Add char rules + fix unit test setup

See:
- https://github.com/dawidd6/action-download-artifact/compare/v2.28.0...v2.28.1

.github/workflows/build.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-22.04 ]
-        jdk: [ 11.0.20, 17.0.8, 20.0.2 ]
+        jdk: [ 11.0.20, 17.0.8, 21.0.0 ]
         distribution: [ temurin ]
         experimental: [ false ]
         include:
@@ -31,11 +31,11 @@ jobs:
       # additionally enabling all checks defined in this project and any Error
       # Prone checks available only from other artifact repositories.
       - name: Check out code
-        uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608 # v4.1.0
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with:
           persist-credentials: false
       - name: Set up JDK
-        uses: actions/setup-java@0ab4596768b603586c0de567f2430c30f5b0d2b0 # v3.13.0
+        uses: actions/setup-java@387ac29b308b003ca37ba93a6cab5eb57c8f5f93 # v4.0.0
         with:
           java-version: ${{ matrix.jdk }}
           distribution: ${{ matrix.distribution }}

.github/workflows/codeql.yml

@@ -22,23 +22,23 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Check out code
-        uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608 # v4.1.0
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with:
           persist-credentials: false
       - name: Set up JDK
-        uses: actions/setup-java@0ab4596768b603586c0de567f2430c30f5b0d2b0 # v3.13.0
+        uses: actions/setup-java@387ac29b308b003ca37ba93a6cab5eb57c8f5f93 # v4.0.0
         with:
           java-version: 17.0.8
           distribution: temurin
           cache: maven
       - name: Initialize CodeQL
-        uses: github/codeql-action/init@2cb752a87e96af96708ab57187ab6372ee1973ab # v2.22.0
+        uses: github/codeql-action/init@407ffafae6a767df3e0230c3df91b6443ae8df75 # v2.22.8
         with:
           languages: ${{ matrix.language }}
       - name: Perform minimal build
         if: matrix.language == 'java'
-        run: mvn -T1C clean install -DskipTests -Dverification.skip
+        run: mvn -T1C clean package -DskipTests -Dverification.skip
       - name: Perform CodeQL analysis
-        uses: github/codeql-action/analyze@2cb752a87e96af96708ab57187ab6372ee1973ab # v2.22.0
+        uses: github/codeql-action/analyze@407ffafae6a767df3e0230c3df91b6443ae8df75 # v2.22.8
         with:
           category: /language:${{ matrix.language }}

.github/workflows/deploy-website.yml

@@ -12,15 +12,15 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Check out code
-        uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608 # v4.1.0
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with:
           persist-credentials: false
-      - uses: ruby/setup-ruby@d37167af451eb51448db3354e1057b75c4b268f7 # v1.155.0
+      - uses: ruby/setup-ruby@8575951200e472d5f2d95c625da0c7bec8217c42 # v1.161.0
         with:
           working-directory: ./website
           bundler-cache: true
       - name: Configure Github Pages
-        uses: actions/configure-pages@f156874f8191504dae5b037505266ed5dda6c382 # v3.0.6
+        uses: actions/configure-pages@1f0c5cde4bc74cd7e1254d0cb4de8d49e9068c7d # v4.0.0
       - name: Generate documentation
         run: ./generate-docs.sh
       - name: Build website with Jekyll
@@ -48,4 +48,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@9dbe3824824f8a1377b8e298bafde1a50ede43e5 # v2.0.4
+        uses: actions/deploy-pages@13b55b33dd8996121833dbc1db458c793a334630 # v3.0.1

.github/workflows/openssf-scorecard.yml

@@ -21,16 +21,16 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Check out code
-        uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608 # v4.1.0
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with:
           persist-credentials: false
       - name: Run OpenSSF Scorecard analysis
-        uses: ossf/scorecard-action@483ef80eb98fb506c348f7d62e28055e49fe2398 # v2.3.0
+        uses: ossf/scorecard-action@0864cf19026789058feabb7e87baa5f140aac736 # v2.3.1
         with:
           results_file: results.sarif
           results_format: sarif
           publish_results: ${{ github.ref == 'refs/heads/master' }}
       - name: Update GitHub's code scanning dashboard
-        uses: github/codeql-action/upload-sarif@2cb752a87e96af96708ab57187ab6372ee1973ab # v2.22.0
+        uses: github/codeql-action/upload-sarif@407ffafae6a767df3e0230c3df91b6443ae8df75 # v2.22.8
         with:
           sarif_file: results.sarif

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

@@ -12,12 +12,12 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Check out code
-        uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608 # v4.1.0
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with:
           fetch-depth: 2
           persist-credentials: false
       - name: Set up JDK
-        uses: actions/setup-java@0ab4596768b603586c0de567f2430c30f5b0d2b0 # v3.13.0
+        uses: actions/setup-java@387ac29b308b003ca37ba93a6cab5eb57c8f5f93 # v4.0.0
         with:
           java-version: 17.0.8
           distribution: temurin

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

@@ -20,17 +20,17 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Check out code
-        uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608 # v4.1.0
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with:
           persist-credentials: false
       - name: Set up JDK
-        uses: actions/setup-java@0ab4596768b603586c0de567f2430c30f5b0d2b0 # v3.13.0
+        uses: actions/setup-java@387ac29b308b003ca37ba93a6cab5eb57c8f5f93 # v4.0.0
         with:
           java-version: 17.0.8
           distribution: temurin
           cache: maven
       - name: Download Pitest analysis artifact
-        uses: dawidd6/action-download-artifact@268677152d06ba59fcec7a7f0b5d961b6ccd7e1e # v2.28.0
+        uses: dawidd6/action-download-artifact@f29d1b6a8930683e80acedfbe6baa2930cd646b4 # v2.28.1
         with:
           workflow: ${{ github.event.workflow_run.workflow_id }}
           name: pitest-reports

.github/workflows/run-integration-tests.yml

@@ -0,0 +1,43 @@
+# If requested by means of a pull request comment, runs integration tests
+# against the project, using the code found on the pull request branch.
+# XXX: Generalize this to a matrix build of multiple integration tests,
+# possibly using multiple JDK or OS versions.
+# XXX: Investigate whether the comment can specify which integration tests run
+# run. See this example of a dynamic build matrix:
+# https://docs.github.com/en/actions/learn-github-actions/expressions#example-returning-a-json-object
+name: "Integration tests"
+on:
+  issue_comment:
+    types: [ created ]
+permissions:
+  contents: read
+jobs:
+  run-integration-tests:
+    name: On-demand integration test
+    if: |
+      github.event.issue.pull_request && contains(github.event.comment.body, '/integration-test')
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Check out code
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+        with:
+          persist-credentials: false
+          ref: refs/pull/${{ github.event.issue.number }}/head
+      - name: Set up JDK
+        uses: actions/setup-java@387ac29b308b003ca37ba93a6cab5eb57c8f5f93 # v4.0.0
+        with:
+          java-version: 17.0.8
+          distribution: temurin
+          cache: maven
+      - name: Install project to local Maven repository
+        run: mvn -T1C install -DskipTests -Dverification.skip
+      - name: Run integration test
+        run: xvfb-run ./integration-tests/checkstyle-10.12.4.sh "${{ runner.temp }}/artifacts"
+      - name: Upload artifacts on failure
+        if: ${{ failure() }}
+        uses: actions/upload-artifact@a8a3f3ad30e3422c9c7b888a15615d19a852ae32 # v3.1.3
+        with:
+          name: integration-test-checkstyle-10.12.4
+          path: "${{ runner.temp }}/artifacts"
+      - name: Remove installed project artifacts
+        run: mvn build-helper:remove-project-artifact

.github/workflows/sonarcloud.yml

@@ -16,12 +16,12 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Check out code
-        uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608 # v4.1.0
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with:
           fetch-depth: 0
           persist-credentials: false
       - name: Set up JDK
-        uses: actions/setup-java@0ab4596768b603586c0de567f2430c30f5b0d2b0 # v3.13.0
+        uses: actions/setup-java@387ac29b308b003ca37ba93a6cab5eb57c8f5f93 # v4.0.0
         with:
           java-version: 17.0.8
           distribution: temurin

.gitignore

@@ -9,3 +9,6 @@
 target
 *.iml
 *.swp
+
+# The Git repositories checked out by the integration test framework.
+integration-tests/.repos

README.md

@@ -15,9 +15,11 @@ focussing on maintainability, consistency and avoidance of common pitfalls.
 > Error Prone is a static analysis tool for Java that catches common
 > programming mistakes at compile-time.
 
-Read more on how Picnic uses Error Prone (Support) in the blog post [_Picnic
-loves Error Prone: producing high-quality and consistent Java
-code_][picnic-blog-ep-post].
+To learn more about Error Prone (Support), how you can start using Error Prone
+in practice, and how we use it at Picnic, watch the conference talk
+[_Automating away bugs with Error Prone in practice_][conference-talk]. Also
+consider checking out the blog post [_Picnic loves Error Prone: producing
+high-quality and consistent Java code_][picnic-blog-ep-post].
 
 [![Maven Central][maven-central-badge]][maven-central-search]
 [![Reproducible Builds][reproducible-builds-badge]][reproducible-builds-report]
@@ -265,6 +267,7 @@ channel; please see our [security policy][security] for details.
 [bug-checks-identity-conversion]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/IdentityConversion.java
 [codeql-badge]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/codeql.yml/badge.svg?branch=master&event=push
 [codeql-master]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/codeql.yml?query=branch:master+event:push
+[conference-talk]: https://www.youtube.com/watch?v=-47WD-3wKBs
 [contributing]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/CONTRIBUTING.md
 [contributing-pull-request]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/CONTRIBUTING.md#-opening-a-pull-request
 [error-prone-bugchecker]: https://github.com/google/error-prone/blob/master/check_api/src/main/java/com/google/errorprone/bugpatterns/BugChecker.java
@@ -274,8 +277,8 @@ channel; please see our [security policy][security] for details.
 [error-prone-installation-guide]: https://errorprone.info/docs/installation#maven
 [error-prone-orig-repo]: https://github.com/google/error-prone
 [error-prone-pull-3301]: https://github.com/google/error-prone/pull/3301
-[github-actions-build-badge]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/build.yaml/badge.svg
-[github-actions-build-master]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/build.yaml?query=branch:master&event=push
+[github-actions-build-badge]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/build.yml/badge.svg
+[github-actions-build-master]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/build.yml?query=branch:master&event=push
 [google-java-format]: https://github.com/google/google-java-format
 [idea-288052]: https://youtrack.jetbrains.com/issue/IDEA-288052
 [license-badge]: https://img.shields.io/github/license/PicnicSupermarket/error-prone-support

cdg-pitest-licence.txt

@@ -1,7 +1,7 @@
 # Arcmutate license for Error Prone Support, requested by sending an email to
 # support@arcmutate.com.
-expires=07/11/2023
+expires=27/10/2025
 keyVersion=1
-signature=MhZxMbnO6UovNfllM0JuVWkZyvRT3/G5o/uT0Mm36c7200VpZNVu03gTAGivnl9W5RzvZhfpIHccuQ5ctjQkrqhsFSrl4fyqPqu3y5V2fsHIdFXP/G72EGj6Kay9ndLpaEHalqE0bEwxdnHMzEYq5y3O9vUPv8MhUl57xk+rvBo\=
+signature=aQLVt0J//7nXDAlJuBe9ru7Dq6oApcLh17rxsgHoJqBkUCd2zvrtRxkcPm5PmF1I8gBDT9PHb+kTf6Kcfz+D1fT0wRrZv38ip56521AQPD6zjRSqak9O2Gisjo+QTPMD7oS009aSWKzQ1SMdtuZ+KIRvw4Gl+frtYzexqnGWEUQ\=
 packages=tech.picnic.errorprone.*
 type=OSSS

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

@@ -5,17 +5,19 @@ 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 com.sun.tools.javac.util.Context;
+import java.util.Optional;
 import javax.lang.model.element.AnnotationValue;
 import tech.picnic.errorprone.documentation.BugPatternExtractor.BugPatternDocumentation;
 
@@ -23,29 +25,39 @@ import tech.picnic.errorprone.documentation.BugPatternExtractor.BugPatternDocume
  * An {@link Extractor} that describes how to extract data from a {@code @BugPattern} annotation.
  */
 @Immutable
-final class BugPatternExtractor implements Extractor<BugPatternDocumentation> {
-  @Override
-  public BugPatternDocumentation extract(ClassTree tree, Context context) {
-    ClassSymbol symbol = ASTHelpers.getSymbol(tree);
-    BugPattern annotation = symbol.getAnnotation(BugPattern.class);
-    requireNonNull(annotation, "BugPattern annotation must be present");
+@AutoService(Extractor.class)
+@SuppressWarnings("rawtypes" /* See https://github.com/google/auto/issues/870. */)
+public final class BugPatternExtractor implements Extractor<BugPatternDocumentation> {
+  /** Instantiates a new {@link BugPatternExtractor} instance. */
+  public BugPatternExtractor() {}
 
-    return 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());
+  @Override
+  public String identifier() {
+    return "bugpattern";
   }
 
   @Override
-  public boolean canExtract(ClassTree tree) {
-    return ASTHelpers.hasDirectAnnotationWithSimpleName(tree, BugPattern.class.getSimpleName());
+  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()));
   }
 
