Move new rule collection

This is a squash commit of the following previous commits:

---

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

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

---

Improve website styling

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

---

Generate Markdown files from existing content for the website

---

Upgrade dependencies to the latest versions

---

Compile and install project jars before docgen

---

Run validation in build and exclude self-url

---

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

---

Delete directory if it exists

---

Add SCSS for GitHub button and fix bug pattern sample rendering

---

Fix bug pattern GitHub link

---

Small styling tweaks (incl. for dark theme)

---

Use single mvn command

---

Move mustache templates

---

Hardcode anchors for headings

---

Add supression to bugpatterns

---

Remove self ignore for html-proofer

---

Add refaster supressions and use callouts

---

Use v0.4.1-SNAPSHOT

---

Revert "Use single mvn command"

This reverts commit 594471d1ed23a1c19d7fe88d925d1b7f828716cd.

---

Extract Refaster samples from source code instead of AST

---

Skip verification, for now

---

Add notes on disabling bugpatterns

---

Set default layout and image

---

Fix mobile navigation

---

Revert "Set default layout and image"

This reverts commit 67a4aa7b5b4d14c0f2b783f345f53affe6ef3ec5.

---

Add supression for refaster rules

---

Post-rebase fixes

---

Fix the tests

---

Doh

---

Version bump

---

Exclude ThirdPartyLibraryTest from Bug Pattern test output

---

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

---

Move `MapRulesTest` resources

---

Add exclusion for docgen of `SourceCodeTest`

---

Bump version

---

Extra fixes after rebase

---

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

---

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

---

Use new BugPatternTest extraction method

.github/ISSUE_TEMPLATE/bug_report.md

@@ -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. `17.0.3`).
-- Error Prone version (e.g. `2.15.0`).
-- Error Prone Support version (e.g. `0.3.0`).
+- Java version (i.e. `java --version`, e.g. `17.0.6`).
+- Error Prone version (e.g. `2.18.0`).
+- Error Prone Support version (e.g. `0.8.0`).
 
 ### Additional context
 

.github/ISSUE_TEMPLATE/feature_request.md

@@ -17,23 +17,24 @@ you'd like to be solved through Error Prone Support. -->
 
 - [ ] Support a stylistic preference.
 - [ ] Avoid a common gotcha, or potential problem.
+- [ ] Improve performance.
 
 <!--
 Here, provide a clear and concise description of the desired change.
 
 If possible, provide a simple and minimal example using the following format:
-
-  I would like to rewrite the following code:
-  ```java
-  // XXX: Write the code to match here.
-  ```
-
-  to:
-  ```java
-  // XXX: Write the desired code here.
-  ```
 -->
 
+I would like to rewrite the following code:
+```java
+// XXX: Write the code to match here.
+```
+
+to:
+```java
+// XXX: Write the desired code here.
+```
+
 ### Considerations
 
 <!--

.github/workflows/build.yaml

@@ -10,16 +10,16 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-22.04 ]
-        jdk: [ 11.0.16, 17.0.4, 19 ]
+        jdk: [ 11.0.18, 17.0.6, 19.0.2 ]
         distribution: [ temurin ]
         experimental: [ false ]
         include:
           - os: macos-12
-            jdk: 17.0.4
+            jdk: 17.0.6
             distribution: temurin
             experimental: false
           - os: windows-2022
-            jdk: 17.0.4
+            jdk: 17.0.6
             distribution: temurin
             experimental: false
           - os: ubuntu-22.04
@@ -37,7 +37,7 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v3.1.0
       - name: Set up JDK
-        uses: actions/setup-java@v3.7.0
+        uses: actions/setup-java@v3.8.0
         with:
           java-version: ${{ matrix.jdk }}
           distribution: ${{ matrix.distribution }}

.github/workflows/deploy-website.yaml

@@ -19,16 +19,21 @@ jobs:
           bundler-cache: true
       - name: Configure Github Pages
         uses: actions/configure-pages@v2.1.3
+      - name: Set up JDK
+        uses: actions/setup-java@v3.5.1
+        with:
+          java-version: 17.0.4
+          distribution: temurin
+          cache: maven
+      - name: Compile project and extract data
+        # XXX: Remove `-Dverification.{skip|warn}` and update `website/README.md`
+        # once module `docgen` has no errors.
+        run: |
+          mvn -T1C clean install -DskipTests -Dverification.warn
+          mvn -T1C clean install -DskipTests -Dverification.skip -Pdocgen
       - name: Generate documentation
-        run: ./generate-docs.sh
-      - name: Build website with Jekyll
         working-directory: ./website
-        run: bundle exec jekyll build
-      - name: Validate HTML output
-        working-directory: ./website
-        # XXX: Drop `--disable_external true` once we fully adopted the
-        # "Refaster rules" terminology on our website and in the code.
-        run: bundle exec htmlproofer --disable_external true --check-external-hash false ./_site
+        run: bundle exec ruby generate-docs.rb
       - name: Upload website as artifact
         uses: actions/upload-pages-artifact@v1.0.5
         with:

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

@@ -16,9 +16,9 @@ jobs:
         with:
           fetch-depth: 2
       - name: Set up JDK
-        uses: actions/setup-java@v3.7.0
+        uses: actions/setup-java@v3.8.0
         with:
-          java-version: 17.0.4
+          java-version: 17.0.6
           distribution: temurin
           cache: maven
       - name: Run Pitest

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

@@ -20,9 +20,9 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v3.1.0
       - name: Set up JDK
-        uses: actions/setup-java@v3.7.0
+        uses: actions/setup-java@v3.8.0
         with:
-          java-version: 17.0.4
+          java-version: 17.0.6
           distribution: temurin
           cache: maven
       - name: Download Pitest analysis artifact

.mvn/maven.config

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

LICENSE.md

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2017-2022 Picnic Technologies BV
+Copyright (c) 2017-2023 Picnic Technologies BV
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -36,7 +36,9 @@ code_][picnic-blog-ep-post].
 ### Installation
 
 This library is built on top of [Error Prone][error-prone-orig-repo]. To use
-it:
+it, read the installation guide for Maven or Gradle below.
+
+#### Maven
 
 1. First, follow Error Prone's [installation
    guide][error-prone-installation-guide].
@@ -94,6 +96,31 @@ it:
 Prone Support. Alternatively reference this project's `self-check` profile
 definition. -->
 
+#### Gradle
+
+1. First, follow the [installation guide]
+   [error-prone-gradle-installation-guide] of the `gradle-errorprone-plugin`.
+2. Next, edit your `build.gradle` file to add one or more Error Prone Support
+   modules:
+
+   ```groovy
+   dependencies {
+       // Error Prone itself.
+       errorprone("com.google.errorprone:error_prone_core:${errorProneVersion}")
+       // Error Prone Support's additional bug checkers.
+       errorprone("tech.picnic.error-prone-support:error-prone-contrib:${errorProneSupportVersion}")
+       // Error Prone Support's Refaster rules.
+       errorprone("tech.picnic.error-prone-support:refaster-runner:${errorProneSupportVersion}")
+   }
+
+   tasks.withType(JavaCompile).configureEach {
+       options.errorprone.disableWarningsInGeneratedCode = true
+       // Add other Error Prone flags here. See:
+       // - https://github.com/tbroyer/gradle-errorprone-plugin#configuration
+       // - https://errorprone.info/docs/flags
+   }
+   ```
+
 ### Seeing it in action
 
 Consider the following example code:
@@ -207,6 +234,7 @@ guidelines][contributing].
 [error-prone-bugchecker]: https://github.com/google/error-prone/blob/master/check_api/src/main/java/com/google/errorprone/bugpatterns/BugChecker.java
 [error-prone-fork-jitpack]: https://jitpack.io/#PicnicSupermarket/error-prone
 [error-prone-fork-repo]: https://github.com/PicnicSupermarket/error-prone
+[error-prone-gradle-installation-guide]: https://github.com/tbroyer/gradle-errorprone-plugin
 [error-prone-installation-guide]: https://errorprone.info/docs/installation#maven
 [error-prone-orig-repo]: https://github.com/google/error-prone
 [error-prone-pull-3301]: https://github.com/google/error-prone/pull/3301

apply-error-prone-suggestions.sh

@@ -9,13 +9,14 @@
 set -e -u -o pipefail
 
 if [ "${#}" -gt 1 ]; then
-  echo "Usage: ./$(basename "${0}") [PatchChecks]"
+  echo "Usage: ${0} [PatchChecks]"
   exit 1
 fi
 
 patchChecks=${1:-}
 
 mvn clean test-compile fmt:format \
+  -s "$(dirname "${0}")/settings.xml" \
   -T 1.0C \
   -Perror-prone \
   -Perror-prone-fork \

documentation-support/pom.xml

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

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

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

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

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

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

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

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

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

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

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

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

@@ -0,0 +1,61 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.annotations.Immutable;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.MethodTree;
+import java.util.Optional;
+import java.util.regex.Pattern;
+import tech.picnic.errorprone.documentation.models.RefasterTemplateCollectionTestData;
+import tech.picnic.errorprone.documentation.models.RefasterTemplateTestData;
+
+@Immutable
+@AutoService(Extractor.class)
+public final class RefasterTestInputExtractor
+    implements Extractor<RefasterTemplateCollectionTestData> {
+  private static final Pattern TEST_INPUT_CLASS_NAME_PATTERN = Pattern.compile("(.*)TestInput");
+
+  @Override
+  public String identifier() {
+    return "refaster-test-input";
+  }
+
+  @Override
+  public Optional<RefasterTemplateCollectionTestData> tryExtract(
+      ClassTree tree, VisitorState state) {
+    Optional<String> className = getClassUnderTest(tree);
+    if (className.isEmpty()) {
+      return Optional.empty();
+    }
+
+    ImmutableList<RefasterTemplateTestData> templateTests =
+        tree.getMembers().stream()
+            .filter(m -> m instanceof MethodTree)
+            .map(MethodTree.class::cast)
+            .filter(m -> m.getName().toString().startsWith("test"))
+            .map(
+                m ->
+                    RefasterTemplateTestData.create(
+                        m.getName().toString().replace("test", ""), getSourceCode(m, state)))
+            .collect(toImmutableList());
+
+    return Optional.of(
+        RefasterTemplateCollectionTestData.create(className.orElseThrow(), true, templateTests));
+  }
+
+  private static Optional<String> getClassUnderTest(ClassTree tree) {
+    return Optional.of(TEST_INPUT_CLASS_NAME_PATTERN.matcher(tree.getSimpleName().toString()))
+        .filter(java.util.regex.Matcher::matches)
+        .map(m -> m.group(1));
+  }
+
+  // XXX: Duplicated from `SourceCode`. Can we do better?
+  private String getSourceCode(MethodTree tree, VisitorState state) {
+    String src = state.getSourceForNode(tree);
+    return src != null ? src : tree.toString();
+  }
+}

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

@@ -0,0 +1,61 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+
+import com.google.auto.service.AutoService;
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.annotations.Immutable;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.MethodTree;
+import java.util.Optional;
+import java.util.regex.Pattern;
+import tech.picnic.errorprone.documentation.models.RefasterTemplateCollectionTestData;
+import tech.picnic.errorprone.documentation.models.RefasterTemplateTestData;
+
+@Immutable
+@AutoService(Extractor.class)
+public final class RefasterTestOutputExtractor
+    implements Extractor<RefasterTemplateCollectionTestData> {
+  private static final Pattern TEST_INPUT_CLASS_NAME_PATTERN = Pattern.compile("(.*)TestOutput");
+
+  @Override
+  public String identifier() {
+    return "refaster-test-output";
+  }
+
+  @Override
+  public Optional<RefasterTemplateCollectionTestData> tryExtract(
+      ClassTree tree, VisitorState state) {
+    Optional<String> className = getClassUnderTest(tree);
+    if (className.isEmpty()) {
+      return Optional.empty();
+    }
+
+    ImmutableList<RefasterTemplateTestData> templateTests =
+        tree.getMembers().stream()
+            .filter(m -> m instanceof MethodTree)
+            .map(MethodTree.class::cast)
+            .filter(m -> m.getName().toString().startsWith("test"))
+            .map(
+                m ->
+                    RefasterTemplateTestData.create(
+                        m.getName().toString().replace("test", ""), getSourceCode(m, state)))
+            .collect(toImmutableList());
+
+    return Optional.of(
+        RefasterTemplateCollectionTestData.create(className.orElseThrow(), true, templateTests));
+  }
+
+  private static Optional<String> getClassUnderTest(ClassTree tree) {
+    return Optional.of(TEST_INPUT_CLASS_NAME_PATTERN.matcher(tree.getSimpleName().toString()))
+        .filter(java.util.regex.Matcher::matches)
+        .map(m -> m.group(1));
+  }
+
+  // XXX: Duplicated from `SourceCode`. Can we do better?
+  private String getSourceCode(MethodTree tree, VisitorState state) {
+    String src = state.getSourceForNode(tree);
+    return src != null ? src : tree.toString();
+  }
+}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

error-prone-contrib/pom.xml

@@ -5,7 +5,7 @@
     <parent>
         <groupId>tech.picnic.error-prone-support</groupId>
         <artifactId>error-prone-support</artifactId>
-        <version>0.5.1-SNAPSHOT</version>
+        <version>0.9.1-SNAPSHOT</version>
     </parent>
 
     <artifactId>error-prone-contrib</artifactId>
@@ -37,7 +37,15 @@
         <dependency>
             <groupId>${groupId.error-prone}</groupId>
             <artifactId>error_prone_test_helpers</artifactId>
-            <scope>test</scope>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>documentation-support</artifactId>
+            <!-- This dependency is declared only as a hint to Maven that
+            compilation depends on it; see the `maven-compiler-plugin`'s
+            `annotationProcessorPaths` configuration below. -->
+            <scope>provided</scope>
         </dependency>
         <dependency>
             <groupId>${project.groupId}</groupId>
@@ -146,7 +154,7 @@
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-api</artifactId>
-            <scope>test</scope>
+            <scope>provided</scope>
         </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>
@@ -213,6 +221,11 @@
                     <artifactId>maven-compiler-plugin</artifactId>
                     <configuration>
                         <annotationProcessorPaths combine.children="append">
+                            <path>
+                                <groupId>${project.groupId}</groupId>
+                                <artifactId>documentation-support</artifactId>
+                                <version>${project.version}</version>
+                            </path>
                             <path>
                                 <groupId>${project.groupId}</groupId>
                                 <artifactId>refaster-compiler</artifactId>
@@ -226,6 +239,7 @@
                         </annotationProcessorPaths>
                         <compilerArgs combine.children="append">
                             <arg>-Xplugin:RefasterRuleCompiler</arg>
+                            <arg>-Xplugin:DocumentationGenerator -XoutputDirectory=${project.build.directory}/docs</arg>
                         </compilerArgs>
                     </configuration>
                 </plugin>
@@ -243,4 +257,33 @@
             </plugins>
         </pluginManagement>
     </build>
+
+    <profiles>
+        <profile>
+            <id>docgen</id>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.codehaus.mojo</groupId>
+                        <artifactId>build-helper-maven-plugin</artifactId>
+                        <version>3.3.0</version>
+                        <executions>
+                            <execution>
+                                <id>add-test-source</id>
+                                <goals>
+                                    <goal>add-test-source</goal>
+                                </goals>
+                                <phase>generate-test-sources</phase>
+                                <configuration>
+                                    <sources>
+                                        <source>src/test/resources</source>
+                                    </sources>
+                                </configuration>
+                            </execution>
+                        </executions>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
+    </profiles>
 </project>

