLast(long,TimeUnit)
+  // XXX: public final Observable throttleLast(long,TimeUnit,Scheduler)
+  // XXX: public final Observable throttleLatest(long,TimeUnit)
+  // XXX: public final Observable throttleLatest(long,TimeUnit,boolean)
+  // XXX: public final Observable throttleLatest(long,TimeUnit,Scheduler)
+  // XXX: public final Observable throttleLatest(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Observable throttleWithTimeout(long,TimeUnit)
+  // XXX: public final Observable throttleWithTimeout(long,TimeUnit,Scheduler)
+  // XXX: public final Observable timeInterval()
+  // XXX: public final Observable timeInterval(Scheduler)
+  // XXX: public final Observable timeInterval(TimeUnit)
+  // XXX: public final Observable timeInterval(TimeUnit,Scheduler)
+  // XXX: public final Observable timeout(Function)
+  // XXX: public final Observable timeout(Function,ObservableSource)
+
+  // Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTimeoutLongTimeUnit<T> {
+    @BeforeTemplate
+    Observable<T> before(Observable<T> observable, long timeout, TimeUnit unit) {
+      return observable.timeout(timeout, unit);
+    }
+
+    @AfterTemplate
+    Observable<T> after(Observable<T> observable, long timeout, TimeUnit unit) {
+      return RxJava2Adapter.fluxToObservable(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+              .timeout(Duration.of(timeout, unit.toChronoUnit())));
+    }
+  }
+
+  // XXX: public final Observable timeout(long,TimeUnit,ObservableSource)
+  // XXX: public final Observable timeout(long,TimeUnit,Scheduler)
+  // XXX: public final Observable timeout(long,TimeUnit,Scheduler,ObservableSource)
+  // XXX: public final Observable timeout(ObservableSource,Function)
+  // XXX: public final Observable timeout(ObservableSource,Function,ObservableSource)
+  // XXX: public final Observable timestamp()
+  // XXX: public final Observable timestamp(Scheduler)
+  // XXX: public final Observable timestamp(TimeUnit)
+  // XXX: public final Observable timestamp(TimeUnit,Scheduler)
+  // XXX: public final Object to(Function)
+
+  static final class ObservableToFlowable<T> {
+    @BeforeTemplate
+    Flowable<T> before(Observable<T> observable, BackpressureStrategy strategy) {
+      return observable.toFlowable(strategy);
+    }
+
+    @AfterTemplate
+    Flowable<T> after(Observable<T> observable, BackpressureStrategy strategy) {
+      return RxJava2Adapter.fluxToFlowable(RxJava2Adapter.observableToFlux(observable, strategy));
+    }
+  }
+
+  // XXX: public final Future toFuture()
+  // XXX: public final Single toList()
+  // XXX: public final Single toList(Callable)
+  // XXX: public final Single toList(int)
+  // XXX: public final Single toMap(Function)
+  // XXX: public final Single toMap(Function,Function)
+  // XXX: public final Single toMap(Function,Function,Callable)
+  // XXX: public final Single toMultimap(Function)
+  // XXX: public final Single toMultimap(Function,Function)
+  // XXX: public final Single toMultimap(Function,Function,Callable)
+  // XXX: public final Single toMultimap(Function,Function,Callable,Function)
+  // XXX: public final Single toSortedList()
+  // XXX: public final Single toSortedList(Comparator)
+  // XXX: public final Single toSortedList(Comparator,int)
+  // XXX: public final Single toSortedList(int)
+  // XXX: public final Observable unsubscribeOn(Scheduler)
+  // XXX: public final Observable window(Callable)
+  // XXX: public final Observable window(Callable,int)
+  // XXX: public final Observable window(long)
+  // XXX: public final Observable window(long,long)
+  // XXX: public final Observable window(long,long,int)
+  // XXX: public final Observable window(long,long,TimeUnit)
+  // XXX: public final Observable window(long,long,TimeUnit,Scheduler)
+  // XXX: public final Observable window(long,long,TimeUnit,Scheduler,int)
+  // XXX: public final Observable window(long,TimeUnit)
+  // XXX: public final Observable window(long,TimeUnit,long)
+  // XXX: public final Observable window(long,TimeUnit,long,boolean)
+  // XXX: public final Observable window(long,TimeUnit,Scheduler)
+  // XXX: public final Observable window(long,TimeUnit,Scheduler,long)
+  // XXX: public final Observable window(long,TimeUnit,Scheduler,long,boolean)
+  // XXX: public final Observable window(long,TimeUnit,Scheduler,long,boolean,int)
+  // XXX: public final Observable window(ObservableSource)
+  // XXX: public final Observable window(ObservableSource,Function)
+  // XXX: public final Observable window(ObservableSource,Function,int)
+  // XXX: public final Observable window(ObservableSource,int)
+  // XXX: public final Observable withLatestFrom(Iterable,Function)
+  // XXX: public final Observable withLatestFrom(ObservableSource,BiFunction)
+  // XXX: public final Observable withLatestFrom(ObservableSource[],Function)
+  // XXX: public final Observable withLatestFrom(ObservableSource,ObservableSource,Function3)
+  // XXX: public final Observable
+  // withLatestFrom(ObservableSource,ObservableSource,ObservableSource,Function4)
+  // XXX: public final Observable
+  // withLatestFrom(ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function5)
+  // XXX: public final Observable zipWith(Iterable,BiFunction)
+  // XXX: public final Observable zipWith(ObservableSource,BiFunction)
+  // XXX: public final Observable zipWith(ObservableSource,BiFunction,boolean)
+  // XXX: public final Observable zipWith(ObservableSource,BiFunction,boolean,int)
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  @SuppressWarnings("unchecked")
+  static final class ObservableTestAssertResultItem<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, T item) throws InterruptedException {
+      Refaster.anyOf(
+          observable.test().await().assertResult(item),
+          observable.test().await().assertValue(item));
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, T item) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectNext(item)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  @SuppressWarnings("unchecked")
+  static final class ObservableTestAssertResult<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable) throws InterruptedException {
+      Refaster.anyOf(observable.test().await().assertResult(), observable.test().await());
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyComplete();
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  static final class ObservableTestAssertResultTwoItems<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, T t1, T t2) throws InterruptedException {
+      observable.test().await().assertResult(t1, t2);
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, T t1, T t2) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectNext(t1, t2)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertValue<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, Predicate<T> predicate) throws InterruptedException {
+      Refaster.anyOf(
+          observable.test().await().assertValue(predicate),
+          observable.test().await().assertValue(predicate).assertNoErrors().assertComplete(),
+          observable.test().await().assertComplete().assertValue(predicate),
+          observable.test().await().assertValue(predicate).assertComplete());
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, Predicate<T> predicate) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(predicate))
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertResultValues<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, @Repeated T item) throws InterruptedException {
+      Refaster.anyOf(
+          observable.test().await().assertResult(Refaster.asVarargs(item)),
+          observable.test().await().assertValues(Refaster.asVarargs(item)));
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, @Repeated T item) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectNext(item)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertComplete<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable) throws InterruptedException {
+      observable.test().await().assertComplete();
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertErrorClass<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, Class<? extends Throwable> errorClass)
+        throws InterruptedException {
+      observable.test().await().assertError(errorClass);
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, Class<? extends Throwable> errorClass) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyError(errorClass);
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertNoErrors<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable) throws InterruptedException {
+      observable.test().await().assertNoErrors();
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertValueCount<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, int count) throws InterruptedException {
+      observable.test().await().assertValueCount(count);
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, int count) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectNextCount(count)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Add test
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  @SuppressWarnings("unchecked")
+  static final class ObservableTestAssertFailure<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, Class<? extends Throwable> error)
+        throws InterruptedException {
+      observable.test().await().assertFailure(error);
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, Class<? extends Throwable> error) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyError(error);
+    }
+  }
+
+  // XXX: Add test
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertNoValues<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable) throws InterruptedException {
+      Refaster.anyOf(
+          observable.test().await().assertNoValues(),
+          observable.test().await().assertNoValues().assertComplete());
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Add test
+  // XXX: This introduces AssertJ dependency
+  @SuppressWarnings("unchecked")
+  static final class ObservableTestAssertFailureAndMessage<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, Class<? extends Throwable> error, String message)
+        throws InterruptedException {
+      observable.test().await().assertFailureAndMessage(error, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    void after(Observable<T> observable, Class<? extends Throwable> error, String message) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectErrorSatisfies(
+              t -> assertThat(t).isInstanceOf(error).hasMessageContaining(message))
+          .verify();
+    }
+  }
+
+  // XXX: public final TestObserver test(boolean)
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/RxJavaSingleToReactorTemplates.java