   /**

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

@@ -0,0 +1,229 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.errorprone.matchers.Matchers.instanceMethod;
+import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
+import static java.util.function.Predicate.not;
+
+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.MethodInvocationTree;
+import com.sun.source.util.TreeScanner;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+import org.jspecify.annotations.Nullable;
+import tech.picnic.errorprone.documentation.BugPatternTestExtractor.TestCases;
+
+/**
+ * An {@link Extractor} that describes how to extract data from classes that test a {@code
+ * BugChecker}.
+ */
+// XXX: Handle other methods from `{BugCheckerRefactoring,Compilation}TestHelper`:
+// - Indicate which custom arguments are specified, if any.
+// - For replacement tests, indicate which `FixChooser` is used.
+// - ... (We don't use all optional features; TBD what else to support.)
+@Immutable
+@AutoService(Extractor.class)
+@SuppressWarnings("rawtypes" /* See https://github.com/google/auto/issues/870. */)
+public final class BugPatternTestExtractor implements Extractor<TestCases> {
+  /** Instantiates a new {@link BugPatternTestExtractor} instance. */
+  public BugPatternTestExtractor() {}
+
+  @Override
+  public String identifier() {
+    return "bugpattern-test";
+  }
+
+  @Override
+  public Optional<TestCases> tryExtract(ClassTree tree, VisitorState state) {
+    BugPatternTestCollector collector = new BugPatternTestCollector();
+
+    collector.scan(tree, state);
+
+    return Optional.of(collector.getCollectedTests())
+        .filter(not(ImmutableList::isEmpty))
+        .map(
+            tests ->
+                new AutoValue_BugPatternTestExtractor_TestCases(
+                    ASTHelpers.getSymbol(tree).className(), tests));
+  }
+
+  private static final class BugPatternTestCollector
+      extends TreeScanner<@Nullable Void, VisitorState> {
+    private static final Matcher<ExpressionTree> COMPILATION_HELPER_DO_TEST =
+        instanceMethod()
+            .onDescendantOf("com.google.errorprone.CompilationTestHelper")
+            .named("doTest");
+    private static final Matcher<ExpressionTree> TEST_HELPER_NEW_INSTANCE =
+        staticMethod()
+            .onDescendantOfAny(
+                "com.google.errorprone.CompilationTestHelper",
+                "com.google.errorprone.BugCheckerRefactoringTestHelper")
+            .named("newInstance")
+            .withParameters("java.lang.Class", "java.lang.Class");
+    private static final Matcher<ExpressionTree> IDENTIFICATION_SOURCE_LINES =
+        instanceMethod()
+            .onDescendantOf("com.google.errorprone.CompilationTestHelper")
+            .named("addSourceLines");
+    private static final Matcher<ExpressionTree> REPLACEMENT_DO_TEST =
+        instanceMethod()
+            .onDescendantOf("com.google.errorprone.BugCheckerRefactoringTestHelper")
+            .named("doTest");
+    private static final Matcher<ExpressionTree> REPLACEMENT_EXPECT_UNCHANGED =
+        instanceMethod()
+            .onDescendantOf("com.google.errorprone.BugCheckerRefactoringTestHelper.ExpectOutput")
+            .named("expectUnchanged");
+    private static final Matcher<ExpressionTree> REPLACEMENT_OUTPUT_SOURCE_LINES =
+        instanceMethod()
+            .onDescendantOf("com.google.errorprone.BugCheckerRefactoringTestHelper.ExpectOutput")
+            .namedAnyOf("addOutputLines", "expectUnchanged");
+
+    private final List<TestCase> collectedTestCases = new ArrayList<>();
+
+    private ImmutableList<TestCase> getCollectedTests() {
+      return ImmutableList.copyOf(collectedTestCases);
+    }
+
+    @Override
+    public @Nullable Void visitMethodInvocation(MethodInvocationTree node, VisitorState state) {
+      boolean isReplacementTest = REPLACEMENT_DO_TEST.matches(node, state);
+      if (isReplacementTest || COMPILATION_HELPER_DO_TEST.matches(node, state)) {
+        getClassUnderTest(node, state)
+            .ifPresent(
+                classUnderTest -> {
+                  List<TestEntry> entries = new ArrayList<>();
+                  if (isReplacementTest) {
+                    extractReplacementTestCases(node, entries, state);
+                  } else {
+                    extractIdentificationTestCases(node, entries, state);
+                  }
+
+                  if (!entries.isEmpty()) {
+                    collectedTestCases.add(
+                        new AutoValue_BugPatternTestExtractor_TestCase(
+                            classUnderTest, ImmutableList.copyOf(entries).reverse()));
+                  }
+                });
+      }
+
+      return super.visitMethodInvocation(node, state);
+    }
+
+    private static Optional<String> getClassUnderTest(
+        MethodInvocationTree tree, VisitorState state) {
+      if (TEST_HELPER_NEW_INSTANCE.matches(tree, state)) {
+        return Optional.ofNullable(ASTHelpers.getSymbol(tree.getArguments().get(0)))
+            .filter(s -> !s.type.allparams().isEmpty())
+            .map(s -> s.type.allparams().get(0).tsym.getQualifiedName().toString());
+      }
+
+      ExpressionTree receiver = ASTHelpers.getReceiver(tree);
+      return receiver instanceof MethodInvocationTree
+          ? getClassUnderTest((MethodInvocationTree) receiver, state)
+          : Optional.empty();
+    }
+
+    private static void extractIdentificationTestCases(
+        MethodInvocationTree tree, List<TestEntry> sink, VisitorState state) {
+      if (IDENTIFICATION_SOURCE_LINES.matches(tree, state)) {
+        String path = ASTHelpers.constValue(tree.getArguments().get(0), String.class);
+        Optional<String> sourceCode =
+            getSourceCode(tree).filter(s -> s.contains("// BUG: Diagnostic"));
+        if (path != null && sourceCode.isPresent()) {
+          sink.add(
+              new AutoValue_BugPatternTestExtractor_IdentificationTestEntry(
+                  path, sourceCode.orElseThrow()));
+        }
+      }
+
+      ExpressionTree receiver = ASTHelpers.getReceiver(tree);
+      if (receiver instanceof MethodInvocationTree) {
+        extractIdentificationTestCases((MethodInvocationTree) receiver, sink, state);
+      }
+    }
+
+    private static void extractReplacementTestCases(
+        MethodInvocationTree tree, List<TestEntry> sink, VisitorState state) {
+      if (REPLACEMENT_OUTPUT_SOURCE_LINES.matches(tree, state)) {
+        /*
+         * Retrieve the method invocation that contains the input source code. Note that this cast
+         * is safe, because this code is guarded by an earlier call to `#getClassUnderTest(..)`,
+         * which ensures that `tree` is part of a longer method invocation chain.
+         */
+        MethodInvocationTree inputTree = (MethodInvocationTree) ASTHelpers.getReceiver(tree);
+
+        String path = ASTHelpers.constValue(inputTree.getArguments().get(0), String.class);
+        Optional<String> inputCode = getSourceCode(inputTree);
+        if (path != null && inputCode.isPresent()) {
+          Optional<String> outputCode =
+              REPLACEMENT_EXPECT_UNCHANGED.matches(tree, state) ? inputCode : getSourceCode(tree);
+
+          if (outputCode.isPresent() && !inputCode.equals(outputCode)) {
+            sink.add(
+                new AutoValue_BugPatternTestExtractor_ReplacementTestEntry(
+                    path, inputCode.orElseThrow(), outputCode.orElseThrow()));
+          }
+        }
+      }
+
+      ExpressionTree receiver = ASTHelpers.getReceiver(tree);
+      if (receiver instanceof MethodInvocationTree) {
+        extractReplacementTestCases((MethodInvocationTree) receiver, sink, state);
+      }
+    }
+
+    // XXX: This logic is duplicated in `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());
+    }
+  }
+
+  @AutoValue
+  abstract static class TestCases {
+    abstract String testClass();
+
+    abstract ImmutableList<TestCase> testCases();
+  }
+
+  @AutoValue
+  abstract static class TestCase {
+    abstract String classUnderTest();
+
+    abstract ImmutableList<TestEntry> entries();
+  }
+
+  interface TestEntry {
+    String path();
+  }
+
+  @AutoValue
+  abstract static class ReplacementTestEntry implements TestEntry {
+    abstract String input();
+
+    abstract String output();
+  }
+
+  @AutoValue
+  abstract static class IdentificationTestEntry implements TestEntry {
+    abstract String code();
+  }
+}

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

@@ -5,10 +5,14 @@ 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;
@@ -19,6 +23,7 @@ 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;
 
 /**
@@ -27,6 +32,13 @@ import javax.tools.JavaFileObject;
  */
 // 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);
 
@@ -51,19 +63,25 @@ final class DocumentationGeneratorTaskListener implements TaskListener {
       return;
     }
 
-    ClassTree classTree = JavacTrees.instance(context).getTree(taskEvent.getTypeElement());
     JavaFileObject sourceFile = taskEvent.getSourceFile();
-    if (classTree == null || sourceFile == null) {
+    CompilationUnitTree compilationUnit = taskEvent.getCompilationUnit();
+    ClassTree classTree = JavacTrees.instance(context).getTree(taskEvent.getTypeElement());
+    if (sourceFile == null || compilationUnit == null || classTree == null) {
       return;
     }
 
-    ExtractorType.findMatchingType(classTree)
-        .ifPresent(
-            extractorType ->
-                writeToFile(
-                    extractorType.getIdentifier(),
-                    getSimpleClassName(sourceFile.toUri()),
-                    extractorType.getExtractor().extract(classTree, context)));
+    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() {

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

@@ -1,8 +1,9 @@
 package tech.picnic.errorprone.documentation;
 
+import com.google.errorprone.VisitorState;
 import com.google.errorprone.annotations.Immutable;
 import com.sun.source.tree.ClassTree;
-import com.sun.tools.javac.util.Context;
+import java.util.Optional;
 
 /**
  * Interface implemented by classes that define how to extract data of some type {@link T} from a
@@ -13,21 +14,20 @@ import com.sun.tools.javac.util.Context;
 @Immutable
 interface Extractor<T> {
   /**
-   * Extracts and returns an instance of {@link T} using the provided arguments.
+   * Returns the unique identifier of this extractor.
    *
-   * @param tree The {@link ClassTree} to analyze and from which to extract instances of {@link T}.
-   * @param context The {@link Context} in which the current compilation takes place.
-   * @return A non-null instance of {@link T}.
+   * @return A non-{@code null} string.
    */
-  // XXX: Drop `Context` parameter unless used.
-  T extract(ClassTree tree, Context context);
+  String identifier();
 
   /**
-   * Tells whether this {@link Extractor} can extract documentation content from the given {@link
-   * ClassTree}.
+   * Attempts to extract an instance of type {@link T} using the provided arguments.
    *
-   * @param tree The {@link ClassTree} of interest.
-   * @return {@code true} iff data extraction is supported.
+   * @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.
    */
-  boolean canExtract(ClassTree tree);
+  Optional<T> tryExtract(ClassTree tree, VisitorState state);
 }

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

@@ -1,36 +0,0 @@
-package tech.picnic.errorprone.documentation;
-
-import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.Sets;
-import com.sun.source.tree.ClassTree;
-import java.util.EnumSet;
-import java.util.Optional;
-
-/** An enumeration of {@link Extractor} types. */
-enum ExtractorType {
-  BUG_PATTERN("bugpattern", new BugPatternExtractor());
-
-  private static final ImmutableSet<ExtractorType> TYPES =
-      Sets.immutableEnumSet(EnumSet.allOf(ExtractorType.class));
-
-  private final String identifier;
-  private final Extractor<?> extractor;
-
-  ExtractorType(String identifier, Extractor<?> extractor) {
-    this.identifier = identifier;
-    this.extractor = extractor;
-  }
-
-  String getIdentifier() {
-    return identifier;
-  }
-
-  @SuppressWarnings("java:S1452" /* The extractor returns data of an unspecified type. */)
-  Extractor<?> getExtractor() {
-    return extractor;
-  }
-
-  static Optional<ExtractorType> findMatchingType(ClassTree tree) {
-    return TYPES.stream().filter(type -> type.getExtractor().canExtract(tree)).findFirst();
-  }
-}

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

@@ -1,18 +1,9 @@
 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 static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 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;
@@ -45,10 +36,7 @@ final class BugPatternExtractorTest {
         "@BugPattern(summary = \"MinimalBugChecker summary\", severity = SeverityLevel.ERROR)",
         "public final class MinimalBugChecker extends BugChecker {}");
 
-    verifyFileMatchesResource(
-        outputDirectory,
-        "bugpattern-MinimalBugChecker.json",
-        "bugpattern-documentation-minimal.json");
+    verifyGeneratedFileContent(outputDirectory, "MinimalBugChecker");
   }
 
   @Test
@@ -76,10 +64,7 @@ final class BugPatternExtractorTest {
         "    suppressionAnnotations = {BugPattern.class, Test.class})",
         "public final class CompleteBugChecker extends BugChecker {}");
 
-    verifyFileMatchesResource(
-        outputDirectory,
-        "bugpattern-CompleteBugChecker.json",
-        "bugpattern-documentation-complete.json");
+    verifyGeneratedFileContent(outputDirectory, "CompleteBugChecker");
   }
 
   @Test
@@ -99,55 +84,23 @@ final class BugPatternExtractorTest {
         "    documentSuppression = false)",
         "public final class UndocumentedSuppressionBugPattern extends BugChecker {}");
 
-    verifyFileMatchesResource(
-        outputDirectory,
-        "bugpattern-UndocumentedSuppressionBugPattern.json",
-        "bugpattern-documentation-undocumented-suppression.json");
+    verifyGeneratedFileContent(outputDirectory, "UndocumentedSuppressionBugPattern");
   }
 
-  @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))
+  private static void verifyGeneratedFileContent(Path outputDirectory, String testClass)
+      throws IOException {
+    String resourceName = String.format("bugpattern-%s.json", testClass);
+    assertThat(outputDirectory.resolve(resourceName))
         .content(UTF_8)
-        .isEqualToIgnoringWhitespace(getResource(resourceName));
+        .isEqualToIgnoringWhitespace(
+            getResource(
+                String.join("-", BugPatternExtractorTest.class.getSimpleName(), 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.)
+  // text blocks in this class.
   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) {
-      BugPatternExtractor extractor = new BugPatternExtractor();
-
-      assertThatThrownBy(() -> extractor.extract(tree, state.context))
-          .isInstanceOf(NullPointerException.class)
-          .hasMessage("BugPattern annotation must be present");
-
-      return buildDescription(tree)
-          .setMessage(String.format("Can extract: %s", extractor.canExtract(tree)))
-          .build();
-    }
-  }
 }