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

@@ -0,0 +1,131 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.argument;
+import static com.google.errorprone.matchers.Matchers.isSameType;
+import static com.google.errorprone.matchers.Matchers.isVariable;
+import static com.google.errorprone.matchers.Matchers.not;
+import static com.google.errorprone.matchers.Matchers.returnStatement;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static com.google.errorprone.matchers.Matchers.toType;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.BlockTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.AssignmentTree;
+import com.sun.source.tree.BlockTree;
+import com.sun.source.tree.ExpressionStatementTree;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.source.tree.ReturnTree;
+import com.sun.source.tree.StatementTree;
+import com.sun.source.tree.Tree;
+import com.sun.source.tree.VariableTree;
+import com.sun.tools.javac.code.Symbol;
+import java.util.List;
+import java.util.Optional;
+import tech.picnic.errorprone.bugpatterns.util.MoreASTHelpers;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags unnecessary local variable assignments preceding a return
+ * statement.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Variable assignment is redundant; value can be returned directly",
+    link = BUG_PATTERNS_BASE_URL + "DirectReturn",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class DirectReturn extends BugChecker implements BlockTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<StatementTree> VARIABLE_RETURN = returnStatement(isVariable());
+  private static final Matcher<ExpressionTree> MOCKITO_MOCK_OR_SPY_WITH_IMPLICIT_TYPE =
+      allOf(
+          not(toType(MethodInvocationTree.class, argument(0, isSameType(Class.class.getName())))),
+          staticMethod().onClass("org.mockito.Mockito").namedAnyOf("mock", "spy"));
+
+  /** Instantiates a new {@link DirectReturn} instance. */
+  public DirectReturn() {}
+
+  @Override
+  public Description matchBlock(BlockTree tree, VisitorState state) {
+    List<? extends StatementTree> statements = tree.getStatements();
+    if (statements.size() < 2) {
+      return Description.NO_MATCH;
+    }
+
+    StatementTree finalStatement = statements.get(statements.size() - 1);
+    if (!VARIABLE_RETURN.matches(finalStatement, state)) {
+      return Description.NO_MATCH;
+    }
+
+    Symbol variableSymbol = ASTHelpers.getSymbol(((ReturnTree) finalStatement).getExpression());
+    StatementTree precedingStatement = statements.get(statements.size() - 2);
+
+    return tryMatchAssignment(variableSymbol, precedingStatement)
+        .filter(resultExpr -> canInlineToReturnStatement(resultExpr, state))
+        .map(
+            resultExpr ->
+                describeMatch(
+                    precedingStatement,
+                    SuggestedFix.builder()
+                        .replace(
+                            precedingStatement,
+                            String.format("return %s;", SourceCode.treeToString(resultExpr, state)))
+                        .delete(finalStatement)
+                        .build()))
+        .orElse(Description.NO_MATCH);
+  }
+
+  private static Optional<ExpressionTree> tryMatchAssignment(Symbol targetSymbol, Tree tree) {
+    if (tree instanceof ExpressionStatementTree) {
+      return tryMatchAssignment(targetSymbol, ((ExpressionStatementTree) tree).getExpression());
+    }
+
+    if (tree instanceof AssignmentTree) {
+      AssignmentTree assignment = (AssignmentTree) tree;
+      return targetSymbol.equals(ASTHelpers.getSymbol(assignment.getVariable()))
+          ? Optional.of(assignment.getExpression())
+          : Optional.empty();
+    }
+
+    if (tree instanceof VariableTree) {
+      VariableTree declaration = (VariableTree) tree;
+      return declaration.getModifiers().getAnnotations().isEmpty()
+              && targetSymbol.equals(ASTHelpers.getSymbol(declaration))
+          ? Optional.ofNullable(declaration.getInitializer())
+          : Optional.empty();
+    }
+
+    return Optional.empty();
+  }
+
+  /**
+   * Tells whether inlining the given expression to the associated return statement can be done
+   * safely.
+   *
+   * <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.
+   */
+  private static boolean canInlineToReturnStatement(
+      ExpressionTree expressionTree, VisitorState state) {
+    return !MOCKITO_MOCK_OR_SPY_WITH_IMPLICIT_TYPE.matches(expressionTree, state)
+        || MoreASTHelpers.findMethodExitedOnReturn(state)
+            .filter(m -> MoreASTHelpers.areSameType(expressionTree, m.getReturnType(), state))
+            .isPresent();
+  }
+}

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

@@ -152,7 +152,7 @@ public final class ErrorProneTestHelperSourceFormat extends BugChecker
     StringBuilder source = new StringBuilder();
 
     for (ExpressionTree sourceLine : sourceLines) {
-      Object value = ASTHelpers.constValue(sourceLine);
+      String value = ASTHelpers.constValue(sourceLine, String.class);
       if (value == null) {
         return Optional.empty();
       }

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

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

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

@@ -32,7 +32,7 @@ import com.sun.source.util.SimpleTreeVisitor;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**

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

@@ -23,6 +23,7 @@ import com.google.errorprone.matchers.Matcher;
 import com.google.errorprone.util.ASTHelpers;
 import com.google.errorprone.util.ASTHelpers.TargetType;
 import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MemberSelectTree;
 import com.sun.source.tree.MethodInvocationTree;
 import com.sun.tools.javac.code.Type;
 import com.sun.tools.javac.code.Types;
@@ -32,7 +33,7 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /** A {@link BugChecker} that flags redundant identity conversions. */
 // XXX: Consider detecting cases where a flagged expression is passed to a method, and where removal
-// of the identify conversion would cause a different method overload to be selected. Depending on
+// 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.
 @AutoService(BugChecker.class)
 @BugPattern(
@@ -45,6 +46,13 @@ public final class IdentityConversion extends BugChecker implements MethodInvoca
   private static final long serialVersionUID = 1L;
   private static final Matcher<ExpressionTree> IS_CONVERSION_METHOD =
       anyOf(
+          staticMethod()
+              .onClassAny(
+                  Primitives.allWrapperTypes().stream()
+                      .map(Class::getName)
+                      .collect(toImmutableSet()))
+              .named("valueOf"),
+          staticMethod().onClass(String.class.getName()).named("valueOf"),
           staticMethod()
               .onClassAny(
                   "com.google.common.collect.ImmutableBiMap",
@@ -60,12 +68,8 @@ public final class IdentityConversion extends BugChecker implements MethodInvoca
                   "com.google.common.collect.ImmutableTable")
               .named("copyOf"),
           staticMethod()
-              .onClassAny(
-                  Primitives.allWrapperTypes().stream()
-                      .map(Class::getName)
-                      .collect(toImmutableSet()))
-              .named("valueOf"),
-          staticMethod().onClass(String.class.getName()).named("valueOf"),
+              .onClass("com.google.errorprone.matchers.Matchers")
+              .namedAnyOf("allOf", "anyOf"),
           staticMethod().onClass("reactor.adapter.rxjava.RxJava2Adapter"),
           staticMethod()
               .onClass("reactor.core.publisher.Flux")
@@ -95,6 +99,15 @@ public final class IdentityConversion extends BugChecker implements MethodInvoca
       return Description.NO_MATCH;
     }
 
+    if (sourceType.isPrimitive()
+        && state.getPath().getParentPath().getLeaf() instanceof MemberSelectTree) {
+      /*
+       * The result of the conversion method is dereferenced, while the source type is a primitive:
+       * dropping the conversion would yield uncompilable code.
+       */
+      return Description.NO_MATCH;
+    }
+
     return buildDescription(tree)
         .setMessage(
             "This method invocation appears redundant; remove it or suppress this warning and "

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

@@ -6,15 +6,18 @@ import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
+import com.google.common.collect.Iterables;
 import com.google.errorprone.BugPattern;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.LambdaExpressionTreeMatcher;
 import com.google.errorprone.fixes.SuggestedFix;
 import com.google.errorprone.matchers.Description;
+import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.InstanceOfTree;
 import com.sun.source.tree.LambdaExpressionTree;
 import com.sun.source.tree.Tree.Kind;
+import com.sun.source.tree.VariableTree;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
@@ -39,15 +42,19 @@ public final class IsInstanceLambdaUsage extends BugChecker implements LambdaExp
 
   @Override
   public Description matchLambdaExpression(LambdaExpressionTree tree, VisitorState state) {
-    if (tree.getKind() != Kind.LAMBDA_EXPRESSION || tree.getBody().getKind() != Kind.INSTANCE_OF) {
+    if (tree.getParameters().size() != 1 || tree.getBody().getKind() != Kind.INSTANCE_OF) {
+      return Description.NO_MATCH;
+    }
+
+    VariableTree param = Iterables.getOnlyElement(tree.getParameters());
+    InstanceOfTree instanceOf = (InstanceOfTree) tree.getBody();
+    if (!ASTHelpers.getSymbol(param).equals(ASTHelpers.getSymbol(instanceOf.getExpression()))) {
       return Description.NO_MATCH;
     }
 
     return describeMatch(
         tree,
         SuggestedFix.replace(
-            tree,
-            SourceCode.treeToString(((InstanceOfTree) tree.getBody()).getType(), state)
-                + ".class::isInstance"));
+            tree, SourceCode.treeToString(instanceOf.getType(), state) + ".class::isInstance"));
   }
 }

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

@@ -3,21 +3,18 @@ package tech.picnic.errorprone.bugpatterns;
 import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
 import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
 import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
-import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
 import static com.google.errorprone.matchers.Matchers.allOf;
-import static com.google.errorprone.matchers.Matchers.annotations;
-import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.Matchers.enclosingClass;
 import static com.google.errorprone.matchers.Matchers.hasModifier;
-import static com.google.errorprone.matchers.Matchers.isType;
+import static com.google.errorprone.matchers.Matchers.not;
 import static java.util.function.Predicate.not;
 import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
-import static tech.picnic.errorprone.bugpatterns.util.JavaKeywords.isReservedKeyword;
 import static tech.picnic.errorprone.bugpatterns.util.MoreJUnitMatchers.SETUP_OR_TEARDOWN_METHOD;
 import static tech.picnic.errorprone.bugpatterns.util.MoreJUnitMatchers.TEST_METHOD;
 
 import com.google.auto.service.AutoService;
 import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Sets;
 import com.google.errorprone.BugPattern;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
@@ -26,15 +23,12 @@ 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.util.ASTHelpers;
-import com.sun.source.tree.ImportTree;
 import com.sun.source.tree.MethodTree;
-import com.sun.source.tree.Tree;
+import com.sun.tools.javac.code.Symbol.MethodSymbol;
 import java.util.Optional;
 import javax.lang.model.element.Modifier;
-import tech.picnic.errorprone.bugpatterns.util.MoreASTHelpers;
-import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+import tech.picnic.errorprone.bugpatterns.util.ConflictDetection;
 
 /** A {@link BugChecker} that flags non-canonical JUnit method declarations. */
 // XXX: Consider introducing a class-level check that enforces that test classes:
@@ -53,21 +47,19 @@ public final class JUnitMethodDeclaration extends BugChecker implements MethodTr
   private static final long serialVersionUID = 1L;
   private static final String TEST_PREFIX = "test";
   private static final ImmutableSet<Modifier> ILLEGAL_MODIFIERS =
-      ImmutableSet.of(Modifier.PRIVATE, Modifier.PROTECTED, Modifier.PUBLIC);
-  private static final Matcher<MethodTree> HAS_UNMODIFIABLE_SIGNATURE =
-      anyOf(
-          annotations(AT_LEAST_ONE, isType("java.lang.Override")),
-          allOf(
-              Matchers.not(hasModifier(Modifier.FINAL)),
-              Matchers.not(hasModifier(Modifier.PRIVATE)),
-              enclosingClass(hasModifier(Modifier.ABSTRACT))));
+      Sets.immutableEnumSet(Modifier.PRIVATE, Modifier.PROTECTED, Modifier.PUBLIC);
+  private static final Matcher<MethodTree> IS_LIKELY_OVERRIDDEN =
+      allOf(
+          not(hasModifier(Modifier.FINAL)),
+          not(hasModifier(Modifier.PRIVATE)),
+          enclosingClass(hasModifier(Modifier.ABSTRACT)));
 
   /** Instantiates a new {@link JUnitMethodDeclaration} instance. */
   public JUnitMethodDeclaration() {}
 
   @Override
   public Description matchMethod(MethodTree tree, VisitorState state) {
-    if (HAS_UNMODIFIABLE_SIGNATURE.matches(tree, state)) {
+    if (IS_LIKELY_OVERRIDDEN.matches(tree, state) || isOverride(tree, state)) {
       return Description.NO_MATCH;
     }
 
@@ -89,10 +81,11 @@ public final class JUnitMethodDeclaration extends BugChecker implements MethodTr
 
   private void suggestTestMethodRenameIfApplicable(
       MethodTree tree, SuggestedFix.Builder fixBuilder, VisitorState state) {
-    tryCanonicalizeMethodName(tree)
+    MethodSymbol symbol = ASTHelpers.getSymbol(tree);
+    tryCanonicalizeMethodName(symbol)
         .ifPresent(
             newName ->
-                findMethodRenameBlocker(newName, state)
+                ConflictDetection.findMethodRenameBlocker(symbol, newName, state)
                     .ifPresentOrElse(
                         blocker -> reportMethodRenameBlocker(tree, blocker, state),
                         () -> fixBuilder.merge(SuggestedFixes.renameMethod(tree, newName, state))));
@@ -108,58 +101,18 @@ public final class JUnitMethodDeclaration extends BugChecker implements MethodTr
             .build());
   }
 
-  /**
-   * If applicable, returns a human-readable argument against assigning the given name to an
-   * existing method.
-   *
-   * <p>This method implements imperfect heuristics. Things it currently does not consider include
-   * the following:
-   *
-   * <ul>
-   *   <li>Whether the rename would merely introduce a method overload, rather than clashing with an
-   *       existing method declaration.
-   *   <li>Whether the rename would cause a method in a superclass to be overridden.
-   *   <li>Whether the rename would in fact clash with a static import. (It could be that a static
-   *       import of the same name is only referenced from lexical scopes in which the method under
-   *       consideration cannot be referenced directly.)
-   * </ul>
-   */
-  private static Optional<String> findMethodRenameBlocker(String methodName, VisitorState state) {
-    if (MoreASTHelpers.methodExistsInEnclosingClass(methodName, state)) {
-      return Optional.of(
-          String.format("a method named `%s` already exists in this class", methodName));
-    }
-
-    if (isSimpleNameStaticallyImported(methodName, state)) {
-      return Optional.of(String.format("`%s` is already statically imported", methodName));
-    }
-
-    if (isReservedKeyword(methodName)) {
-      return Optional.of(String.format("`%s` is a reserved keyword", methodName));
-    }
-
-    return Optional.empty();
-  }
-
-  private static boolean isSimpleNameStaticallyImported(String simpleName, VisitorState state) {
-    return state.getPath().getCompilationUnit().getImports().stream()
-        .filter(ImportTree::isStatic)
-        .map(ImportTree::getQualifiedIdentifier)
-        .map(tree -> getStaticImportSimpleName(tree, state))
-        .anyMatch(simpleName::contentEquals);
-  }
-
-  private static CharSequence getStaticImportSimpleName(Tree tree, VisitorState state) {
-    String source = SourceCode.treeToString(tree, state);
-    return source.subSequence(source.lastIndexOf('.') + 1, source.length());
-  }
-
-  private static Optional<String> tryCanonicalizeMethodName(MethodTree tree) {
-    return Optional.of(ASTHelpers.getSymbol(tree).getQualifiedName().toString())
+  private static Optional<String> tryCanonicalizeMethodName(MethodSymbol symbol) {
+    return Optional.of(symbol.getQualifiedName().toString())
         .filter(name -> name.startsWith(TEST_PREFIX))
         .map(name -> name.substring(TEST_PREFIX.length()))
         .filter(not(String::isEmpty))
         .map(name -> Character.toLowerCase(name.charAt(0)) + name.substring(1))
         .filter(name -> !Character.isDigit(name.charAt(0)));
   }
+
+  private static boolean isOverride(MethodTree tree, VisitorState state) {
+    return ASTHelpers.streamSuperMethods(ASTHelpers.getSymbol(tree), state.getTypes())
+        .findAny()
+        .isPresent();
+  }
 }