@@ -0,0 +1,816 @@
+package tech.picnic.errorprone.refasterrules;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.refaster.ImportPolicy;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.MayOptionallyUse;
+import com.google.errorprone.refaster.annotation.Placeholder;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Single;
+import io.reactivex.SingleSource;
+import io.reactivex.disposables.Disposable;
+import io.reactivex.functions.BiFunction;
+import io.reactivex.functions.Consumer;
+import io.reactivex.functions.Function;
+import io.reactivex.functions.Predicate;
+import io.reactivex.schedulers.Schedulers;
+import java.time.Duration;
+import java.util.concurrent.Callable;
+import java.util.concurrent.TimeUnit;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+/** The Refaster templates for the migration of the RxJava {@link Single} to Reactor. */
+final class RxJavaSingleToReactorTemplates {
+  private RxJavaSingleToReactorTemplates() {}
+
+  // XXX: public static Single amb(Iterable)
+  // XXX: public static Single ambArray(SingleSource[])
+  // XXX: public static Flowable concat(Iterable)
+  // XXX: public static Observable concat(ObservableSource)
+  // XXX: public static Flowable concat(Publisher)
+  // XXX: public static Flowable concat(Publisher,int)
+  // XXX: public static Flowable concat(SingleSource,SingleSource)
+  // XXX: public static Flowable concat(SingleSource,SingleSource,SingleSource)
+  // XXX: public static Flowable concat(SingleSource,SingleSource,SingleSource,SingleSource)
+  // XXX: public static Flowable concatArray(SingleSource[])
+  // XXX: public static Flowable concatArrayEager(SingleSource[])
+  // XXX: public static Flowable concatEager(Iterable)
+  // XXX: public static Flowable concatEager(Publisher)
+  // XXX: public static Single create(SingleOnSubscribe)
+
+  abstract static class SingleDeferFirst<T> {
+    @Placeholder
+    abstract Single<? extends T> singleProducer();
+
+    @BeforeTemplate
+    @SuppressWarnings("Convert2MethodRef")
+    Single<T> before() {
+      return Single.defer(() -> singleProducer());
+    }
+
+    @AfterTemplate
+    Single<? extends T> after() {
+      return RxJava2Adapter.monoToSingle(
+          Mono.defer(() -> RxJava2Adapter.singleToMono(singleProducer())));
+    }
+  }
+
+  // XXX: public static Single equals(SingleSource,SingleSource)
+
+  static final class SingleErrorCallable<T> {
+    @BeforeTemplate
+    Single<T> before(Callable<? extends Throwable> throwable) {
+      return Single.error(throwable);
+    }
+
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    @AfterTemplate
+    Single<T> after(Callable<? extends Throwable> throwable) {
+      return RxJava2Adapter.monoToSingle(
+          Mono.error(RxJavaReactorMigrationUtil.callableAsSupplier(throwable)));
+    }
+  }
+
+  static final class SingleErrorThrowable<T> {
+    @BeforeTemplate
+    Single<T> before(Throwable throwable) {
+      return Single.error(throwable);
+    }
+
+    @AfterTemplate
+    Single<T> after(Throwable throwable) {
+      return RxJava2Adapter.monoToSingle(Mono.error(throwable));
+    }
+  }
+
+  static final class SingleFromCallable<T> {
+    @BeforeTemplate
+    Single<T> before(Callable<? extends T> callable) {
+      return Single.fromCallable(callable);
+    }
+
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    @AfterTemplate
+    Single<T> after(Callable<? extends T> callable) {
+      return RxJava2Adapter.monoToSingle(
+          Mono.fromSupplier(RxJavaReactorMigrationUtil.callableAsSupplier(callable)));
+    }
+  }
+
+  // XXX: public static Single fromFuture(Future)
+  // XXX: public static Single fromFuture(Future,long,TimeUnit)
+  // XXX: public static Single fromFuture(Future,long,TimeUnit,Scheduler)
+  // XXX: public static Single fromFuture(Future,Scheduler)
+  // XXX: public static Single fromObservable(ObservableSource)
+
+  static final class SingleFromPublisher<T> {
+    @BeforeTemplate
+    Single<T> before(Publisher<? extends T> source) {
+      return Single.fromPublisher(source);
+    }
+
+    @AfterTemplate
+    Single<T> after(Publisher<? extends T> source) {
+      return RxJava2Adapter.monoToSingle(Mono.from(source));
+    }
+  }
+
+  static final class SingleJust<T> {
+    @BeforeTemplate
+    Single<T> before(T item) {
+      return Single.just(item);
+    }
+
+    @AfterTemplate
+    Single<T> after(T item) {
+      return RxJava2Adapter.monoToSingle(Mono.just(item));
+    }
+  }
+
+  // XXX: public static Flowable merge(Iterable)
+  // XXX: public static Flowable merge(Publisher)
+  // XXX: public static Single merge(SingleSource)
+  // XXX: public static Flowable merge(SingleSource,SingleSource)
+  // XXX: public static Flowable merge(SingleSource,SingleSource,SingleSource)
+  // XXX: public static Flowable merge(SingleSource,SingleSource,SingleSource,SingleSource)
+  // XXX: public static Flowable mergeDelayError(Iterable)
+  // XXX: public static Flowable mergeDelayError(Publisher)
+  // XXX: public static Flowable mergeDelayError(SingleSource,SingleSource)
+  // XXX: public static Flowable mergeDelayError(SingleSource,SingleSource,SingleSource)
+  // XXX: public static Flowable
+  // mergeDelayError(SingleSource,SingleSource,SingleSource,SingleSource)
+
+  static final class SingleNever<T> {
+    @BeforeTemplate
+    Single<T> before() {
+      return Single.never();
+    }
+
+    @AfterTemplate
+    Single<T> after() {
+      return RxJava2Adapter.monoToSingle(Mono.never());
+    }
+  }
+  // XXX: public static Single timer(long,TimeUnit)
+  // XXX: public static Single timer(long,TimeUnit,Scheduler)
+  // XXX: public static Single unsafeCreate(SingleSource)
+  // XXX: public static Single using(Callable,Function,Consumer)
+  // XXX: public static Single using(Callable,Function,Consumer,boolean)
+
+  static final class SingleWrap<T> {
+    @BeforeTemplate
+    Single<T> before(Single<T> single) {
+      return Single.wrap(single);
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single) {
+      return single;
+    }
+  }
+
+  // XXX: public static Single zip(Iterable,Function)
+  // XXX: public static Single zip(SingleSource,SingleSource,BiFunction)
+  // XXX: public static Single zip(SingleSource,SingleSource,SingleSource,Function3)
+  // XXX: public static Single zip(SingleSource,SingleSource,SingleSource,SingleSource,Function4)
+  // XXX: public static Single
+  // zip(SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,Function5)
+  // XXX: public static Single
+  // zip(SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,Function6)
+  // XXX: public static Single
+  // zip(SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,Function7)
+  // XXX: public static Single
+  // zip(SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,Function8)
+  // XXX: public static Single
+  // zip(SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,Function9)
+  // XXX: public static Single zipArray(Function,SingleSource[])
+  // XXX: public final Single ambWith(SingleSource)
+  // XXX: public final Object as(SingleConverter)
+
+  static final class SingleBlockingGet<T> {
+    @BeforeTemplate
+    Object before(Single<T> single) {
+      return single.blockingGet();
+    }
+
+    @AfterTemplate
+    Object after(Single<T> single) {
+      return RxJava2Adapter.singleToMono(single).block();
+    }
+  }
+
+  // XXX: public final Single cache()
+  // XXX: public final Single cast(Class)
+  // XXX: public final Single compose(SingleTransformer)
+
+  static final class SingleConcatWith<T> {
+    @BeforeTemplate
+    Flowable<T> before(Single<T> single, SingleSource<? extends T> source) {
+      return single.concatWith(source);
+    }
+
+    @AfterTemplate
+    Flowable<T> after(Single<T> single, SingleSource<? extends T> source) {
+      return RxJava2Adapter.fluxToFlowable(
+          RxJava2Adapter.singleToMono(single)
+              .concatWith(RxJava2Adapter.singleToMono(Single.wrap(source))));
+    }
+  }
+
+  // XXX: public final Single contains(Object)
+  // XXX: public final Single contains(Object,BiPredicate)
+  // XXX: public final Single delay(long,TimeUnit)
+  // XXX: public final Single delay(long,TimeUnit,boolean)
+  // XXX: public final Single delay(long,TimeUnit,Scheduler)
+  // XXX: public final Single delay(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Single delaySubscription(CompletableSource)
+  // XXX: public final Single delaySubscription(long,TimeUnit)
+  // XXX: public final Single delaySubscription(long,TimeUnit,Scheduler)
+  // XXX: public final Single delaySubscription(ObservableSource)
+  // XXX: public final Single delaySubscription(Publisher)
+  // XXX: public final Single delaySubscription(SingleSource)
+  // XXX: public final Maybe dematerialize(Function)
+  // XXX: public final Single doAfterSuccess(Consumer)
+  // XXX: public final Single doAfterTerminate(Action)
+  // XXX: public final Single doFinally(Action)
+  // XXX: public final Single doOnDispose(Action)
+
+  static final class SingleDoOnError<T> {
+    @BeforeTemplate
+    Single<T> before(Single<T> single, Consumer<? super Throwable> consumer) {
+      return single.doOnError(consumer);
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single, Consumer<? super Throwable> consumer) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .doOnError(RxJavaReactorMigrationUtil.toJdkConsumer(consumer)));
+    }
+  }
+
+  // XXX: public final Single doOnEvent(BiConsumer)
+  // XXX: public final Single doOnSubscribe(Consumer)
+
+  static final class SingleDoOnSuccess<T> {
+    @BeforeTemplate
+    Single<T> before(Single<T> single, Consumer<T> consumer) {
+      return single.doOnSuccess(consumer);
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single, Consumer<T> consumer) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .doOnSuccess(RxJavaReactorMigrationUtil.toJdkConsumer(consumer)));
+    }
+  }
+
+  // XXX: public final Single doOnTerminate(Action)
+
+  static final class SingleFilter<S, T extends S> {
+    @BeforeTemplate
+    Maybe<T> before(Single<T> single, Predicate<S> predicate) {
+      return single.filter(predicate);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Single<T> single, Predicate<S> predicate) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.singleToMono(single)
+              .filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate)));
+    }
+  }
+
+  // XXX: Add test
+  static final class SingleFlatMapFunction<I, T extends I, O, M extends SingleSource<O>> {
+    @BeforeTemplate
+    Single<O> before(
+        Single<T> single, Function<? super I, ? extends SingleSource<? extends O>> function) {
+      return single.flatMap(function);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    Single<O> after(Single<T> single, Function<I, M> function) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .flatMap(
+                  v ->
+                      RxJava2Adapter.singleToMono(
+                          Single.wrap(
+                              RxJavaReactorMigrationUtil.<I, M>toJdkFunction(function).apply(v)))));
+    }
+  }
+
+  abstract static class SingleFlatMapLambda<S, T> {
+    @Placeholder
+    abstract Single<T> toSingleFunction(@MayOptionallyUse S element);
+
+    @BeforeTemplate
+    Single<T> before(Single<S> single) {
+      return Refaster.anyOf(
+          single.flatMap(v -> toSingleFunction(v)), single.flatMap((S v) -> toSingleFunction(v)));
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<S> single) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .flatMap(v -> RxJava2Adapter.singleToMono(toSingleFunction(v))));
+    }
+  }
+
+  static final class SingleFlatMapCompletable<T, R extends CompletableSource> {
+    @BeforeTemplate
+    Completable before(
+        Single<T> single, Function<? super T, ? extends CompletableSource> function) {
+      return single.flatMapCompletable(function);
+    }
+
+    @AfterTemplate
+    Completable after(Single<T> single, Function<T, R> function) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.singleToMono(single)
+              .flatMap(
+                  z ->
+                      RxJava2Adapter.completableToMono(
+                          Completable.wrap(
+                              RxJavaReactorMigrationUtil.<T, R>toJdkFunction(function).apply(z))))
+              .then());
+    }
+  }
+
+  // XXX: Add test
+  static final class SingleFlatMapMaybe<T, R, M extends MaybeSource<R>> {
+    @BeforeTemplate
+    Maybe<R> before(
+        Single<T> single, Function<? super T, ? extends MaybeSource<? extends R>> mapper) {
+      return single.flatMapMaybe(mapper);
+    }
+
+    @AfterTemplate
+    Maybe<R> after(Single<T> single, Function<T, M> mapper) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.singleToMono(single)
+              .flatMap(
+                  e ->
+                      RxJava2Adapter.maybeToMono(
+                          Maybe.wrap(
+                              RxJavaReactorMigrationUtil.<T, M>toJdkFunction(mapper).apply(e)))));
+    }
+  }
+
+  // XXX: public final Observable flatMapObservable(Function)
+
+  static final class SingleFlatMapPublisher<T, R> {
+    @BeforeTemplate
+    Flowable<R> before(
+        Single<T> single, Function<? super T, ? extends Publisher<? extends R>> mapper) {
+      return single.flatMapPublisher(mapper);
+    }
+
+    @AfterTemplate
+    Flowable<R> after(
+        Single<T> single, Function<? super T, ? extends Publisher<? extends R>> mapper) {
+      return RxJava2Adapter.fluxToFlowable(
+          RxJava2Adapter.singleToMono(single)
+              .flatMapMany(RxJavaReactorMigrationUtil.toJdkFunction(mapper)));
+    }
+  }
+
+  // XXX: public final Flowable flattenAsFlowable(Function)
+  // XXX: public final Observable flattenAsObservable(Function)
+  // XXX: public final Single hide()
+
+  static final class CompletableIgnoreElement<T> {
+    @BeforeTemplate
+    Completable before(Single<T> single) {
+      return single.ignoreElement();
+    }
+
+    @AfterTemplate
+    Completable after(Single<T> single) {
+      return RxJava2Adapter.monoToCompletable(RxJava2Adapter.singleToMono(single).then());
+    }
+  }
+
+  // XXX: public final Single lift(SingleOperator)
+
+  static final class SingleMap<I, T extends I, O> {
+    @BeforeTemplate
+    Single<O> before(Single<T> single, Function<? super I, ? extends O> function) {
+      return single.map(function);
+    }
+
+    @AfterTemplate
+    Single<O> after(Single<T> single, Function<I, O> function) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .map(RxJavaReactorMigrationUtil.toJdkFunction(function)));
+    }
+  }
+
+  // XXX: public final Single materialize()
+  // XXX: public final Flowable mergeWith(SingleSource)
+  // XXX: public final Single observeOn(Scheduler)
+
+  static final class SingleOnErrorResumeNext<
+      S, T extends S, R, P extends Throwable, Q extends Single<T>> {
+    @BeforeTemplate
+    Single<T> before(
+        Single<T> single,
+        Function<? super Throwable, ? extends SingleSource<? extends T>> function) {
+      return single.onErrorResumeNext(function);
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single, Function<Throwable, Q> function) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .onErrorResume(
+                  err ->
+                      RxJava2Adapter.singleToMono(
+                          RxJavaReactorMigrationUtil.<Throwable, Q>toJdkFunction(function)
+                              .apply(err))));
+    }
+  }
+
+  // XXX: public final Single onErrorResumeNext(Single)
+  // XXX: public final Single onErrorReturn(Function)
+
+  // XXX: Add test -> Works in PRP.
+  abstract static class SingleOnErrorReturn<T, S extends T> {
+    @Placeholder
+    abstract S placeholder(@MayOptionallyUse Throwable throwable);
+
+    @BeforeTemplate
+    Single<T> before(Single<T> single) {
+      return single.onErrorReturn(t -> placeholder(t));
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single).onErrorResume(t -> Mono.just(placeholder(t))));
+    }
+  }
+
+  // XXX: public final Single onErrorReturnItem(Object)
+  // XXX: public final Single onTerminateDetach()
+  // XXX: public final Flowable repeat()
+  // XXX: public final Flowable repeat(long)
+  // XXX: public final Flowable repeatUntil(BooleanSupplier)
+  // XXX: public final Flowable repeatWhen(Function)
+  // XXX: public final Single retry()
+  // XXX: public final Single retry(BiPredicate)
+  // XXX: public final Single retry(long)
+  // XXX: public final Single retry(long,Predicate)
+  // XXX: public final Single retry(Predicate)
+  // XXX: public final Single retryWhen(Function)
+
+  // XXX: Add test
+  static final class SingleSubscribe<T> {
+    @BeforeTemplate
+    Disposable before(Single<T> single) {
+      return single.subscribe();
+    }
+
+    @AfterTemplate
+    reactor.core.Disposable after(Single<T> single) {
+      return RxJava2Adapter.singleToMono(single).subscribe();
+    }
+  }
+
+  // XXX: public final Disposable subscribe(BiConsumer)
+
+  // XXX: Add test
+  static final class SingleSubscribeConsumer<T> {
+    @BeforeTemplate
+    Disposable before(Single<T> single, Consumer<? super T> consumer) {
+      return single.subscribe(consumer);
+    }
+
+    @AfterTemplate
+    reactor.core.Disposable after(Single<T> single, Consumer<? super T> consumer) {
+      return RxJava2Adapter.singleToMono(single)
+          .subscribe(RxJavaReactorMigrationUtil.toJdkConsumer(consumer));
+    }
+  }
+
+  // XXX: Add test
+  static final class SingleSubscribeTwoConsumers<T> {
+    @BeforeTemplate
+    Disposable before(
+        Single<T> single, Consumer<? super T> consumer1, Consumer<? super Throwable> consumer2) {
+      return single.subscribe(consumer1, consumer2);
+    }
+
+    @AfterTemplate
+    reactor.core.Disposable after(
+        Single<T> single, Consumer<? super T> consumer1, Consumer<? super Throwable> consumer2) {
+      return RxJava2Adapter.singleToMono(single)
+          .subscribe(
+              RxJavaReactorMigrationUtil.toJdkConsumer(consumer1),
+              RxJavaReactorMigrationUtil.toJdkConsumer(consumer2));
+    }
+  }
+
+  // XXX: public final void subscribe(SingleObserver)
+
+  // XXX: We are currently not accounting for the Schedulers.computation()
+  static final class SingleSubscribeOn<T> {
+    @BeforeTemplate
+    Single<T> before(Single<T> single) {
+      return single.subscribeOn(Schedulers.io());
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .subscribeOn(reactor.core.scheduler.Schedulers.boundedElastic()));
+    }
+  }
+
+  // XXX: public final SingleObserver subscribeWith(SingleObserver)
+  // XXX: public final Single takeUntil(CompletableSource)
+  // XXX: public final Single takeUntil(Publisher)
+  // XXX: public final Single takeUntil(SingleSource)
+
+  static final class SingleTimeoutLongTimeUnit<T> {
+    @BeforeTemplate
+    Single<T> before(Single<T> single, long timeout, TimeUnit unit) {
+      return single.timeout(timeout, unit);
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single, long timeout, TimeUnit unit) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single).timeout(Duration.of(timeout, unit.toChronoUnit())));
+    }
+  }
+
+  // XXX: public final Single timeout(long,TimeUnit,Scheduler)
+  // XXX: public final Single timeout(long,TimeUnit,Scheduler,SingleSource)
+
+  static final class SingleTimeoutLongTimeUnitSingleSource<T> {
+    @BeforeTemplate
+    Single<T> before(
+        Single<T> single, long timeout, TimeUnit unit, SingleSource<? extends T> other) {
+      return single.timeout(timeout, unit, other);
+    }
+
+    @AfterTemplate
+    Single<T> after(
+        Single<T> single, long timeout, TimeUnit unit, SingleSource<? extends T> other) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .timeout(
+                  Duration.of(timeout, unit.toChronoUnit()),
+                  RxJava2Adapter.singleToMono(Single.wrap(other))));
+    }
+  }
+  // XXX: public final Single timeout(long,TimeUnit,SingleSource)
+  // XXX: public final Object to(Function)
+  // XXX: public final Completable toCompletable()
+
+  static final class SingleToFlowable<T> {
+    @BeforeTemplate
+    Flowable<T> before(Single<T> single) {
+      return single.toFlowable();
+    }
+
+    @AfterTemplate
+    Flowable<T> after(Single<T> single) {
+      return RxJava2Adapter.fluxToFlowable(RxJava2Adapter.singleToMono(single).flux());
+    }
+  }
+
+  // XXX: public final Future toFuture()
+
+  static final class SingleToMaybe<T> {
+    @BeforeTemplate
+    Maybe<T> before(Single<T> single) {
+      return single.toMaybe();
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Single<T> single) {
+      return RxJava2Adapter.monoToMaybe(RxJava2Adapter.singleToMono(single));
+    }
+  }
+
+  // XXX: public final Observable toObservable()
+  // XXX: public final Single unsubscribeOn(Scheduler)
+
+  static final class SingleZipWith<T, R, U> {
+    @BeforeTemplate
+    Single<R> before(
+        Single<T> single,
+        SingleSource<U> source,
+        BiFunction<? super T, ? super U, ? extends R> biFunction) {
+      return single.zipWith(source, biFunction);
+    }
+
+    @AfterTemplate
+    Single<R> after(
+        Single<T> single,
+        SingleSource<U> source,
+        BiFunction<? super T, ? super U, ? extends R> biFunction) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .zipWith(
+                  RxJava2Adapter.singleToMono(Single.wrap(source)),
+                  RxJavaReactorMigrationUtil.toJdkBiFunction(biFunction)));
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  static final class SingleTestAssertResultItem<T> {
+    @BeforeTemplate
+    void before(Single<T> single, T item) throws InterruptedException {
+      Refaster.anyOf(
+          single.test().assertResult(item),
+          single.test().await().assertResult(item),
+          single.test().await().assertComplete().assertResult(item),
+          single.test().await().assertResult(item).assertComplete(),
+          single.test().await().assertValue(item),
+          single.test().await().assertComplete().assertValue(item),
+          single.test().assertValue(item),
+          single.test().await().assertValue(item).assertComplete());
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, T item) {
+      RxJava2Adapter.singleToMono(single)
+          .as(StepVerifier::create)
+          .expectNext(item)
+          .verifyComplete();
+    }
+  }
+
+  static final class SingleAssertValueSet<T> {
+    @BeforeTemplate
+    void before(Single<T> single, ImmutableSet<? extends T> set) throws InterruptedException {
+      single.test().await().assertNoErrors().assertValueSet(set).assertComplete();
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, ImmutableSet<? extends T> set) {
+      RxJava2Adapter.singleToMono(single)
+          .map(ImmutableSet::of)
+          .as(StepVerifier::create)
+          .expectNext(ImmutableSet.copyOf(set))
+          .verifyComplete();
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  static final class SingleTestAssertResult<T> {
+    @BeforeTemplate
+    void before(Single<T> single) throws InterruptedException {
+      single.test().await().assertResult();
+    }
+
+    @AfterTemplate
+    void after(Single<T> single) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class SingleTestAssertValue<T> {
+    @BeforeTemplate
+    void before(Single<T> single, Predicate<T> predicate) throws InterruptedException {
+      Refaster.anyOf(
+          single.test().await().assertValue(predicate),
+          single.test().await().assertValue(predicate).assertComplete(),
+          single.test().await().assertValue(predicate).assertNoErrors().assertComplete(),
+          single.test().await().assertComplete().assertValue(predicate));
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, Predicate<T> predicate) {
+      RxJava2Adapter.singleToMono(single)
+          .as(StepVerifier::create)
+          .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(predicate))
+          .verifyComplete();
+    }
+  }
+
+  static final class SingleTestAssertComplete<T> {
+    @BeforeTemplate
+    void before(Single<T> single) throws InterruptedException {
+      single.test().await().assertComplete();
+    }
+
+    @AfterTemplate
+    void after(Single<T> single) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class SingleTestAssertErrorClass<T> {
+    @BeforeTemplate
+    void before(Single<T> single, Class<? extends Throwable> errorClass)
+        throws InterruptedException {
+      single.test().await().assertError(errorClass);
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, Class<? extends Throwable> errorClass) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyError(errorClass);
+    }
+  }
+
+  static final class SingleTestAssertNoErrors<T> {
+    @BeforeTemplate
+    void before(Single<T> single) throws InterruptedException {
+      single.test().await().assertNoErrors();
+    }
+
+    @AfterTemplate
+    void after(Single<T> single) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class SingleTestAssertValueCount<T> {
+    @BeforeTemplate
+    void before(Single<T> single, int count) throws InterruptedException {
+      single.test().await().assertValueCount(count);
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, int count) {
+      RxJava2Adapter.singleToMono(single)
+          .as(StepVerifier::create)
+          .expectNextCount(count)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("unchecked")
+  static final class SingleTestAssertFailure<T> {
+    @BeforeTemplate
+    void before(Single<T> single, Class<? extends Throwable> error) throws InterruptedException {
+      single.test().await().assertFailure(error);
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, Class<? extends Throwable> error) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyError(error);
+    }
+  }
+
+  // XXX: Add test
+  static final class SingleTestAssertNoValues<T> {
+    @BeforeTemplate
+    void before(Single<T> single) throws InterruptedException {
+      Refaster.anyOf(
+          single.test().await().assertNoValues(),
+          single.test().await().assertNoValues().assertComplete());
+    }
+
+    @AfterTemplate
+    void after(Single<T> single) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  // XXX: Add test
+  // XXX: This introduces AssertJ dependency
+  @SuppressWarnings("unchecked")
+  static final class SingleTestAssertFailureAndMessage<T> {
+    @BeforeTemplate
+    void before(Single<T> single, Class<? extends Throwable> error, String message)
+        throws InterruptedException {
+      single.test().await().assertFailureAndMessage(error, message);
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, Class<? extends Throwable> error, String message) {
+      RxJava2Adapter.singleToMono(single)
+          .as(StepVerifier::create)
+          .expectErrorSatisfies(
+              t -> assertThat(t).isInstanceOf(error).hasMessageContaining(message))
+          .verify();
+    }
+  }
+
+  // XXX: public final TestObserver test(boolean)
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/RxJavaToReactorTemplates.java