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

@@ -0,0 +1,468 @@
+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 noTestClass(@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 noDoTestInvocation(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"// BUG: Diagnostic contains:\", \"class A {}\");",
+        "",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A { /* This is a change. */ }\");",
+        "  }",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void nullBugCheckerInstance(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class TestCheckerTest {",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance((Class<BugChecker>) null, getClass())",
+        "        .addSourceLines(\"A.java\", \"// BUG: Diagnostic contains:\", \"class A {}\")",
+        "        .doTest();",
+        "",
+        "    BugCheckerRefactoringTestHelper.newInstance((Class<BugChecker>) null, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A { /* This is a change. */ }\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void rawBugCheckerInstance(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  @SuppressWarnings(\"unchecked\")",
+        "  void m() {",
+        "    @SuppressWarnings(\"rawtypes\")",
+        "    Class bugChecker = TestChecker.class;",
+        "",
+        "    CompilationTestHelper.newInstance(bugChecker, getClass())",
+        "        .addSourceLines(\"A.java\", \"// BUG: Diagnostic contains:\", \"class A {}\")",
+        "        .doTest();",
+        "",
+        "    BugCheckerRefactoringTestHelper.newInstance(bugChecker, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A { /* This is a change. */ }\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void scannerSupplierInstance(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import com.google.errorprone.scanner.ScannerSupplier;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance(",
+        "            ScannerSupplier.fromBugCheckerClasses(TestChecker.class), getClass())",
+        "        .addSourceLines(\"A.java\", \"// BUG: Diagnostic contains:\", \"class A {}\")",
+        "        .doTest();",
+        "",
+        "    BugCheckerRefactoringTestHelper.newInstance(",
+        "            ScannerSupplier.fromBugCheckerClasses(TestChecker.class), getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A { /* This is a change. */ }\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void nonCompileTimeConstantStrings(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(toString() + \"A.java\", \"// BUG: Diagnostic contains:\", \"class A {}\")",
+        "        .addSourceLines(\"B.java\", \"// BUG: Diagnostic contains:\", \"class B {}\", toString())",
+        "        .doTest();",
+        "",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(toString() + \"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A { /* This is a change. */ }\")",
+        "        .addInputLines(\"B.java\", \"class B {}\", toString())",
+        "        .addOutputLines(\"B.java\", \"class B { /* This is a change. */ }\")",
+        "        .addInputLines(\"C.java\", \"class C {}\")",
+        "        .addOutputLines(\"C.java\", \"class C { /* This is a change. */ }\", toString())",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void nonFluentTestHelperExpressions(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper testHelper =",
+        "        CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "            .addSourceLines(\"A.java\", \"class A {}\");",
+        "    testHelper.doTest();",
+        "",
+        "    BugCheckerRefactoringTestHelper.ExpectOutput expectedOutput =",
+        "        BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "            .addInputLines(\"A.java\", \"class A {}\");",
+        "    expectedOutput.addOutputLines(\"A.java\", \"class A {}\").doTest();",
+        "    expectedOutput.expectUnchanged().doTest();",
+        "  }",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void noSource(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass()).doTest();",
+        "",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass()).doTest();",
+        "  }",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void noDiagnostics(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class TestCheckerTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"class A {}\")",
+        "        .doTest();",
+        "",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A {}\")",
+        "        .addInputLines(\"B.java\", \"class B {}\")",
+        "        .expectUnchanged()",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void singleFileCompilationTestHelper(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "SingleFileCompilationTestHelperTest.java",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class SingleFileCompilationTestHelperTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"// BUG: Diagnostic contains:\", \"class A {}\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    verifyGeneratedFileContent(outputDirectory, "SingleFileCompilationTestHelperTest");
+  }
+
+  @Test
+  void singleFileCompilationTestHelperWithSetArgs(@TempDir Path outputDirectory)
+      throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "SingleFileCompilationTestHelperWithSetArgsTest.java",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class SingleFileCompilationTestHelperWithSetArgsTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .setArgs(\"-XepAllSuggestionsAsWarnings\")",
+        "        .addSourceLines(\"A.java\", \"// BUG: Diagnostic contains:\", \"class A {}\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    verifyGeneratedFileContent(outputDirectory, "SingleFileCompilationTestHelperWithSetArgsTest");
+  }
+
+  @Test
+  void multiFileCompilationTestHelper(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "MultiFileCompilationTestHelperTest.java",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class MultiFileCompilationTestHelperTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"// BUG: Diagnostic contains:\", \"class A {}\")",
+        "        .addSourceLines(\"B.java\", \"// BUG: Diagnostic contains:\", \"class B {}\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    verifyGeneratedFileContent(outputDirectory, "MultiFileCompilationTestHelperTest");
+  }
+
+  @Test
+  void singleFileBugCheckerRefactoringTestHelper(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "SingleFileBugCheckerRefactoringTestHelperTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class SingleFileBugCheckerRefactoringTestHelperTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A { /* This is a change. */ }\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    verifyGeneratedFileContent(outputDirectory, "SingleFileBugCheckerRefactoringTestHelperTest");
+  }
+
+  @Test
+  void singleFileBugCheckerRefactoringTestHelperWithSetArgsFixChooserAndCustomTestMode(
+      @TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "SingleFileBugCheckerRefactoringTestHelperWithSetArgsFixChooserAndCustomTestModeTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers;",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class SingleFileBugCheckerRefactoringTestHelperWithSetArgsFixChooserAndCustomTestModeTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .setArgs(\"-XepAllSuggestionsAsWarnings\")",
+        "        .setFixChooser(FixChoosers.SECOND)",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A { /* This is a change. */ }\")",
+        "        .doTest(TestMode.TEXT_MATCH);",
+        "  }",
+        "}");
+
+    verifyGeneratedFileContent(
+        outputDirectory,
+        "SingleFileBugCheckerRefactoringTestHelperWithSetArgsFixChooserAndCustomTestModeTest");
+  }
+
+  @Test
+  void multiFileBugCheckerRefactoringTestHelper(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "MultiFileBugCheckerRefactoringTestHelperTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class MultiFileBugCheckerRefactoringTestHelperTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A { /* This is a change. */ }\")",
+        "        .addInputLines(\"B.java\", \"class B {}\")",
+        "        .addOutputLines(\"B.java\", \"class B { /* This is a change. */ }\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    verifyGeneratedFileContent(outputDirectory, "MultiFileBugCheckerRefactoringTestHelperTest");
+  }
+
+  @Test
+  void compilationAndBugCheckerRefactoringTestHelpers(@TempDir Path outputDirectory)
+      throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "CompilationAndBugCheckerRefactoringTestHelpersTest.java",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class CompilationAndBugCheckerRefactoringTestHelpersTest {",
+        "  private static class TestChecker extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"// BUG: Diagnostic contains:\", \"class A {}\")",
+        "        .doTest();",
+        "",
+        "    BugCheckerRefactoringTestHelper.newInstance(TestChecker.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A { /* This is a change. */ }\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    verifyGeneratedFileContent(
+        outputDirectory, "CompilationAndBugCheckerRefactoringTestHelpersTest");
+  }
+
+  @Test
+  void compilationAndBugCheckerRefactoringTestHelpersWithCustomCheckerPackageAndNames(
+      @TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "CompilationAndBugCheckerRefactoringTestHelpersWithCustomCheckerPackageAndNamesTest.java",
+        "package pkg;",
+        "",
+        "import com.google.errorprone.BugCheckerRefactoringTestHelper;",
+        "import com.google.errorprone.CompilationTestHelper;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "final class CompilationAndBugCheckerRefactoringTestHelpersWithCustomCheckerPackageAndNamesTest {",
+        "  private static class CustomTestChecker extends BugChecker {}",
+        "",
+        "  private static class CustomTestChecker2 extends BugChecker {}",
+        "",
+        "  void m() {",
+        "    CompilationTestHelper.newInstance(CustomTestChecker.class, getClass())",
+        "        .addSourceLines(\"A.java\", \"// BUG: Diagnostic contains:\", \"class A {}\")",
+        "        .doTest();",
+        "",
+        "    BugCheckerRefactoringTestHelper.newInstance(CustomTestChecker2.class, getClass())",
+        "        .addInputLines(\"A.java\", \"class A {}\")",
+        "        .addOutputLines(\"A.java\", \"class A { /* This is a change. */ }\")",
+        "        .doTest();",
+        "  }",
+        "}");
+
+    verifyGeneratedFileContent(
+        outputDirectory,
+        "CompilationAndBugCheckerRefactoringTestHelpersWithCustomCheckerPackageAndNamesTest");
+  }
+
+  private static void verifyGeneratedFileContent(Path outputDirectory, String testClass)
+      throws IOException {
+    String resourceName = String.format("bugpattern-test-%s.json", testClass);
+    assertThat(outputDirectory.resolve(resourceName))
+        .content(UTF_8)
+        .isEqualToIgnoringWhitespace(
+            getResource(
+                String.join("-", BugPatternTestExtractorTest.class.getSimpleName(), resourceName)));
+  }
+
+  // XXX: Once we support only JDK 15+, drop this method in favour of including the resources as
+  // text blocks in this class.
+  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

@@ -1,5 +1,7 @@
 package tech.picnic.errorprone.documentation;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 import com.google.common.collect.ImmutableList;
 import com.google.errorprone.FileManagers;
 import com.google.errorprone.FileObjects;
@@ -7,39 +9,66 @@ 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 java.util.ArrayList;
+import java.util.List;
+import javax.tools.Diagnostic;
 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.
+// XXX: This class is supported by the `ErrorProneTestHelperSourceFormat` check, but until that
+// support is covered by unit tests, make sure to update that logic if this class or its methods are
+// moved/renamed.
 public final class Compilation {
   private Compilation() {}
 
   public static void compileWithDocumentationGenerator(
-      Path outputDirectory, String fileName, String... lines) {
-    compileWithDocumentationGenerator(outputDirectory.toAbsolutePath().toString(), fileName, lines);
+      Path outputDirectory, String path, String... lines) {
+    compileWithDocumentationGenerator(outputDirectory.toAbsolutePath().toString(), path, lines);
   }
 
   public static void compileWithDocumentationGenerator(
-      String outputDirectory, String fileName, String... lines) {
+      String outputDirectory, String path, String... lines) {
+    /*
+     * The compiler options specified here largely match those used by Error Prone's
+     * `CompilationTestHelper`. A key difference is the stricter linting configuration. When
+     * compiling using JDK 21+, these lint options also require that certain JDK modules are
+     * explicitly exported.
+     */
     compile(
-        ImmutableList.of("-Xplugin:DocumentationGenerator -XoutputDirectory=" + outputDirectory),
-        FileObjects.forSourceLines(fileName, lines));
+        ImmutableList.of(
+            "--add-exports=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED",
+            "--add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED",
+            "--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED",
+            "-encoding",
+            "UTF-8",
+            "-parameters",
+            "-proc:none",
+            "-Werror",
+            "-Xlint:all,-serial",
+            "-Xplugin:DocumentationGenerator -XoutputDirectory=" + outputDirectory,
+            "-XDdev",
+            "-XDcompilePolicy=simple"),
+        FileObjects.forSourceLines(path, lines));
   }
 
   private static void compile(ImmutableList<String> options, JavaFileObject javaFileObject) {
     JavacFileManager javacFileManager = FileManagers.testFileManager();
     JavaCompiler compiler = JavacTool.create();
+
+    List<Diagnostic<?>> diagnostics = new ArrayList<>();
     JavacTaskImpl task =
         (JavacTaskImpl)
             compiler.getTask(
                 null,
                 javacFileManager,
-                null,
+                diagnostics::add,
                 options,
                 ImmutableList.of(),
                 ImmutableList.of(javaFileObject));
 
-    task.call();
+    Boolean result = task.call();
+    assertThat(diagnostics).isEmpty();
+    assertThat(result).isTrue();
   }
 }

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

@@ -1,19 +1,29 @@
 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;
@@ -75,4 +85,56 @@ final class DocumentationGeneratorTaskListenerTest {
         .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)
+  @SuppressWarnings("rawtypes" /* See https://github.com/google/auto/issues/870. */)
+  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/resources/tech/picnic/errorprone/documentation/BugPatternTestExtractorTest-bugpattern-test-CompilationAndBugCheckerRefactoringTestHelpersTest.json

@@ -0,0 +1,24 @@
+{
+  "testClass": "CompilationAndBugCheckerRefactoringTestHelpersTest",
+  "testCases": [
+    {
+      "classUnderTest": "CompilationAndBugCheckerRefactoringTestHelpersTest.TestChecker",
+      "entries": [
+        {
+          "path": "A.java",
+          "code": "// BUG: Diagnostic contains:\nclass A {}\n"
+        }
+      ]
+    },
+    {
+      "classUnderTest": "CompilationAndBugCheckerRefactoringTestHelpersTest.TestChecker",
+      "entries": [
+        {
+          "path": "A.java",
+          "input": "class A {}\n",
+          "output": "class A { /* This is a change. */ }\n"
+        }
+      ]
+    }
+  ]
+}

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

@@ -0,0 +1,24 @@
+{
+  "testClass": "pkg.CompilationAndBugCheckerRefactoringTestHelpersWithCustomCheckerPackageAndNamesTest",
+  "testCases": [
+    {
+      "classUnderTest": "pkg.CompilationAndBugCheckerRefactoringTestHelpersWithCustomCheckerPackageAndNamesTest.CustomTestChecker",
+      "entries": [
+        {
+          "path": "A.java",
+          "code": "// BUG: Diagnostic contains:\nclass A {}\n"
+        }
+      ]
+    },
+    {
+      "classUnderTest": "pkg.CompilationAndBugCheckerRefactoringTestHelpersWithCustomCheckerPackageAndNamesTest.CustomTestChecker2",
+      "entries": [
+        {
+          "path": "A.java",
+          "input": "class A {}\n",
+          "output": "class A { /* This is a change. */ }\n"
+        }
+      ]
+    }
+  ]
+}

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

@@ -0,0 +1,20 @@
+{
+  "testClass": "MultiFileBugCheckerRefactoringTestHelperTest",
+  "testCases": [
+    {
+      "classUnderTest": "MultiFileBugCheckerRefactoringTestHelperTest.TestChecker",
+      "entries": [
+        {
+          "path": "A.java",
+          "input": "class A {}\n",
+          "output": "class A { /* This is a change. */ }\n"
+        },
+        {
+          "path": "B.java",
+          "input": "class B {}\n",
+          "output": "class B { /* This is a change. */ }\n"
+        }
+      ]
+    }
+  ]
+}