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

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

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

@@ -40,8 +40,9 @@ import java.util.List;
 import java.util.Optional;
 import java.util.Set;
 import java.util.stream.Stream;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.bugpatterns.util.AnnotationAttributeMatcher;
+import tech.picnic.errorprone.bugpatterns.util.Flags;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
@@ -220,7 +221,7 @@ public final class LexicographicalAnnotationAttributeListing extends BugChecker
 
   private static ImmutableList<String> excludedAnnotations(ErrorProneFlags flags) {
     Set<String> exclusions = new HashSet<>();
-    flags.getList(EXCLUDED_ANNOTATIONS_FLAG).ifPresent(exclusions::addAll);
+    exclusions.addAll(Flags.getList(flags, EXCLUDED_ANNOTATIONS_FLAG));
     exclusions.addAll(BLACKLISTED_ANNOTATIONS);
     return ImmutableList.copyOf(exclusions);
   }

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

@@ -27,7 +27,7 @@ import com.sun.tools.javac.code.Symbol;
 import com.sun.tools.javac.code.TypeAnnotations.AnnotationType;
 import java.util.Comparator;
 import java.util.List;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**

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

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

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

@@ -41,8 +41,11 @@ public final class NestedOptionals extends BugChecker implements MethodInvocatio
 
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
-    return state.getTypes().isSubtype(ASTHelpers.getType(tree), OPTIONAL_OF_OPTIONAL.get(state))
-        ? describeMatch(tree)
-        : Description.NO_MATCH;
+    Type type = OPTIONAL_OF_OPTIONAL.get(state);
+    if (type == null || !state.getTypes().isSubtype(ASTHelpers.getType(tree), type)) {
+      return Description.NO_MATCH;
+    }
+
+    return describeMatch(tree);
   }
 }

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

@@ -7,6 +7,7 @@ import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static com.google.errorprone.matchers.Matchers.allOf;
 import static com.google.errorprone.matchers.Matchers.anyMethod;
 import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.anything;
 import static com.google.errorprone.matchers.Matchers.argumentCount;
 import static com.google.errorprone.matchers.Matchers.isNonNullUsingDataflow;
 import static com.google.errorprone.matchers.Matchers.isSameType;
@@ -49,6 +50,7 @@ import java.util.Locale;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.stream.Stream;
+import tech.picnic.errorprone.bugpatterns.util.Flags;
 import tech.picnic.errorprone.bugpatterns.util.MethodMatcherFactory;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
@@ -63,13 +65,10 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 public final class RedundantStringConversion extends BugChecker
     implements BinaryTreeMatcher, CompoundAssignmentTreeMatcher, MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
-  private static final String FLAG_PREFIX = "RedundantStringConversion:";
   private static final String EXTRA_STRING_CONVERSION_METHODS_FLAG =
-      FLAG_PREFIX + "ExtraConversionMethods";
-
-  @SuppressWarnings("UnnecessaryLambda")
-  private static final Matcher<ExpressionTree> ANY_EXPR = (t, s) -> true;
+      "RedundantStringConversion:ExtraConversionMethods";
 
+  private static final Matcher<ExpressionTree> ANY_EXPR = anything();
   private static final Matcher<ExpressionTree> LOCALE = isSameType(Locale.class);
   private static final Matcher<ExpressionTree> MARKER = isSubtypeOf("org.slf4j.Marker");
   private static final Matcher<ExpressionTree> STRING = isSameType(String.class);
@@ -374,10 +373,9 @@ public final class RedundantStringConversion extends BugChecker
       ErrorProneFlags flags) {
     // XXX: ErrorProneFlags#getList splits by comma, but method signatures may also contain commas.
     // For this class methods accepting more than one argument are not valid, but still: not nice.
-    return flags
-        .getList(EXTRA_STRING_CONVERSION_METHODS_FLAG)
-        .map(new MethodMatcherFactory()::create)
-        .map(m -> anyOf(WELL_KNOWN_STRING_CONVERSION_METHODS, m))
-        .orElse(WELL_KNOWN_STRING_CONVERSION_METHODS);
+    return anyOf(
+        WELL_KNOWN_STRING_CONVERSION_METHODS,
+        new MethodMatcherFactory()
+            .create(Flags.getList(flags, EXTRA_STRING_CONVERSION_METHODS_FLAG)));
   }
 }

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

@@ -74,9 +74,13 @@ public final class RequestMappingAnnotation extends BugChecker implements Method
                   isSameType("java.time.ZoneId"),
                   isSameType("java.util.Locale"),
                   isSameType("java.util.TimeZone"),
+                  isSameType("jakarta.servlet.http.HttpServletRequest"),
+                  isSameType("jakarta.servlet.http.HttpServletResponse"),
                   isSameType("javax.servlet.http.HttpServletRequest"),
                   isSameType("javax.servlet.http.HttpServletResponse"),
                   isSameType("org.springframework.http.HttpMethod"),
+                  isSameType("org.springframework.ui.Model"),
+                  isSameType("org.springframework.validation.BindingResult"),
                   isSameType("org.springframework.web.context.request.NativeWebRequest"),
                   isSameType("org.springframework.web.context.request.WebRequest"),
                   isSameType("org.springframework.web.server.ServerWebExchange"),

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

@@ -1,5 +1,6 @@
 package tech.picnic.errorprone.bugpatterns;
 
+import static com.google.common.collect.ImmutableList.toImmutableList;
 import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
 import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
 import static com.google.errorprone.BugPattern.StandardTags.LIKELY_ERROR;
@@ -9,41 +10,72 @@ import static com.google.errorprone.matchers.Matchers.annotations;
 import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
 import static com.google.errorprone.matchers.Matchers.isType;
+import static com.google.errorprone.matchers.Matchers.not;
 import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.common.collect.ImmutableCollection;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.errorprone.BugPattern;
+import com.google.errorprone.ErrorProneFlags;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.VariableTreeMatcher;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.suppliers.Suppliers;
+import com.sun.source.tree.Tree;
 import com.sun.source.tree.VariableTree;
+import tech.picnic.errorprone.bugpatterns.util.Flags;
 
 /** A {@link BugChecker} that flags {@code @RequestParam} parameters with an unsupported type. */
 @AutoService(BugChecker.class)
 @BugPattern(
-    summary = "`@RequestParam` does not support `ImmutableCollection` and `ImmutableMap` subtypes",
+    summary =
+        "By default, `@RequestParam` does not support `ImmutableCollection` and `ImmutableMap` subtypes",
     link = BUG_PATTERNS_BASE_URL + "RequestParamType",
     linkType = CUSTOM,
     severity = ERROR,
     tags = LIKELY_ERROR)
 public final class RequestParamType extends BugChecker implements VariableTreeMatcher {
   private static final long serialVersionUID = 1L;
-  private static final Matcher<VariableTree> HAS_UNSUPPORTED_REQUEST_PARAM =
-      allOf(
-          annotations(AT_LEAST_ONE, isType("org.springframework.web.bind.annotation.RequestParam")),
-          anyOf(isSubtypeOf(ImmutableCollection.class), isSubtypeOf(ImmutableMap.class)));
+  private static final String SUPPORTED_CUSTOM_TYPES_FLAG = "RequestParamType:SupportedCustomTypes";
 
-  /** Instantiates a new {@link RequestParamType} instance. */
-  public RequestParamType() {}
+  private final Matcher<VariableTree> hasUnsupportedRequestParamType;
+
+  /** Instantiates a default {@link RequestParamType} instance. */
+  public RequestParamType() {
+    this(ErrorProneFlags.empty());
+  }
+
+  /**
+   * Instantiates a customized {@link RequestParamType} instance.
+   *
+   * @param flags Any provided command line flags.
+   */
+  public RequestParamType(ErrorProneFlags flags) {
+    hasUnsupportedRequestParamType = hasUnsupportedRequestParamType(flags);
+  }
 
   @Override
   public Description matchVariable(VariableTree tree, VisitorState state) {
-    return HAS_UNSUPPORTED_REQUEST_PARAM.matches(tree, state)
+    return hasUnsupportedRequestParamType.matches(tree, state)
         ? describeMatch(tree)
         : Description.NO_MATCH;
   }
+
+  private static Matcher<VariableTree> hasUnsupportedRequestParamType(ErrorProneFlags flags) {
+    return allOf(
+        annotations(AT_LEAST_ONE, isType("org.springframework.web.bind.annotation.RequestParam")),
+        anyOf(isSubtypeOf(ImmutableCollection.class), isSubtypeOf(ImmutableMap.class)),
+        not(isSubtypeOfAny(Flags.getList(flags, SUPPORTED_CUSTOM_TYPES_FLAG))));
+  }
+
+  private static Matcher<Tree> isSubtypeOfAny(ImmutableList<String> inclusions) {
+    return anyOf(
+        inclusions.stream()
+            .map(inclusion -> isSubtypeOf(Suppliers.typeFromString(inclusion)))
+            .collect(toImmutableList()));
+  }
 }

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

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

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

@@ -27,7 +27,7 @@ import com.sun.tools.javac.util.Convert;
 import java.util.Formattable;
 import java.util.Iterator;
 import java.util.List;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**

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

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

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

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

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

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

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

@@ -4,7 +4,19 @@ import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Sets;
 
 /** Utility class that can be used to identify reserved keywords of the Java language. */
+// XXX: This class is no longer only about keywords. Consider changing its name and class-level
+// documentation.
 public final class JavaKeywords {
+  /**
+   * Enumeration of boolean and null literals.
+   *
+   * @see <a href="https://docs.oracle.com/javase/specs/jls/se17/html/jls-3.html#jls-3.10.3">JDK 17
+   *     JLS section 3.10.3: Boolean Literals</a>
+   * @see <a href="https://docs.oracle.com/javase/specs/jls/se17/html/jls-3.html#jls-3.10.8">JDK 17
+   *     JLS section 3.10.8: The Null Literal</a>
+   */
+  private static final ImmutableSet<String> BOOLEAN_AND_NULL_LITERALS =
+      ImmutableSet.of("true", "false", "null");
   /**
    * List of all reserved keywords in the Java language.
    *
@@ -64,7 +76,6 @@ public final class JavaKeywords {
           "void",
           "volatile",
           "while");
-
   /**
    * List of all contextual keywords in the Java language.
    *
@@ -89,13 +100,28 @@ public final class JavaKeywords {
           "var",
           "with",
           "yield");
-
   /** List of all keywords in the Java language. */
   private static final ImmutableSet<String> ALL_KEYWORDS =
       Sets.union(RESERVED_KEYWORDS, CONTEXTUAL_KEYWORDS).immutableCopy();
 
   private JavaKeywords() {}
 
+  /**
+   * Tells whether the given string is a valid identifier in the Java language.
+   *
+   * @param str The string of interest.
+   * @return {@code true} if the given string is a valid identifier in the Java language.
+   * @see <a href="https://docs.oracle.com/javase/specs/jls/se17/html/jls-3.html#jls-3.8">JDK 17 JLS
+   *     section 3.8: Identifiers</a>
+   */
+  public static boolean isValidIdentifier(String str) {
+    return !str.isEmpty()
+        && !isReservedKeyword(str)
+        && !BOOLEAN_AND_NULL_LITERALS.contains(str)
+        && Character.isJavaIdentifierStart(str.codePointAt(0))
+        && str.codePoints().skip(1).allMatch(Character::isUnicodeIdentifierPart);
+  }
+
   /**
    * Tells whether the given string is a reserved keyword in the Java language.
    *

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

@@ -5,8 +5,12 @@ import static com.google.common.collect.ImmutableList.toImmutableList;
 
 import com.google.common.collect.ImmutableList;
 import com.google.errorprone.VisitorState;
+import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.LambdaExpressionTree;
 import com.sun.source.tree.MethodTree;
+import com.sun.source.tree.Tree;
+import java.util.Optional;
 
 /**
  * A collection of helper methods for working with the AST.
@@ -46,4 +50,33 @@ public final class MoreASTHelpers {
   public static boolean methodExistsInEnclosingClass(CharSequence methodName, VisitorState state) {
     return !findMethods(methodName, state).isEmpty();
   }
+
+  /**
+   * Returns the {@link MethodTree} from which control flow would exit if there would be a {@code
+   * return} statement at the given {@link VisitorState}'s current {@link VisitorState#getPath()
+   * path}.
+   *
+   * @param state The {@link VisitorState} from which to derive the AST location of interest.
+   * @return A {@link MethodTree}, unless the {@link VisitorState}'s path does not point to an AST
+   *     node located inside a method, or if the (hypothetical) {@code return} statement would exit
+   *     a lambda expression instead.
+   */
+  public static Optional<MethodTree> findMethodExitedOnReturn(VisitorState state) {
+    return Optional.ofNullable(state.findEnclosing(LambdaExpressionTree.class, MethodTree.class))
+        .filter(MethodTree.class::isInstance)
+        .map(MethodTree.class::cast);
+  }
+
+  /**
+   * Tells whether the given trees are of the same type, after type erasure.
+   *
+   * @param treeA The first tree of interest.
+   * @param treeB The second tree of interest.
+   * @param state The {@link VisitorState} describing the context in which the given trees were
+   *     found.
+   * @return Whether the specified trees have the same erased types.
+   */
+  public static boolean areSameType(Tree treeA, Tree treeB, VisitorState state) {
+    return ASTHelpers.isSameType(ASTHelpers.getType(treeA), ASTHelpers.getType(treeB), state);
+  }
 }

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

@@ -1,6 +1,6 @@
 package tech.picnic.errorprone.bugpatterns.util;
 