@@ -0,0 +1,495 @@
+package tech.picnic.errorprone.refasterrules;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static com.google.common.collect.ImmutableMap.toImmutableMap;
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
+import static java.util.function.Function.identity;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.matchers.IsMethodReferenceOrLambdaHasReturnStatement;
+import com.google.errorprone.refaster.ImportPolicy;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.CanTransformToTargetType;
+import com.google.errorprone.refaster.annotation.NotMatches;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import io.reactivex.BackpressureStrategy;
+import io.reactivex.Flowable;
+import io.reactivex.functions.Action;
+import io.reactivex.functions.BiFunction;
+import io.reactivex.functions.Consumer;
+import io.reactivex.functions.Predicate;
+import java.time.Duration;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.Callable;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+/** Assorted Refaster templates for the migration of RxJava to Reactor. */
+final class RxJavaToReactorTemplates {
+  private RxJavaToReactorTemplates() {}
+
+  @SuppressWarnings("NullableProblems")
+  static final class FluxToFlowableToFlux<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, BackpressureStrategy strategy) {
+      return Refaster.anyOf(
+          RxJava2Adapter.fluxToFlowable(flux).as(RxJava2Adapter::flowableToFlux),
+          RxJava2Adapter.flowableToFlux(RxJava2Adapter.fluxToFlowable(flux)),
+          RxJava2Adapter.flowableToFlux(flux.as(RxJava2Adapter::fluxToFlowable)),
+          RxJava2Adapter.observableToFlux(flux.as(RxJava2Adapter::fluxToObservable), strategy),
+          flux.as(RxJava2Adapter::fluxToObservable)
+              .toFlowable(strategy)
+              .as(RxJava2Adapter::flowableToFlux),
+          RxJava2Adapter.observableToFlux(RxJava2Adapter.fluxToObservable(flux), strategy),
+          flux.as(RxJava2Adapter::fluxToFlowable).as(RxJava2Adapter::flowableToFlux));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux) {
+      return flux;
+    }
+  }
+
+  @SuppressWarnings("NullableProblems")
+  static final class MonoToFlowableToMono<T> {
+    @BeforeTemplate
+    Mono<T> before(Mono<T> mono) {
+      return Refaster.anyOf(
+          RxJava2Adapter.monoToMaybe(mono).as(RxJava2Adapter::maybeToMono),
+          RxJava2Adapter.maybeToMono(RxJava2Adapter.monoToMaybe(mono)),
+          RxJava2Adapter.maybeToMono(mono.as(RxJava2Adapter::monoToMaybe)),
+          mono.as(RxJava2Adapter::monoToMaybe).as(RxJava2Adapter::maybeToMono),
+          RxJava2Adapter.monoToSingle(mono).as(RxJava2Adapter::singleToMono),
+          RxJava2Adapter.singleToMono(RxJava2Adapter.monoToSingle(mono)),
+          RxJava2Adapter.singleToMono(mono.as(RxJava2Adapter::monoToSingle)),
+          mono.as(RxJava2Adapter::monoToSingle).as(RxJava2Adapter::singleToMono));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<T> mono) {
+      return mono;
+    }
+  }
+
+  @SuppressWarnings("NullableProblems")
+  static final class MonoToFlowableToMonoThen<T> {
+    @BeforeTemplate
+    Mono<Void> before(Mono<Void> mono) {
+      return Refaster.anyOf(
+          RxJava2Adapter.monoToCompletable(mono).as(RxJava2Adapter::completableToMono),
+          mono.as(RxJava2Adapter::monoToCompletable).as(RxJava2Adapter::completableToMono),
+          RxJava2Adapter.completableToMono(RxJava2Adapter.monoToCompletable(mono)),
+          RxJava2Adapter.completableToMono(mono.as(RxJava2Adapter::monoToCompletable)));
+    }
+
+    @BeforeTemplate
+    Mono<Void> before2(Mono<T> mono) {
+      return Refaster.anyOf(
+          RxJava2Adapter.completableToMono(RxJava2Adapter.monoToCompletable(mono)),
+          RxJava2Adapter.completableToMono(mono.as(RxJava2Adapter::monoToCompletable)),
+          RxJava2Adapter.monoToCompletable(mono).as(RxJava2Adapter::completableToMono));
+    }
+
+    @AfterTemplate
+    Mono<Void> after(Mono<T> mono) {
+      return mono.then();
+    }
+  }
+
+  // XXX: Add test cases
+  static final class MonoToFlowableToFlux<T> {
+    @BeforeTemplate
+    @SuppressWarnings("NullableProblems")
+    Flux<T> before(Mono<T> mono) {
+      return mono.as(RxJava2Adapter::monoToFlowable).as(RxJava2Adapter::flowableToFlux);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Mono<T> mono) {
+      return mono.flux();
+    }
+  }
+
+  static final class MonoErrorCallableSupplierUtil<T> {
+    @BeforeTemplate
+    Mono<T> before(@CanTransformToTargetType Callable<? extends Throwable> callable) {
+      return Mono.error(RxJavaReactorMigrationUtil.callableAsSupplier(callable));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Supplier<? extends Throwable> callable) {
+      return Mono.error(callable);
+    }
+  }
+
+  @SuppressWarnings({"NoFunctionalReturnType", "FunctionalInterfaceClash"})
+  static final class RemoveUtilCallable<T> {
+    @BeforeTemplate
+    Supplier<T> before(
+        @NotMatches(IsMethodReferenceOrLambdaHasReturnStatement.class) @CanTransformToTargetType
+            Callable<T> callable) {
+      return RxJavaReactorMigrationUtil.callableAsSupplier(callable);
+    }
+
+    @AfterTemplate
+    Supplier<T> before(Supplier<T> callable) {
+      return callable;
+    }
+  }
+
+  @SuppressWarnings("NoFunctionalReturnType")
+  static final class UnnecessaryFunctionConversion<I, O> {
+    @BeforeTemplate
+    java.util.function.Function<? extends I, ? extends O> before(
+        @NotMatches(IsMethodReferenceOrLambdaHasReturnStatement.class) @CanTransformToTargetType
+            io.reactivex.functions.Function<? extends I, ? extends O> function) {
+      return RxJavaReactorMigrationUtil.toJdkFunction(function);
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? extends I, ? extends O> after(
+        java.util.function.Function<? extends I, ? extends O> function) {
+      return function;
+    }
+  }
+
+  @SuppressWarnings("NoFunctionalReturnType")
+  static final class UnnecessaryBiFunctionConversion<T, U, R> {
+    @BeforeTemplate
+    java.util.function.BiFunction<? super T, ? super U, ? extends R> before(
+        @CanTransformToTargetType BiFunction<? super T, ? super U, ? extends R> zipper) {
+      return RxJavaReactorMigrationUtil.toJdkBiFunction(zipper);
+    }
+
+    @AfterTemplate
+    java.util.function.BiFunction<? super T, ? super U, ? extends R> after(
+        java.util.function.BiFunction<? super T, ? super U, ? extends R> zipper) {
+      return zipper;
+    }
+  }
+
+  @SuppressWarnings("NoFunctionalReturnType")
+  static final class UnnecessaryConsumerConversion<T> {
+    @BeforeTemplate
+    java.util.function.Consumer<? extends T> before(
+        @CanTransformToTargetType Consumer<? extends T> consumer) {
+      return RxJavaReactorMigrationUtil.toJdkConsumer(consumer);
+    }
+
+    @AfterTemplate
+    java.util.function.Consumer<? extends T> after(
+        java.util.function.Consumer<? extends T> consumer) {
+      return consumer;
+    }
+  }
+
+  static final class UnnecessaryRunnableConversion {
+    @BeforeTemplate
+    Runnable before(@CanTransformToTargetType Action action) {
+      return RxJavaReactorMigrationUtil.toRunnable(action);
+    }
+
+    @AfterTemplate
+    Runnable after(Runnable action) {
+      return action;
+    }
+  }
+
+  @SuppressWarnings("NoFunctionalReturnType")
+  static final class UnnecessaryPredicateConversion<T> {
+    @BeforeTemplate
+    java.util.function.Predicate<? extends T> before(
+        @CanTransformToTargetType Predicate<? extends T> predicate) {
+      return RxJavaReactorMigrationUtil.toJdkPredicate(predicate);
+    }
+
+    @AfterTemplate
+    java.util.function.Predicate<? extends T> after(
+        java.util.function.Predicate<? extends T> predicate) {
+      return predicate;
+    }
+  }
+
+  static final class FlowableBiFunctionRemoveUtil<T, U, R> {
+    @BeforeTemplate
+    Flowable<R> before(
+        Publisher<? extends T> source1,
+        Publisher<? extends U> source2,
+        @CanTransformToTargetType BiFunction<? super T, ? super U, ? extends R> zipper) {
+      return RxJava2Adapter.fluxToFlowable(
+          Flux.<T, U, R>zip(source1, source2, RxJavaReactorMigrationUtil.toJdkBiFunction(zipper)));
+    }
+
+    @AfterTemplate
+    Flowable<R> after(
+        Publisher<? extends T> source1,
+        Publisher<? extends U> source2,
+        java.util.function.BiFunction<? super T, ? super U, ? extends R> zipper) {
+      return RxJava2Adapter.fluxToFlowable(Flux.<T, U, R>zip(source1, source2, zipper));
+    }
+  }
+
+  ///////////////////////////////////////////
+  //////////// ASSORTED TEMPLATES ///////////
+  ///////////////////////////////////////////
+
+  static final class MonoFromNestedPublisher<T> {
+    @BeforeTemplate
+    Mono<T> before(Flux<T> flux) {
+      return Mono.from(RxJava2Adapter.fluxToFlowable(flux));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Flux<T> flux) {
+      return Mono.from(flux);
+    }
+  }
+
+  static final class FlowableToFluxWithFilter<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<T> predicate) {
+      return RxJava2Adapter.flowableToFlux(
+          flux.filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate))
+              .as(RxJava2Adapter::fluxToFlowable));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<T> predicate) {
+      return flux.filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate));
+    }
+  }
+
+  static final class ObservableToFlux<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<T> predicate, BackpressureStrategy strategy) {
+      return RxJava2Adapter.observableToFlux(
+          RxJava2Adapter.fluxToObservable(flux).filter(predicate), strategy);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<T> predicate, BackpressureStrategy strategy) {
+      return flux.filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate));
+    }
+  }
+
+  static final class MonoFromToFlowableToFlux<T> {
+    @BeforeTemplate
+    Flux<T> before(Mono<T> mono) {
+      return RxJava2Adapter.flowableToFlux(mono.as(RxJava2Adapter::monoToFlowable));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Mono<T> mono) {
+      return mono.flux();
+    }
+  }
+
+  /** Remove unnecessary {@code Mono#then}. */
+  static final class MonoThen<T, S> {
+    @BeforeTemplate
+    Mono<S> before(Mono<T> mono, Mono<S> other) {
+      return mono.then().then(other);
+    }
+
+    @AfterTemplate
+    Mono<S> after(Mono<T> mono, Mono<S> other) {
+      return mono.then(other);
+    }
+  }
+
+  /** Prefer {@link Mono#thenMany(Publisher)} without first calling {@code Mono#then}. */
+  static final class MonoThenMany<T> {
+    @BeforeTemplate
+    Flux<T> before(Mono<T> mono, Publisher<T> publisher) {
+      return mono.then().thenMany(publisher);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Mono<T> mono, Publisher<T> publisher) {
+      return mono.thenMany(publisher);
+    }
+  }
+
+  /** Remove unnecessary {@code Flux#ignoreElements} */
+  static final class FluxThen<T> {
+    @BeforeTemplate
+    Mono<Void> before(Flux<T> flux) {
+      return flux.ignoreElements().then();
+    }
+
+    @AfterTemplate
+    Mono<Void> after(Flux<T> flux) {
+      return flux.then();
+    }
+  }
+
+  static final class MonoCollectToImmutableList<T> {
+    @BeforeTemplate
+    Mono<List<T>> before(Flux<T> flux) {
+      return flux.collectList();
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.STATIC_IMPORT_ALWAYS)
+    Mono<List<T>> after(Flux<T> flux) {
+      return flux.collect(toImmutableList());
+    }
+  }
+
+  static final class MonoDefaultIfEmpty<T> {
+    @BeforeTemplate
+    Mono<T> before(Mono<T> mono, T item) {
+      return mono.switchIfEmpty(Mono.just(item));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<T> mono, T item) {
+      return mono.defaultIfEmpty(item);
+    }
+  }
+
+  static final class FluxDefaultIfEmpty<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, T item) {
+      return flux.switchIfEmpty(Flux.just(item));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, T item) {
+      return flux.defaultIfEmpty(item);
+    }
+  }
+
+  /** Remove unnecessary {@code Mono#then} */
+  static final class MonoVoid {
+    @BeforeTemplate
+    Mono<Void> before(Mono<Void> mono) {
+      return mono.then();
+    }
+
+    @AfterTemplate
+    Mono<Void> after(Mono<Void> mono) {
+      return mono;
+    }
+  }
+
+  static final class FlatMapFluxFromArray<T> {
+    @BeforeTemplate
+    @SuppressWarnings("unchecked")
+    Flux<Object> before(Flux<T[]> flux) {
+      return flux.flatMap(Flowable::fromArray);
+    }
+
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    @AfterTemplate
+    Flux<Object> after(Flux<T[]> flux) {
+      return flux.flatMap(Flux::fromArray);
+    }
+  }
+
+  // XXX: Move this to correct class later on.
+  static final class FluxToImmutableSet<T> {
+    @BeforeTemplate
+    Mono<ImmutableSet<T>> before(Flux<T> flux) {
+      return flux.collect(toImmutableList()).map(ImmutableSet::copyOf);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.STATIC_IMPORT_ALWAYS)
+    Mono<ImmutableSet<T>> after(Flux<T> flux) {
+      return flux.collect(toImmutableSet());
+    }
+  }
+
+  static final class MonoBlock<T> {
+    @BeforeTemplate
+    T before(Mono<T> mono, Duration timeout) {
+      return mono.timeout(timeout).block();
+    }
+
+    @AfterTemplate
+    T after(Mono<T> mono, Duration timeout) {
+      return mono.block(timeout);
+    }
+  }
+
+  ImmutableSet<Flux<String>> testConcatMapIterable() {
+    return ImmutableSet.of(
+        Flux.just(ImmutableList.of("1")).flatMap(Flux::fromIterable),
+        Flux.just(ImmutableList.of("2")).concatMap(Flux::fromIterable));
+  }
+
+  static final class FluxCollectBlock<T> {
+    @BeforeTemplate
+    ImmutableList<T> before(Flux<T> flux) {
+      return ImmutableList.copyOf(flux.toIterable());
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.STATIC_IMPORT_ALWAYS)
+    ImmutableList<T> after(Flux<T> flux) {
+      return flux.collect(toImmutableList()).block();
+    }
+  }
+
+  static final class ConcatMapIterable<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<? extends Iterable<? extends T>> flux) {
+      return Refaster.anyOf(flux.flatMap(Flux::fromIterable), flux.concatMap(Flux::fromIterable));
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.STATIC_IMPORT_ALWAYS)
+    Flux<T> after(Flux<? extends Iterable<? extends T>> flux) {
+      return flux.concatMapIterable(identity());
+    }
+  }
+
+  static final class CollectToImmutableMap<K, V> {
+    @BeforeTemplate
+    Mono<Map<K, V>> before(Flux<V> flux, Function<? super V, ? extends K> keyExtractor) {
+      return flux.collectMap(keyExtractor);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.STATIC_IMPORT_ALWAYS)
+    Mono<Map<K, V>> after(Flux<V> flux, Function<? super V, ? extends K> keyExtractor) {
+      return flux.collect(toImmutableMap(keyExtractor, identity()));
+    }
+  }
+
+  //  /** Remove unnecessary {@code Flux#next}. This is not *strictly* behavior preserving. */
+  //  static final class FluxSingle<T> {
+  //    @BeforeTemplate
+  //    Mono<T> before(Flux<T> flux) {
+  //      return flux.next().single();
+  //    }
+  //
+  //    @AfterTemplate
+  //    Mono<T> after(Flux<T> flux) {
+  //      return flux.single();
+  //    }
+  //  }
+
+  // XXX: Find out how we can use this in the future.
+  //  static final class RemoveRedundantCast<T> {
+  //    @BeforeTemplate
+  //    T before(T object) {
+  //      return (T) object;
+  //    }
+  //
+  //    @AfterTemplate
+  //    T after(T object) {
+  //      return object;
+  //    }
+  //  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/RxJavaToReactorUnwrapTemplates.java