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

@@ -0,0 +1,18 @@
+{
+  "testClass": "MultiFileCompilationTestHelperTest",
+  "testCases": [
+    {
+      "classUnderTest": "MultiFileCompilationTestHelperTest.TestChecker",
+      "entries": [
+        {
+          "path": "A.java",
+          "code": "// BUG: Diagnostic contains:\nclass A {}\n"
+        },
+        {
+          "path": "B.java",
+          "code": "// BUG: Diagnostic contains:\nclass B {}\n"
+        }
+      ]
+    }
+  ]
+}

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

@@ -0,0 +1,15 @@
+{
+  "testClass": "SingleFileBugCheckerRefactoringTestHelperTest",
+  "testCases": [
+    {
+      "classUnderTest": "SingleFileBugCheckerRefactoringTestHelperTest.TestChecker",
+      "entries": [
+        {
+          "path": "A.java",
+          "input": "class A {}\n",
+          "output": "class A { /* This is a change. */ }\n"
+        }
+      ]
+    }
+  ]
+}

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

@@ -0,0 +1,15 @@
+{
+  "testClass": "SingleFileBugCheckerRefactoringTestHelperWithSetArgsFixChooserAndCustomTestModeTest",
+  "testCases": [
+    {
+      "classUnderTest": "SingleFileBugCheckerRefactoringTestHelperWithSetArgsFixChooserAndCustomTestModeTest.TestChecker",
+      "entries": [
+        {
+          "path": "A.java",
+          "input": "class A {}\n",
+          "output": "class A { /* This is a change. */ }\n"
+        }
+      ]
+    }
+  ]
+}

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

@@ -0,0 +1,14 @@
+{
+  "testClass": "SingleFileCompilationTestHelperTest",
+  "testCases": [
+    {
+      "classUnderTest": "SingleFileCompilationTestHelperTest.TestChecker",
+      "entries": [
+        {
+          "path": "A.java",
+          "code": "// BUG: Diagnostic contains:\nclass A {}\n"
+        }
+      ]
+    }
+  ]
+}

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

@@ -0,0 +1,14 @@
+{
+  "testClass": "SingleFileCompilationTestHelperWithSetArgsTest",
+  "testCases": [
+    {
+      "classUnderTest": "SingleFileCompilationTestHelperWithSetArgsTest.TestChecker",
+      "entries": [
+        {
+          "path": "A.java",
+          "code": "// BUG: Diagnostic contains:\nclass A {}\n"
+        }
+      ]
+    }
+  ]
+}

error-prone-contrib/pom.xml

@@ -72,6 +72,11 @@
             <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.googlejavaformat</groupId>
             <artifactId>google-java-format</artifactId>
@@ -248,17 +253,6 @@
                         </compilerArgs>
                     </configuration>
                 </plugin>
-                <plugin>
-                    <groupId>org.apache.maven.plugins</groupId>
-                    <artifactId>maven-dependency-plugin</artifactId>
-                    <configuration>
-                        <ignoredUnusedDeclaredDependencies>
-                            <!-- XXX: Figure out why the plugin thinks this
-                            dependency is unused. -->
-                            <ignoredUnusedDeclaredDependency>${project.groupId}:refaster-support</ignoredUnusedDeclaredDependency>
-                        </ignoredUnusedDeclaredDependencies>
-                    </configuration>
-                </plugin>
             </plugins>
         </pluginManagement>
     </build>

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

@@ -9,7 +9,6 @@ import static com.google.errorprone.matchers.Matchers.isType;
 import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.errorprone.BugPattern;
 import com.google.errorprone.VisitorState;
@@ -17,6 +16,7 @@ import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.matchers.MultiMatcher;
+import com.google.errorprone.matchers.MultiMatcher.MultiMatchResult;
 import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.AnnotationTree;
 import com.sun.source.tree.ClassTree;
@@ -48,11 +48,9 @@ public final class AutowiredConstructor extends BugChecker implements ClassTreeM
       return Description.NO_MATCH;
     }
 
-    ImmutableList<AnnotationTree> annotations =
-        AUTOWIRED_ANNOTATION
-            .multiMatchResult(Iterables.getOnlyElement(constructors), state)
-            .matchingNodes();
-    if (annotations.size() != 1) {
+    MultiMatchResult<AnnotationTree> hasAutowiredAnnotation =
+        AUTOWIRED_ANNOTATION.multiMatchResult(Iterables.getOnlyElement(constructors), state);
+    if (!hasAutowiredAnnotation.matches()) {
       return Description.NO_MATCH;
     }
 
@@ -61,7 +59,7 @@ public final class AutowiredConstructor extends BugChecker implements ClassTreeM
      * means that the associated import can be removed as well. Rather than adding code for this
      * case we leave flagging the unused import to Error Prone's `RemoveUnusedImports` check.
      */
-    AnnotationTree annotation = Iterables.getOnlyElement(annotations);
+    AnnotationTree annotation = hasAutowiredAnnotation.onlyMatchingNode();
     return describeMatch(annotation, SourceCode.deleteWithTrailingWhitespace(annotation, state));
   }
 }

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

@@ -5,6 +5,7 @@ import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
 import static com.google.errorprone.BugPattern.StandardTags.STYLE;
 import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.Matchers.instanceMethod;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
 import static java.util.stream.Collectors.joining;
 import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
@@ -66,7 +67,12 @@ public final class ErrorProneTestHelperSourceFormat extends BugChecker
               .named("addSourceLines"),
           instanceMethod()
               .onDescendantOf("com.google.errorprone.BugCheckerRefactoringTestHelper")
-              .named("addInputLines"));
+              .named("addInputLines"),
+          // XXX: Add tests for `Compilation.compileWithDocumentationGenerator`. Until done, make
+          // sure to update this matcher if that method's class or name is changed/moved.
+          staticMethod()
+              .onClass("tech.picnic.errorprone.documentation.Compilation")
+              .named("compileWithDocumentationGenerator"));
   private static final Matcher<ExpressionTree> OUTPUT_SOURCE_ACCEPTING_METHOD =
       instanceMethod()
           .onDescendantOf("com.google.errorprone.BugCheckerRefactoringTestHelper.ExpectOutput")
@@ -83,7 +89,8 @@ public final class ErrorProneTestHelperSourceFormat extends BugChecker
     }
 
     List<? extends ExpressionTree> sourceLines =
-        tree.getArguments().subList(1, tree.getArguments().size());
+        tree.getArguments()
+            .subList(ASTHelpers.getSymbol(tree).params().size() - 1, tree.getArguments().size());
     if (sourceLines.isEmpty()) {
       return buildDescription(tree).setMessage("No source code provided").build();
     }
@@ -149,12 +156,13 @@ public final class ErrorProneTestHelperSourceFormat extends BugChecker
     return FORMATTER.formatSource(withOptionallyRemovedImports);
   }
 
+  // XXX: This logic is duplicated in `BugPatternTestExtractor`. Can we do better?
   private static Optional<String> getConstantSourceCode(
       List<? extends ExpressionTree> sourceLines) {
     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/IdentityConversion.java

@@ -37,6 +37,8 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 // the target method such a modification may change the code's semantics or performance.
 // XXX: Also flag `Stream#map`, `Mono#map` and `Flux#map` invocations where the given transformation
 // is effectively the identity operation.
+// XXX: Also flag nullary instance method invocations that represent an identity conversion, such as
+// `Boolean#booleanValue()`, `Byte#byteValue()` and friends.
 @AutoService(BugChecker.class)
 @BugPattern(
     summary = "Avoid or clarify identity conversions",

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

@@ -0,0 +1,91 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
+import static com.google.errorprone.matchers.Matchers.annotations;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.isType;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+import static tech.picnic.errorprone.bugpatterns.util.MoreMatchers.hasMetaAnnotation;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.matchers.MultiMatcher;
+import com.google.errorprone.matchers.MultiMatcher.MultiMatchResult;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.MethodTree;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags nullary {@link
+ * org.junit.jupiter.params.ParameterizedTest @ParameterizedTest} test methods.
+ *
+ * <p>Such tests are unnecessarily executed more than necessary. This checker suggests annotating
+ * the method with {@link org.junit.jupiter.api.Test @Test}, and to drop all declared {@link
+ * org.junit.jupiter.params.provider.ArgumentsSource argument sources}.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Nullary JUnit test methods should not be parameterized",
+    link = BUG_PATTERNS_BASE_URL + "JUnitNullaryParameterizedTestDeclaration",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class JUnitNullaryParameterizedTestDeclaration extends BugChecker
+    implements MethodTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final MultiMatcher<MethodTree, AnnotationTree> IS_PARAMETERIZED_TEST =
+      annotations(AT_LEAST_ONE, isType("org.junit.jupiter.params.ParameterizedTest"));
+  private static final Matcher<AnnotationTree> IS_ARGUMENT_SOURCE =
+      anyOf(
+          isType("org.junit.jupiter.params.provider.ArgumentsSource"),
+          isType("org.junit.jupiter.params.provider.ArgumentsSources"),
+          hasMetaAnnotation("org.junit.jupiter.params.provider.ArgumentsSource"));
+
+  /** Instantiates a new {@link JUnitNullaryParameterizedTestDeclaration} instance. */
+  public JUnitNullaryParameterizedTestDeclaration() {}
+
+  @Override
+  public Description matchMethod(MethodTree tree, VisitorState state) {
+    if (!tree.getParameters().isEmpty()) {
+      return Description.NO_MATCH;
+    }
+
+    MultiMatchResult<AnnotationTree> isParameterizedTest =
+        IS_PARAMETERIZED_TEST.multiMatchResult(tree, state);
+    if (!isParameterizedTest.matches()) {
+      return Description.NO_MATCH;
+    }
+
+    /*
+     * This method is vacuously parameterized. Suggest replacing `@ParameterizedTest` with `@Test`.
+     * (As each method is checked independently, we cannot in general determine whether this
+     * suggestion makes a `ParameterizedTest` type import obsolete; that task is left to Error
+     * Prone's `RemoveUnusedImports` check.)
+     */
+    SuggestedFix.Builder fix = SuggestedFix.builder();
+    fix.merge(
+        SuggestedFix.replace(
+            isParameterizedTest.onlyMatchingNode(),
+            '@' + SuggestedFixes.qualifyType(state, fix, "org.junit.jupiter.api.Test")));
+
+    /*
+     * Also suggest dropping all (explicit and implicit) `@ArgumentsSource`s. No attempt is made to
+     * assess whether a dropped `@MethodSource` also makes the referenced factory method(s) unused.
+     */
+    tree.getModifiers().getAnnotations().stream()
+        .filter(a -> IS_ARGUMENT_SOURCE.matches(a, state))
+        .forEach(a -> fix.merge(SourceCode.deleteWithTrailingWhitespace(a, state)));
+
+    return describeMatch(tree, fix.build());
+  }
+}

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

@@ -71,7 +71,7 @@ public final class MockitoMockClassReference extends BugChecker
     Tree parent = state.getPath().getParentPath().getLeaf();
     switch (parent.getKind()) {
       case VARIABLE:
-        return !ASTHelpers.hasNoExplicitType((VariableTree) parent, state)
+        return !ASTHelpers.hasImplicitType((VariableTree) parent, state)
             && MoreASTHelpers.areSameType(tree, parent, state);
       case ASSIGNMENT:
         return MoreASTHelpers.areSameType(tree, parent, state);