-import static com.google.common.collect.ImmutableSet.toImmutableSet;
+import static com.google.common.collect.ImmutableList.toImmutableList;
 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;
@@ -9,7 +9,7 @@ import static java.util.Objects.requireNonNullElse;
 import static tech.picnic.errorprone.bugpatterns.util.MoreMatchers.hasMetaAnnotation;
 
 import com.google.common.base.Strings;
-import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.ImmutableList;
 import com.google.errorprone.matchers.AnnotationMatcherUtils;
 import com.google.errorprone.matchers.Matcher;
 import com.google.errorprone.matchers.MultiMatcher;
@@ -18,7 +18,7 @@ import com.sun.source.tree.AnnotationTree;
 import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.MethodTree;
 import com.sun.source.tree.NewArrayTree;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A collection of JUnit-specific helper methods and {@link Matcher}s.
@@ -55,25 +55,59 @@ public final class MoreJUnitMatchers {
    * Returns the names of the JUnit value factory methods specified by the given {@link
    * org.junit.jupiter.params.provider.MethodSource} annotation.
    *
+   * <p>This method differs from {@link #getMethodSourceFactoryDescriptors(AnnotationTree,
+   * MethodTree)} in that it drops any parenthesized method parameter type enumerations. That is,
+   * method descriptors such as {@code factoryMethod()} and {@code factoryMethod(java.lang.String)}
+   * are both simplified to just {@code factoryMethod}. This also means that the returned method
+   * names may not unambiguously reference a single value factory method; in such a case JUnit will
+   * throw an error at runtime.
+   *
    * @param methodSourceAnnotation The annotation from which to extract value factory method names.
-   * @return One or more value factory names.
+   * @param method The method on which the annotation is located.
+   * @return One or more value factory descriptors, in the order defined.
+   * @see #getMethodSourceFactoryDescriptors(AnnotationTree, MethodTree)
    */
-  static ImmutableSet<String> getMethodSourceFactoryNames(
+  // XXX: Drop this method in favour of `#getMethodSourceFactoryDescriptors`. That will require
+  // callers to either explicitly drop information, or perform a more advanced analysis.
+  public static ImmutableList<String> getMethodSourceFactoryNames(
+      AnnotationTree methodSourceAnnotation, MethodTree method) {
+    return getMethodSourceFactoryDescriptors(methodSourceAnnotation, method).stream()
+        .map(
+            descriptor -> {
+              int index = descriptor.indexOf('(');
+              return index < 0 ? descriptor : descriptor.substring(0, index);
+            })
+        .collect(toImmutableList());
+  }
+
+  /**
+   * Returns the descriptors of the JUnit value factory methods specified by the given {@link
+   * org.junit.jupiter.params.provider.MethodSource} annotation.
+   *
+   * @param methodSourceAnnotation The annotation from which to extract value factory method
+   *     descriptors.
+   * @param method The method on which the annotation is located.
+   * @return One or more value factory descriptors, in the order defined.
+   * @see #getMethodSourceFactoryNames(AnnotationTree, MethodTree)
+   */
+  // XXX: Rather than strings, have this method return instances of a value type capable of
+  // resolving the value factory method pointed to.
+  public static ImmutableList<String> getMethodSourceFactoryDescriptors(
       AnnotationTree methodSourceAnnotation, MethodTree method) {
     String methodName = method.getName().toString();
     ExpressionTree value = AnnotationMatcherUtils.getArgument(methodSourceAnnotation, "value");
 
     if (!(value instanceof NewArrayTree)) {
-      return ImmutableSet.of(toMethodSourceFactoryName(value, methodName));
+      return ImmutableList.of(toMethodSourceFactoryDescriptor(value, methodName));
     }
 
     return ((NewArrayTree) value)
         .getInitializers().stream()
-            .map(name -> toMethodSourceFactoryName(name, methodName))
-            .collect(toImmutableSet());
+            .map(name -> toMethodSourceFactoryDescriptor(name, methodName))
+            .collect(toImmutableList());
   }
 
-  private static String toMethodSourceFactoryName(
+  private static String toMethodSourceFactoryDescriptor(
       @Nullable ExpressionTree tree, String annotatedMethodName) {
     return requireNonNullElse(
         Strings.emptyToNull(ASTHelpers.constValue(tree, String.class)), annotatedMethodName);

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

@@ -1,4 +1,4 @@
 /** Auxiliary utilities for use by Error Prone checks. */
 @com.google.errorprone.annotations.CheckReturnValue
-@org.jspecify.nullness.NullMarked
+@org.jspecify.annotations.NullMarked
 package tech.picnic.errorprone.bugpatterns.util;

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

@@ -22,7 +22,6 @@ final class AssertJOptionalRules {
 
   static final class AssertThatOptional<T> {
     @BeforeTemplate
-    @SuppressWarnings("NullAway")
     ObjectAssert<T> before(Optional<T> optional) {
       return assertThat(optional.orElseThrow());
     }

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

@@ -1,11 +1,16 @@
 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 org.assertj.core.api.Assertions.assertThat;
 
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.nio.file.Files;
+import java.nio.file.Path;
 import org.assertj.core.api.AbstractAssert;
 import org.assertj.core.api.AbstractStringAssert;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
@@ -89,4 +94,30 @@ final class AssertJStringRules {
       return assertThat(string).doesNotMatch(regex);
     }
   }
+
+  static final class AssertThatPathContent {
+    @BeforeTemplate
+    AbstractStringAssert<?> before(Path path, Charset charset) throws IOException {
+      return assertThat(Files.readString(path, charset));
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    AbstractStringAssert<?> after(Path path, Charset charset) {
+      return assertThat(path).content(charset);
+    }
+  }
+
+  static final class AssertThatPathContentUtf8 {
+    @BeforeTemplate
+    AbstractStringAssert<?> before(Path path) throws IOException {
+      return assertThat(Files.readString(path));
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    AbstractStringAssert<?> after(Path path) {
+      return assertThat(path).content(UTF_8);
+    }
+  }
 }

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

@@ -24,7 +24,7 @@ import java.util.Iterator;
 import java.util.Objects;
 import java.util.Set;
 import java.util.stream.Stream;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /**
@@ -103,7 +103,8 @@ final class AssortedRules {
     }
 
     @AfterTemplate
-    @Nullable T after(Iterator<T> iterator, T defaultValue) {
+    @Nullable
+    T after(Iterator<T> iterator, T defaultValue) {
       return Iterators.getNext(iterator, defaultValue);
     }
   }

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

@@ -50,17 +50,18 @@ final class BigDecimalRules {
     }
   }
 
-  /** Prefer {@link BigDecimal#valueOf(long)} over the associated constructor. */
-  // XXX: Ideally we'd also rewrite `BigDecimal.valueOf("<some-integer-value>")`, but it doesn't
-  // appear that's currently possible with Error Prone.
-  static final class BigDecimalFactoryMethod {
+  /** Prefer {@link BigDecimal#valueOf(double)} over the associated constructor. */
+  // XXX: Ideally we also rewrite `new BigDecimal("<some-integer-value>")` in cases where the
+  // specified number can be represented as an `int` or `long`, but that requires a custom
+  // `BugChecker`.
+  static final class BigDecimalValueOf {
     @BeforeTemplate
-    BigDecimal before(long value) {
+    BigDecimal before(double value) {
       return new BigDecimal(value);
     }
 
     @AfterTemplate
-    BigDecimal after(long value) {
+    BigDecimal after(double value) {
       return BigDecimal.valueOf(value);
     }
   }

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

@@ -0,0 +1,53 @@
+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.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+
+/** Refaster rules related to {@link com.google.errorprone.bugpatterns.BugChecker} classes. */
+@OnlineDocumentation
+final class BugCheckerRules {
+  private BugCheckerRules() {}
+
+  /**
+   * Avoid calling {@link BugCheckerRefactoringTestHelper#setFixChooser(FixChooser)} or {@link
+   * BugCheckerRefactoringTestHelper#setImportOrder(String)} with their respective default values.
+   */
+  static final class BugCheckerRefactoringTestHelperIdentity {
+    @BeforeTemplate
+    BugCheckerRefactoringTestHelper before(BugCheckerRefactoringTestHelper helper) {
+      return Refaster.anyOf(
+          helper.setFixChooser(FixChoosers.FIRST), helper.setImportOrder("static-first"));
+    }
+
+    @AfterTemplate
+    BugCheckerRefactoringTestHelper after(BugCheckerRefactoringTestHelper helper) {
+      return helper;
+    }
+  }
+
+  /**
+   * Prefer {@link BugCheckerRefactoringTestHelper.ExpectOutput#expectUnchanged()} over repeating
+   * the input.
+   */
+  // XXX: This rule assumes that the full source code is specified as a single string, e.g. using a
+  // text block. Support for multi-line source code input would require a `BugChecker`
+  // implementation instead.
+  static final class BugCheckerRefactoringTestHelperAddInputLinesExpectUnchanged {
+    @BeforeTemplate
+    BugCheckerRefactoringTestHelper before(
+        BugCheckerRefactoringTestHelper helper, String path, String source) {
+      return helper.addInputLines(path, source).addOutputLines(path, source);
+    }
+
+    @AfterTemplate
+    BugCheckerRefactoringTestHelper after(
+        BugCheckerRefactoringTestHelper helper, String path, String source) {
+      return helper.addInputLines(path, source).expectUnchanged();
+    }
+  }
+}

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

@@ -17,6 +17,7 @@ import java.util.Optional;
 import java.util.Queue;
 import java.util.Set;
 import java.util.SortedSet;
+import java.util.function.Consumer;
 import java.util.function.IntFunction;
 import java.util.stream.Stream;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
@@ -404,6 +405,19 @@ final class CollectionRules {
     }
   }
 
+  /** Prefer {@link Collection#forEach(Consumer)} over more contrived alternatives. */
+  static final class CollectionForEach<T> {
+    @BeforeTemplate
+    void before(Collection<T> collection, Consumer<? super T> consumer) {
+      collection.stream().forEach(consumer);
+    }
+
+    @AfterTemplate
+    void after(Collection<T> collection, Consumer<? super T> consumer) {
+      collection.forEach(consumer);
+    }
+  }
+
   // XXX: collection.stream().noneMatch(e -> e.equals(other))
   // ^ This is !collection.contains(other). Do we already rewrite variations on this?
 }

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

@@ -15,6 +15,7 @@ import com.google.common.collect.ImmutableSet;
 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 java.util.Arrays;
 import java.util.Collections;
@@ -24,6 +25,7 @@ import java.util.function.Function;
 import java.util.function.ToDoubleFunction;
 import java.util.function.ToIntFunction;
 import java.util.function.ToLongFunction;
+import java.util.stream.Stream;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to expressions dealing with {@link Comparator}s. */
@@ -37,7 +39,10 @@ final class ComparatorRules {
     @BeforeTemplate
     Comparator<T> before() {
       return Refaster.anyOf(
-          comparing(Refaster.anyOf(identity(), v -> v)), Comparator.<T>reverseOrder().reversed());
+          T::compareTo,
+          comparing(Refaster.anyOf(identity(), v -> v)),
+          Collections.<T>reverseOrder(reverseOrder()),
+          Comparator.<T>reverseOrder().reversed());
     }
 
     @AfterTemplate
@@ -51,11 +56,15 @@ final class ComparatorRules {
   static final class ReverseOrder<T extends Comparable<? super T>> {
     @BeforeTemplate
     Comparator<T> before() {
-      return Comparator.<T>naturalOrder().reversed();
+      return Refaster.anyOf(
+          Collections.reverseOrder(),
+          Collections.<T>reverseOrder(naturalOrder()),
+          Comparator.<T>naturalOrder().reversed());
     }
 
+    // XXX: Add `@UseImportPolicy(STATIC_IMPORT_ALWAYS)` if/when
+    // https://github.com/google/error-prone/pull/3584 is merged and released.
     @AfterTemplate
-    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
     Comparator<T> after() {
       return reverseOrder();
     }
@@ -189,15 +198,54 @@ final class ComparatorRules {
     }
   }
 
+  /** Prefer {@link Comparable#compareTo(Object)}} over more verbose alternatives. */
+  static final class CompareTo<T extends Comparable<? super T>> {
+    @BeforeTemplate
+    int before(T value1, T value2) {
+      return Refaster.anyOf(
+          Comparator.<T>naturalOrder().compare(value1, value2),
+          Comparator.<T>reverseOrder().compare(value2, value1));
+    }
+
+    @AfterTemplate
+    int after(T value1, T value2) {
+      return value1.compareTo(value2);
+    }
+  }
+
+  /**
+   * Avoid unnecessary creation of a {@link Stream} to determine the minimum of a known collection
+   * of values.
+   */
+  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();
+    }
+
+    @AfterTemplate
+    T after(@Repeated T value, Comparator<T> cmp) {
+      return Collections.min(Arrays.asList(value), cmp);
+    }
+  }
+
   /** Prefer {@link Comparators#min(Comparable, Comparable)}} over more verbose alternatives. */
   static final class MinOfPairNaturalOrder<T extends Comparable<? super T>> {
     @BeforeTemplate
     T before(T value1, T value2) {
-      return Collections.min(
-          Refaster.anyOf(
-              Arrays.asList(value1, value2),
-              ImmutableList.of(value1, value2),
-              ImmutableSet.of(value1, value2)));
+      return Refaster.anyOf(
+          value1.compareTo(value2) <= 0 ? value1 : value2,
+          value1.compareTo(value2) > 0 ? value2 : value1,
+          value2.compareTo(value1) < 0 ? value2 : value1,
+          value2.compareTo(value1) >= 0 ? value1 : value2,
+          Comparators.min(value1, value2, naturalOrder()),
+          Comparators.max(value1, value2, reverseOrder()),
+          Collections.min(
+              Refaster.anyOf(
+                  Arrays.asList(value1, value2),
+                  ImmutableList.of(value1, value2),
+                  ImmutableSet.of(value1, value2))));
     }
 
     @AfterTemplate
@@ -212,12 +260,17 @@ final class ComparatorRules {
   static final class MinOfPairCustomOrder<T> {
     @BeforeTemplate
     T before(T value1, T value2, Comparator<T> cmp) {
-      return Collections.min(
-          Refaster.anyOf(
-              Arrays.asList(value1, value2),
-              ImmutableList.of(value1, value2),
-              ImmutableSet.of(value1, value2)),
-          cmp);
+      return Refaster.anyOf(
+          cmp.compare(value1, value2) <= 0 ? value1 : value2,
+          cmp.compare(value1, value2) > 0 ? value2 : value1,
+          cmp.compare(value2, value1) < 0 ? value2 : value1,
+          cmp.compare(value2, value1) >= 0 ? value1 : value2,
+          Collections.min(
+              Refaster.anyOf(
+                  Arrays.asList(value1, value2),
+                  ImmutableList.of(value1, value2),
+                  ImmutableSet.of(value1, value2)),
+              cmp));
     }
 
     @AfterTemplate
@@ -226,15 +279,39 @@ final class ComparatorRules {
     }
   }
 
+  /**
+   * Avoid unnecessary creation of a {@link Stream} to determine the maximum of a known collection
+   * of values.
+   */
+  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();
+    }
+
+    @AfterTemplate
+    T after(@Repeated T value, Comparator<T> cmp) {
+      return Collections.max(Arrays.asList(value), cmp);
+    }
+  }
+
   /** Prefer {@link Comparators#max(Comparable, Comparable)}} over more verbose alternatives. */
   static final class MaxOfPairNaturalOrder<T extends Comparable<? super T>> {
     @BeforeTemplate
     T before(T value1, T value2) {
-      return Collections.max(
-          Refaster.anyOf(
-              Arrays.asList(value1, value2),
-              ImmutableList.of(value1, value2),
-              ImmutableSet.of(value1, value2)));
+      return Refaster.anyOf(
+          value1.compareTo(value2) >= 0 ? value1 : value2,
+          value1.compareTo(value2) < 0 ? value2 : value1,
+          value2.compareTo(value1) > 0 ? value2 : value1,
+          value2.compareTo(value1) <= 0 ? value1 : value2,
+          Comparators.max(value1, value2, naturalOrder()),
+          Comparators.min(value1, value2, reverseOrder()),
+          Collections.max(
+              Refaster.anyOf(
+                  Arrays.asList(value1, value2),
+                  ImmutableList.of(value1, value2),
+                  ImmutableSet.of(value1, value2))));
     }
 
     @AfterTemplate
@@ -249,12 +326,17 @@ final class ComparatorRules {
   static final class MaxOfPairCustomOrder<T> {
     @BeforeTemplate
     T before(T value1, T value2, Comparator<T> cmp) {
-      return Collections.max(
-          Refaster.anyOf(
-              Arrays.asList(value1, value2),
-              ImmutableList.of(value1, value2),
-              ImmutableSet.of(value1, value2)),
-          cmp);
+      return Refaster.anyOf(
+          cmp.compare(value1, value2) >= 0 ? value1 : value2,
+          cmp.compare(value1, value2) < 0 ? value2 : value1,
+          cmp.compare(value2, value1) > 0 ? value2 : value1,
+          cmp.compare(value2, value1) <= 0 ? value1 : value2,
+          Collections.max(
+              Refaster.anyOf(
+                  Arrays.asList(value1, value2),
+                  ImmutableList.of(value1, value2),
+                  ImmutableSet.of(value1, value2)),
+              cmp));
     }
 