@@ -0,0 +1,441 @@
+package tech.picnic.errorprone.refasterrules;
+
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.MayOptionallyUse;
+import com.google.errorprone.refaster.annotation.Placeholder;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Single;
+import io.reactivex.SingleSource;
+import io.reactivex.functions.Function;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+/** Templates to clean up nested lambdas. */
+@SuppressWarnings({"Convert2MethodRef", "NoFunctionalReturnType"})
+final class RxJavaToReactorUnwrapTemplates {
+  private RxJavaToReactorUnwrapTemplates() {}
+
+  // XXX: Add test
+  abstract static class FlowableConcatMapCompletableUnwrapLambda<T> {
+    @Placeholder
+    abstract Mono<?> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Publisher<?>> before() {
+      return e ->
+          RxJava2Adapter.completableToMono(
+              RxJavaReactorMigrationUtil.toJdkFunction(
+                      (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                  .apply(e));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, ? extends Publisher<?>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  abstract static class MaybeFlatMapUnwrapLambda<I, T extends I, O> {
+    @Placeholder
+    abstract Mono<? extends O> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    @SuppressWarnings("unchecked")
+    java.util.function.Function<? super T, ? extends Mono<? extends O>> before() {
+      return Refaster.anyOf(
+          v ->
+              RxJava2Adapter.maybeToMono(
+                  (Maybe<O>)
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (T ident) -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(v)),
+          v ->
+              RxJava2Adapter.maybeToMono(
+                  RxJavaReactorMigrationUtil.toJdkFunction(
+                          (T ident) -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                      .apply(v)));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends O>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  abstract static class MaybeFlatMapSingleElementUnwrapLambda<T, R> {
+    @Placeholder
+    abstract Mono<R> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<T, ? extends Mono<? extends R>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.singleToMono(
+                  Single.wrap(
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (Function<T, SingleSource<R>>)
+                                  (T ident) -> RxJava2Adapter.monoToSingle(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.singleToMono(
+                  Single.wrap(
+                      RxJavaReactorMigrationUtil.<T, SingleSource<R>>toJdkFunction(
+                              (T ident) -> RxJava2Adapter.monoToSingle(placeholder(ident)))
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, ? extends Mono<? extends R>> after() {
+      return e -> placeholder(e);
+    }
+  }
+
+  // XXX: Add test
+  abstract static class SingleFlatMapMaybeUnwrapLambda<T, R> {
+    @Placeholder
+    abstract Mono<R> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends R>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.maybeToMono(
+                  Maybe.wrap(
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (Function<T, MaybeSource<R>>)
+                                  (T ident) -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.maybeToMono(
+                  Maybe.wrap(
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (Function<T, MaybeSource<R>>)
+                                  ident -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.maybeToMono(
+                  Maybe.wrap(
+                      RxJavaReactorMigrationUtil.<T, MaybeSource<R>>toJdkFunction(
+                              ident -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends R>> after() {
+      return e -> placeholder(e);
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("unchecked")
+  abstract static class SingleOnResumeUnwrapLambda<T, R> {
+    @Placeholder
+    abstract Mono<? extends R> placeholder(@MayOptionallyUse Throwable input);
+
+    @BeforeTemplate
+    java.util.function.Function<? extends Throwable, ? extends Mono<? extends R>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.singleToMono(
+                  RxJavaReactorMigrationUtil.toJdkFunction(
+                          ident -> RxJava2Adapter.monoToSingle(placeholder(e)))
+                      .apply(e)),
+          e ->
+              RxJava2Adapter.singleToMono(
+                  Single.wrap(
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (Function<Throwable, ? extends SingleSource<? extends R>>)
+                                  placeholder(e))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.singleToMono(
+                  Single.wrap(
+                      RxJavaReactorMigrationUtil.<Throwable, SingleSource<R>>toJdkFunction(
+                              (Function<Throwable, SingleSource<R>>) placeholder(e))
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<Throwable, ? extends Mono<? extends R>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("unchecked")
+  abstract static class SingleOnResumeUnwrapLambdaSpecialCase<T, R> {
+    @Placeholder
+    abstract Mono<R> placeholder(@MayOptionallyUse Throwable input);
+
+    @BeforeTemplate
+    java.util.function.Function<? extends Throwable, ? extends Mono<? extends R>> before() {
+      return e ->
+          RxJava2Adapter.singleToMono(
+              RxJavaReactorMigrationUtil.<Throwable, Single<R>>toJdkFunction(
+                      t -> RxJava2Adapter.monoToSingle(placeholder(t)))
+                  .apply(e));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<Throwable, ? extends Mono<? extends R>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  abstract static class FlowableConcatMapMaybeDelayErrorUnwrapLambda<T, R> {
+    @Placeholder
+    abstract Mono<R> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Publisher<? extends R>> after() {
+      return Refaster.anyOf(
+          e ->
+              Maybe.wrap(
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (Function<T, MaybeSource<R>>)
+                                  ident -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(e))
+                  .toFlowable(),
+          e ->
+              Maybe.wrap(
+                      RxJavaReactorMigrationUtil.<T, MaybeSource<R>>toJdkFunction(
+                              ident -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(e))
+                  .toFlowable());
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Publisher<? extends R>> before() {
+      return e -> placeholder(e);
+    }
+  }
+
+  // XXX: Add test
+  abstract static class FlowableFlatMapCompletableUnwrapLambda<T> {
+    @Placeholder
+    abstract Mono<?> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Publisher<? extends Void>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                              (Function<T, Completable>)
+                                  (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                          (Function<T, Completable>)
+                              (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                      .apply(e)),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                              (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                              (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                          (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                      .apply(e)));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, Mono<?>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Improve naming and add test case
+  abstract static class FlowableUnwrapLambda<T> {
+    @Placeholder
+    abstract Completable placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<T, Publisher<? extends Void>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                              (Function<T, CompletableSource>) v -> placeholder(v))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                              v -> placeholder(v))
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, Mono<? extends Void>> after() {
+      return v -> RxJava2Adapter.completableToMono(Completable.wrap(placeholder(v)));
+    }
+  }
+
+  abstract static class FlowableFlatMapUnwrapLambda<T> {
+    @Placeholder
+    abstract CompletableSource placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<T, ? extends Publisher<? extends Void>> before() {
+      return e ->
+          RxJava2Adapter.completableToMono(
+              Completable.wrap(
+                  RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                          (Function<T, CompletableSource>) v -> placeholder(v))
+                      .apply(e)));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, Mono<? extends Void>> after() {
+      return v -> RxJava2Adapter.completableToMono(Completable.wrap(placeholder(v)));
+    }
+  }
+
+  abstract static class UnwrapCompletableExtendsMono<T, R> {
+    @Placeholder
+    abstract Mono<? extends R> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends Void>> before() {
+      return e ->
+          RxJava2Adapter.completableToMono(
+              Completable.wrap(
+                  RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                          (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                      .apply(e)));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, Mono<? extends R>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  abstract static class SingleFlatMapUnwrapLambda<T, R> {
+    @Placeholder
+    abstract Mono<? extends R> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<T, ? extends Mono<? extends R>> before() {
+      return v ->
+          RxJava2Adapter.singleToMono(
+              (Single<? extends R>)
+                  RxJavaReactorMigrationUtil.toJdkFunction(
+                          (T ident) -> RxJava2Adapter.monoToSingle(placeholder(ident)))
+                      .apply(v));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, ? extends Mono<? extends R>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  abstract static class SingleRemoveLambdaWithCast<T> {
+    @Placeholder
+    abstract Mono<?> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Publisher<? extends Void>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                              (Function<T, Completable>)
+                                  v -> placeholder(v).as(RxJava2Adapter::monoToCompletable))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                              (Function<T, Completable>)
+                                  v -> RxJava2Adapter.monoToCompletable(placeholder(v)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                              v -> RxJava2Adapter.monoToCompletable(placeholder(v)))
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Mono<?>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  abstract static class SingleRemoveLambdaWithCompletable<T> {
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends Void>> before(
+        Completable completable) {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                              (Function<T, CompletableSource>) v -> completable)
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                              v -> completable)
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends Void>> after(
+        Completable completable) {
+      return v -> RxJava2Adapter.completableToMono(completable);
+    }
+  }
+
+  // XXX: Verify if this template still flags other cases than the one above.
+  abstract static class SingleRemoveLambdaWithCompletableExtra<T> {
+    @Placeholder
+    abstract Completable placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends Void>> before() {
+      return e ->
+          RxJava2Adapter.completableToMono(
+              Completable.wrap(
+                  RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                          (Function<T, CompletableSource>) v -> placeholder(v))
+                      .apply(e)));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends Void>> after() {
+      return v -> RxJava2Adapter.completableToMono(placeholder(v));
+    }
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/StreamRules.java

@@ -3,21 +3,43 @@ package tech.picnic.errorprone.refasterrules;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 import static java.util.Comparator.naturalOrder;
 import static java.util.Comparator.reverseOrder;
+import static java.util.function.Function.identity;
 import static java.util.function.Predicate.not;
+import static java.util.stream.Collectors.counting;
+import static java.util.stream.Collectors.filtering;
+import static java.util.stream.Collectors.flatMapping;
 import static java.util.stream.Collectors.joining;
+import static java.util.stream.Collectors.mapping;
+import static java.util.stream.Collectors.maxBy;
+import static java.util.stream.Collectors.minBy;
+import static java.util.stream.Collectors.reducing;
+import static java.util.stream.Collectors.summarizingDouble;
+import static java.util.stream.Collectors.summarizingInt;
+import static java.util.stream.Collectors.summarizingLong;
+import static java.util.stream.Collectors.summingDouble;
+import static java.util.stream.Collectors.summingInt;
+import static java.util.stream.Collectors.summingLong;
 
 import com.google.common.collect.Streams;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import com.google.errorprone.refaster.annotation.Matches;
 import com.google.errorprone.refaster.annotation.MayOptionallyUse;
+import com.google.errorprone.refaster.annotation.NotMatches;
 import com.google.errorprone.refaster.annotation.Placeholder;
+import com.google.errorprone.refaster.annotation.Repeated;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Comparator;
+import java.util.DoubleSummaryStatistics;
+import java.util.IntSummaryStatistics;
+import java.util.LongSummaryStatistics;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.function.BinaryOperator;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.ToDoubleFunction;
@@ -28,6 +50,7 @@ import java.util.stream.Collectors;
 import java.util.stream.Stream;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 import tech.picnic.errorprone.refaster.matchers.IsLambdaExpressionOrMethodReference;
+import tech.picnic.errorprone.refaster.matchers.IsRefasterAsVarargs;
 
 /** Refaster rules related to expressions dealing with {@link Stream}s. */
 @OnlineDocumentation
@@ -82,12 +105,9 @@ final class StreamRules {
    * Prefer {@link Arrays#stream(Object[])} over {@link Stream#of(Object[])}, as the former is
    * clearer.
    */
-  // XXX: Introduce a `Matcher` that identifies `Refaster.asVarargs(...)` invocations and annotate
-  // the `array` parameter as `@NotMatches(IsRefasterAsVarargs.class)`. Then elsewhere
-  // `@SuppressWarnings("StreamOfArray")` annotations can be dropped.
   static final class StreamOfArray<T> {
     @BeforeTemplate
-    Stream<T> before(T[] array) {
+    Stream<T> before(@NotMatches(IsRefasterAsVarargs.class) T[] array) {
       return Stream.of(array);
     }
 
@@ -105,6 +125,7 @@ final class StreamRules {
     }
 
     @AfterTemplate
+    @CanIgnoreReturnValue
     Stream<T> after(Stream<T> stream) {
       return stream;
     }
@@ -228,14 +249,18 @@ final class StreamRules {
   }
 
   /** In order to test whether a stream has any element, simply try to find one. */
+  // XXX: This rule assumes that any matched `Collector` does not perform any filtering.
+  // (Perhaps we could add a `@Matches` guard that validates that the collector expression does not
+  // contain a `Collectors#filtering` call. That'd still not be 100% accurate, though.)
   static final class StreamIsEmpty<T> {
     @BeforeTemplate
-    boolean before(Stream<T> stream) {
+    boolean before(Stream<T> stream, Collector<? super T, ?, ? extends Collection<?>> collector) {
       return Refaster.anyOf(
           stream.count() == 0,
           stream.count() <= 0,
           stream.count() < 1,
-          stream.findFirst().isEmpty());
+          stream.findFirst().isEmpty(),
+          stream.collect(collector).isEmpty());
     }
 