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

@@ -0,0 +1,215 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.BugPattern.StandardTags.STYLE;
+import static tech.picnic.errorprone.bugpatterns.StaticImport.STATIC_IMPORT_CANDIDATE_MEMBERS;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+
+import com.google.auto.service.AutoService;
+import com.google.auto.value.AutoValue;
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.ImmutableSetMultimap;
+import com.google.common.collect.ImmutableTable;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.CompilationUnitTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.fixes.SuggestedFixes;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.CompilationUnitTree;
+import com.sun.source.tree.IdentifierTree;
+import com.sun.source.tree.ImportTree;
+import com.sun.source.tree.MemberSelectTree;
+import com.sun.source.tree.Tree;
+import com.sun.source.util.TreeScanner;
+import com.sun.tools.javac.code.Symbol;
+import org.jspecify.annotations.Nullable;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} that flags static imports of type members that should *not* be statically
+ * imported.
+ */
+// XXX: This check is closely linked to `StaticImport`. Consider merging the two.
+// XXX: Add suppression support. If qualification of one more more identifiers is suppressed, then
+// the associated static import should *not* be removed.
+// XXX: Also introduce logic that disallows statically importing `ZoneOffset.ofHours` and other
+// `ofXXX`-style methods.
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Member should not be statically imported",
+    link = BUG_PATTERNS_BASE_URL + "NonStaticImport",
+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = STYLE)
+public final class NonStaticImport extends BugChecker implements CompilationUnitTreeMatcher {
+  private static final long serialVersionUID = 1L;
+
+  /**
+   * Types whose members should not be statically imported, unless exempted by {@link
+   * StaticImport#STATIC_IMPORT_CANDIDATE_MEMBERS}.
+   *
+   * <p>Types listed here should be mutually exclusive with {@link
+   * StaticImport#STATIC_IMPORT_CANDIDATE_TYPES}.
+   */
+  @VisibleForTesting
+  static final ImmutableSet<String> NON_STATIC_IMPORT_CANDIDATE_TYPES =
+      ImmutableSet.of(
+          "com.google.common.base.Strings",
+          "com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode",
+          "java.time.Clock",
+          "java.time.ZoneOffset");
+
+  /**
+   * Type members that should never be statically imported.
+   *
+   * <p>Please note that:
+   *
+   * <ul>
+   *   <li>Types listed by {@link #NON_STATIC_IMPORT_CANDIDATE_TYPES} and members listed by {@link
+   *       #NON_STATIC_IMPORT_CANDIDATE_IDENTIFIERS} should be omitted from this collection.
+   *   <li>This collection should be mutually exclusive with {@link
+   *       StaticImport#STATIC_IMPORT_CANDIDATE_MEMBERS}.
+   * </ul>
+   */
+  // XXX: Perhaps the set of exempted `java.util.Collections` methods is too strict. For now any
+  // method name that could be considered "too vague" or could conceivably mean something else in a
+  // specific context is left out.
+  static final ImmutableSetMultimap<String, String> NON_STATIC_IMPORT_CANDIDATE_MEMBERS =
+      ImmutableSetMultimap.<String, String>builder()
+          .put("com.google.common.base.Predicates", "contains")
+          .putAll(
+              "java.util.Collections",
+              "addAll",
+              "copy",
+              "fill",
+              "list",
+              "max",
+              "min",
+              "nCopies",
+              "rotate",
+              "sort",
+              "swap")
+          .put("java.util.Locale", "ROOT")
+          .putAll("java.util.regex.Pattern", "compile", "matches", "quote")
+          .put("org.springframework.http.MediaType", "ALL")
+          .build();
+
+  /**
+   * Identifiers that should never be statically imported.
+   *
+   * <p>Please note that:
+   *
+   * <ul>
+   *   <li>Identifiers listed by {@link StaticImport#STATIC_IMPORT_CANDIDATE_MEMBERS} should be
+   *       mutually exclusive with identifiers listed here.
+   *   <li>This list should contain a superset of the identifiers flagged by {@link
+   *       com.google.errorprone.bugpatterns.BadImport}.
+   * </ul>
+   */
+  static final ImmutableSet<String> NON_STATIC_IMPORT_CANDIDATE_IDENTIFIERS =
+      ImmutableSet.of(
+          "builder",
+          "copyOf",
+          "create",
+          "empty",
+          "from",
+          "getDefaultInstance",
+          "INSTANCE",
+          "MAX",
+          "MAX_VALUE",
+          "MIN",
+          "MIN_VALUE",
+          "newBuilder",
+          "newInstance",
+          "of",
+          "ONE",
+          "parse",
+          "valueOf",
+          "ZERO");
+
+  /** Instantiates a new {@link NonStaticImport} instance. */
+  public NonStaticImport() {}
+
+  @Override
+  public Description matchCompilationUnit(CompilationUnitTree tree, VisitorState state) {
+    ImmutableTable<String, String, UndesiredStaticImport> undesiredStaticImports =
+        getUndesiredStaticImports(tree, state);
+
+    if (!undesiredStaticImports.isEmpty()) {
+      replaceUndesiredStaticImportUsages(tree, undesiredStaticImports, state);
+
+      for (UndesiredStaticImport staticImport : undesiredStaticImports.values()) {
+        state.reportMatch(
+            describeMatch(staticImport.importTree(), staticImport.fixBuilder().build()));
+      }
+    }
+
+    /* Any violations have been flagged against the offending static import statement. */
+    return Description.NO_MATCH;
+  }
+
+  private static ImmutableTable<String, String, UndesiredStaticImport> getUndesiredStaticImports(
+      CompilationUnitTree tree, VisitorState state) {
+    ImmutableTable.Builder<String, String, UndesiredStaticImport> imports =
+        ImmutableTable.builder();
+    for (ImportTree importTree : tree.getImports()) {
+      Tree qualifiedIdentifier = importTree.getQualifiedIdentifier();
+      if (importTree.isStatic() && qualifiedIdentifier instanceof MemberSelectTree) {
+        MemberSelectTree memberSelectTree = (MemberSelectTree) qualifiedIdentifier;
+        String type = SourceCode.treeToString(memberSelectTree.getExpression(), state);
+        String member = memberSelectTree.getIdentifier().toString();
+        if (shouldNotBeStaticallyImported(type, member)) {
+          imports.put(
+              type,
+              member,
+              new AutoValue_NonStaticImport_UndesiredStaticImport(
+                  importTree, SuggestedFix.builder().removeStaticImport(type + '.' + member)));
+        }
+      }
+    }
+
+    return imports.build();
+  }
+
+  private static boolean shouldNotBeStaticallyImported(String type, String member) {
+    return (NON_STATIC_IMPORT_CANDIDATE_TYPES.contains(type)
+            && !STATIC_IMPORT_CANDIDATE_MEMBERS.containsEntry(type, member))
+        || NON_STATIC_IMPORT_CANDIDATE_MEMBERS.containsEntry(type, member)
+        || NON_STATIC_IMPORT_CANDIDATE_IDENTIFIERS.contains(member);
+  }
+
+  private static void replaceUndesiredStaticImportUsages(
+      CompilationUnitTree tree,
+      ImmutableTable<String, String, UndesiredStaticImport> undesiredStaticImports,
+      VisitorState state) {
+    new TreeScanner<@Nullable Void, @Nullable Void>() {
+      @Override
+      public @Nullable Void visitIdentifier(IdentifierTree node, @Nullable Void unused) {
+        Symbol symbol = ASTHelpers.getSymbol(node);
+        if (symbol != null) {
+          UndesiredStaticImport staticImport =
+              undesiredStaticImports.get(
+                  symbol.owner.getQualifiedName().toString(), symbol.name.toString());
+          if (staticImport != null) {
+            SuggestedFix.Builder fix = staticImport.fixBuilder();
+            fix.prefixWith(node, SuggestedFixes.qualifyType(state, fix, symbol.owner) + '.');
+          }
+        }
+
+        return super.visitIdentifier(node, unused);
+      }
+    }.scan(tree, null);
+  }
+
+  @AutoValue
+  abstract static class UndesiredStaticImport {
+    abstract ImportTree importTree();
+
+    abstract SuggestedFix.Builder fixBuilder();
+  }
+}

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

@@ -2,8 +2,10 @@ 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.BugPattern.StandardTags.STYLE;
 import static java.util.Objects.requireNonNull;
+import static tech.picnic.errorprone.bugpatterns.NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_IDENTIFIERS;
+import static tech.picnic.errorprone.bugpatterns.NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_MEMBERS;
 import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
@@ -27,35 +29,30 @@ import com.sun.source.tree.Tree;
 import com.sun.tools.javac.code.Type;
 import java.util.Optional;
 
-/**
- * A {@link BugChecker} that flags methods and constants that can and should be statically imported.
- */
+/** A {@link BugChecker} that flags type members that can and should be statically imported. */
+// XXX: This check is closely linked to `NonStaticImport`. Consider merging the two.
 // XXX: Tricky cases:
 // - `org.springframework.http.HttpStatus` (not always an improvement, and `valueOf` must
 //    certainly be excluded)
 // - `com.google.common.collect.Tables`
-// - `ch.qos.logback.classic.Level.{DEBUG, ERROR, INFO, TRACE, WARN"}`
-// XXX: Also introduce a check that disallows static imports of certain methods. Candidates:
-// - `com.google.common.base.Strings`
-// - `java.util.Optional.empty`
-// - `java.util.Locale.ROOT`
-// - `ZoneOffset.ofHours` and other `ofXXX`-style methods.
-// - `java.time.Clock`.
-// - Several other `java.time` classes.
-// - Likely any of `*.{ZERO, ONE, MIX, MAX, MIN_VALUE, MAX_VALUE}`.
+// - `ch.qos.logback.classic.Level.{DEBUG, ERROR, INFO, TRACE, WARN}`
 @AutoService(BugChecker.class)
 @BugPattern(
     summary = "Identifier should be statically imported",
     link = BUG_PATTERNS_BASE_URL + "StaticImport",
     linkType = CUSTOM,
     severity = SUGGESTION,
-    tags = SIMPLIFICATION)
+    tags = STYLE)
 public final class StaticImport extends BugChecker implements MemberSelectTreeMatcher {
   private static final long serialVersionUID = 1L;
 
   /**
    * Types whose members should be statically imported, unless exempted by {@link
-   * #STATIC_IMPORT_EXEMPTED_MEMBERS} or {@link #STATIC_IMPORT_EXEMPTED_IDENTIFIERS}.
+   * NonStaticImport#NON_STATIC_IMPORT_CANDIDATE_MEMBERS} or {@link
+   * NonStaticImport#NON_STATIC_IMPORT_CANDIDATE_IDENTIFIERS}.
+   *
+   * <p>Types listed here should be mutually exclusive with {@link
+   * NonStaticImport#NON_STATIC_IMPORT_CANDIDATE_TYPES}.
    */
   @VisibleForTesting
   static final ImmutableSet<String> STATIC_IMPORT_CANDIDATE_TYPES =
@@ -104,8 +101,20 @@ public final class StaticImport extends BugChecker implements MemberSelectTreeMa
           "reactor.function.TupleUtils",
           "tech.picnic.errorprone.bugpatterns.util.MoreTypes");
 
-  /** Type members that should be statically imported. */
-  @VisibleForTesting
+  /**
+   * Type members that should be statically imported.
+   *
+   * <p>Please note that:
+   *
+   * <ul>
+   *   <li>Types listed by {@link #STATIC_IMPORT_CANDIDATE_TYPES} should be omitted from this
+   *       collection.
+   *   <li>This collection should be mutually exclusive with {@link
+   *       NonStaticImport#NON_STATIC_IMPORT_CANDIDATE_MEMBERS}.
+   *   <li>This collection should not list members contained in {@link
+   *       NonStaticImport#NON_STATIC_IMPORT_CANDIDATE_IDENTIFIERS}.
+   * </ul>
+   */
   static final ImmutableSetMultimap<String, String> STATIC_IMPORT_CANDIDATE_MEMBERS =
       ImmutableSetMultimap.<String, String>builder()
           .putAll(
@@ -143,55 +152,6 @@ public final class StaticImport extends BugChecker implements MemberSelectTreeMa
           .putAll("com.google.common.collect.Comparators", "emptiesFirst", "emptiesLast")
           .build();
 
-  /**
-   * Type members that should never be statically imported.
-   *
-   * <p>Identifiers listed by {@link #STATIC_IMPORT_EXEMPTED_IDENTIFIERS} should be omitted from
-   * this collection.
-   */
-  // XXX: Perhaps the set of exempted `java.util.Collections` methods is too strict. For now any
-  // method name that could be considered "too vague" or could conceivably mean something else in a
-  // specific context is left out.
-  @VisibleForTesting
-  static final ImmutableSetMultimap<String, String> STATIC_IMPORT_EXEMPTED_MEMBERS =
-      ImmutableSetMultimap.<String, String>builder()
-          .put("com.google.common.base.Predicates", "contains")
-          .put("com.mongodb.client.model.Filters", "empty")
-          .putAll(
-              "java.util.Collections",
-              "addAll",
-              "copy",
-              "fill",
-              "list",
-              "max",
-              "min",
-              "nCopies",
-              "rotate",
-              "sort",
-              "swap")
-          .putAll("java.util.regex.Pattern", "compile", "matches", "quote")
-          .put("org.springframework.http.MediaType", "ALL")
-          .build();
-
-  /**
-   * Identifiers that should never be statically imported.
-   *
-   * <p>This should be a superset of the identifiers flagged by {@link
-   * com.google.errorprone.bugpatterns.BadImport}.
-   */
-  @VisibleForTesting
-  static final ImmutableSet<String> STATIC_IMPORT_EXEMPTED_IDENTIFIERS =
-      ImmutableSet.of(
-          "builder",
-          "create",
-          "copyOf",
-          "from",
-          "getDefaultInstance",
-          "INSTANCE",
-          "newBuilder",
-          "of",
-          "valueOf");
-
   /** Instantiates a new {@link StaticImport} instance. */
   public StaticImport() {}
 
@@ -229,13 +189,13 @@ public final class StaticImport extends BugChecker implements MemberSelectTreeMa
 
   private static boolean isCandidate(MemberSelectTree tree) {
     String identifier = tree.getIdentifier().toString();
-    if (STATIC_IMPORT_EXEMPTED_IDENTIFIERS.contains(identifier)) {
+    if (NON_STATIC_IMPORT_CANDIDATE_IDENTIFIERS.contains(identifier)) {
       return false;
     }
 
     Type type = ASTHelpers.getType(tree.getExpression());
     return type != null
-        && !STATIC_IMPORT_EXEMPTED_MEMBERS.containsEntry(type.toString(), identifier);
+        && !NON_STATIC_IMPORT_CANDIDATE_MEMBERS.containsEntry(type.toString(), identifier);
   }
 
   private static Optional<String> getCandidateSimpleName(StaticImportInfo importInfo) {

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

@@ -23,7 +23,7 @@ import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.MethodInvocationTree;
 import com.sun.tools.javac.code.Type;
-import com.sun.tools.javac.util.Convert;
+import com.sun.tools.javac.util.Constants;
 import java.util.Formattable;
 import java.util.Iterator;
 import java.util.List;
@@ -150,7 +150,7 @@ public final class StringJoin extends BugChecker implements MethodInvocationTree
     SuggestedFix.Builder fix =
         SuggestedFix.builder()
             .replace(tree.getMethodSelect(), "String.join")
-            .replace(arguments.next(), String.format("\"%s\"", Convert.quote(separator)));
+            .replace(arguments.next(), Constants.format(separator));
 
     while (arguments.hasNext()) {
       ExpressionTree argument = arguments.next();

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

@@ -3,80 +3,40 @@ package tech.picnic.errorprone.refasterrules;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 import static org.assertj.core.api.Assertions.assertThat;
 
-import com.google.common.collect.ImmutableBiMap;
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
-import com.google.common.collect.ImmutableMultiset;
-import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.ImmutableSortedMap;
-import com.google.common.collect.ImmutableSortedMultiset;
-import com.google.common.collect.ImmutableSortedSet;
 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.UseImportPolicy;
-import java.util.ArrayList;
 import java.util.Collection;
-import java.util.HashMap;
-import java.util.HashSet;
-import java.util.LinkedHashMap;
-import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Set;
-import java.util.TreeMap;
-import java.util.TreeSet;
 import org.assertj.core.api.AbstractAssert;
 import org.assertj.core.api.AbstractBooleanAssert;
 import org.assertj.core.api.AbstractCollectionAssert;
 import org.assertj.core.api.AbstractMapAssert;
 import org.assertj.core.api.MapAssert;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+import tech.picnic.errorprone.refaster.matchers.IsEmpty;
 