     @AfterTemplate

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

@@ -141,6 +141,22 @@ final class DoubleStreamRules {
     }
   }
 
+  /**
+   * Apply {@link DoubleStream#filter(DoublePredicate)} before {@link DoubleStream#sorted()} to
+   * reduce the number of elements to sort.
+   */
+  static final class DoubleStreamFilterSorted {
+    @BeforeTemplate
+    DoubleStream before(DoubleStream stream, DoublePredicate predicate) {
+      return stream.sorted().filter(predicate);
+    }
+
+    @AfterTemplate
+    DoubleStream after(DoubleStream stream, DoublePredicate predicate) {
+      return stream.filter(predicate).sorted();
+    }
+  }
+
   /** In order to test whether a stream has any element, simply try to find one. */
   static final class DoubleStreamIsEmpty {
     @BeforeTemplate

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

@@ -6,6 +6,7 @@ import static java.util.Collections.emptyMap;
 import static java.util.Collections.singletonMap;
 import static java.util.function.Function.identity;
 
+import com.google.common.base.Predicate;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Streams;
@@ -126,8 +127,8 @@ final class ImmutableMapRules {
   }
 
   /**
-   * Don't map a a stream's elements to map entries, only to subsequently collect them into an
-   * {@link ImmutableMap}. The collection can be performed directly.
+   * Don't map a stream's elements to map entries, only to subsequently collect them into an {@link
+   * ImmutableMap}. The collection can be performed directly.
    */
   abstract static class StreamOfMapEntriesToImmutableMap<E, K, V> {
     @Placeholder(allowsIdentity = true)
@@ -315,6 +316,48 @@ final class ImmutableMapRules {
     }
   }
 
+  /**
+   * Prefer creation of an immutable submap using {@link Maps#filterKeys(Map, Predicate)} over more
+   * contrived alternatives.
+   */
+  abstract static class ImmutableMapCopyOfMapsFilterKeys<K, V> {
+    @Placeholder(allowsIdentity = true)
+    abstract boolean keyFilter(@MayOptionallyUse K key);
+
+    @BeforeTemplate
+    ImmutableMap<K, V> before(ImmutableMap<K, V> map) {
+      return map.entrySet().stream()
+          .filter(e -> keyFilter(e.getKey()))
+          .collect(toImmutableMap(Map.Entry::getKey, Map.Entry::getValue));
+    }
+
+    @AfterTemplate
+    ImmutableMap<K, V> after(ImmutableMap<K, V> map) {
+      return ImmutableMap.copyOf(Maps.filterKeys(map, k -> keyFilter(k)));
+    }
+  }
+
+  /**
+   * Prefer creation of an immutable submap using {@link Maps#filterValues(Map, Predicate)} over
+   * more contrived alternatives.
+   */
+  abstract static class ImmutableMapCopyOfMapsFilterValues<K, V> {
+    @Placeholder(allowsIdentity = true)
+    abstract boolean valueFilter(@MayOptionallyUse V value);
+
+    @BeforeTemplate
+    ImmutableMap<K, V> before(ImmutableMap<K, V> map) {
+      return map.entrySet().stream()
+          .filter(e -> valueFilter(e.getValue()))
+          .collect(toImmutableMap(Map.Entry::getKey, Map.Entry::getValue));
+    }
+
+    @AfterTemplate
+    ImmutableMap<K, V> after(ImmutableMap<K, V> map) {
+      return ImmutableMap.copyOf(Maps.filterValues(map, v -> valueFilter(v)));
+    }
+  }
+
   // XXX: Add a rule for this:
   // Maps.transformValues(streamOfEntries.collect(groupBy(fun)), ImmutableMap::copyOf)
   // ->
@@ -323,9 +366,4 @@ final class ImmutableMapRules {
   // map.entrySet().stream().filter(keyPred).forEach(mapBuilder::put)
   // ->
   // mapBuilder.putAll(Maps.filterKeys(map, pred))
-  //
-  // map.entrySet().stream().filter(entry ->
-  // pred(entry.getKey())).collect(toImmutableMap(Map.Entry::getKey, Map.Entry::getValue))
-  // ->
-  // ImmutableMap.copyOf(Maps.filterKeys(map, pred))
 }

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

@@ -154,6 +154,22 @@ final class IntStreamRules {
     }
   }
 
+  /**
+   * Apply {@link IntStream#filter(IntPredicate)} before {@link IntStream#sorted()} to reduce the
+   * number of elements to sort.
+   */
+  static final class IntStreamFilterSorted {
+    @BeforeTemplate
+    IntStream before(IntStream stream, IntPredicate predicate) {
+      return stream.sorted().filter(predicate);
+    }
+
+    @AfterTemplate
+    IntStream after(IntStream stream, IntPredicate predicate) {
+      return stream.filter(predicate).sorted();
+    }
+  }
+
   /** In order to test whether a stream has any element, simply try to find one. */
   static final class IntStreamIsEmpty {
     @BeforeTemplate

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

@@ -0,0 +1,521 @@
+package tech.picnic.errorprone.refasterrules;
+
+import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatCode;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.assertj.core.api.Assertions.fail;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertThrowsExactly;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.annotations.DoNotCall;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import java.util.function.Supplier;
+import org.assertj.core.api.ThrowableAssert.ThrowingCallable;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.function.Executable;
+import org.junit.jupiter.api.function.ThrowingSupplier;
+import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+
+/**
+ * Refaster rules to replace JUnit assertions with AssertJ equivalents.
+ *
+ * <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: 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
+// `() -> toString()` match both `ThrowingSupplier` and `ThrowingCallable`, but `() -> "constant"`
+// is only compatible with the former.
+@OnlineDocumentation
+final class JUnitToAssertJRules {
+  private JUnitToAssertJRules() {}
+
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(
+        Assertions.class,
+        assertDoesNotThrow(() -> null),
+        assertInstanceOf(null, null),
+        assertThrows(null, null),
+        assertThrowsExactly(null, null),
+        (Runnable) () -> assertFalse(true),
+        (Runnable) () -> assertNotNull(null),
+        (Runnable) () -> assertNotSame(null, null),
+        (Runnable) () -> assertNull(null),
+        (Runnable) () -> assertSame(null, null),
+        (Runnable) () -> assertTrue(true));
+  }
+
+  static final class ThrowNewAssertionError {
+    @BeforeTemplate
+    void before() {
+      Assertions.fail();
+    }
+
+    @AfterTemplate
+    @DoNotCall
+    void after() {
+      throw new AssertionError();
+    }
+  }
+
+  static final class FailWithMessage<T> {
+    @BeforeTemplate
+    T before(String message) {
+      return Assertions.fail(message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    T after(String message) {
+      return fail(message);
+    }
+  }
+
+  static final class FailWithMessageAndThrowable<T> {
+    @BeforeTemplate
+    T before(String message, Throwable throwable) {
+      return Assertions.fail(message, throwable);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    T after(String message, Throwable throwable) {
+      return fail(message, throwable);
+    }
+  }
+
+  static final class FailWithThrowable {
+    @BeforeTemplate
+    void before(Throwable throwable) {
+      Assertions.fail(throwable);
+    }
+
+    @AfterTemplate
+    @DoNotCall
+    void after(Throwable throwable) {
+      throw new AssertionError(throwable);
+    }
+  }
+
+  static final class AssertThatIsTrue {
+    @BeforeTemplate
+    void before(boolean actual) {
+      assertTrue(actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual) {
+      assertThat(actual).isTrue();
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsTrue {
+    @BeforeTemplate
+    void before(boolean actual, String message) {
+      assertTrue(actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual, String message) {
+      assertThat(actual).withFailMessage(message).isTrue();
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsTrue {
+    @BeforeTemplate
+    void before(boolean actual, Supplier<String> supplier) {
+      assertTrue(actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isTrue();
+    }
+  }
+
+  static final class AssertThatIsFalse {
+    @BeforeTemplate
+    void before(boolean actual) {
+      assertFalse(actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual) {
+      assertThat(actual).isFalse();
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsFalse {
+    @BeforeTemplate
+    void before(boolean actual, String message) {
+      assertFalse(actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual, String message) {
+      assertThat(actual).withFailMessage(message).isFalse();
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsFalse {
+    @BeforeTemplate
+    void before(boolean actual, Supplier<String> supplier) {
+      assertFalse(actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isFalse();
+    }
+  }
+
+  static final class AssertThatIsNull {
+    @BeforeTemplate
+    void before(Object actual) {
+      assertNull(actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual) {
+      assertThat(actual).isNull();
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsNull {
+    @BeforeTemplate
+    void before(Object actual, String message) {
+      assertNull(actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, String message) {
+      assertThat(actual).withFailMessage(message).isNull();
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsNull {
+    @BeforeTemplate
+    void before(Object actual, Supplier<String> supplier) {
+      assertNull(actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isNull();
+    }
+  }
+
+  static final class AssertThatIsNotNull {
+    @BeforeTemplate
+    void before(Object actual) {
+      assertNotNull(actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual) {
+      assertThat(actual).isNotNull();
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsNotNull {
+    @BeforeTemplate
+    void before(Object actual, String message) {
+      assertNotNull(actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, String message) {
+      assertThat(actual).withFailMessage(message).isNotNull();
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsNotNull {
+    @BeforeTemplate
+    void before(Object actual, Supplier<String> supplier) {
+      assertNotNull(actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isNotNull();
+    }
+  }
+
+  static final class AssertThatIsSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected) {
+      assertSame(expected, actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected) {
+      assertThat(actual).isSameAs(expected);
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected, String message) {
+      assertSame(expected, actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected, String message) {
+      assertThat(actual).withFailMessage(message).isSameAs(expected);
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected, Supplier<String> supplier) {
+      assertSame(expected, actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isSameAs(expected);
+    }
+  }
+
+  static final class AssertThatIsNotSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected) {
+      assertNotSame(expected, actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected) {
+      assertThat(actual).isNotSameAs(expected);
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsNotSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected, String message) {
+      assertNotSame(expected, actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected, String message) {
+      assertThat(actual).withFailMessage(message).isNotSameAs(expected);
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsNotSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected, Supplier<String> supplier) {
+      assertNotSame(expected, actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isNotSameAs(expected);
+    }
+  }
+
+  static final class AssertThatThrownByIsExactlyInstanceOf<T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz) {
+      assertThrowsExactly(clazz, throwingCallable);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz) {
+      assertThatThrownBy(throwingCallable).isExactlyInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatThrownByWithFailMessageStringIsExactlyInstanceOf<
+      T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz, String message) {
+      assertThrowsExactly(clazz, throwingCallable, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz, String message) {
+      assertThatThrownBy(throwingCallable).withFailMessage(message).isExactlyInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatThrownByWithFailMessageSupplierIsExactlyInstanceOf<
+      T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz, Supplier<String> supplier) {
+      assertThrowsExactly(clazz, throwingCallable, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz, Supplier<String> supplier) {
+      assertThatThrownBy(throwingCallable).withFailMessage(supplier).isExactlyInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatThrownByIsInstanceOf<T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz) {
+      assertThrows(clazz, throwingCallable);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz) {
+      assertThatThrownBy(throwingCallable).isInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatThrownByWithFailMessageStringIsInstanceOf<T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz, String message) {
+      assertThrows(clazz, throwingCallable, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz, String message) {
+      assertThatThrownBy(throwingCallable).withFailMessage(message).isInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatThrownByWithFailMessageSupplierIsInstanceOf<T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz, Supplier<String> supplier) {
+      assertThrows(clazz, throwingCallable, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz, Supplier<String> supplier) {
+      assertThatThrownBy(throwingCallable).withFailMessage(supplier).isInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatCodeDoesNotThrowAnyException {
+    @BeforeTemplate
+    void before(Executable throwingCallable) {
+      assertDoesNotThrow(throwingCallable);
+    }
+
+    @BeforeTemplate
+    void before(ThrowingSupplier<?> throwingCallable) {
+      assertDoesNotThrow(throwingCallable);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable) {
+      assertThatCode(throwingCallable).doesNotThrowAnyException();
+    }
+  }
+
+  static final class AssertThatCodeWithFailMessageStringDoesNotThrowAnyException {
+    @BeforeTemplate
+    void before(Executable throwingCallable, String message) {
+      assertDoesNotThrow(throwingCallable, message);
+    }
+
+    @BeforeTemplate
+    void before(ThrowingSupplier<?> throwingCallable, String message) {
+      assertDoesNotThrow(throwingCallable, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, String message) {
+      assertThatCode(throwingCallable).withFailMessage(message).doesNotThrowAnyException();
+    }
+  }
+
+  static final class AssertThatCodeWithFailMessageSupplierDoesNotThrowAnyException {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Supplier<String> supplier) {
+      assertDoesNotThrow(throwingCallable, supplier);
+    }
+
+    @BeforeTemplate
+    void before(ThrowingSupplier<?> throwingCallable, Supplier<String> supplier) {
+      assertDoesNotThrow(throwingCallable, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Supplier<String> supplier) {
+      assertThatCode(throwingCallable).withFailMessage(supplier).doesNotThrowAnyException();
+    }
+  }
+
+  static final class AssertThatIsInstanceOf<T> {
+    @BeforeTemplate
+    void before(Object actual, Class<T> clazz) {
+      assertInstanceOf(clazz, actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Class<T> clazz) {
+      assertThat(actual).isInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsInstanceOf<T> {
+    @BeforeTemplate
+    void before(Object actual, Class<T> clazz, String message) {
+      assertInstanceOf(clazz, actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Class<T> clazz, String message) {
+      assertThat(actual).withFailMessage(message).isInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsInstanceOf<T> {
+    @BeforeTemplate
+    void before(Object actual, Class<T> clazz, Supplier<String> supplier) {
+      assertInstanceOf(clazz, actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Class<T> clazz, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isInstanceOf(clazz);
+    }
+  }
+}

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

@@ -154,6 +154,22 @@ final class LongStreamRules {
     }
   }
 
+  /**
+   * Apply {@link LongStream#filter(LongPredicate)} before {@link LongStream#sorted()} to reduce the
+   * number of elements to sort.
+   */
+  static final class LongStreamFilterSorted {
+    @BeforeTemplate
+    LongStream before(LongStream stream, LongPredicate predicate) {
+      return stream.sorted().filter(predicate);
+    }
+
+    @AfterTemplate
+    LongStream after(LongStream stream, LongPredicate predicate) {
+      return stream.filter(predicate).sorted();
+    }
+  }
+
   /** In order to test whether a stream has any element, simply try to find one. */
   static final class LongStreamIsEmpty {
     @BeforeTemplate

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

@@ -1,5 +1,7 @@
 package tech.picnic.errorprone.refasterrules;
 
+import static java.util.Objects.requireNonNullElse;
+
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
@@ -7,7 +9,7 @@ import java.util.EnumMap;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.stream.Stream;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to expressions dealing with {@link Map} instances. */
@@ -31,16 +33,33 @@ final class MapRules {
 
   static final class MapGetOrNull<K, V, T> {
     @BeforeTemplate
-    @Nullable V before(Map<K, V> map, T key) {
+    @Nullable
+    V before(Map<K, V> map, T key) {
       return map.getOrDefault(key, null);
     }
 
     @AfterTemplate
-    @Nullable V after(Map<K, V> map, T key) {
+    @Nullable
+    V after(Map<K, V> map, T key) {
       return map.get(key);
     }
   }
 