     @AfterTemplate
@@ -263,9 +288,12 @@ final class StreamRules {
 
   static final class StreamMin<T> {
     @BeforeTemplate
+    @SuppressWarnings("java:S4266" /* This violation will be rewritten. */)
     Optional<T> before(Stream<T> stream, Comparator<? super T> comparator) {
       return Refaster.anyOf(
-          stream.max(comparator.reversed()), stream.sorted(comparator).findFirst());
+          stream.max(comparator.reversed()),
+          stream.sorted(comparator).findFirst(),
+          stream.collect(minBy(comparator)));
     }
 
     @AfterTemplate
@@ -289,9 +317,12 @@ final class StreamRules {
 
   static final class StreamMax<T> {
     @BeforeTemplate
+    @SuppressWarnings("java:S4266" /* This violation will be rewritten. */)
     Optional<T> before(Stream<T> stream, Comparator<? super T> comparator) {
       return Refaster.anyOf(
-          stream.min(comparator.reversed()), Streams.findLast(stream.sorted(comparator)));
+          stream.min(comparator.reversed()),
+          Streams.findLast(stream.sorted(comparator)),
+          stream.collect(maxBy(comparator)));
     }
 
     @AfterTemplate
@@ -316,6 +347,7 @@ final class StreamRules {
   /** Prefer {@link Stream#noneMatch(Predicate)} over more contrived alternatives. */
   static final class StreamNoneMatch<T> {
     @BeforeTemplate
+    @SuppressWarnings("java:S4034" /* This violation will be rewritten. */)
     boolean before(Stream<T> stream, Predicate<? super T> predicate) {
       return Refaster.anyOf(
           !stream.anyMatch(predicate),
@@ -323,6 +355,14 @@ final class StreamRules {
           stream.filter(predicate).findAny().isEmpty());
     }
 
+    @BeforeTemplate
+    boolean before2(
+        Stream<T> stream,
+        @Matches(IsLambdaExpressionOrMethodReference.class)
+            Function<? super T, Boolean> predicate) {
+      return stream.map(predicate).noneMatch(Refaster.anyOf(Boolean::booleanValue, b -> b));
+    }
+
     @AfterTemplate
     boolean after(Stream<T> stream, Predicate<? super T> predicate) {
       return stream.noneMatch(predicate);
@@ -347,11 +387,20 @@ final class StreamRules {
   /** Prefer {@link Stream#anyMatch(Predicate)} over more contrived alternatives. */
   static final class StreamAnyMatch<T> {
     @BeforeTemplate
+    @SuppressWarnings("java:S4034" /* This violation will be rewritten. */)
     boolean before(Stream<T> stream, Predicate<? super T> predicate) {
       return Refaster.anyOf(
           !stream.noneMatch(predicate), stream.filter(predicate).findAny().isPresent());
     }
 
+    @BeforeTemplate
+    boolean before2(
+        Stream<T> stream,
+        @Matches(IsLambdaExpressionOrMethodReference.class)
+            Function<? super T, Boolean> predicate) {
+      return stream.map(predicate).anyMatch(Refaster.anyOf(Boolean::booleanValue, b -> b));
+    }
+
     @AfterTemplate
     boolean after(Stream<T> stream, Predicate<? super T> predicate) {
       return stream.anyMatch(predicate);
@@ -364,6 +413,14 @@ final class StreamRules {
       return stream.noneMatch(Refaster.anyOf(not(predicate), predicate.negate()));
     }
 
+    @BeforeTemplate
+    boolean before2(
+        Stream<T> stream,
+        @Matches(IsLambdaExpressionOrMethodReference.class)
+            Function<? super T, Boolean> predicate) {
+      return stream.map(predicate).allMatch(Refaster.anyOf(Boolean::booleanValue, b -> b));
+    }
+
     @AfterTemplate
     boolean after(Stream<T> stream, Predicate<? super T> predicate) {
       return stream.allMatch(predicate);
@@ -387,7 +444,13 @@ final class StreamRules {
 
   static final class StreamMapToIntSum<T> {
     @BeforeTemplate
-    int before(
+    @SuppressWarnings("java:S4266" /* This violation will be rewritten. */)
+    long before(Stream<T> stream, ToIntFunction<T> mapper) {
+      return stream.collect(summingInt(mapper));
+    }
+
+    @BeforeTemplate
+    int before2(
         Stream<T> stream,
         @Matches(IsLambdaExpressionOrMethodReference.class) Function<? super T, Integer> mapper) {
       return stream.map(mapper).reduce(0, Integer::sum);
@@ -401,7 +464,13 @@ final class StreamRules {
 
   static final class StreamMapToDoubleSum<T> {
     @BeforeTemplate
-    double before(
+    @SuppressWarnings("java:S4266" /* This violation will be rewritten. */)
+    double before(Stream<T> stream, ToDoubleFunction<T> mapper) {
+      return stream.collect(summingDouble(mapper));
+    }
+
+    @BeforeTemplate
+    double before2(
         Stream<T> stream,
         @Matches(IsLambdaExpressionOrMethodReference.class) Function<? super T, Double> mapper) {
       return stream.map(mapper).reduce(0.0, Double::sum);
@@ -415,7 +484,13 @@ final class StreamRules {
 
   static final class StreamMapToLongSum<T> {
     @BeforeTemplate
-    long before(
+    @SuppressWarnings("java:S4266" /* This violation will be rewritten. */)
+    long before(Stream<T> stream, ToLongFunction<T> mapper) {
+      return stream.collect(summingLong(mapper));
+    }
+
+    @BeforeTemplate
+    long before2(
         Stream<T> stream,
         @Matches(IsLambdaExpressionOrMethodReference.class) Function<? super T, Long> mapper) {
       return stream.map(mapper).reduce(0L, Long::sum);
@@ -426,4 +501,142 @@ final class StreamRules {
       return stream.mapToLong(mapper).sum();
     }
   }
+
+  static final class StreamMapToIntSummaryStatistics<T> {
+    @BeforeTemplate
+    IntSummaryStatistics before(Stream<T> stream, ToIntFunction<T> mapper) {
+      return stream.collect(summarizingInt(mapper));
+    }
+
+    @AfterTemplate
+    IntSummaryStatistics after(Stream<T> stream, ToIntFunction<T> mapper) {
+      return stream.mapToInt(mapper).summaryStatistics();
+    }
+  }
+
+  static final class StreamMapToDoubleSummaryStatistics<T> {
+    @BeforeTemplate
+    DoubleSummaryStatistics before(Stream<T> stream, ToDoubleFunction<T> mapper) {
+      return stream.collect(summarizingDouble(mapper));
+    }
+
+    @AfterTemplate
+    DoubleSummaryStatistics after(Stream<T> stream, ToDoubleFunction<T> mapper) {
+      return stream.mapToDouble(mapper).summaryStatistics();
+    }
+  }
+
+  static final class StreamMapToLongSummaryStatistics<T> {
+    @BeforeTemplate
+    LongSummaryStatistics before(Stream<T> stream, ToLongFunction<T> mapper) {
+      return stream.collect(summarizingLong(mapper));
+    }
+
+    @AfterTemplate
+    LongSummaryStatistics after(Stream<T> stream, ToLongFunction<T> mapper) {
+      return stream.mapToLong(mapper).summaryStatistics();
+    }
+  }
+
+  static final class StreamCount<T> {
+    @BeforeTemplate
+    @SuppressWarnings("java:S4266" /* This violation will be rewritten. */)
+    long before(Stream<T> stream) {
+      return stream.collect(counting());
+    }
+
+    @AfterTemplate
+    long after(Stream<T> stream) {
+      return stream.count();
+    }
+  }
+
+  static final class StreamReduce<T> {
+    @BeforeTemplate
+    @SuppressWarnings("java:S4266" /* This violation will be rewritten. */)
+    Optional<T> before(Stream<T> stream, BinaryOperator<T> accumulator) {
+      return stream.collect(reducing(accumulator));
+    }
+
+    @AfterTemplate
+    Optional<T> after(Stream<T> stream, BinaryOperator<T> accumulator) {
+      return stream.reduce(accumulator);
+    }
+  }
+
+  static final class StreamReduceWithIdentity<T> {
+    @BeforeTemplate
+    @SuppressWarnings("java:S4266" /* This violation will be rewritten. */)
+    T before(Stream<T> stream, T identity, BinaryOperator<T> accumulator) {
+      return stream.collect(reducing(identity, accumulator));
+    }
+
+    @AfterTemplate
+    T after(Stream<T> stream, T identity, BinaryOperator<T> accumulator) {
+      return stream.reduce(identity, accumulator);
+    }
+  }
+
+  static final class StreamFilterCollect<T, R> {
+    @BeforeTemplate
+    R before(
+        Stream<T> stream, Predicate<? super T> predicate, Collector<? super T, ?, R> collector) {
+      return stream.collect(filtering(predicate, collector));
+    }
+
+    @AfterTemplate
+    R after(
+        Stream<T> stream, Predicate<? super T> predicate, Collector<? super T, ?, R> collector) {
+      return stream.filter(predicate).collect(collector);
+    }
+  }
+
+  static final class StreamMapCollect<T, U, R> {
+    @BeforeTemplate
+    @SuppressWarnings("java:S4266" /* This violation will be rewritten. */)
+    R before(
+        Stream<T> stream,
+        Function<? super T, ? extends U> mapper,
+        Collector<? super U, ?, R> collector) {
+      return stream.collect(mapping(mapper, collector));
+    }
+
+    @AfterTemplate
+    R after(
+        Stream<T> stream,
+        Function<? super T, ? extends U> mapper,
+        Collector<? super U, ?, R> collector) {
+      return stream.map(mapper).collect(collector);
+    }
+  }
+
+  static final class StreamFlatMapCollect<T, U, R> {
+    @BeforeTemplate
+    R before(
+        Stream<T> stream,
+        Function<? super T, ? extends Stream<? extends U>> mapper,
+        Collector<? super U, ?, R> collector) {
+      return stream.collect(flatMapping(mapper, collector));
+    }
+
+    @AfterTemplate
+    R after(
+        Stream<T> stream,
+        Function<? super T, ? extends Stream<? extends U>> mapper,
+        Collector<? super U, ?, R> collector) {
+      return stream.flatMap(mapper).collect(collector);
+    }
+  }
+
+  static final class StreamsConcat<T> {
+    @BeforeTemplate
+    Stream<T> before(@Repeated Stream<T> stream) {
+      return Stream.of(Refaster.asVarargs(stream)).flatMap(Refaster.anyOf(identity(), s -> s));
+    }
+
+    @AfterTemplate
+    Stream<T> after(@Repeated Stream<T> stream) {
+      return Streams.concat(Refaster.asVarargs(stream));
+    }
+  }
 }

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/StringRules.java

@@ -1,6 +1,8 @@
 package tech.picnic.errorprone.refasterrules;
 
+import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 import static java.nio.charset.StandardCharsets.UTF_8;
+import static java.util.function.Predicate.not;
 import static java.util.stream.Collectors.joining;
 
 import com.google.common.base.Joiner;
@@ -11,21 +13,23 @@ import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.AlsoNegation;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.function.Function;
+import java.util.function.Predicate;
 import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to expressions dealing with {@link String}s. */
-// XXX: Should we prefer `s -> !s.isEmpty()` or `not(String::isEmpty)`?
 @OnlineDocumentation
 final class StringRules {
   private StringRules() {}
 
   /** Prefer {@link String#isEmpty()} over alternatives that consult the string's length. */
+  // XXX: Once we target JDK 15+, generalize this rule to cover all `CharSequence` subtypes.
   static final class StringIsEmpty {
     @BeforeTemplate
     boolean before(String str) {
@@ -39,6 +43,37 @@ final class StringRules {
     }
   }
 
+  /** Prefer a method reference to {@link String#isEmpty()} over the equivalent lambda function. */
+  // XXX: Once we target JDK 15+, generalize this rule to cover all `CharSequence` subtypes.
+  // XXX: As it stands, this rule is a special case of what `MethodReferenceUsage` tries to achieve.
+  // If/when `MethodReferenceUsage` becomes production ready, we should simply drop this check.
+  static final class StringIsEmptyPredicate {
+    @BeforeTemplate
+    Predicate<String> before() {
+      return s -> s.isEmpty();
+    }
+
+    @AfterTemplate
+    Predicate<String> after() {
+      return String::isEmpty;
+    }
+  }
+
+  /** Prefer a method reference to {@link String#isEmpty()} over the equivalent lambda function. */
+  // XXX: Once we target JDK 15+, generalize this rule to cover all `CharSequence` subtypes.
+  static final class StringIsNotEmptyPredicate {
+    @BeforeTemplate
+    Predicate<String> before() {
+      return s -> !s.isEmpty();
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    Predicate<String> after() {
+      return not(String::isEmpty);
+    }
+  }
+
   /** Prefer {@link Strings#isNullOrEmpty(String)} over the more verbose alternative. */
   static final class StringIsNullOrEmpty {
     @BeforeTemplate
@@ -65,7 +100,7 @@ final class StringRules {
 
     @AfterTemplate
     Optional<String> after(String str) {
-      return Optional.ofNullable(str).filter(s -> !s.isEmpty());
+      return Optional.ofNullable(str).filter(not(String::isEmpty));
     }
   }
 
@@ -76,8 +111,9 @@ final class StringRules {
     }
 
     @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
     Optional<String> after(Optional<String> optional) {
-      return optional.filter(s -> !s.isEmpty());
+      return optional.filter(not(String::isEmpty));
     }
   }
 

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/SuggestedFixRules.java

@@ -0,0 +1,106 @@
+package tech.picnic.errorprone.refasterrules;
+
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.sun.source.tree.Tree;
+import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+
+/** Refaster rules related to expressions dealing with {@link SuggestedFix}es. */
+@OnlineDocumentation
+final class SuggestedFixRules {
+  private SuggestedFixRules() {}
+
+  /** Prefer {@link SuggestedFix#delete(Tree)} over more contrived alternatives. */
+  static final class SuggestedFixDelete {
+    @BeforeTemplate
+    SuggestedFix before(Tree tree) {
+      return SuggestedFix.builder().delete(tree).build();
+    }
+
+    @AfterTemplate
+    SuggestedFix after(Tree tree) {
+      return SuggestedFix.delete(tree);
+    }
+  }
+
+  /** Prefer {@link SuggestedFix#replace(Tree, String)}} over more contrived alternatives. */
+  static final class SuggestedFixReplaceTree {
+    @BeforeTemplate
+    SuggestedFix before(Tree tree, String replaceWith) {
+      return SuggestedFix.builder().replace(tree, replaceWith).build();
+    }
+
+    @AfterTemplate
+    SuggestedFix after(Tree tree, String replaceWith) {
+      return SuggestedFix.replace(tree, replaceWith);
+    }
+  }
+
+  /** Prefer {@link SuggestedFix#replace(int, int, String)}} over more contrived alternatives. */
+  static final class SuggestedFixReplaceStartEnd {
+    @BeforeTemplate
+    SuggestedFix before(int start, int end, String replaceWith) {
+      return SuggestedFix.builder().replace(start, end, replaceWith).build();
+    }
+
+    @AfterTemplate
+    SuggestedFix after(int start, int end, String replaceWith) {
+      return SuggestedFix.replace(start, end, replaceWith);
+    }
+  }
+
+  /**
+   * Prefer {@link SuggestedFix#replace(Tree, String, int, int)}} over more contrived alternatives.
+   */
+  static final class SuggestedFixReplaceTreeStartEnd {
+    @BeforeTemplate
+    SuggestedFix before(Tree tree, String replaceWith, int start, int end) {
+      return SuggestedFix.builder().replace(tree, replaceWith, start, end).build();
+    }
+
+    @AfterTemplate
+    SuggestedFix after(Tree tree, String replaceWith, int start, int end) {
+      return SuggestedFix.replace(tree, replaceWith, start, end);
+    }
+  }
+
+  /** Prefer {@link SuggestedFix#swap(Tree, Tree)} over more contrived alternatives. */
+  static final class SuggestedFixSwap {
+    @BeforeTemplate
+    SuggestedFix before(Tree tree1, Tree tree2) {
+      return SuggestedFix.builder().swap(tree1, tree2).build();
+    }
+
+    @AfterTemplate
+    SuggestedFix after(Tree tree1, Tree tree2) {
+      return SuggestedFix.swap(tree1, tree2);
+    }
+  }
+
+  /** Prefer {@link SuggestedFix#prefixWith(Tree, String)} over more contrived alternatives. */
+  static final class SuggestedFixPrefixWith {
+    @BeforeTemplate
+    SuggestedFix before(Tree tree, String prefix) {
+      return SuggestedFix.builder().prefixWith(tree, prefix).build();
+    }
+
+    @AfterTemplate
+    SuggestedFix after(Tree tree, String prefix) {
+      return SuggestedFix.prefixWith(tree, prefix);
+    }
+  }
+
+  /** Prefer {@link SuggestedFix#postfixWith(Tree, String)}} over more contrived alternatives. */
+  static final class SuggestedFixPostfixWith {
+    @BeforeTemplate
+    SuggestedFix before(Tree tree, String postfix) {
+      return SuggestedFix.builder().postfixWith(tree, postfix).build();
+    }
+
+    @AfterTemplate
+    SuggestedFix after(Tree tree, String postfix) {
+      return SuggestedFix.postfixWith(tree, postfix);
+    }
+  }
+}