 @OnlineDocumentation
 final class AssertJMapRules {
   private AssertJMapRules() {}
 
-  // XXX: Reduce boilerplate using a `Matcher` that identifies "empty" instances.
   static final class AbstractMapAssertIsEmpty<K, V> {
     @BeforeTemplate
-    @SuppressWarnings("unchecked")
-    void before(AbstractMapAssert<?, ?, K, V> mapAssert) {
+    void before(
+        AbstractMapAssert<?, ?, K, V> mapAssert,
+        @Matches(IsEmpty.class) Map<? extends K, ? extends V> wellTypedMap,
+        @Matches(IsEmpty.class) Map<?, ?> arbitrarilyTypedMap,
+        @Matches(IsEmpty.class) Iterable<? extends K> keys) {
       Refaster.anyOf(
-          mapAssert.containsExactlyEntriesOf(
-              Refaster.anyOf(
-                  ImmutableMap.of(),
-                  ImmutableBiMap.of(),
-                  ImmutableSortedMap.of(),
-                  new HashMap<>(),
-                  new LinkedHashMap<>(),
-                  new TreeMap<>())),
-          mapAssert.hasSameSizeAs(
-              Refaster.anyOf(
-                  ImmutableMap.of(),
-                  ImmutableBiMap.of(),
-                  ImmutableSortedMap.of(),
-                  new HashMap<>(),
-                  new LinkedHashMap<>(),
-                  new TreeMap<>())),
-          mapAssert.isEqualTo(
-              Refaster.anyOf(
-                  ImmutableMap.of(),
-                  ImmutableBiMap.of(),
-                  ImmutableSortedMap.of(),
-                  new HashMap<>(),
-                  new LinkedHashMap<>(),
-                  new TreeMap<>())),
-          mapAssert.containsOnlyKeys(
-              Refaster.anyOf(
-                  ImmutableList.of(),
-                  new ArrayList<>(),
-                  ImmutableSet.of(),
-                  new HashSet<>(),
-                  new LinkedHashSet<>(),
-                  ImmutableSortedSet.of(),
-                  new TreeSet<>(),
-                  ImmutableMultiset.of(),
-                  ImmutableSortedMultiset.of())),
+          mapAssert.containsExactlyEntriesOf(wellTypedMap),
+          mapAssert.containsExactlyInAnyOrderEntriesOf(wellTypedMap),
+          mapAssert.hasSameSizeAs(arbitrarilyTypedMap),
+          mapAssert.isEqualTo(arbitrarilyTypedMap),
+          mapAssert.containsOnlyKeys(keys),
           mapAssert.containsExactly(),
           mapAssert.containsOnly(),
           mapAssert.containsOnlyKeys());
@@ -112,15 +72,9 @@ final class AssertJMapRules {
 
   static final class AbstractMapAssertIsNotEmpty<K, V> {
     @BeforeTemplate
-    AbstractMapAssert<?, ?, K, V> before(AbstractMapAssert<?, ?, K, V> mapAssert) {
-      return mapAssert.isNotEqualTo(
-          Refaster.anyOf(
-              ImmutableMap.of(),
-              ImmutableBiMap.of(),
-              ImmutableSortedMap.of(),
-              new HashMap<>(),
-              new LinkedHashMap<>(),
-              new TreeMap<>()));
+    AbstractMapAssert<?, ?, K, V> before(
+        AbstractMapAssert<?, ?, K, V> mapAssert, @Matches(IsEmpty.class) Map<?, ?> map) {
+      return mapAssert.isNotEqualTo(map);
     }
 
     @AfterTemplate
@@ -148,12 +102,14 @@ final class AssertJMapRules {
 
   static final class AbstractMapAssertContainsExactlyInAnyOrderEntriesOf<K, V> {
     @BeforeTemplate
-    AbstractMapAssert<?, ?, K, V> before(AbstractMapAssert<?, ?, K, V> mapAssert, Map<K, V> map) {
+    AbstractMapAssert<?, ?, K, V> before(
+        AbstractMapAssert<?, ?, K, V> mapAssert, Map<? extends K, ? extends V> map) {
       return mapAssert.isEqualTo(map);
     }
 
     @AfterTemplate
-    AbstractMapAssert<?, ?, K, V> after(AbstractMapAssert<?, ?, K, V> mapAssert, Map<K, V> map) {
+    AbstractMapAssert<?, ?, K, V> after(
+        AbstractMapAssert<?, ?, K, V> mapAssert, Map<? extends K, ? extends V> map) {
       return mapAssert.containsExactlyInAnyOrderEntriesOf(map);
     }
   }
@@ -187,12 +143,12 @@ final class AssertJMapRules {
 
   static final class AbstractMapAssertHasSameSizeAs<K, V> {
     @BeforeTemplate
-    AbstractMapAssert<?, ?, K, V> before(AbstractMapAssert<?, ?, K, V> mapAssert, Map<K, V> map) {
+    AbstractMapAssert<?, ?, K, V> before(AbstractMapAssert<?, ?, K, V> mapAssert, Map<?, ?> map) {
       return mapAssert.hasSize(map.size());
     }
 
     @AfterTemplate
-    AbstractMapAssert<?, ?, K, V> after(AbstractMapAssert<?, ?, K, V> mapAssert, Map<K, V> map) {
+    AbstractMapAssert<?, ?, K, V> after(AbstractMapAssert<?, ?, K, V> mapAssert, Map<?, ?> map) {
       return mapAssert.hasSameSizeAs(map);
     }
   }
@@ -225,13 +181,14 @@ final class AssertJMapRules {
 
   static final class AssertThatMapContainsOnlyKeys<K, V> {
     @BeforeTemplate
-    AbstractCollectionAssert<?, Collection<? extends K>, K, ?> before(Map<K, V> map, Set<K> keys) {
+    AbstractCollectionAssert<?, Collection<? extends K>, K, ?> before(
+        Map<K, V> map, Set<? extends K> keys) {
       return assertThat(map.keySet()).hasSameElementsAs(keys);
     }
 
     @AfterTemplate
     @UseImportPolicy(STATIC_IMPORT_ALWAYS)
-    MapAssert<K, V> after(Map<K, V> map, Set<K> keys) {
+    MapAssert<K, V> after(Map<K, V> map, Set<? extends K> keys) {
       return assertThat(map).containsOnlyKeys(keys);
     }
   }

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

@@ -6,28 +6,23 @@ import static org.assertj.core.api.Assertions.assertThat;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMultiset;
 import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.ImmutableSortedMultiset;
-import com.google.common.collect.ImmutableSortedSet;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Multiset;
 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.NotMatches;
 import com.google.errorprone.refaster.annotation.Repeated;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.HashSet;
-import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.OptionalDouble;
 import java.util.OptionalInt;
 import java.util.OptionalLong;
 import java.util.Set;
-import java.util.TreeSet;
 import java.util.function.Predicate;
 import java.util.stream.Collector;
 import java.util.stream.Stream;
@@ -47,6 +42,7 @@ import org.assertj.core.api.OptionalIntAssert;
 import org.assertj.core.api.OptionalLongAssert;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 import tech.picnic.errorprone.refaster.matchers.IsArray;
+import tech.picnic.errorprone.refaster.matchers.IsEmpty;
 
 /** Refaster rules related to AssertJ expressions and statements. */
 // XXX: Most `AbstractIntegerAssert` rules can also be applied for other primitive types. Generate
@@ -181,63 +177,16 @@ final class AssertJRules {
   static final class AssertThatObjectEnumerableIsEmpty<E> {
     @BeforeTemplate
     @SuppressWarnings("unchecked")
-    void before(ObjectEnumerableAssert<?, E> enumAssert) {
+    void before(
+        ObjectEnumerableAssert<?, E> enumAssert,
+        @Matches(IsEmpty.class) Iterable<? extends E> wellTypedIterable,
+        @Matches(IsEmpty.class) Iterable<?> arbitrarilyTypedIterable) {
       Refaster.anyOf(
-          enumAssert.containsExactlyElementsOf(
-              Refaster.anyOf(
-                  ImmutableList.of(),
-                  new ArrayList<>(),
-                  ImmutableSet.of(),
-                  new HashSet<>(),
-                  new LinkedHashSet<>(),
-                  ImmutableSortedSet.of(),
-                  new TreeSet<>(),
-                  ImmutableMultiset.of(),
-                  ImmutableSortedMultiset.of())),
-          enumAssert.containsExactlyInAnyOrderElementsOf(
-              Refaster.anyOf(
-                  ImmutableList.of(),
-                  new ArrayList<>(),
-                  ImmutableSet.of(),
-                  new HashSet<>(),
-                  new LinkedHashSet<>(),
-                  ImmutableSortedSet.of(),
-                  new TreeSet<>(),
-                  ImmutableMultiset.of(),
-                  ImmutableSortedMultiset.of())),
-          enumAssert.hasSameElementsAs(
-              Refaster.anyOf(
-                  ImmutableList.of(),
-                  new ArrayList<>(),
-                  ImmutableSet.of(),
-                  new HashSet<>(),
-                  new LinkedHashSet<>(),
-                  ImmutableSortedSet.of(),
-                  new TreeSet<>(),
-                  ImmutableMultiset.of(),
-                  ImmutableSortedMultiset.of())),
-          enumAssert.hasSameSizeAs(
-              Refaster.anyOf(
-                  ImmutableList.of(),
-                  new ArrayList<>(),
-                  ImmutableSet.of(),
-                  new HashSet<>(),
-                  new LinkedHashSet<>(),
-                  ImmutableSortedSet.of(),
-                  new TreeSet<>(),
-                  ImmutableMultiset.of(),
-                  ImmutableSortedMultiset.of())),
-          enumAssert.isSubsetOf(
-              Refaster.anyOf(
-                  ImmutableList.of(),
-                  new ArrayList<>(),
-                  ImmutableSet.of(),
-                  new HashSet<>(),
-                  new LinkedHashSet<>(),
-                  ImmutableSortedSet.of(),
-                  new TreeSet<>(),
-                  ImmutableMultiset.of(),
-                  ImmutableSortedMultiset.of())),
+          enumAssert.containsExactlyElementsOf(wellTypedIterable),
+          enumAssert.containsExactlyInAnyOrderElementsOf(wellTypedIterable),
+          enumAssert.hasSameElementsAs(wellTypedIterable),
+          enumAssert.hasSameSizeAs(arbitrarilyTypedIterable),
+          enumAssert.isSubsetOf(wellTypedIterable),
           enumAssert.containsExactly(),
           enumAssert.containsExactlyInAnyOrder(),
           enumAssert.containsOnly(),

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

@@ -2,6 +2,7 @@ package tech.picnic.errorprone.refasterrules;
 
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.AlsoNegation;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import java.math.BigDecimal;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
@@ -66,4 +67,61 @@ final class BigDecimalRules {
       return BigDecimal.valueOf(value);
     }
   }
+
+  /** Prefer using {@link BigDecimal#signum()} over more contrived alternatives. */
+  static final class BigDecimalSignumIsZero {
+    @BeforeTemplate
+    boolean before(BigDecimal value) {
+      return Refaster.anyOf(
+          value.compareTo(BigDecimal.ZERO) == 0, BigDecimal.ZERO.compareTo(value) == 0);
+    }
+
+    @AfterTemplate
+    @AlsoNegation
+    boolean after(BigDecimal value) {
+      return value.signum() == 0;
+    }
+  }
+
+  /**
+   * Prefer a {@link BigDecimal#signum()} comparison to 1 over more contrived or less clear
+   * alternatives.
+   */
+  static final class BigDecimalSignumIsPositive {
+    @BeforeTemplate
+    boolean before(BigDecimal value) {
+      return Refaster.anyOf(
+          value.compareTo(BigDecimal.ZERO) > 0,
+          BigDecimal.ZERO.compareTo(value) < 0,
+          value.signum() > 0,
+          value.signum() >= 1);
+    }
+
+    @AfterTemplate
+    @AlsoNegation
+    boolean after(BigDecimal value) {
+      return value.signum() == 1;
+    }
+  }
+
+  /**
+   * Prefer a {@link BigDecimal#signum()} comparison to -1 over more contrived or less clear
+   * alternatives.
+   */
+  static final class BigDecimalSignumIsNegative {
+    @BeforeTemplate
+    boolean before(BigDecimal value) {
+      return Refaster.anyOf(
+          value.compareTo(BigDecimal.ZERO) < 0,
+          BigDecimal.ZERO.compareTo(value) > 0,
+          value.signum() < 0,
+          value.signum() <= -1);
+    }
+
+    @AfterTemplate
+    @AlsoNegation
+    boolean after(BigDecimal value) {
+      return value.signum() == -1;
+    }
+  }
 }

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

@@ -7,6 +7,8 @@ import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.sun.tools.javac.util.Constants;
+import com.sun.tools.javac.util.Convert;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to {@link com.google.errorprone.bugpatterns.BugChecker} classes. */
@@ -52,4 +54,17 @@ final class BugCheckerRules {
       return helper.addInputLines(path, source).expectUnchanged();
     }
   }
+
+  /** Prefer using the {@link Constants} API over more verbose alternatives. */
+  static final class ConstantsFormat {
+    @BeforeTemplate
+    String before(String value) {
+      return String.format("\"%s\"", Convert.quote(value));
+    }
+
+    @AfterTemplate
+    String after(String value) {
+      return Constants.format(value);
+    }
+  }
 }

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

@@ -7,7 +7,6 @@ import static java.util.Comparator.comparingInt;
 import static java.util.Comparator.comparingLong;
 import static java.util.Comparator.naturalOrder;
 import static java.util.Comparator.reverseOrder;
-import static java.util.function.Function.identity;
 
 import com.google.common.collect.Comparators;
 import com.google.common.collect.ImmutableList;
@@ -16,6 +15,7 @@ import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.Matches;
 import com.google.errorprone.refaster.annotation.Repeated;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.Arrays;
@@ -28,6 +28,7 @@ import java.util.function.ToIntFunction;
 import java.util.function.ToLongFunction;
 import java.util.stream.Stream;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+import tech.picnic.errorprone.refaster.matchers.IsIdentityOperation;
 