+  /** Prefer {@link Map#getOrDefault(Object, Object)} over more contrived alternatives. */
+  // XXX: Note that `requireNonNullElse` throws an NPE if the second argument is `null`, while the
+  // alternative does not.
+  static final class MapGetOrDefault<K, V, T> {
+    @BeforeTemplate
+    V before(Map<K, V> map, T key, V defaultValue) {
+      return requireNonNullElse(map.get(key), defaultValue);
+    }
+
+    @AfterTemplate
+    V after(Map<K, V> map, T key, V defaultValue) {
+      return map.getOrDefault(key, defaultValue);
+    }
+  }
+
   /** Prefer {@link Map#isEmpty()} over more contrived alternatives. */
   static final class MapIsEmpty<K, V> {
     @BeforeTemplate

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

@@ -7,7 +7,7 @@ import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import java.util.Collection;
 import java.util.Set;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to expressions dealing with {@link Multimap}s. */
@@ -50,7 +50,8 @@ final class MultimapRules {
    */
   static final class MultimapGet<K, V> {
     @BeforeTemplate
-    @Nullable Collection<V> before(Multimap<K, V> multimap, K key) {
+    @Nullable
+    Collection<V> before(Multimap<K, V> multimap, K key) {
       return Refaster.anyOf(multimap.asMap(), Multimaps.asMap(multimap)).get(key);
     }
 

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

@@ -2,14 +2,18 @@ package tech.picnic.errorprone.refasterrules;
 
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 import static java.util.Objects.requireNonNullElse;
+import static java.util.Objects.requireNonNullElseGet;
 
 import com.google.common.base.MoreObjects;
+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 java.util.Objects;
+import java.util.Optional;
 import java.util.function.Predicate;
-import org.jspecify.nullness.Nullable;
+import java.util.function.Supplier;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to expressions dealing with (possibly) null values. */
@@ -17,11 +21,14 @@ import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 final class NullRules {
   private NullRules() {}
 
-  /** Prefer the {@code ==} operator over {@link Objects#isNull(Object)}. */
+  /**
+   * Prefer the {@code ==} operator (with {@code null} as the second operand) over {@link
+   * Objects#isNull(Object)}.
+   */
   static final class IsNull {
     @BeforeTemplate
     boolean before(@Nullable Object object) {
-      return Objects.isNull(object);
+      return Refaster.anyOf(null == object, Objects.isNull(object));
     }
 
     @AfterTemplate
@@ -30,11 +37,14 @@ final class NullRules {
     }
   }
 
-  /** Prefer the {@code !=} operator over {@link Objects#nonNull(Object)}. */
+  /**
+   * Prefer the {@code !=} operator (with {@code null} as the second operand) over {@link
+   * Objects#nonNull(Object)}.
+   */
   static final class IsNotNull {
     @BeforeTemplate
     boolean before(@Nullable Object object) {
-      return Objects.nonNull(object);
+      return Refaster.anyOf(null != object, Objects.nonNull(object));
     }
 
     @AfterTemplate
@@ -43,13 +53,18 @@ final class NullRules {
     }
   }
 
-  /** Prefer {@link Objects#requireNonNullElse(Object, Object)} over the Guava alternative. */
-  // XXX: This rule is not valid in case `second` is `@Nullable`: in that case the Guava variant
-  // will return `null`, while the JDK variant will throw an NPE.
+  /**
+   * Prefer {@link Objects#requireNonNullElse(Object, Object)} over non-JDK or more contrived
+   * alternatives.
+   */
+  // XXX: This rule is not valid in case `second` is `@Nullable`: in that case the Guava and
+  // `Optional` variants will return `null`, where the `requireNonNullElse` alternative will throw
+  // an NPE.
   static final class RequireNonNullElse<T> {
     @BeforeTemplate
     T before(T first, T second) {
-      return MoreObjects.firstNonNull(first, second);
+      return Refaster.anyOf(
+          MoreObjects.firstNonNull(first, second), Optional.ofNullable(first).orElse(second));
     }
 
     @AfterTemplate
@@ -59,6 +74,26 @@ final class NullRules {
     }
   }
 
+  /**
+   * Prefer {@link Objects#requireNonNullElseGet(Object, Supplier)} over more contrived
+   * alternatives.
+   */
+  // XXX: This rule is not valid in case `supplier` yields `@Nullable` values: in that case the
+  // `Optional` variant will return `null`, where the `requireNonNullElseGet` alternative will throw
+  // an NPE.
+  static final class RequireNonNullElseGet<T, S extends T> {
+    @BeforeTemplate
+    T before(T object, Supplier<S> supplier) {
+      return Optional.ofNullable(object).orElseGet(supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    T after(T object, Supplier<S> supplier) {
+      return requireNonNullElseGet(object, supplier);
+    }
+  }
+
   /** Prefer {@link Objects#isNull(Object)} over the equivalent lambda function. */
   static final class IsNullFunction<T> {
     @BeforeTemplate

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

@@ -16,7 +16,7 @@ import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
 import java.util.stream.Stream;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to expressions dealing with {@link Optional}s. */

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

@@ -6,11 +6,13 @@ import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkPositionIndex;
 import static com.google.common.base.Preconditions.checkState;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
+import static java.util.Objects.requireNonNull;
 
 import com.google.common.base.Preconditions;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import java.util.Objects;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster templates related to statements dealing with {@link Preconditions}. */
@@ -72,8 +74,22 @@ final class PreconditionsRules {
     }
   }
 
-  /** Prefer {@link Preconditions#checkNotNull(Object)} over more verbose alternatives. */
-  static final class CheckNotNull<T> {
+  /** Prefer {@link Objects#requireNonNull(Object)} over non-JDK alternatives. */
+  static final class RequireNonNull<T> {
+    @BeforeTemplate
+    T before(T object) {
+      return checkNotNull(object);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    T after(T object) {
+      return requireNonNull(object);
+    }
+  }
+
+  /** Prefer {@link Objects#requireNonNull(Object)} over more verbose alternatives. */
+  static final class RequireNonNullStatement<T> {
     @BeforeTemplate
     void before(T object) {
       if (object == null) {
@@ -84,12 +100,26 @@ final class PreconditionsRules {
     @AfterTemplate
     @UseImportPolicy(STATIC_IMPORT_ALWAYS)
     void after(T object) {
-      checkNotNull(object);
+      requireNonNull(object);
     }
   }
 
-  /** Prefer {@link Preconditions#checkNotNull(Object, Object)} over more verbose alternatives. */
-  static final class CheckNotNullWithMessage<T> {
+  /** Prefer {@link Objects#requireNonNull(Object, String)} over non-JDK alternatives. */
+  static final class RequireNonNullWithMessage<T> {
+    @BeforeTemplate
+    T before(T object, String message) {
+      return checkNotNull(object, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    T after(T object, String message) {
+      return requireNonNull(object, message);
+    }
+  }
+
+  /** Prefer {@link Objects#requireNonNull(Object, String)} over more verbose alternatives. */
+  static final class RequireNonNullWithMessageStatement<T> {
     @BeforeTemplate
     void before(T object, String message) {
       if (object == null) {
@@ -100,7 +130,7 @@ final class PreconditionsRules {
     @AfterTemplate
     @UseImportPolicy(STATIC_IMPORT_ALWAYS)
     void after(T object, String message) {
-      checkNotNull(object, message);
+      requireNonNull(object, message);
     }
   }
 

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

@@ -1,14 +1,17 @@
 package tech.picnic.errorprone.refasterrules;
 
+import static com.google.common.collect.ImmutableList.toImmutableList;
 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;
 import static java.util.function.Function.identity;
+import static java.util.stream.Collectors.toCollection;
 import static org.assertj.core.api.Assertions.assertThat;
 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.MoreCollectors;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
@@ -17,7 +20,11 @@ import com.google.errorprone.refaster.annotation.NotMatches;
 import com.google.errorprone.refaster.annotation.Placeholder;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.time.Duration;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Comparator;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Optional;
 import java.util.concurrent.Callable;
 import java.util.function.BiConsumer;
@@ -26,6 +33,7 @@ import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
+import org.jspecify.annotations.Nullable;
 import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -59,6 +67,45 @@ final class ReactorRules {
     }
   }
 
+  /** Prefer {@link Mono#empty()} over more contrived alternatives. */
+  static final class MonoEmpty<T> {
+    @BeforeTemplate
+    Mono<T> before() {
+      return Refaster.anyOf(Mono.justOrEmpty(null), Mono.justOrEmpty(Optional.empty()));
+    }
+
+    @AfterTemplate
+    Mono<T> after() {
+      return Mono.empty();
+    }
+  }
+
+  /** Prefer {@link Mono#just(Object)} over more contrived alternatives. */
+  static final class MonoJust<T> {
+    @BeforeTemplate
+    Mono<T> before(T value) {
+      return Mono.justOrEmpty(Optional.of(value));
+    }
+
+    @AfterTemplate
+    Mono<T> after(T value) {
+      return Mono.just(value);
+    }
+  }
+
+  /** Prefer {@link Mono#justOrEmpty(Object)} over more contrived alternatives. */
+  static final class MonoJustOrEmpty<@Nullable T> {
+    @BeforeTemplate
+    Mono<T> before(T value) {
+      return Mono.justOrEmpty(Optional.ofNullable(value));
+    }
+
+    @AfterTemplate
+    Mono<T> after(T value) {
+      return Mono.justOrEmpty(value);
+    }
+  }
+
   /** 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.
@@ -78,6 +125,40 @@ final class ReactorRules {
     }
   }
 
+  /**
+   * Try to avoid expressions of type {@code Optional<Mono<T>>}, but if you must map an {@link
+   * Optional} to this type, prefer using {@link Mono#just(Object)}.
+   */
+  static final class OptionalMapMonoJust<T> {
+    @BeforeTemplate
+    Optional<Mono<T>> before(Optional<T> optional) {
+      return optional.map(Mono::justOrEmpty);
+    }
+
+    @AfterTemplate
+    Optional<Mono<T>> after(Optional<T> optional) {
+      return optional.map(Mono::just);
+    }
+  }
+
+  /**
+   * Prefer a {@link Mono#justOrEmpty(Optional)} and {@link Mono#switchIfEmpty(Mono)} chain over
+   * more contrived alternatives.
+   *
+   * <p>In particular, avoid mixing of the {@link Optional} and {@link Mono} APIs.
+   */
+  static final class MonoFromOptionalSwitchIfEmpty<T> {
+    @BeforeTemplate
+    Mono<T> before(Optional<T> optional, Mono<T> mono) {
+      return optional.map(Mono::just).orElse(mono);
+    }
+
+    @AfterTemplate
+    Mono<T> after(Optional<T> optional, Mono<T> mono) {
+      return Mono.justOrEmpty(optional).switchIfEmpty(mono);
+    }
+  }
+
   /**
    * Prefer {@link Mono#zip(Mono, Mono)} over a chained {@link Mono#zipWith(Mono)}, as the former
    * better conveys that the {@link Mono}s may be subscribed to concurrently, and generalizes to
@@ -290,11 +371,17 @@ final class ReactorRules {
     }
   }
 
-  /** Don't unnecessarily pass an empty publisher to {@link Mono#switchIfEmpty(Mono)}. */
-  static final class MonoSwitchIfEmptyOfEmptyPublisher<T> {
+  /** Don't unnecessarily transform a {@link Mono} to an equivalent instance. */
+  static final class MonoIdentity<T> {
     @BeforeTemplate
     Mono<T> before(Mono<T> mono) {
-      return mono.switchIfEmpty(Mono.empty());
+      return Refaster.anyOf(
+          mono.switchIfEmpty(Mono.empty()), mono.flux().next(), mono.flux().singleOrEmpty());
+    }
+
+    @BeforeTemplate
+    Mono<@Nullable Void> before2(Mono<@Nullable Void> mono) {
+      return mono.then();
     }
 
     @AfterTemplate
@@ -393,6 +480,11 @@ final class ReactorRules {
    * Flux}.
    */
   abstract static class MonoFlatMapToFlux<T, S> {
+    // XXX: It would be more expressive if this `@Placeholder` were replaced with a `Function<?
+    // super T, ? extends Mono<? extends S>>` parameter, so that compatible non-lambda expression
+    // arguments to `flatMapMany` are also matched. However, the type inferred for lambda and method
+    // reference expressions passed to `flatMapMany` appears to always be `Function<T, Publisher<?
+    // extends S>>`, which doesn't match. Find a solution.
     @Placeholder(allowsIdentity = true)
     abstract Mono<S> transformation(@MayOptionallyUse T value);
 
@@ -600,21 +692,34 @@ final class ReactorRules {
     }
   }
 
-  /**
-   * Prefer a collection using {@link MoreCollectors#toOptional()} over more contrived alternatives.
-   */
+  /** Prefer direct invocation of {@link Mono#then()}} over more contrived alternatives. */
+  static final class MonoThen<T> {
+    @BeforeTemplate
+    Mono<@Nullable Void> before(Mono<T> mono) {
+      return mono.flux().then();
+    }
+
+    @AfterTemplate
+    Mono<@Nullable Void> after(Mono<T> mono) {
+      return mono.then();
+    }
+  }
+
+  /** Prefer {@link Mono#singleOptional()} over more contrived alternatives. */
   // XXX: Consider creating a plugin that flags/discourages `Mono<Optional<T>>` method return
   // types, just as we discourage nullable `Boolean`s and `Optional`s.
-  static final class MonoCollectToOptional<T> {
+  static final class MonoSingleOptional<T> {
     @BeforeTemplate
     Mono<Optional<T>> before(Mono<T> mono) {
-      return mono.map(Optional::of).defaultIfEmpty(Optional.empty());
+      return Refaster.anyOf(
+          mono.flux().collect(toOptional()),
+          mono.map(Optional::of).defaultIfEmpty(Optional.empty()));
     }
 
     @AfterTemplate
     @UseImportPolicy(STATIC_IMPORT_ALWAYS)
     Mono<Optional<T>> after(Mono<T> mono) {
-      return mono.flux().collect(toOptional());
+      return mono.singleOptional();
     }
   }
 
@@ -707,6 +812,31 @@ final class ReactorRules {
     }
   }
 
+  /**
+   * Prefer {@link Flux#count()} followed by a conversion from {@code long} to {@code int} over
+   * collecting into a list and counting its elements.
+   */
+  static final class FluxCountMapMathToIntExact<T> {
+    @BeforeTemplate
+    Mono<Integer> before(Flux<T> flux) {
+      return Refaster.anyOf(
+          flux.collect(toImmutableList())
+              .map(
+                  Refaster.anyOf(
+                      Collection::size,
+                      List::size,
+                      ImmutableCollection::size,
+                      ImmutableList::size)),
+          flux.collect(toCollection(ArrayList::new))
+              .map(Refaster.anyOf(Collection::size, List::size)));
+    }
+
+    @AfterTemplate
+    Mono<Integer> after(Flux<T> flux) {
+      return flux.count().map(Math::toIntExact);
+    }
+  }
+
   /**
    * Prefer {@link Mono#doOnError(Class, Consumer)} over {@link Mono#doOnError(Predicate, Consumer)}
    * where possible.
@@ -988,6 +1118,38 @@ final class ReactorRules {
     }
   }
 
+  /**
+   * Apply {@link Flux#filter(Predicate)} before {@link Flux#sort()} to reduce the number of
+   * elements to sort.
+   */
+  static final class FluxFilterSort<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<? super T> predicate) {
+      return flux.sort().filter(predicate);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<? super T> predicate) {
+      return flux.filter(predicate).sort();
+    }
+  }
+
+  /**
+   * Apply {@link Flux#filter(Predicate)} before {@link Flux#sort(Comparator)} to reduce the number
+   * of elements to sort.
+   */
+  static final class FluxFilterSortWithComparator<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return flux.sort(comparator).filter(predicate);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return flux.filter(predicate).sort(comparator);
+    }
+  }
+
   /** 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.
@@ -1042,12 +1204,14 @@ final class ReactorRules {
     }
   }
 