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/AssertJIsNullTest.java

@@ -1,8 +1,7 @@
 package tech.picnic.errorprone.bugpatterns;
 
-import static com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode.TEXT_MATCH;
-
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
 import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
@@ -54,6 +53,6 @@ final class AssertJIsNullTest {
             "    assertThat(\"foo\").isNull();",
             "  }",
             "}")
-        .doTest(TEXT_MATCH);
+        .doTest(TestMode.TEXT_MATCH);
   }
 }

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/AssociativeMethodInvocationTest.java

@@ -0,0 +1,110 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Test;
+
+final class AssociativeMethodInvocationTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(AssociativeMethodInvocation.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import com.google.common.collect.ImmutableList;",
+            "import com.google.errorprone.matchers.Matchers;",
+            "import com.google.errorprone.refaster.Refaster;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Matchers.allOf();",
+            "    Matchers.anyOf();",
+            "    Refaster.anyOf();",
+            "",
+            "    Matchers.allOf((t, s) -> true);",
+            "    Matchers.anyOf((t, s) -> true);",
+            "    Refaster.anyOf(0);",
+            "",
+            "    Matchers.allOf(Matchers.anyOf((t, s) -> true));",
+            "    Matchers.anyOf(Matchers.allOf((t, s) -> true));",
+            "    Refaster.anyOf(Matchers.allOf((t, s) -> true));",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Matchers.allOf(Matchers.allOf((t, s) -> true));",
+            "    // BUG: Diagnostic contains:",
+            "    Matchers.anyOf(Matchers.anyOf((t, s) -> true));",
+            "    // BUG: Diagnostic contains:",
+            "    Refaster.anyOf(Refaster.anyOf(0));",
+            "",
+            "    Matchers.allOf(Matchers.allOf(ImmutableList.of((t, s) -> true)));",
+            "    Matchers.anyOf(Matchers.anyOf(ImmutableList.of((t, s) -> true)));",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Matchers.allOf(",
+            "        (t, s) -> true, Matchers.allOf((t, s) -> false, (t, s) -> true), (t, s) -> false);",
+            "    // BUG: Diagnostic contains:",
+            "    Matchers.anyOf(",
+            "        (t, s) -> true, Matchers.anyOf((t, s) -> false, (t, s) -> true), (t, s) -> false);",
+            "    // BUG: Diagnostic contains:",
+            "    Refaster.anyOf(0, Refaster.anyOf(1, 2), 3);",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    BugCheckerRefactoringTestHelper.newInstance(AssociativeMethodInvocation.class, getClass())
+        .addInputLines(
+            "A.java",
+            "import com.google.errorprone.matchers.Matchers;",
+            "import com.google.errorprone.refaster.Refaster;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Matchers.allOf(Matchers.allOf());",
+            "    Matchers.anyOf(Matchers.anyOf());",
+            "    Refaster.anyOf(Refaster.anyOf());",
+            "",
+            "    Matchers.allOf(Matchers.allOf((t, s) -> true));",
+            "    Matchers.anyOf(Matchers.anyOf((t, s) -> true));",
+            "    Refaster.anyOf(Refaster.anyOf(0));",
+            "",
+            "    Matchers.allOf(",
+            "        Matchers.anyOf(),",
+            "        Matchers.allOf((t, s) -> false, (t, s) -> true),",
+            "        Matchers.allOf(),",
+            "        Matchers.anyOf((t, s) -> false));",
+            "    Matchers.anyOf(",
+            "        Matchers.allOf(),",
+            "        Matchers.anyOf((t, s) -> false, (t, s) -> true),",
+            "        Matchers.anyOf(),",
+            "        Matchers.allOf((t, s) -> false));",
+            "    Refaster.anyOf(Matchers.allOf(), Refaster.anyOf(1, 2), Matchers.anyOf());",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import com.google.errorprone.matchers.Matchers;",
+            "import com.google.errorprone.refaster.Refaster;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Matchers.allOf();",
+            "    Matchers.anyOf();",
+            "    Refaster.anyOf();",
+            "",
+            "    Matchers.allOf((t, s) -> true);",
+            "    Matchers.anyOf((t, s) -> true);",
+            "    Refaster.anyOf(0);",
+            "",
+            "    Matchers.allOf(",
+            "        Matchers.anyOf(), (t, s) -> false, (t, s) -> true, Matchers.anyOf((t, s) -> false));",
+            "    Matchers.anyOf(",
+            "        Matchers.allOf(), (t, s) -> false, (t, s) -> true, Matchers.allOf((t, s) -> false));",
+            "    Refaster.anyOf(Matchers.allOf(), 1, 2, Matchers.anyOf());",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/CanonicalAnnotationSyntaxTest.java

@@ -34,9 +34,11 @@ final class CanonicalAnnotationSyntaxTest {
             "  // BUG: Diagnostic contains:",
             "  @pkg.A.Foo()",
             "  A functional1();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @A.Foo()",
             "  A functional2();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo()",
             "  A functional3();",
@@ -53,9 +55,11 @@ final class CanonicalAnnotationSyntaxTest {
             "  // BUG: Diagnostic contains:",
             "  @pkg.A.Foo({1})",
             "  A singleton1();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @A.Foo({1})",
             "  A singleton2();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo({1})",
             "  A singleton3();",
@@ -63,9 +67,11 @@ final class CanonicalAnnotationSyntaxTest {
             "  // BUG: Diagnostic contains:",
             "  @pkg.A.Foo(value = 1)",
             "  A verbose1();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @A.Foo(value = 1)",
             "  A verbose2();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo(value = 1)",
             "  A verbose3();",
@@ -82,9 +88,11 @@ final class CanonicalAnnotationSyntaxTest {
             "  // BUG: Diagnostic contains:",
             "  @pkg.A.Foo(value2 = {2})",
             "  A customSingleton1();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @A.Foo(value2 = {2})",
             "  A customSingleton2();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo(value2 = {2})",
             "  A customSingleton3();",
@@ -112,11 +120,13 @@ final class CanonicalAnnotationSyntaxTest {
             "    1, 1,",
             "  })",
             "  A trailingComma1();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @A.Foo({",
             "    1, 1,",
             "  })",
             "  A trailingComma2();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo({",
             "    1, 1,",

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/DirectReturnTest.java

@@ -136,6 +136,58 @@ final class DirectReturnTest {
             "      return variable;",
             "    };",
             "  }",
+            "",
+            "  String redundantAssignmentInsideTryBlock(AutoCloseable closeable) throws Exception {",
+            "    try (closeable) {",
+            "      // BUG: Diagnostic contains:",
+            "      String variable = toString();",
+            "      return variable;",
+            "    }",
+            "  }",
+            "",
+            "  String redundantAssignmentsInsideTryAndFinallyBlocks() {",
+            "    String variable = toString();",
+            "    try {",
+            "      // BUG: Diagnostic contains:",
+            "      variable = \"foo\";",
+            "      return variable;",
+            "    } finally {",
+            "      String variable2 = toString();",
+            "      if (true) {",
+            "        // BUG: Diagnostic contains:",
+            "        String variable3 = toString();",
+            "        return variable3;",
+            "      }",
+            "      return variable2;",
+            "    }",
+            "  }",
+            "",
+            "  String assignmentUsedInsideFinallyBlock() {",
+            "    String variable = toString();",
+            "    try {",
+            "      variable = \"foo\";",
+            "      return variable;",
+            "    } finally {",
+            "      String variable2 = toString();",
+            "      return variable + variable2;",
+            "    }",
+            "  }",
+            "",
+            "  String redundantAssignmentToVariableUsedInsideUnexecutedFinallyBlock(AutoCloseable closeable)",
+            "      throws Exception {",
+            "    String variable = toString();",
+            "    try (closeable) {",
+            "      if (true) {",
+            "        // BUG: Diagnostic contains:",
+            "        variable = \"foo\";",
+            "        return variable;",
+            "      }",
+            "    }",
+            "    try {",
+            "    } finally {",
+            "      return variable;",
+            "    }",
+            "  }",
             "}")
         .doTest();
   }

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/LexicographicalAnnotationAttributeListingTest.java

@@ -50,18 +50,21 @@ final class LexicographicalAnnotationAttributeListingTest {
             "",
             "  @Foo({\"a\", \"b\"})",
             "  A sortedStrings();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo({\"b\", \"a\"})",
             "  A unsortedString();",
             "",
             "  @Foo({\"ab\", \"Ac\"})",
             "  A sortedStringCaseInsensitive();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo({\"ac\", \"Ab\"})",
             "  A unsortedStringCaseInsensitive();",
             "",
             "  @Foo({\"A\", \"a\"})",
             "  A sortedStringCaseInsensitiveWithTotalOrderFallback();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo({\"a\", \"A\"})",
             "  A unsortedStringCaseInsensitiveWithTotalOrderFallback();",
@@ -86,6 +89,7 @@ final class LexicographicalAnnotationAttributeListingTest {
             "",
             "  @Foo(cls = {int.class, long.class})",
             "  A sortedClasses();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo(cls = {long.class, int.class})",
             "  A unsortedClasses();",
@@ -98,6 +102,7 @@ final class LexicographicalAnnotationAttributeListingTest {
             "",
             "  @Foo(enums = {DOWN, UP})",
             "  A sortedEnums();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo(enums = {UP, DOWN})",
             "  A unsortedEnums();",
@@ -110,15 +115,18 @@ final class LexicographicalAnnotationAttributeListingTest {
             "",
             "  @Foo(anns = {@Bar(\"a\"), @Bar(\"b\")})",
             "  A sortedAnns();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo(anns = {@Bar(\"b\"), @Bar(\"a\")})",
             "  A unsortedAnns();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo(anns = {@Bar(\"a\"), @Bar({\"b\", \"a\"})})",
             "  A unsortedInnderAnns();",
             "",
             "  @Foo({\"a=foo\", \"a.b=bar\", \"a.c=baz\"})",
             "  A hierarchicallySorted();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo({\"a.b=bar\", \"a.c=baz\", \"a=foo\"})",
             "  A hierarchicallyUnsorted();",
@@ -265,12 +273,14 @@ final class LexicographicalAnnotationAttributeListingTest {
             "  // BUG: Diagnostic contains:",
             "  @Foo({\"b\", \"a\"})",
             "  A fooValue();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo(value2 = {\"b\", \"a\"})",
             "  A fooValue2();",
             "",
             "  @Bar({\"b\", \"a\"})",
             "  A barValue();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Bar(value2 = {\"b\", \"a\"})",
             "  A barValue2();",

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/LexicographicalAnnotationListingTest.java

@@ -52,6 +52,7 @@ final class LexicographicalAnnotationListingTest {
             "  @Foo",
             "  @Bar",
             "  A unsortedSimpleCase();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo()",
             "  @Bar()",
@@ -69,6 +70,7 @@ final class LexicographicalAnnotationListingTest {
             "  @Baz",
             "  @Bar",
             "  A threeUnsortedAnnotationsSameInitialLetter();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Bar",
             "  @Foo()",
@@ -84,11 +86,13 @@ final class LexicographicalAnnotationListingTest {
             "  @Foo({\"b\"})",
             "  @Bar({\"a\"})",
             "  A unsortedWithStringAttributes();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Baz(str = {\"a\", \"b\"})",
             "  @Foo(ints = {1, 0})",
             "  @Bar",
             "  A unsortedWithAttributes();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Bar",
             "  @Foo(anns = {@Bar(\"b\"), @Bar(\"a\")})",
@@ -104,6 +108,7 @@ final class LexicographicalAnnotationListingTest {
             "  @Foo(ints = {1, 2})",
             "  @Foo({\"b\"})",
             "  A sortedRepeatableAnnotation();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @Foo(anns = {@Bar(\"b\"), @Bar(\"a\")})",
             "  @Bar",

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/MissingRefasterAnnotationTest.java

@@ -1,89 +0,0 @@
-package tech.picnic.errorprone.bugpatterns;
-
-import static com.google.common.base.Predicates.containsPattern;
-
-import com.google.errorprone.CompilationTestHelper;
-import org.junit.jupiter.api.Test;
-
-final class MissingRefasterAnnotationTest {
-  @Test
-  void identification() {
-    CompilationTestHelper.newInstance(MissingRefasterAnnotation.class, getClass())
-        .expectErrorMessage(
-            "X",
-            containsPattern("The Refaster rule contains a method without any Refaster annotations"))
-        .addSourceLines(
-            "A.java",
-            "import com.google.errorprone.refaster.annotation.AfterTemplate;",
-            "import com.google.errorprone.refaster.annotation.AlsoNegation;",
-            "import com.google.errorprone.refaster.annotation.BeforeTemplate;",
-            "import java.util.Map;",
-            "",
-            "class A {",
-            "  // BUG: Diagnostic matches: X",
-            "  static final class MethodLacksBeforeTemplateAnnotation {",
-            "    @BeforeTemplate",
-            "    boolean before1(String string) {",
-            "      return string.equals(\"\");",
-            "    }",
-            "",
-            "    // @BeforeTemplate is missing",
-            "    boolean before2(String string) {",
-            "      return string.length() == 0;",
-            "    }",
-            "",
-            "    @AfterTemplate",
-            "    @AlsoNegation",
-            "    boolean after(String string) {",
-            "      return string.isEmpty();",
-            "    }",
-            "  }",
-            "",
-            "  // BUG: Diagnostic matches: X",
-            "  static final class MethodLacksAfterTemplateAnnotation {",
-            "    @BeforeTemplate",
-            "    boolean before(String string) {",
-            "      return string.equals(\"\");",
-            "    }",
-            "",
-            "    // @AfterTemplate is missing",
-            "    boolean after(String string) {",
-            "      return string.isEmpty();",
-            "    }",
-            "  }",
-            "",
-            "  // BUG: Diagnostic matches: X",
-            "  abstract class MethodLacksPlaceholderAnnotation<K, V> {",
-            "    // @Placeholder is missing",
-            "    abstract V function(K key);",
-            "",
-            "    @BeforeTemplate",
-            "    void before(Map<K, V> map, K key) {",
-            "      if (!map.containsKey(key)) {",
-            "        map.put(key, function(key));",
-            "      }",
-            "    }",
-            "",
-            "    @AfterTemplate",
-            "    void after(Map<K, V> map, K key) {",
-            "      map.computeIfAbsent(key, k -> function(k));",
-            "    }",
-            "  }",
-            "",
-            "  static final class ValidRefasterRule {",
-            "    @BeforeTemplate",
-            "    void unusedPureFunctionCall(Object o) {",
-            "      o.toString();",
-            "    }",
-            "  }",
-            "",
-            "  static final class NotARefasterRule {",
-            "    @Override",
-            "    public String toString() {",
-            "      return \"This is not a Refaster rule\";",
-            "    }",
-            "  }",
-            "}")
-        .doTest();
-  }
-}