 /** Refaster rules related to expressions dealing with {@link Comparator}s. */
 @OnlineDocumentation
@@ -36,12 +37,12 @@ final class ComparatorRules {
 
   /** Prefer {@link Comparator#naturalOrder()} over more complicated constructs. */
   static final class NaturalOrder<T extends Comparable<? super T>> {
-    // XXX: Drop the `Refaster.anyOf` if/when we decide to rewrite one to the other.
     @BeforeTemplate
-    Comparator<T> before() {
+    Comparator<T> before(
+        @Matches(IsIdentityOperation.class) Function<? super T, ? extends T> keyExtractor) {
       return Refaster.anyOf(
           T::compareTo,
-          comparing(Refaster.anyOf(identity(), v -> v)),
+          comparing(keyExtractor),
           Collections.<T>reverseOrder(reverseOrder()),
           Comparator.<T>reverseOrder().reversed());
     }
@@ -72,10 +73,11 @@ final class ComparatorRules {
   }
 
   static final class CustomComparator<T> {
-    // XXX: Drop the `Refaster.anyOf` if/when we decide to rewrite one to the other.
     @BeforeTemplate
-    Comparator<T> before(Comparator<T> cmp) {
-      return comparing(Refaster.anyOf(identity(), v -> v), cmp);
+    Comparator<T> before(
+        Comparator<T> cmp,
+        @Matches(IsIdentityOperation.class) Function<? super T, ? extends T> keyExtractor) {
+      return comparing(keyExtractor, cmp);
     }
 
     @AfterTemplate
@@ -183,14 +185,15 @@ final class ComparatorRules {
   }
 
   /**
-   * Where applicable, prefer {@link Comparator#naturalOrder()} over {@link Function#identity()}, as
-   * it more clearly states intent.
+   * Where applicable, prefer {@link Comparator#naturalOrder()} over identity function-based
+   * comparisons, as the former more clearly states intent.
    */
   static final class ThenComparingNaturalOrder<T extends Comparable<? super T>> {
-    // XXX: Drop the `Refaster.anyOf` if/when we decide to rewrite one to the other.
     @BeforeTemplate
-    Comparator<T> before(Comparator<T> cmp) {
-      return cmp.thenComparing(Refaster.anyOf(identity(), v -> v));
+    Comparator<T> before(
+        Comparator<T> cmp,
+        @Matches(IsIdentityOperation.class) Function<? super T, ? extends T> keyExtractor) {
+      return cmp.thenComparing(keyExtractor);
     }
 
     @AfterTemplate

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

@@ -3,7 +3,6 @@ package tech.picnic.errorprone.refasterrules;
 import static com.google.common.collect.ImmutableListMultimap.flatteningToImmutableListMultimap;
 import static com.google.common.collect.ImmutableListMultimap.toImmutableListMultimap;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
-import static java.util.function.Function.identity;
 
 import com.google.common.collect.ImmutableListMultimap;
 import com.google.common.collect.ImmutableMultimap;
@@ -16,6 +15,7 @@ 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;
@@ -25,6 +25,7 @@ import java.util.Map;
 import java.util.function.Function;
 import java.util.stream.Stream;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+import tech.picnic.errorprone.refaster.matchers.IsIdentityOperation;
 
 /** Refaster rules related to expressions dealing with {@link ImmutableListMultimap}s. */
 @OnlineDocumentation
@@ -173,27 +174,29 @@ final class ImmutableListMultimapRules {
    * Prefer {@link Multimaps#index(Iterable, com.google.common.base.Function)} over the stream-based
    * alternative.
    */
-  // XXX: Drop the `Refaster.anyOf` if/when we decide to rewrite one to the other.
   static final class IndexIterableToImmutableListMultimap<K, V> {
     @BeforeTemplate
     ImmutableListMultimap<K, V> before(
-        Iterator<V> iterable, Function<? super V, ? extends K> keyFunction) {
-      return Streams.stream(iterable)
-          .collect(toImmutableListMultimap(keyFunction, Refaster.anyOf(identity(), v -> v)));
+        Iterator<V> iterable,
+        Function<? super V, ? extends K> keyFunction,
+        @Matches(IsIdentityOperation.class) Function<? super V, ? extends V> valueFunction) {
+      return Streams.stream(iterable).collect(toImmutableListMultimap(keyFunction, valueFunction));
     }
 
     @BeforeTemplate
     ImmutableListMultimap<K, V> before(
-        Iterable<V> iterable, Function<? super V, ? extends K> keyFunction) {
-      return Streams.stream(iterable)
-          .collect(toImmutableListMultimap(keyFunction, Refaster.anyOf(identity(), v -> v)));
+        Iterable<V> iterable,
+        Function<? super V, ? extends K> keyFunction,
+        @Matches(IsIdentityOperation.class) Function<? super V, ? extends V> valueFunction) {
+      return Streams.stream(iterable).collect(toImmutableListMultimap(keyFunction, valueFunction));
     }
 
     @BeforeTemplate
     ImmutableListMultimap<K, V> before(
-        Collection<V> iterable, Function<? super V, ? extends K> keyFunction) {
-      return iterable.stream()
-          .collect(toImmutableListMultimap(keyFunction, Refaster.anyOf(identity(), v -> v)));
+        Collection<V> iterable,
+        Function<? super V, ? extends K> keyFunction,
+        @Matches(IsIdentityOperation.class) Function<? super V, ? extends V> valueFunction) {
+      return iterable.stream().collect(toImmutableListMultimap(keyFunction, valueFunction));
     }
 
     @AfterTemplate

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

@@ -4,7 +4,6 @@ import static com.google.common.collect.ImmutableMap.toImmutableMap;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 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;
@@ -13,6 +12,7 @@ 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;
@@ -23,6 +23,7 @@ import java.util.Set;
 import java.util.function.Function;
 import java.util.stream.Stream;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+import tech.picnic.errorprone.refaster.matchers.IsIdentityOperation;
 
 /** Refaster rules related to expressions dealing with {@link ImmutableMap}s. */
 @OnlineDocumentation
@@ -63,27 +64,29 @@ final class ImmutableMapRules {
    * Prefer {@link Maps#toMap(Iterable, com.google.common.base.Function)} over more contrived
    * alternatives.
    */
-  // XXX: Drop the `Refaster.anyOf` if/when we decide to rewrite one to the other.
   static final class IterableToImmutableMap<K, V> {
     @BeforeTemplate
     ImmutableMap<K, V> before(
-        Iterator<K> iterable, Function<? super K, ? extends V> valueFunction) {
-      return Streams.stream(iterable)
-          .collect(toImmutableMap(Refaster.anyOf(identity(), k -> k), valueFunction));
+        Iterator<K> iterable,
+        Function<? super K, ? extends V> valueFunction,
+        @Matches(IsIdentityOperation.class) Function<? super K, ? extends K> keyFunction) {
+      return Streams.stream(iterable).collect(toImmutableMap(keyFunction, valueFunction));
     }
 
     @BeforeTemplate
     ImmutableMap<K, V> before(
-        Iterable<K> iterable, Function<? super K, ? extends V> valueFunction) {
-      return Streams.stream(iterable)
-          .collect(toImmutableMap(Refaster.anyOf(identity(), k -> k), valueFunction));
+        Iterable<K> iterable,
+        Function<? super K, ? extends V> valueFunction,
+        @Matches(IsIdentityOperation.class) Function<? super K, ? extends K> keyFunction) {
+      return Streams.stream(iterable).collect(toImmutableMap(keyFunction, valueFunction));
     }
 
     @BeforeTemplate
     ImmutableMap<K, V> before(
-        Collection<K> iterable, Function<? super K, ? extends V> valueFunction) {
-      return iterable.stream()
-          .collect(toImmutableMap(Refaster.anyOf(identity(), k -> k), valueFunction));
+        Collection<K> iterable,
+        Function<? super K, ? extends V> valueFunction,
+        @Matches(IsIdentityOperation.class) Function<? super K, ? extends K> keyFunction) {
+      return iterable.stream().collect(toImmutableMap(keyFunction, valueFunction));
     }
 
     @BeforeTemplate
@@ -157,25 +160,29 @@ final class ImmutableMapRules {
    * Prefer {@link Maps#uniqueIndex(Iterable, com.google.common.base.Function)} over the
    * stream-based alternative.
    */
-  // XXX: Drop the `Refaster.anyOf` if/when we decide to rewrite one to the other.
   static final class IndexIterableToImmutableMap<K, V> {
     @BeforeTemplate
-    ImmutableMap<K, V> before(Iterator<V> iterable, Function<? super V, ? extends K> keyFunction) {
-      return Streams.stream(iterable)
-          .collect(toImmutableMap(keyFunction, Refaster.anyOf(identity(), v -> v)));
-    }
-
-    @BeforeTemplate
-    ImmutableMap<K, V> before(Iterable<V> iterable, Function<? super V, ? extends K> keyFunction) {
-      return Streams.stream(iterable)
-          .collect(toImmutableMap(keyFunction, Refaster.anyOf(identity(), v -> v)));
+    ImmutableMap<K, V> before(
+        Iterator<V> iterable,
+        Function<? super V, ? extends K> keyFunction,
+        @Matches(IsIdentityOperation.class) Function<? super V, ? extends V> valueFunction) {
+      return Streams.stream(iterable).collect(toImmutableMap(keyFunction, valueFunction));
     }
 
     @BeforeTemplate
     ImmutableMap<K, V> before(
-        Collection<V> iterable, Function<? super V, ? extends K> keyFunction) {
-      return iterable.stream()
-          .collect(toImmutableMap(keyFunction, Refaster.anyOf(identity(), v -> v)));
+        Iterable<V> iterable,
+        Function<? super V, ? extends K> keyFunction,
+        @Matches(IsIdentityOperation.class) Function<? super V, ? extends V> valueFunction) {
+      return Streams.stream(iterable).collect(toImmutableMap(keyFunction, valueFunction));
+    }
+
+    @BeforeTemplate
+    ImmutableMap<K, V> before(
+        Collection<V> iterable,
+        Function<? super V, ? extends K> keyFunction,
+        @Matches(IsIdentityOperation.class) Function<? super V, ? extends V> valueFunction) {
+      return iterable.stream().collect(toImmutableMap(keyFunction, valueFunction));
     }
 
     @AfterTemplate

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

@@ -6,6 +6,7 @@ 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.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
@@ -517,4 +518,82 @@ final class JUnitToAssertJRules {
       assertThat(actual).withFailMessage(supplier).isInstanceOf(clazz);
     }
   }
+
+  static final class AssertThatByteIsEqualTo {
+    @BeforeTemplate
+    void before(byte actual, byte expected) {
+      assertEquals(actual, expected);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(byte actual, byte expected) {
+      assertThat(actual).isEqualTo(expected);
+    }
+  }
+
+  static final class AssertThatByteWithFailMessageStringIsEqualTo {
+    @BeforeTemplate
+    void before(byte actual, byte expected, String message) {
+      assertEquals(actual, expected, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(byte actual, byte expected, String message) {
+      assertThat(actual).withFailMessage(message).isEqualTo(expected);
+    }
+  }
+
+  static final class AssertThatByteWithFailMessageSupplierIsEqualTo {
+    @BeforeTemplate
+    void before(byte actual, byte expected, Supplier<String> message) {
+      assertEquals(actual, expected, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(byte actual, byte expected, Supplier<String> message) {
+      assertThat(actual).withFailMessage(message).isEqualTo(expected);
+    }
+  }
+
+  static final class AssertThatCharIsEqualTo {
+    @BeforeTemplate
+    void before(char actual, char expected) {
+      assertEquals(actual, expected);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(char actual, char expected) {
+      assertThat(actual).isEqualTo(expected);
+    }
+  }
+
+  static final class AssertThatCharWithFailMessageStringIsEqualTo {
+    @BeforeTemplate
+    void before(char actual, char expected, String message) {
+      assertEquals(actual, expected, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(char actual, char expected, String message) {
+      assertThat(actual).withFailMessage(message).isEqualTo(expected);
+    }
+  }
+
+  static final class AssertThatCharWithFailMessageSupplierIsEqualTo {
+    @BeforeTemplate
+    void before(char actual, char expected, Supplier<String> message) {
+      assertEquals(actual, expected, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(char actual, char expected, Supplier<String> message) {
+      assertThat(actual).withFailMessage(message).isEqualTo(expected);
+    }
+  }
 }

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

@@ -8,7 +8,9 @@ import com.google.common.primitives.Floats;
 import com.google.common.primitives.Ints;
 import com.google.common.primitives.Longs;
 import com.google.common.primitives.Shorts;
+import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.AlsoNegation;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
@@ -384,4 +386,60 @@ final class PrimitiveRules {
       return Double.isFinite(d);
     }
   }
+
+  /** Prefer an {@link Integer#signum(int)} comparison to 1 over less clear alternatives. */
+  static final class IntegerSignumIsPositive {
+    @BeforeTemplate
+    boolean before(int i) {
+      return Refaster.anyOf(Integer.signum(i) > 0, Integer.signum(i) >= 1);
+    }
+
+    @AfterTemplate
+    @AlsoNegation
+    boolean after(int i) {
+      return Integer.signum(i) == 1;
+    }
+  }
+
+  /** Prefer an {@link Integer#signum(int)} comparison to -1 over less clear alternatives. */
+  static final class IntegerSignumIsNegative {
+    @BeforeTemplate
+    boolean before(int i) {
+      return Refaster.anyOf(Integer.signum(i) < 0, Integer.signum(i) <= -1);
+    }
+
+    @AfterTemplate
+    @AlsoNegation
+    boolean after(int i) {
+      return Integer.signum(i) == -1;
+    }
+  }
+
+  /** Prefer an {@link Long#signum(long)} comparison to 1 over less clear alternatives. */
+  static final class LongSignumIsPositive {
+    @BeforeTemplate
+    boolean before(long l) {
+      return Refaster.anyOf(Long.signum(l) > 0, Long.signum(l) >= 1);
+    }
+
+    @AfterTemplate
+    @AlsoNegation
+    boolean after(long l) {
+      return Long.signum(l) == 1;
+    }
+  }
+
+  /** Prefer an {@link Long#signum(long)} comparison to -1 over less clear alternatives. */
+  static final class LongSignumIsNegative {
+    @BeforeTemplate
+    boolean before(long l) {
+      return Refaster.anyOf(Long.signum(l) < 0, Long.signum(l) <= -1);
+    }
+
+    @AfterTemplate
+    @AlsoNegation
+    boolean after(long l) {
+      return Long.signum(l) == -1;
+    }
+  }
 }