-  /** Don't unnecessarily call {@link StepVerifier.Step#expectNext(Object[])}. */
-  static final class StepVerifierStepExpectNextEmpty<T> {
+  /** Don't unnecessarily have {@link StepVerifier.Step} expect no elements. */
+  // XXX: Given an `IsEmpty` matcher that identifies a wide range of guaranteed-empty `Iterable`
+  // expressions, consider also simplifying `step.expectNextSequence(someEmptyIterable)`.
+  static final class StepVerifierStepIdentity<T> {
     @BeforeTemplate
     @SuppressWarnings("unchecked")
     StepVerifier.Step<T> before(StepVerifier.Step<T> step) {
-      return step.expectNext();
+      return Refaster.anyOf(step.expectNext(), step.expectNextCount(0));
     }
 
     @AfterTemplate

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

@@ -9,7 +9,7 @@ import io.reactivex.Flowable;
 import io.reactivex.Maybe;
 import io.reactivex.Observable;
 import io.reactivex.Single;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 import reactor.adapter.rxjava.RxJava2Adapter;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;

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

@@ -10,6 +10,7 @@ import com.google.common.collect.Streams;
 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.Placeholder;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
@@ -19,10 +20,14 @@ import java.util.Objects;
 import java.util.Optional;
 import java.util.function.Function;
 import java.util.function.Predicate;
+import java.util.function.ToDoubleFunction;
+import java.util.function.ToIntFunction;
+import java.util.function.ToLongFunction;
 import java.util.stream.Collector;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+import tech.picnic.errorprone.refaster.matchers.IsLambdaExpressionOrMethodReference;
 
 /** Refaster rules related to expressions dealing with {@link Stream}s. */
 @OnlineDocumentation
@@ -77,6 +82,9 @@ 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) {
@@ -164,6 +172,40 @@ final class StreamRules {
     }
   }
 
+  /**
+   * Apply {@link Stream#filter(Predicate)} before {@link Stream#sorted()} to reduce the number of
+   * elements to sort.
+   */
+  static final class StreamFilterSorted<T> {
+    @BeforeTemplate
+    Stream<T> before(Stream<T> stream, Predicate<? super T> predicate) {
+      return stream.sorted().filter(predicate);
+    }
+
+    @AfterTemplate
+    Stream<T> after(Stream<T> stream, Predicate<? super T> predicate) {
+      return stream.filter(predicate).sorted();
+    }
+  }
+
+  /**
+   * Apply {@link Stream#filter(Predicate)} before {@link Stream#sorted(Comparator)} to reduce the
+   * number of elements to sort.
+   */
+  static final class StreamFilterSortedWithComparator<T> {
+    @BeforeTemplate
+    Stream<T> before(
+        Stream<T> stream, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return stream.sorted(comparator).filter(predicate);
+    }
+
+    @AfterTemplate
+    Stream<T> after(
+        Stream<T> stream, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return stream.filter(predicate).sorted(comparator);
+    }
+  }
+
   /**
    * Where possible, clarify that a mapping operation will be applied only to a single stream
    * element.
@@ -342,4 +384,46 @@ final class StreamRules {
       return stream.allMatch(e -> test(e));
     }
   }
+
+  static final class StreamMapToIntSum<T> {
+    @BeforeTemplate
+    int before(
+        Stream<T> stream,
+        @Matches(IsLambdaExpressionOrMethodReference.class) Function<? super T, Integer> mapper) {
+      return stream.map(mapper).reduce(0, Integer::sum);
+    }
+
+    @AfterTemplate
+    int after(Stream<T> stream, ToIntFunction<T> mapper) {
+      return stream.mapToInt(mapper).sum();
+    }
+  }
+
+  static final class StreamMapToDoubleSum<T> {
+    @BeforeTemplate
+    double before(
+        Stream<T> stream,
+        @Matches(IsLambdaExpressionOrMethodReference.class) Function<? super T, Double> mapper) {
+      return stream.map(mapper).reduce(0.0, Double::sum);
+    }
+
+    @AfterTemplate
+    double after(Stream<T> stream, ToDoubleFunction<T> mapper) {
+      return stream.mapToDouble(mapper).sum();
+    }
+  }
+
+  static final class StreamMapToLongSum<T> {
+    @BeforeTemplate
+    long before(
+        Stream<T> stream,
+        @Matches(IsLambdaExpressionOrMethodReference.class) Function<? super T, Long> mapper) {
+      return stream.map(mapper).reduce(0L, Long::sum);
+    }
+
+    @AfterTemplate
+    long after(Stream<T> stream, ToLongFunction<T> mapper) {
+      return stream.mapToLong(mapper).sum();
+    }
+  }
 }

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

@@ -16,7 +16,7 @@ import java.util.Collection;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.function.Function;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to expressions dealing with {@link String}s. */

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

@@ -28,6 +28,7 @@ import java.util.Set;
 import org.assertj.core.api.ThrowableAssert.ThrowingCallable;
 import org.testng.Assert;
 import org.testng.Assert.ThrowingRunnable;
+import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /**
  * Refaster rules that replace TestNG assertions with equivalent AssertJ assertions.
@@ -72,6 +73,7 @@ import org.testng.Assert.ThrowingRunnable;
 // XXX: As-is these rules do not result in a complete migration:
 // - Expressions containing comments are skipped due to a limitation of Refaster.
 // - Assertions inside lambda expressions are also skipped. Unclear why.
+@OnlineDocumentation
 final class TestNGToAssertJRules {
   private TestNGToAssertJRules() {}
 

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

@@ -1,4 +1,4 @@
 /** Picnic Refaster rules. */
 @com.google.errorprone.annotations.CheckReturnValue
-@org.jspecify.nullness.NullMarked
+@org.jspecify.annotations.NullMarked
 package tech.picnic.errorprone.refasterrules;

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

@@ -3,21 +3,16 @@ package tech.picnic.errorprone.bugpatterns;
 import static com.google.common.base.Predicates.containsPattern;
 
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
 import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class AmbiguousJsonCreatorTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(AmbiguousJsonCreator.class, getClass())
-          .expectErrorMessage(
-              "X",
-              containsPattern("`JsonCreator.Mode` should be set for single-argument creators"));
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(AmbiguousJsonCreator.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(AmbiguousJsonCreator.class, getClass())
+        .expectErrorMessage(
+            "X", containsPattern("`JsonCreator.Mode` should be set for single-argument creators"))
         .addSourceLines(
             "Container.java",
             "import com.fasterxml.jackson.annotation.JsonCreator;",
@@ -118,7 +113,7 @@ final class AmbiguousJsonCreatorTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(AmbiguousJsonCreator.class, getClass())
         .addInputLines(
             "A.java",
             "import com.fasterxml.jackson.annotation.JsonCreator;",
@@ -143,6 +138,6 @@ final class AmbiguousJsonCreatorTest {
             "    return FOO;",
             "  }",
             "}")
-        .doTest(BugCheckerRefactoringTestHelper.TestMode.TEXT_MATCH);
+        .doTest(TestMode.TEXT_MATCH);
   }
 }

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

@@ -7,14 +7,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class AssertJIsNullTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(AssertJIsNull.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(AssertJIsNull.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(AssertJIsNull.class, getClass())
         .addSourceLines(
             "A.java",
             "import static org.assertj.core.api.Assertions.assertThat;",
@@ -38,7 +33,7 @@ final class AssertJIsNullTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(AssertJIsNull.class, getClass())
         .addInputLines(
             "A.java",
             "import static org.assertj.core.api.Assertions.assertThat;",

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class AutowiredConstructorTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(AutowiredConstructor.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(AutowiredConstructor.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(AutowiredConstructor.class, getClass())
         .addSourceLines(
             "Container.java",
             "import com.google.errorprone.annotations.Immutable;",
@@ -71,7 +66,7 @@ final class AutowiredConstructorTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(AutowiredConstructor.class, getClass())
         .addInputLines(
             "Container.java",
             "import org.springframework.beans.factory.annotation.Autowired;",

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class CanonicalAnnotationSyntaxTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(CanonicalAnnotationSyntax.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(CanonicalAnnotationSyntax.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(CanonicalAnnotationSyntax.class, getClass())
         .addSourceLines(
             "pkg/A.java",
             "package pkg;",
@@ -133,7 +128,7 @@ final class CanonicalAnnotationSyntaxTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(CanonicalAnnotationSyntax.class, getClass())
         .addInputLines(
             "pkg/A.java",
             "package pkg;",

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

@@ -8,14 +8,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class CollectorMutabilityTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(CollectorMutability.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(CollectorMutability.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(CollectorMutability.class, getClass())
         .addSourceLines(
             "A.java",
             "import static com.google.common.collect.ImmutableList.toImmutableList;",
@@ -67,7 +62,7 @@ final class CollectorMutabilityTest {
 
   @Test
   void identificationWithoutGuavaOnClasspath() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(CollectorMutability.class, getClass())
         .withClasspath()
         .addSourceLines(
             "A.java",
@@ -84,7 +79,7 @@ final class CollectorMutabilityTest {
 
   @Test
   void replacementFirstSuggestedFix() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(CollectorMutability.class, getClass())
         .addInputLines(
             "A.java",
             "import static java.util.stream.Collectors.toList;",
@@ -141,7 +136,7 @@ final class CollectorMutabilityTest {
 
   @Test
   void replacementSecondSuggestedFix() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(CollectorMutability.class, getClass())
         .setFixChooser(SECOND)
         .addInputLines(
             "A.java",

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

@@ -0,0 +1,174 @@
+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 DirectReturnTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(DirectReturn.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import static org.mockito.Mockito.mock;",
+            "import static org.mockito.Mockito.spy;",
+            "",
+            "import java.util.function.Supplier;",
+            "",
+            "class A {",
+            "  private String field;",
+            "",
+            "  void emptyMethod() {}",
+            "",
+            "  void voidMethod() {",
+            "    toString();",
+            "    return;",
+            "  }",
+            "",
+            "  String directReturnOfParam(String param) {",
+            "    return param;",
+            "  }",
+            "",
+            "  String assignmentToField() {",
+            "    field = toString();",
+            "    return field;",
+            "  }",
+            "",
+            "  Object redundantAssignmentToParam(String param) {",
+            "    // BUG: Diagnostic contains:",
+            "    param = toString();",
+            "    return param;",
+            "  }",
+            "",
+            "  String redundantMockAssignmentToParam(String param) {",
+            "    // BUG: Diagnostic contains:",
+            "    param = mock();",
+            "    return param;",
+            "  }",
+            "",
+            "  Object redundantMockWithExplicitTypeAssignmentToParam(String param) {",
+            "    // BUG: Diagnostic contains:",
+            "    param = mock(String.class);",
+            "    return param;",
+            "  }",
+            "",
+            "  Object salientMockAssignmentToParam(String param) {",
+            "    param = mock();",
+            "    return param;",
+            "  }",
+            "",
+            "  String redundantAssignmentToLocalVariable() {",
+            "    String variable = null;",
+            "    // BUG: Diagnostic contains:",
+            "    variable = toString();",
+            "    return variable;",
+            "  }",
+            "",
+            "  String unusedAssignmentToLocalVariable(String param) {",
+            "    String variable = null;",
+            "    variable = toString();",
+            "    return param;",
+            "  }",
+            "",
+            "  String redundantVariableDeclaration() {",
+            "    // BUG: Diagnostic contains:",
+            "    String variable = toString();",
+            "    return variable;",
+            "  }",
+            "",
+            "  String redundantSpyVariableDeclaration() {",
+            "    // BUG: Diagnostic contains:",
+            "    String variable = spy();",
+            "    return variable;",
+            "  }",
+            "",
+            "  Object redundantSpyWithExplicitTypeVariableDeclaration() {",
+            "    // BUG: Diagnostic contains:",
+            "    String variable = spy(String.class);",
+            "    return variable;",
+            "  }",
+            "",
+            "  Object salientSpyTypeVariableDeclaration() {",
+            "    String variable = spy(\"name\");",
+            "    return variable;",
+            "  }",
+            "",
+            "  String unusedVariableDeclaration(String param) {",
+            "    String variable = toString();",
+            "    return param;",
+            "  }",
+            "",
+            "  String assignmentToAnnotatedVariable() {",
+            "    @SuppressWarnings(\"HereBeDragons\")",
+            "    String variable = toString();",
+            "    return variable;",
+            "  }",
+            "",
+            "  String complexReturnStatement() {",
+            "    String variable = toString();",
+            "    return variable + toString();",
+            "  }",
+            "",
+            "  String assignmentInsideIfClause() {",
+            "    String variable = null;",
+            "    if (true) {",
+            "      variable = toString();",
+            "    }",
+            "    return variable;",
+            "  }",
+            "",
+            "  String redundantAssignmentInsideElseClause() {",
+            "    String variable = toString();",
+            "    if (true) {",
+            "      return variable;",
+            "    } else {",
+            "      // BUG: Diagnostic contains:",
+            "      variable = \"foo\";",
+            "      return variable;",
+            "    }",
+            "  }",
+            "",
+            "  Supplier<String> redundantAssignmentInsideLambda() {",
+            "    return () -> {",
+            "      // BUG: Diagnostic contains:",
+            "      String variable = toString();",
+            "      return variable;",
+            "    };",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    BugCheckerRefactoringTestHelper.newInstance(DirectReturn.class, getClass())
+        .addInputLines(
+            "A.java",
+            "class A {",
+            "  String m1() {",
+            "    String variable = null;",
+            "    variable = toString();",
+            "    return variable;",
+            "  }",
+            "",
+            "  String m2() {",
+            "    String variable = toString();",
+            "    return variable;",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "class A {",
+            "  String m1() {",
+            "    String variable = null;",
+            "    return toString();",
+            "  }",
+            "",
+            "  String m2() {",
+            "    return toString();",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class EmptyMethodTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(EmptyMethod.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(EmptyMethod.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(EmptyMethod.class, getClass())
         .addSourceLines(
             "A.java",
             "class A {",
@@ -69,7 +64,7 @@ final class EmptyMethodTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(EmptyMethod.class, getClass())
         .addInputLines(
             "A.java",
             "final class A {",

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

@@ -6,15 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class ErrorProneTestHelperSourceFormatTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(ErrorProneTestHelperSourceFormat.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(
-          ErrorProneTestHelperSourceFormat.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(ErrorProneTestHelperSourceFormat.class, getClass())
         .addSourceLines(
             "A.java",
             "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
@@ -63,7 +57,7 @@ final class ErrorProneTestHelperSourceFormatTest {
      * Verifies that import sorting and code formatting is performed unconditionally, while unused
      * imports are removed unless part of a `BugCheckerRefactoringTestHelper` expected output file.
      */
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(ErrorProneTestHelperSourceFormat.class, getClass())
         .addInputLines(
             "A.java",
             "import com.google.errorprone.BugCheckerRefactoringTestHelper;",

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

@@ -4,12 +4,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class ExplicitEnumOrderingTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(ExplicitEnumOrdering.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(ExplicitEnumOrdering.class, getClass())
         .addSourceLines(
             "A.java",
             "import static java.lang.annotation.RetentionPolicy.CLASS;",

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

@@ -1,7 +1,5 @@
 package tech.picnic.errorprone.bugpatterns;
 