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/NonEmptyMonoTest.java

@@ -1,8 +1,7 @@
 package tech.picnic.errorprone.bugpatterns;
 
-import static com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode.TEXT_MATCH;
-
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
 import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
@@ -145,6 +144,6 @@ final class NonEmptyMonoTest {
             "    Mono.just(2).hasElement();",
             "  }",
             "}")
-        .doTest(TEXT_MATCH);
+        .doTest(TestMode.TEXT_MATCH);
   }
 }

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/RedundantStringConversionTest.java

@@ -10,12 +10,9 @@ import org.junit.jupiter.api.Test;
 // `String.valueOf(null)` may not. That is because the latter matches `String#valueOf(char[])`. We
 // could special-case `null` arguments, but that doesn't seem worth the trouble.
 final class RedundantStringConversionTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass());
-
   @Test
   void identificationOfIdentityTransformation() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass())
         .addSourceLines(
             "A.java",
             "class A {",
@@ -38,7 +35,7 @@ final class RedundantStringConversionTest {
 
   @Test
   void identificationWithinMutatingAssignment() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.math.BigInteger;",
@@ -99,7 +96,7 @@ final class RedundantStringConversionTest {
 
   @Test
   void identificationWithinBinaryOperation() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.math.BigInteger;",
@@ -194,7 +191,7 @@ final class RedundantStringConversionTest {
 
   @Test
   void identificationWithinStringBuilderMethod() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.math.BigInteger;",
@@ -249,7 +246,7 @@ final class RedundantStringConversionTest {
   // XXX: Also test the other formatter methods.
   @Test
   void identificationWithinFormatterMethod() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.Formattable;",
@@ -294,7 +291,7 @@ final class RedundantStringConversionTest {
 
   @Test
   void identificationWithinGuavaGuardMethod() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass())
         .addSourceLines(
             "A.java",
             "import static com.google.common.base.Preconditions.checkArgument;",
@@ -354,7 +351,7 @@ final class RedundantStringConversionTest {
 
   @Test
   void identificationWithinSlf4jLoggerMethod() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.Formattable;",

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/RefasterCheckTest.java

@@ -0,0 +1,192 @@
+// package tech.picnic.errorprone.bugpatterns;
+//
+// import static com.google.common.collect.ImmutableSetMultimap.toImmutableSetMultimap;
+// import static java.util.function.Function.identity;
+// import static java.util.function.Predicate.not;
+// import static org.assertj.core.api.Assertions.assertThat;
+// import static org.assertj.core.api.Assertions.assertThatCode;
+// import static org.junit.jupiter.params.provider.Arguments.arguments;
+//
+// import com.google.common.collect.ImmutableSet;
+// import com.google.common.collect.ImmutableSetMultimap;
+// import com.google.errorprone.BugCheckerRefactoringTestHelper;
+// import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+// import java.util.regex.Pattern;
+// import java.util.stream.Stream;
+// import org.junit.jupiter.api.Disabled;
+// import org.junit.jupiter.api.Test;
+// import org.junit.jupiter.params.ParameterizedTest;
+// import org.junit.jupiter.params.provider.Arguments;
+// import org.junit.jupiter.params.provider.MethodSource;
+//
+// public final class RefasterCheckTest {
+//  /** The names of all Refaster template groups defined in this module. */
+//  private static final ImmutableSet<String> TEMPLATE_GROUPS =
+//      ImmutableSet.of(
+//          "AssertJ",
+//          "AssertJBigDecimal",
+//          "AssertJBigInteger",
+//          "AssertJBoolean",
+//          "AssertJByte",
+//          "AssertJCharSequence",
+//          "AssertJDouble",
+//          "AssertJEnumerable",
+//          "AssertJFloat",
+//          "AssertJInteger",
+//          "AssertJLong",
+//          "AssertJNumber",
+//          "AssertJObject",
+//          "AssertJOptional",
+//          "AssertJShort",
+//          "AssertJString",
+//          "Assorted",
+//          "BigDecimal",
+//          "Collection",
+//          "Comparator",
+//          "DoubleStream",
+//          "Equality",
+//          "ImmutableList",
+//          "ImmutableListMultimap",
+//          "ImmutableMap",
+//          "ImmutableMultiset",
+//          "ImmutableSet",
+//          "ImmutableSetMultimap",
+//          "ImmutableSortedMap",
+//          "ImmutableSortedMultiset",
+//          "ImmutableSortedSet",
+//          "IntStream",
+//          "JUnit",
+//          "LongStream",
+//          "MapEntry",
+//          "Mockito",
+//          "Multimap",
+//          "Null",
+//          "Optional",
+//          "Primitive",
+//          "Reactor",
+//          "RxJava2Adapter",
+//          "RxJavaCompletableToReactor",
+//          "RxJavaFlowableToReactor",
+//          "RxJavaMaybeToReactor",
+//          "RxJavaObservableToReactor",
+//          "RxJavaSingleToReactor",
+//          "RxJavaToReactor",
+//          "RxJavaToReactorUnwrap",
+//          "Stream",
+//          "String",
+//          "TestNGToAssertJ",
+//          "Time",
+//          "WebClient");
+//  /**
+//   * Matches the parts of the fully-qualified name of a template class that should be removed in
+//   * order to produce the associated {@link #TEMPLATE_GROUPS template group name}.
+//   */
+//  private static final Pattern TEMPLATE_FQCN_TRIM_FOR_GROUP_NAME =
+//      Pattern.compile(".*\\.|Templates\\$.*");
+//  /**
+//   * A mapping from template group names to associated template names.
+//   *
+//   * <p>In effect, the values correspond to nested classes that represent individual Refaster
+//   * templates, while the keys correspond to the associated top-level "aggregator" classes.
+//   */
+//  private static final ImmutableSetMultimap<String, String> TEMPLATES_BY_GROUP =
+//      indexTemplateNamesByGroup(RefasterCheck.ALL_CODE_TRANSFORMERS.get().keySet());
+//
+//  /** Returns every known template group name as a parameterized test argument. */
+//  @SuppressWarnings("UnusedMethod" /* Used as a `@MethodSource`. */)
+//  private static Stream<Arguments> templateGroupsUnderTest() {
+//    // XXX: Drop the filter once we have added tests for AssertJ!
+//    return TEMPLATES_BY_GROUP.keySet().stream()
+//        .filter(not("AssertJ"::equals))
+//        .filter(not("Immutable"::equals))
+//        .filter(not("Reactor"::equals))
+//        .filter(not("RxJava2Adapter"::equals))
+//        .map(Arguments::of);
+//  }
+//
+//  /**
+//   * Returns every known (template group name, template name) pair as a parameterized test
+// argument.
+//   */
+//  @SuppressWarnings("UnusedMethod" /* Used as a `@MethodSource`. */)
+//  private static Stream<Arguments> templatesUnderTest() {
+//    // XXX: Drop the filter once we have added tests for AssertJ!
+//    return TEMPLATES_BY_GROUP.entries().stream()
+//        .filter(e -> !"AssertJ".equals(e.getKey()))
+//        .filter(e -> !"AssertJ".contains(e.getKey()))
+//        .filter(e -> !"Immutable".contains(e.getKey()))
+//        .filter(e -> !"Immutable".equals(e.getKey()))
+//        .map(e -> arguments(e.getKey(), e.getValue()));
+//  }
+//
+//  /**
+//   * Verifies that {@link RefasterCheck#loadAllCodeTransformers} finds at least one code
+// transformer
+//   * for all of the {@link #TEMPLATE_GROUPS}.
+//   *
+//   * <p>This test is just as much about ensuring that {@link #TEMPLATE_GROUPS} is exhaustive, so
+//   * that in turn {@link #replacement}'s coverage is exhaustive.
+//   */
+//  @Test
+//  void loadAllCodeTransformers() {
+//    assertThat(TEMPLATES_BY_GROUP.keySet()).hasSameElementsAs(TEMPLATE_GROUPS);
+//  }
+//
+//  /**
+//   * Verifies for each of the {@link #TEMPLATE_GROUPS} that the associated code transformers have
+//   * the desired effect.
+//   */
+//  @MethodSource("templateGroupsUnderTest")
+//  @ParameterizedTest
+//  void replacement(String group) {
+//    verifyRefactoring(group, namePattern(group));
+//  }
+//
+//  /**
+//   * Verifies that all loaded Refaster templates are covered by at least one test.
+//   *
+//   * <p>Note that this doesn't guarantee full coverage: this test cannot ascertain that all {@link
+//   * com.google.errorprone.refaster.Refaster#anyOf} branches are tested. Idem for {@link
+//   * com.google.errorprone.refaster.annotation.BeforeTemplate} methods in case there are multiple
+// .
+//   */
+//  @Disabled
+//  @MethodSource("templatesUnderTest")
+//  @ParameterizedTest
+//  void coverage(String group, String template) {
+//    assertThatCode(() -> verifyRefactoring(group, namePattern(group, template)))
+//        .withFailMessage(
+//            "Template %s does not affect the tests for group %s; is it tested?", template, group)
+//        .isInstanceOf(AssertionError.class)
+//        .hasMessageFindingMatch("^(diff|expected):");
+//  }
+//
+//  private static ImmutableSetMultimap<String, String> indexTemplateNamesByGroup(
+//      ImmutableSet<String> templateNames) {
+//    return templateNames.stream()
+//        .collect(
+//            toImmutableSetMultimap(
+//                n -> TEMPLATE_FQCN_TRIM_FOR_GROUP_NAME.matcher(n).replaceAll(""), identity()));
+//  }
+//
+//  private static String namePattern(String groupName, String excludedTemplate) {
+//    return "(?!" + Pattern.quote(excludedTemplate) + ')' + namePattern(groupName);
+//  }
+//
+//  private static String namePattern(String groupName) {
+//    return Pattern.compile(Pattern.quote(groupName)) + "Templates.*";
+//  }
+//
+//  private void verifyRefactoring(String groupName, String templateNamePattern) {
+//    createRestrictedRefactoringTestHelper(templateNamePattern)
+//        .addInput(groupName + "TemplatesTestInput.java")
+//        .addOutput(groupName + "TemplatesTestOutput.java")
+//        .doTest(TestMode.TEXT_MATCH);
+//  }
+//
+//  private BugCheckerRefactoringTestHelper createRestrictedRefactoringTestHelper(
+//      String namePattern) {
+//    return BugCheckerRefactoringTestHelper.newInstance(RefasterCheck.class, getClass())
+//        .setArgs("-XepOpt:Refaster:NamePattern=" + namePattern);
+//  }
+// }

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/RequestMappingAnnotationTest.java

@@ -9,12 +9,12 @@ final class RequestMappingAnnotationTest {
     CompilationTestHelper.newInstance(RequestMappingAnnotation.class, getClass())
         .addSourceLines(
             "A.java",
+            "import jakarta.servlet.http.HttpServletRequest;",
+            "import jakarta.servlet.http.HttpServletResponse;",
             "import java.io.InputStream;",
             "import java.time.ZoneId;",
             "import java.util.Locale;",
             "import java.util.TimeZone;",
-            "import javax.servlet.http.HttpServletRequest;",
-            "import javax.servlet.http.HttpServletResponse;",
             "import org.springframework.http.HttpMethod;",
             "import org.springframework.ui.Model;",
             "import org.springframework.validation.BindingResult;",

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/SpringMvcAnnotationTest.java

@@ -32,18 +32,23 @@ final class SpringMvcAnnotationTest {
             "",
             "  @RequestMapping(method = {})",
             "  A explicitDefault();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @RequestMapping(method = RequestMethod.GET)",
             "  A get();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @RequestMapping(method = {RequestMethod.POST})",
             "  A post();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @RequestMapping(method = {PUT})",
             "  A put();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @RequestMapping(method = {DELETE})",
             "  A delete();",
+            "",
             "  // BUG: Diagnostic contains:",
             "  @RequestMapping(method = {PATCH})",
             "  A patch();",

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/StringCaseLocaleUsageTest.java

@@ -1,124 +0,0 @@
-package tech.picnic.errorprone.bugpatterns;
-
-import com.google.errorprone.BugCheckerRefactoringTestHelper;
-import com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers;
-import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
-import com.google.errorprone.CompilationTestHelper;
-import org.junit.jupiter.api.Test;
-
-final class StringCaseLocaleUsageTest {
-  @Test
-  void identification() {
-    CompilationTestHelper.newInstance(StringCaseLocaleUsage.class, getClass())
-        .addSourceLines(
-            "A.java",
-            "import static java.util.Locale.ROOT;",
-            "",
-            "import java.util.Locale;",
-            "",
-            "class A {",
-            "  void m() {",
-            "    \"a\".toLowerCase(Locale.ROOT);",
-            "    \"a\".toUpperCase(Locale.ROOT);",
-            "    \"b\".toLowerCase(ROOT);",
-            "    \"b\".toUpperCase(ROOT);",
-            "    \"c\".toLowerCase(Locale.getDefault());",
-            "    \"c\".toUpperCase(Locale.getDefault());",
-            "    \"d\".toLowerCase(Locale.ENGLISH);",
-            "    \"d\".toUpperCase(Locale.ENGLISH);",
-            "    \"e\".toLowerCase(new Locale(\"foo\"));",
-            "    \"e\".toUpperCase(new Locale(\"foo\"));",
-            "",
-            "    // BUG: Diagnostic contains:",
-            "    \"f\".toLowerCase();",
-            "    // BUG: Diagnostic contains:",
-            "    \"g\".toUpperCase();",
-            "",
-            "    String h = \"h\";",
-            "    // BUG: Diagnostic contains:",
-            "    h.toLowerCase();",
-            "    String i = \"i\";",
-            "    // BUG: Diagnostic contains:",
-            "    i.toUpperCase();",
-            "  }",
-            "}")
-        .doTest();
-  }
-
-  @Test
-  void replacementFirstSuggestedFix() {
-    BugCheckerRefactoringTestHelper.newInstance(StringCaseLocaleUsage.class, getClass())
-        .addInputLines(
-            "A.java",
-            "class A {",
-            "  void m() {",
-            "    \"a\".toLowerCase(/* Comment with parens: (). */ );",
-            "    \"b\".toUpperCase();",
-            "    \"c\".toLowerCase().toString();",
-            "",
-            "    toString().toLowerCase();",
-            "    toString().toUpperCase /* Comment with parens: (). */();",
-            "",
-            "    this.toString().toLowerCase() /* Comment with parens: (). */;",
-            "    this.toString().toUpperCase();",
-            "  }",
-            "}")
-        .addOutputLines(
-            "A.java",
-            "import java.util.Locale;",
-            "",
-            "class A {",
-            "  void m() {",
-            "    \"a\".toLowerCase(/* Comment with parens: (). */ Locale.ROOT);",
-            "    \"b\".toUpperCase(Locale.ROOT);",
-            "    \"c\".toLowerCase(Locale.ROOT).toString();",
-            "",
-            "    toString().toLowerCase(Locale.ROOT);",
-            "    toString().toUpperCase /* Comment with parens: (). */(Locale.ROOT);",
-            "",
-            "    this.toString().toLowerCase(Locale.ROOT) /* Comment with parens: (). */;",
-            "    this.toString().toUpperCase(Locale.ROOT);",
-            "  }",
-            "}")
-        .doTest(TestMode.TEXT_MATCH);
-  }
-
-  @Test
-  void replacementSecondSuggestedFix() {
-    BugCheckerRefactoringTestHelper.newInstance(StringCaseLocaleUsage.class, getClass())
-        .setFixChooser(FixChoosers.SECOND)
-        .addInputLines(
-            "A.java",
-            "class A {",
-            "  void m() {",
-            "    \"a\".toLowerCase();",
-            "    \"b\".toUpperCase(/* Comment with parens: (). */ );",
-            "    \"c\".toLowerCase().toString();",
-            "",
-            "    toString().toLowerCase();",
-            "    toString().toUpperCase /* Comment with parens: (). */();",
-            "",
-            "    this.toString().toLowerCase() /* Comment with parens: (). */;",
-            "    this.toString().toUpperCase();",
-            "  }",
-            "}")
-        .addOutputLines(
-            "A.java",
-            "import java.util.Locale;",
-            "",
-            "class A {",
-            "  void m() {",
-            "    \"a\".toLowerCase(Locale.getDefault());",
-            "    \"b\".toUpperCase(/* Comment with parens: (). */ Locale.getDefault());",
-            "    \"c\".toLowerCase(Locale.getDefault()).toString();",
-            "",
-            "    toString().toLowerCase(Locale.getDefault());",
-            "    toString().toUpperCase /* Comment with parens: (). */(Locale.getDefault());",
-            "",
-            "    this.toString().toLowerCase(Locale.getDefault()) /* Comment with parens: (). */;",
-            "    this.toString().toUpperCase(Locale.getDefault());",
-            "  }",
-            "}")
-        .doTest(TestMode.TEXT_MATCH);
-  }
-}

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/util/JavaKeywordsTest.java

@@ -10,7 +10,7 @@ import org.junit.jupiter.params.provider.MethodSource;
 
 final class JavaKeywordsTest {
   private static Stream<Arguments> isValidIdentifierTestCases() {
-    /* { str, expected } */
+    /* { string, expected } */
     return Stream.of(
         arguments("", false),
         arguments("public", false),
@@ -28,7 +28,7 @@ final class JavaKeywordsTest {
 
   @MethodSource("isValidIdentifierTestCases")
   @ParameterizedTest
-  void isValidIdentifier(String str, boolean expected) {
-    assertThat(JavaKeywords.isValidIdentifier(str)).isEqualTo(expected);
+  void isValidIdentifier(String string, boolean expected) {
+    assertThat(JavaKeywords.isValidIdentifier(string)).isEqualTo(expected);
   }
 }

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/util/MethodMatcherFactoryTest.java

@@ -2,6 +2,7 @@ package tech.picnic.errorprone.bugpatterns.util;
 
 import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.junit.jupiter.params.provider.Arguments.arguments;
 
 import com.google.common.collect.ImmutableList;
 import com.google.errorprone.BugPattern;
@@ -13,25 +14,13 @@ 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.Stream;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
 final class MethodMatcherFactoryTest {
-  /** A {@link BugChecker} that flags method invocations matched by {@link #TEST_MATCHER}. */
-  @BugPattern(severity = SUGGESTION, summary = "Flags methods matched by the test matcher.")
-  public static final class MatchedMethodsFlagger extends BugChecker
-      implements MethodInvocationTreeMatcher {
-    private static final long serialVersionUID = 1L;
-
-    @Override
-    public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
-      if (TEST_MATCHER.matches(tree, state)) {
-        return buildDescription(tree).build();
-      }
-
-      return Description.NO_MATCH;
-    }
-  }
-
   private static final Matcher<ExpressionTree> TEST_MATCHER =
       new MethodMatcherFactory()
           .create(
@@ -40,16 +29,20 @@ final class MethodMatcherFactoryTest {
                   "com.example.A#m2(java.lang.String)",
                   "com.example.sub.B#m3(int,int)"));
 
-  @Test
-  void createWithMalformedSignatures() {
+  private static Stream<Arguments> createWithMalformedSignaturesTestCases() {
+    /* { signatures } */
+    return Stream.of(
+        arguments(ImmutableList.of("foo.bar")),
+        arguments(ImmutableList.of("foo.bar#baz")),
+        arguments(ImmutableList.of("a", "foo.bar#baz()")),
+        arguments(ImmutableList.of("foo.bar#baz()", "a")));
+  }
+
+  @MethodSource("createWithMalformedSignaturesTestCases")
+  @ParameterizedTest
+  void createWithMalformedSignatures(ImmutableList<String> signatures) {
     MethodMatcherFactory factory = new MethodMatcherFactory();
-    assertThatThrownBy(() -> factory.create(ImmutableList.of("foo.bar")))
-        .isInstanceOf(IllegalArgumentException.class);
-    assertThatThrownBy(() -> factory.create(ImmutableList.of("foo.bar#baz")))
-        .isInstanceOf(IllegalArgumentException.class);
-    assertThatThrownBy(() -> factory.create(ImmutableList.of("a", "foo.bar#baz()")))
-        .isInstanceOf(IllegalArgumentException.class);
-    assertThatThrownBy(() -> factory.create(ImmutableList.of("foo.bar#baz()", "a")))
+    assertThatThrownBy(() -> factory.create(signatures))
         .isInstanceOf(IllegalArgumentException.class);
   }
 
@@ -207,4 +200,20 @@ final class MethodMatcherFactoryTest {
             "}")
         .doTest();
   }
+
+  /** A {@link BugChecker} that flags method invocations matched by {@link #TEST_MATCHER}. */
+  @BugPattern(severity = SUGGESTION, summary = "Flags methods matched by the test matcher.")
+  public static final class MatchedMethodsFlagger extends BugChecker
+      implements MethodInvocationTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+      if (TEST_MATCHER.matches(tree, state)) {
+        return buildDescription(tree).build();
+      }
+
+      return Description.NO_MATCH;
+    }
+  }
 }

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/util/SourceCodeTest.java

@@ -8,22 +8,22 @@ import com.google.errorprone.BugPattern;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.AnnotationTreeMatcher;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
 import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.MethodInvocationTree;
 import com.sun.source.tree.MethodTree;
 import com.sun.source.tree.Tree;
 import javax.lang.model.element.Name;
 import org.junit.jupiter.api.Test;
 
 final class SourceCodeTest {
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass());
-
   @Test
   void deleteWithTrailingWhitespaceAnnotations() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(
+            DeleteWithTrailingWhitespaceTestChecker.class, getClass())
         .addInputLines("AnnotationToBeDeleted.java", "@interface AnnotationToBeDeleted {}")
         .expectUnchanged()
         .addInputLines(
@@ -96,7 +96,8 @@ final class SourceCodeTest {
 
   @Test
   void deleteWithTrailingWhitespaceMethods() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(
+            DeleteWithTrailingWhitespaceTestChecker.class, getClass())
         .addInputLines(
             "MethodDeletions.java",
             "interface MethodDeletions {",
@@ -162,13 +163,78 @@ final class SourceCodeTest {
         .doTest(TestMode.TEXT_MATCH);
   }
 
+  @Test
+  void unwrapMethodInvocation() {
+    BugCheckerRefactoringTestHelper.newInstance(UnwrapMethodInvocationTestChecker.class, getClass())
+        .addInputLines(
+            "A.java",
+            "import com.google.common.collect.ImmutableList;",
+            "",
+            "class A {",
+            "  Object[] m() {",
+            "    return new Object[][] {",
+            "      {ImmutableList.of()},",
+            "      {ImmutableList.of(1)},",
+            "      {com.google.common.collect.ImmutableList.of(1, 2)},",
+            "      {",
+            "        0, /*a*/",
+            "        ImmutableList /*b*/./*c*/ <Integer> /*d*/of /*e*/(/*f*/ 1 /*g*/, /*h*/ 2 /*i*/) /*j*/",
+            "      }",
+            "    };",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import com.google.common.collect.ImmutableList;",
+            "",
+            "class A {",
+            "  Object[] m() {",
+            "    return new Object[][] {{}, {1}, {1, 2}, {0, /*a*/ /*f*/ 1 /*g*/, /*h*/ 2 /*i*/ /*j*/}};",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+
+  @Test
+  void unwrapMethodInvocationDroppingWhitespaceAndComments() {
+    BugCheckerRefactoringTestHelper.newInstance(
+            UnwrapMethodInvocationDroppingWhitespaceAndCommentsTestChecker.class, getClass())
+        .addInputLines(
+            "A.java",
+            "import com.google.common.collect.ImmutableList;",
+            "",
+            "class A {",
+            "  Object[] m() {",
+            "    return new Object[][] {",
+            "      {ImmutableList.of()},",
+            "      {ImmutableList.of(1)},",
+            "      {com.google.common.collect.ImmutableList.of(1, 2)},",
+            "      {",
+            "        0, /*a*/",
+            "        ImmutableList /*b*/./*c*/ <Integer> /*d*/of /*e*/(/*f*/ 1 /*g*/, /*h*/ 2 /*i*/) /*j*/",
+            "      }",
+            "    };",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import com.google.common.collect.ImmutableList;",
+            "",
+            "class A {",
+            "  Object[] m() {",
+            "    return new Object[][] {{}, {1}, {1, 2}, {0, /*a*/ 1, 2 /*j*/}};",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+
   /**
    * A {@link BugChecker} that uses {@link SourceCode#deleteWithTrailingWhitespace(Tree,
    * VisitorState)} to suggest the deletion of annotations and methods with a name containing
    * {@value DELETION_MARKER}.
    */
   @BugPattern(severity = ERROR, summary = "Interacts with `SourceCode` for testing purposes")
-  public static final class TestChecker extends BugChecker
+  public static final class DeleteWithTrailingWhitespaceTestChecker extends BugChecker
       implements AnnotationTreeMatcher, MethodTreeMatcher {
     private static final long serialVersionUID = 1L;
     private static final String DELETION_MARKER = "ToBeDeleted";
@@ -192,4 +258,37 @@ final class SourceCodeTest {
           : Description.NO_MATCH;
     }
   }
+
+  /**
+   * A {@link BugChecker} that applies {@link
+   * SourceCode#unwrapMethodInvocation(MethodInvocationTree, VisitorState)} to all method
+   * invocations.
+   */
+  @BugPattern(severity = ERROR, summary = "Interacts with `SourceCode` for testing purposes")
+  public static final class UnwrapMethodInvocationTestChecker extends BugChecker
+      implements MethodInvocationTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+      return describeMatch(tree, SourceCode.unwrapMethodInvocation(tree, state));
+    }
+  }
+
+  /**
+   * A {@link BugChecker} that applies {@link
+   * SourceCode#unwrapMethodInvocationDroppingWhitespaceAndComments(MethodInvocationTree,
+   * VisitorState)} to all method invocations.
+   */
+  @BugPattern(severity = ERROR, summary = "Interacts with `SourceCode` for testing purposes")
+  public static final class UnwrapMethodInvocationDroppingWhitespaceAndCommentsTestChecker
+      extends BugChecker implements MethodInvocationTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+      return describeMatch(
+          tree, SourceCode.unwrapMethodInvocationDroppingWhitespaceAndComments(tree, state));
+    }
+  }
 }

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/util/ThirdPartyLibraryTest.java

@@ -18,12 +18,9 @@ import org.junit.jupiter.params.provider.ValueSource;
 import reactor.core.publisher.Flux;
 
 final class ThirdPartyLibraryTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(TestChecker.class, getClass());
-
   @Test
   void isIntroductionAllowed() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(TestChecker.class, getClass())
         .addSourceLines(
             "A.java",
             "// BUG: Diagnostic contains: ASSERTJ: true, GUAVA: true, NEW_RELIC_AGENT_API: true, REACTOR: true",
@@ -33,7 +30,7 @@ final class ThirdPartyLibraryTest {
 
   @Test
   void isIntroductionAllowedWitnessClassesInSymtab() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(TestChecker.class, getClass())
         .addSourceLines(
             "A.java",
             "import com.google.common.collect.ImmutableList;",
@@ -55,7 +52,7 @@ final class ThirdPartyLibraryTest {
 
   @Test
   void isIntroductionAllowedWitnessClassesPartiallyOnClassPath() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(TestChecker.class, getClass())
         .withClasspath(ImmutableList.class, Flux.class)
         .addSourceLines(
             "A.java",
@@ -66,7 +63,7 @@ final class ThirdPartyLibraryTest {
 
   @Test
   void isIntroductionAllowedWitnessClassesNotOnClassPath() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(TestChecker.class, getClass())
         .withClasspath()
         .addSourceLines(
             "A.java",
@@ -79,7 +76,7 @@ final class ThirdPartyLibraryTest {
   @ParameterizedTest
   @ValueSource(booleans = {true, false})
   void isIntroductionAllowedIgnoreClasspathCompat(boolean ignoreClassPath) {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(TestChecker.class, getClass())
         .setArgs("-XepOpt:ErrorProneSupport:IgnoreClasspathCompat=" + ignoreClassPath)
         .withClasspath(ImmutableList.class, Flux.class)
         .addSourceLines(

error-prone-contrib/src/test/java/tech/picnic/errorprone/refasterrules/RefasterRulesTest.java

@@ -13,7 +13,6 @@ final class RefasterRulesTest {
   /** The names of all Refaster rule groups defined in this module. */
   private static final ImmutableSet<Class<?>> RULE_COLLECTIONS =
       ImmutableSet.of(
-          AssertJRules.class,
           AssertJBigDecimalRules.class,
           AssertJBigIntegerRules.class,
           AssertJBooleanRules.class,
@@ -25,11 +24,12 @@ final class RefasterRulesTest {
           AssertJFloatRules.class,
           AssertJIntegerRules.class,
           AssertJLongRules.class,
-          AssertJNumberRules.class,
           AssertJMapRules.class,
+          AssertJNumberRules.class,
           AssertJObjectRules.class,
           AssertJOptionalRules.class,
           AssertJPrimitiveRules.class,
+          AssertJRules.class,
           AssertJShortRules.class,
           AssertJStringRules.class,
           AssertJThrowingCallableRules.class,
@@ -65,6 +65,7 @@ final class RefasterRulesTest {
           RxJava2AdapterRules.class,
           StreamRules.class,
           StringRules.class,
+          SuggestedFixRules.class,
           TestNGToAssertJRules.class,
           TimeRules.class,
           WebClientRules.class);

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssertJBigDecimalRulesTestInput.java

@@ -11,7 +11,7 @@ import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssertJBigDecimalRulesTest implements RefasterRuleCollectionTestCase {
   @Override
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(offset(0), withPercentage(0));
   }
 

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssertJBigDecimalRulesTestOutput.java

@@ -11,7 +11,7 @@ import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssertJBigDecimalRulesTest implements RefasterRuleCollectionTestCase {
   @Override
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(offset(0), withPercentage(0));
   }
 

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssertJBigIntegerRulesTestInput.java

@@ -11,7 +11,7 @@ import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssertJBigIntegerRulesTest implements RefasterRuleCollectionTestCase {
   @Override
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(offset(0), withPercentage(0));
   }
 

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssertJBigIntegerRulesTestOutput.java

@@ -11,7 +11,7 @@ import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssertJBigIntegerRulesTest implements RefasterRuleCollectionTestCase {
   @Override
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(offset(0), withPercentage(0));
   }
 

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssertJByteRulesTestInput.java

@@ -10,7 +10,7 @@ import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssertJByteRulesTest implements RefasterRuleCollectionTestCase {
   @Override
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(offset(0), withPercentage(0));
   }
 

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssertJByteRulesTestOutput.java

@@ -10,7 +10,7 @@ import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssertJByteRulesTest implements RefasterRuleCollectionTestCase {
   @Override
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(offset(0), withPercentage(0));
   }
 

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssertJDoubleRulesTestInput.java

@@ -10,7 +10,7 @@ import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssertJDoubleRulesTest implements RefasterRuleCollectionTestCase {
   @Override
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(withPercentage(0));
   }
 

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssertJDoubleRulesTestOutput.java

@@ -10,7 +10,7 @@ import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssertJDoubleRulesTest implements RefasterRuleCollectionTestCase {
   @Override
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(withPercentage(0));
   }
 

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssertJEnumerableRulesTestInput.java

@@ -9,7 +9,7 @@ import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssertJEnumerableRulesTest implements RefasterRuleCollectionTestCase {
   @Override
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(Iterables.class);
   }
 

error-prone-contrib/src/test/resources/tech/picnic/errorprone/refasterrules/AssertJEnumerableRulesTestOutput.java

@@ -9,7 +9,7 @@ import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class AssertJEnumerableRulesTest implements RefasterRuleCollectionTestCase {
   @Override
-  public ImmutableSet<?> elidedTypesAndStaticImports() {
+  public ImmutableSet<Object> elidedTypesAndStaticImports() {
     return ImmutableSet.of(Iterables.class);
   }