-import static com.google.errorprone.BugCheckerRefactoringTestHelper.newInstance;
-
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
@@ -9,14 +7,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class FluxFlatMapUsageTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(FluxFlatMapUsage.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      newInstance(FluxFlatMapUsage.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(FluxFlatMapUsage.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.function.BiFunction;",
@@ -73,8 +66,7 @@ final class FluxFlatMapUsageTest {
 
   @Test
   void replacementFirstSuggestedFix() {
-    refactoringTestHelper
-        .setFixChooser(FixChoosers.FIRST)
+    BugCheckerRefactoringTestHelper.newInstance(FluxFlatMapUsage.class, getClass())
         .addInputLines(
             "A.java",
             "import reactor.core.publisher.Flux;",
@@ -108,7 +100,7 @@ final class FluxFlatMapUsageTest {
 
   @Test
   void replacementSecondSuggestedFix() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(FluxFlatMapUsage.class, getClass())
         .setFixChooser(FixChoosers.SECOND)
         .addInputLines(
             "A.java",

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

@@ -0,0 +1,182 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.common.base.Predicates.and;
+import static com.google.common.base.Predicates.containsPattern;
+import static com.google.common.base.Predicates.not;
+import static com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers.SECOND;
+import static com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers.THIRD;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Test;
+import org.reactivestreams.Publisher;
+import reactor.core.CorePublisher;
+import reactor.core.publisher.Flux;
+
+final class FluxImplicitBlockTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(FluxImplicitBlock.class, getClass())
+        .expectErrorMessage(
+            "X",
+            and(
+                containsPattern("SuppressWarnings"),
+                containsPattern("toImmutableList"),
+                containsPattern("toList")))
+        .addSourceLines(
+            "A.java",
+            "import com.google.common.collect.ImmutableList;",
+            "import java.util.stream.Stream;",
+            "import reactor.core.publisher.Flux;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    // BUG: Diagnostic matches: X",
+            "    Flux.just(1).toIterable();",
+            "    // BUG: Diagnostic matches: X",
+            "    Flux.just(2).toStream();",
+            "    // BUG: Diagnostic matches: X",
+            "    long count = Flux.just(3).toStream().count();",
+            "",
+            "    Flux.just(4).toIterable(1);",
+            "    Flux.just(5).toIterable(2, null);",
+            "    Flux.just(6).toStream(3);",
+            "    new Foo().toIterable();",
+            "    new Foo().toStream();",
+            "  }",
+            "",
+            "  class Foo<T> {",
+            "    Iterable<T> toIterable() {",
+            "      return ImmutableList.of();",
+            "    }",
+            "",
+            "    Stream<T> toStream() {",
+            "      return Stream.empty();",
+            "    }",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void identificationWithoutGuavaOnClasspath() {
+    CompilationTestHelper.newInstance(FluxImplicitBlock.class, getClass())
+        .withClasspath(CorePublisher.class, Flux.class, Publisher.class)
+        .expectErrorMessage("X", not(containsPattern("toImmutableList")))
+        .addSourceLines(
+            "A.java",
+            "import reactor.core.publisher.Flux;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    // BUG: Diagnostic matches: X",
+            "    Flux.just(1).toIterable();",
+            "    // BUG: Diagnostic matches: X",
+            "    Flux.just(2).toStream();",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacementFirstSuggestedFix() {
+    BugCheckerRefactoringTestHelper.newInstance(FluxImplicitBlock.class, getClass())
+        .addInputLines(
+            "A.java",
+            "import reactor.core.publisher.Flux;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Flux.just(1).toIterable();",
+            "    Flux.just(2).toStream();",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import reactor.core.publisher.Flux;",
+            "",
+            "class A {",
+            "  @SuppressWarnings(\"FluxImplicitBlock\")",
+            "  void m() {",
+            "    Flux.just(1).toIterable();",
+            "    Flux.just(2).toStream();",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+
+  @Test
+  void replacementSecondSuggestedFix() {
+    BugCheckerRefactoringTestHelper.newInstance(FluxImplicitBlock.class, getClass())
+        .setFixChooser(SECOND)
+        .addInputLines(
+            "A.java",
+            "import reactor.core.publisher.Flux;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Flux.just(1).toIterable();",
+            "    Flux.just(2).toStream();",
+            "    Flux.just(3).toIterable().iterator();",
+            "    Flux.just(4).toStream().count();",
+            "    Flux.just(5) /* a */./* b */ toIterable /* c */(/* d */ ) /* e */;",
+            "    Flux.just(6) /* a */./* b */ toStream /* c */(/* d */ ) /* e */;",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import static com.google.common.collect.ImmutableList.toImmutableList;",
+            "",
+            "import reactor.core.publisher.Flux;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Flux.just(1).collect(toImmutableList()).block();",
+            "    Flux.just(2).collect(toImmutableList()).block().stream();",
+            "    Flux.just(3).collect(toImmutableList()).block().iterator();",
+            "    Flux.just(4).collect(toImmutableList()).block().stream().count();",
+            "    Flux.just(5).collect(toImmutableList()).block() /* e */;",
+            "    Flux.just(6).collect(toImmutableList()).block().stream() /* e */;",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+
+  @Test
+  void replacementThirdSuggestedFix() {
+    BugCheckerRefactoringTestHelper.newInstance(FluxImplicitBlock.class, getClass())
+        .setFixChooser(THIRD)
+        .addInputLines(
+            "A.java",
+            "import reactor.core.publisher.Flux;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Flux.just(1).toIterable();",
+            "    Flux.just(2).toStream();",
+            "    Flux.just(3).toIterable().iterator();",
+            "    Flux.just(4).toStream().count();",
+            "    Flux.just(5) /* a */./* b */ toIterable /* c */(/* d */ ) /* e */;",
+            "    Flux.just(6) /* a */./* b */ toStream /* c */(/* d */ ) /* e */;",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import static java.util.stream.Collectors.toList;",
+            "",
+            "import reactor.core.publisher.Flux;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Flux.just(1).collect(toList()).block();",
+            "    Flux.just(2).collect(toList()).block().stream();",
+            "    Flux.just(3).collect(toList()).block().iterator();",
+            "    Flux.just(4).collect(toList()).block().stream().count();",
+            "    Flux.just(5).collect(toList()).block() /* e */;",
+            "    Flux.just(6).collect(toList()).block().stream() /* e */;",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class FormatStringConcatenationTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(FormatStringConcatenation.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(FormatStringConcatenation.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(FormatStringConcatenation.class, getClass())
         .addSourceLines(
             "A.java",
             "import static com.google.common.base.Preconditions.checkArgument;",
@@ -309,7 +304,7 @@ final class FormatStringConcatenationTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(FormatStringConcatenation.class, getClass())
         .addInputLines(
             "A.java",
             "import static com.google.common.base.Preconditions.checkArgument;",

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

@@ -7,16 +7,14 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class IdentityConversionTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(IdentityConversion.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(IdentityConversion.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(IdentityConversion.class, getClass())
         .addSourceLines(
-            "Foo.java",
+            "A.java",
+            "import static com.google.errorprone.matchers.Matchers.instanceMethod;",
+            "import static com.google.errorprone.matchers.Matchers.staticMethod;",
+            "",
             "import com.google.common.collect.ImmutableBiMap;",
             "import com.google.common.collect.ImmutableList;",
             "import com.google.common.collect.ImmutableListMultimap;",
@@ -28,12 +26,14 @@ final class IdentityConversionTest {
             "import com.google.common.collect.ImmutableSet;",
             "import com.google.common.collect.ImmutableSetMultimap;",
             "import com.google.common.collect.ImmutableTable;",
+            "import com.google.errorprone.matchers.Matcher;",
+            "import com.google.errorprone.matchers.Matchers;",
             "import reactor.adapter.rxjava.RxJava2Adapter;",
             "import reactor.core.publisher.Flux;",
             "import reactor.core.publisher.Mono;",
             "",
-            "public final class Foo {",
-            "  public void foo() {",
+            "public final class A {",
+            "  public void m() {",
             "    // BUG: Diagnostic contains:",
             "    Boolean b1 = Boolean.valueOf(Boolean.FALSE);",
             "    // BUG: Diagnostic contains:",
@@ -113,6 +113,13 @@ final class IdentityConversionTest {
             "    // BUG: Diagnostic contains:",
             "    short s4 = Short.valueOf(Short.MIN_VALUE);",
             "",
+            "    // BUG: Diagnostic contains:",
+            "    String boolStr = Boolean.valueOf(Boolean.FALSE).toString();",
+            "    int boolHash = Boolean.valueOf(false).hashCode();",
+            "    // BUG: Diagnostic contains:",
+            "    int byteHash = Byte.valueOf((Byte) Byte.MIN_VALUE).hashCode();",
+            "    String byteStr = Byte.valueOf(Byte.MIN_VALUE).toString();",
+            "",
             "    String str1 = String.valueOf(0);",
             "    // BUG: Diagnostic contains:",
             "    String str2 = String.valueOf(\"1\");",
@@ -143,7 +150,15 @@ final class IdentityConversionTest {
             "    ImmutableTable<Object, Object, Object> o11 = ImmutableTable.copyOf(ImmutableTable.of());",
             "",
             "    // BUG: Diagnostic contains:",
+            "    Matcher allOf1 = Matchers.allOf(instanceMethod());",
+            "    Matcher allOf2 = Matchers.allOf(instanceMethod(), staticMethod());",
+            "    // BUG: Diagnostic contains:",
+            "    Matcher anyOf1 = Matchers.anyOf(staticMethod());",
+            "    Matcher anyOf2 = Matchers.anyOf(instanceMethod(), staticMethod());",
+            "",
+            "    // BUG: Diagnostic contains:",
             "    Flux<Integer> flux1 = Flux.just(1).flatMap(e -> RxJava2Adapter.fluxToFlowable(Flux.just(2)));",
+            "",
             "    // BUG: Diagnostic contains:",
             "    Flux<Integer> flux2 = Flux.concat(Flux.just(1));",
             "    // BUG: Diagnostic contains:",
@@ -154,9 +169,9 @@ final class IdentityConversionTest {
             "    Flux<Integer> flux5 = Flux.merge(Flux.just(1));",
             "",
             "    // BUG: Diagnostic contains:",
-            "    Mono<Integer> m1 = Mono.from(Mono.just(1));",
+            "    Mono<Integer> mono1 = Mono.from(Mono.just(1));",
             "    // BUG: Diagnostic contains:",
-            "    Mono<Integer> m2 = Mono.fromDirect(Mono.just(1));",
+            "    Mono<Integer> mono2 = Mono.fromDirect(Mono.just(1));",
             "  }",
             "}")
         .doTest();
@@ -164,15 +179,17 @@ final class IdentityConversionTest {
 
   @Test
   void replacementFirstSuggestedFix() {
-    refactoringTestHelper
-        .setFixChooser(FixChoosers.FIRST)
+    BugCheckerRefactoringTestHelper.newInstance(IdentityConversion.class, getClass())
         .addInputLines(
-            "Foo.java",
+            "A.java",
+            "import static com.google.errorprone.matchers.Matchers.staticMethod;",
             "import static org.mockito.Mockito.when;",
             "",
             "import com.google.common.collect.ImmutableCollection;",
             "import com.google.common.collect.ImmutableList;",
             "import com.google.common.collect.ImmutableSet;",
+            "import com.google.errorprone.matchers.Matcher;",
+            "import com.google.errorprone.matchers.Matchers;",
             "import java.util.ArrayList;",
             "import java.util.Collection;",
             "import org.reactivestreams.Publisher;",
@@ -180,8 +197,8 @@ final class IdentityConversionTest {
             "import reactor.core.publisher.Flux;",
             "import reactor.core.publisher.Mono;",
             "",
-            "public final class Foo {",
-            "  public void foo() {",
+            "public final class A {",
+            "  public void m() {",
             "    ImmutableSet<Object> set1 = ImmutableSet.copyOf(ImmutableSet.of());",
             "    ImmutableSet<Object> set2 = ImmutableSet.copyOf(ImmutableList.of());",
             "",
@@ -206,18 +223,23 @@ final class IdentityConversionTest {
             "    Object o1 = ImmutableSet.copyOf(ImmutableList.of());",
             "    Object o2 = ImmutableSet.copyOf(ImmutableSet.of());",
             "",
+            "    Matcher matcher = Matchers.allOf(staticMethod());",
+            "",
             "    when(\"foo\".contains(\"f\")).thenAnswer(inv -> ImmutableSet.copyOf(ImmutableList.of(1)));",
             "  }",
             "",
             "  void bar(Publisher<Integer> publisher) {}",
             "}")
         .addOutputLines(
-            "Foo.java",
+            "A.java",
+            "import static com.google.errorprone.matchers.Matchers.staticMethod;",
             "import static org.mockito.Mockito.when;",
             "",
             "import com.google.common.collect.ImmutableCollection;",
             "import com.google.common.collect.ImmutableList;",
             "import com.google.common.collect.ImmutableSet;",
+            "import com.google.errorprone.matchers.Matcher;",
+            "import com.google.errorprone.matchers.Matchers;",
             "import java.util.ArrayList;",
             "import java.util.Collection;",
             "import org.reactivestreams.Publisher;",
@@ -225,8 +247,8 @@ final class IdentityConversionTest {
             "import reactor.core.publisher.Flux;",
             "import reactor.core.publisher.Mono;",
             "",
-            "public final class Foo {",
-            "  public void foo() {",
+            "public final class A {",
+            "  public void m() {",
             "    ImmutableSet<Object> set1 = ImmutableSet.of();",
             "    ImmutableSet<Object> set2 = ImmutableSet.copyOf(ImmutableList.of());",
             "",
@@ -251,6 +273,8 @@ final class IdentityConversionTest {
             "    Object o1 = ImmutableSet.copyOf(ImmutableList.of());",
             "    Object o2 = ImmutableSet.of();",
             "",
+            "    Matcher matcher = staticMethod();",
+            "",
             "    when(\"foo\".contains(\"f\")).thenAnswer(inv -> ImmutableSet.copyOf(ImmutableList.of(1)));",
             "  }",
             "",
@@ -261,17 +285,17 @@ final class IdentityConversionTest {
 
   @Test
   void replacementSecondSuggestedFix() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(IdentityConversion.class, getClass())
         .setFixChooser(FixChoosers.SECOND)
         .addInputLines(
-            "Foo.java",
+            "A.java",
             "import com.google.common.collect.ImmutableCollection;",
             "import com.google.common.collect.ImmutableList;",
             "import com.google.common.collect.ImmutableSet;",
             "import java.util.ArrayList;",
             "",
-            "public final class Foo {",
-            "  public void foo() {",
+            "public final class A {",
+            "  public void m() {",
             "    ImmutableSet<Object> set1 = ImmutableSet.copyOf(ImmutableSet.of());",
             "    ImmutableSet<Object> set2 = ImmutableSet.copyOf(ImmutableList.of());",
             "",
@@ -280,14 +304,14 @@ final class IdentityConversionTest {
             "  }",
             "}")
         .addOutputLines(
-            "Foo.java",
+            "A.java",
             "import com.google.common.collect.ImmutableCollection;",
             "import com.google.common.collect.ImmutableList;",
             "import com.google.common.collect.ImmutableSet;",
             "import java.util.ArrayList;",
             "",
-            "public final class Foo {",
-            "  public void foo() {",
+            "public final class A {",
+            "  public void m() {",
             "    @SuppressWarnings(\"IdentityConversion\")",
             "    ImmutableSet<Object> set1 = ImmutableSet.copyOf(ImmutableSet.of());",
             "    ImmutableSet<Object> set2 = ImmutableSet.copyOf(ImmutableList.of());",