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

@@ -12,12 +12,12 @@ import static reactor.function.TupleUtils.function;
 
 import com.google.common.collect.ImmutableCollection;
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.Matches;
 import com.google.errorprone.refaster.annotation.MayOptionallyUse;
 import com.google.errorprone.refaster.annotation.NotMatches;
 import com.google.errorprone.refaster.annotation.Placeholder;
@@ -26,8 +26,8 @@ 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.Map;
 import java.util.Optional;
 import java.util.concurrent.Callable;
 import java.util.function.BiConsumer;
@@ -48,6 +48,8 @@ import reactor.util.function.Tuple2;
 import tech.picnic.errorprone.refaster.annotation.Description;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 import tech.picnic.errorprone.refaster.annotation.Severity;
+import tech.picnic.errorprone.refaster.matchers.IsEmpty;
+import tech.picnic.errorprone.refaster.matchers.IsIdentityOperation;
 import tech.picnic.errorprone.refaster.matchers.ThrowsCheckedException;
 
 /** Refaster rules related to Reactor expressions and statements. */
@@ -508,7 +510,8 @@ final class ReactorRules {
     }
 
     // XXX: Replace this rule with an extension of the `IdentityConversion` rule, supporting
-    // `Stream#map`, `Mono#map` and `Flux#map`.
+    // `Stream#map`, `Mono#map` and `Flux#map`. Alternatively, extend the `IsIdentityOperation`
+    // matcher and use it to constrain the matched `map` argument.
     @BeforeTemplate
     Mono<ImmutableList<T>> before3(Mono<ImmutableList<T>> mono) {
       return mono.map(ImmutableList::copyOf);
@@ -549,51 +552,59 @@ final class ReactorRules {
   }
 
   /** Prefer {@link Flux#concatMap(Function)} over more contrived alternatives. */
-  static final class FluxConcatMap<T, S> {
+  static final class FluxConcatMap<T, S, P extends Publisher<? extends S>> {
     @BeforeTemplate
     @SuppressWarnings("NestedPublishers")
-    Flux<S> before(Flux<T> flux, Function<? super T, ? extends Publisher<? extends S>> function) {
+    Flux<S> before(
+        Flux<T> flux,
+        Function<? super T, ? extends P> function,
+        @Matches(IsIdentityOperation.class)
+            Function<? super P, ? extends Publisher<? extends S>> identityOperation) {
       return Refaster.anyOf(
           flux.flatMap(function, 1),
           flux.flatMapSequential(function, 1),
-          flux.map(function).concatMap(identity()));
+          flux.map(function).concatMap(identityOperation));
     }
 
     @AfterTemplate
-    Flux<S> after(Flux<T> flux, Function<? super T, ? extends Publisher<? extends S>> function) {
+    Flux<S> after(Flux<T> flux, Function<? super T, ? extends P> function) {
       return flux.concatMap(function);
     }
   }
 
   /** Prefer {@link Flux#concatMap(Function, int)} over more contrived alternatives. */
-  static final class FluxConcatMapWithPrefetch<T, S> {
+  static final class FluxConcatMapWithPrefetch<T, S, P extends Publisher<? extends S>> {
     @BeforeTemplate
     @SuppressWarnings("NestedPublishers")
     Flux<S> before(
         Flux<T> flux,
-        Function<? super T, ? extends Publisher<? extends S>> function,
-        int prefetch) {
+        Function<? super T, ? extends P> function,
+        int prefetch,
+        @Matches(IsIdentityOperation.class)
+            Function<? super P, ? extends Publisher<? extends S>> identityOperation) {
       return Refaster.anyOf(
           flux.flatMap(function, 1, prefetch),
           flux.flatMapSequential(function, 1, prefetch),
-          flux.map(function).concatMap(identity(), prefetch));
+          flux.map(function).concatMap(identityOperation, prefetch));
     }
 
     @AfterTemplate
-    Flux<S> after(
-        Flux<T> flux,
-        Function<? super T, ? extends Publisher<? extends S>> function,
-        int prefetch) {
+    Flux<S> after(Flux<T> flux, Function<? super T, ? extends P> function, int prefetch) {
       return flux.concatMap(function, prefetch);
     }
   }
 
   /** Avoid contrived alternatives to {@link Mono#flatMapIterable(Function)}. */
-  static final class MonoFlatMapIterable<T, S> {
+  static final class MonoFlatMapIterable<T, S, I extends Iterable<? extends S>> {
     @BeforeTemplate
-    Flux<S> before(Mono<T> mono, Function<? super T, ? extends Iterable<? extends S>> function) {
+    Flux<S> before(
+        Mono<T> mono,
+        Function<? super T, I> function,
+        @Matches(IsIdentityOperation.class)
+            Function<? super I, ? extends Iterable<? extends S>> identityOperation) {
       return Refaster.anyOf(
-          mono.map(function).flatMapIterable(identity()), mono.flux().concatMapIterable(function));
+          mono.map(function).flatMapIterable(identityOperation),
+          mono.flux().concatMapIterable(function));
     }
 
     @AfterTemplate
@@ -623,11 +634,15 @@ final class ReactorRules {
    * Prefer {@link Flux#concatMapIterable(Function)} over alternatives with less clear syntax or
    * semantics.
    */
-  static final class FluxConcatMapIterable<T, S> {
+  static final class FluxConcatMapIterable<T, S, I extends Iterable<? extends S>> {
     @BeforeTemplate
-    Flux<S> before(Flux<T> flux, Function<? super T, ? extends Iterable<? extends S>> function) {
+    Flux<S> before(
+        Flux<T> flux,
+        Function<? super T, I> function,
+        @Matches(IsIdentityOperation.class)
+            Function<? super I, ? extends Iterable<? extends S>> identityOperation) {
       return Refaster.anyOf(
-          flux.flatMapIterable(function), flux.map(function).concatMapIterable(identity()));
+          flux.flatMapIterable(function), flux.map(function).concatMapIterable(identityOperation));
     }
 
     @AfterTemplate
@@ -640,13 +655,17 @@ final class ReactorRules {
    * Prefer {@link Flux#concatMapIterable(Function, int)} over alternatives with less clear syntax
    * or semantics.
    */
-  static final class FluxConcatMapIterableWithPrefetch<T, S> {
+  static final class FluxConcatMapIterableWithPrefetch<T, S, I extends Iterable<? extends S>> {
     @BeforeTemplate
     Flux<S> before(
-        Flux<T> flux, Function<? super T, ? extends Iterable<? extends S>> function, int prefetch) {
+        Flux<T> flux,
+        Function<? super T, I> function,
+        int prefetch,
+        @Matches(IsIdentityOperation.class)
+            Function<? super I, ? extends Iterable<? extends S>> identityOperation) {
       return Refaster.anyOf(
           flux.flatMapIterable(function, prefetch),
-          flux.map(function).concatMapIterable(identity(), prefetch));
+          flux.map(function).concatMapIterable(identityOperation, prefetch));
     }
 
     @AfterTemplate
@@ -1080,31 +1099,37 @@ final class ReactorRules {
   }
 
   /** Prefer {@link Mono#flatMap(Function)} over more contrived alternatives. */
-  static final class MonoFlatMap<S, T> {
+  static final class MonoFlatMap<S, T, P extends Mono<? extends T>> {
     @BeforeTemplate
     @SuppressWarnings("NestedPublishers")
-    Mono<T> before(Mono<S> mono, Function<? super S, ? extends Mono<? extends T>> function) {
-      return mono.map(function).flatMap(identity());
+    Mono<T> before(
+        Mono<S> mono,
+        Function<? super S, ? extends P> function,
+        @Matches(IsIdentityOperation.class)
+            Function<? super P, ? extends Mono<? extends T>> identityOperation) {
+      return mono.map(function).flatMap(identityOperation);
     }
 
     @AfterTemplate
-    Mono<T> after(Mono<S> mono, Function<? super S, ? extends Mono<? extends T>> function) {
+    Mono<T> after(Mono<S> mono, Function<? super S, ? extends P> function) {
       return mono.flatMap(function);
     }
   }
 
   /** Prefer {@link Mono#flatMapMany(Function)} over more contrived alternatives. */
-  static final class MonoFlatMapMany<S, T> {
+  static final class MonoFlatMapMany<S, T, P extends Publisher<? extends T>> {
     @BeforeTemplate
     @SuppressWarnings("NestedPublishers")
     Flux<T> before(
         Mono<S> mono,
-        Function<? super S, ? extends Publisher<? extends T>> function,
+        Function<? super S, P> function,
+        @Matches(IsIdentityOperation.class)
+            Function<? super P, ? extends Publisher<? extends T>> identityOperation,
         boolean delayUntilEnd,
         int maxConcurrency,
         int prefetch) {
       return Refaster.anyOf(
-          mono.map(function).flatMapMany(identity()),
+          mono.map(function).flatMapMany(identityOperation),
           mono.flux().concatMap(function),
           mono.flux().concatMap(function, prefetch),
           mono.flux().concatMapDelayError(function),
@@ -1124,7 +1149,7 @@ final class ReactorRules {
     }
 
     @AfterTemplate
-    Flux<T> after(Mono<S> mono, Function<? super S, ? extends Publisher<? extends T>> function) {
+    Flux<T> after(Mono<S> mono, Function<? super S, ? extends P> function) {
       return mono.flatMapMany(function);
     }
   }
@@ -1555,12 +1580,12 @@ final class ReactorRules {
   }
 
   /** 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.
+  // XXX: Introduce Refaster rules or a `BugChecker` that maps `(Immutable)Map.of(k, v)` to
+  // `Context.of(k, v)` and likewise for multi-pair overloads.
   static final class ContextEmpty {
     @BeforeTemplate
-    Context before() {
-      return Context.of(Refaster.anyOf(new HashMap<>(), ImmutableMap.of()));
+    Context before(@Matches(IsEmpty.class) Map<?, ?> map) {
+      return Context.of(map);
     }
 
     @AfterTemplate
@@ -1609,13 +1634,13 @@ final class ReactorRules {
   }
 
   /** 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 Refaster.anyOf(step.expectNext(), step.expectNextCount(0));
+    StepVerifier.Step<T> before(
+        StepVerifier.Step<T> step, @Matches(IsEmpty.class) Iterable<? extends T> iterable) {
+      return Refaster.anyOf(
+          step.expectNext(), step.expectNextCount(0), step.expectNextSequence(iterable));
     }
 
     @AfterTemplate

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

@@ -3,7 +3,6 @@ package tech.picnic.errorprone.refasterrules;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 import static java.util.Comparator.naturalOrder;
 import static java.util.Comparator.reverseOrder;
-import static java.util.function.Function.identity;
 import static java.util.function.Predicate.not;
 import static java.util.stream.Collectors.counting;
 import static java.util.stream.Collectors.filtering;
@@ -51,6 +50,7 @@ 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.IsIdentityOperation;
 import tech.picnic.errorprone.refaster.matchers.IsLambdaExpressionOrMethodReference;
 import tech.picnic.errorprone.refaster.matchers.IsRefasterAsVarargs;
 
@@ -357,6 +357,8 @@ final class StreamRules {
           stream.filter(predicate).findAny().isEmpty());
     }
 
+    // XXX: Consider extending `@Matches(IsIdentityOperation.class)` such that it can replace this
+    // template's `Refaster.anyOf` usage.
     @BeforeTemplate
     boolean before2(
         Stream<T> stream,
@@ -395,6 +397,8 @@ final class StreamRules {
           !stream.noneMatch(predicate), stream.filter(predicate).findAny().isPresent());
     }
 
+    // XXX: Consider extending `@Matches(IsIdentityOperation.class)` such that it can replace this
+    // template's `Refaster.anyOf` usage.
     @BeforeTemplate
     boolean before2(
         Stream<T> stream,
@@ -415,6 +419,8 @@ final class StreamRules {
       return stream.noneMatch(Refaster.anyOf(not(predicate), predicate.negate()));
     }
 
+    // XXX: Consider extending `@Matches(IsIdentityOperation.class)` such that it can replace this
+    // template's `Refaster.anyOf` usage.
     @BeforeTemplate
     boolean before2(
         Stream<T> stream,
@@ -632,8 +638,11 @@ final class StreamRules {
 
   static final class StreamsConcat<T> {
     @BeforeTemplate
-    Stream<T> before(@Repeated Stream<T> stream) {
-      return Stream.of(Refaster.asVarargs(stream)).flatMap(Refaster.anyOf(identity(), s -> s));
+    Stream<T> before(
+        @Repeated Stream<T> stream,
+        @Matches(IsIdentityOperation.class)
+            Function<? super Stream<T>, ? extends Stream<? extends T>> mapper) {
+      return Stream.of(Refaster.asVarargs(stream)).flatMap(mapper);
     }
 
     @AfterTemplate

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

@@ -0,0 +1,155 @@
+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 JUnitNullaryParameterizedTestDeclarationTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(JUnitNullaryParameterizedTestDeclaration.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import org.junit.jupiter.api.Test;",
+            "import org.junit.jupiter.params.ParameterizedTest;",
+            "import org.junit.jupiter.params.provider.ValueSource;",
+            "",
+            "class A {",
+            "  void nonTest() {}",
+            "",
+            "  @Test",
+            "  void nonParameterizedTest() {}",
+            "",
+            "  @ParameterizedTest",
+            "  @ValueSource(ints = {0, 1})",
+            "  void goodParameterizedTest(int someInt) {}",
+            "",
+            "  @ParameterizedTest",
+            "  @ValueSource(ints = {0, 1})",
+            "  // BUG: Diagnostic contains:",
+            "  void nullaryParameterizedTest() {}",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    BugCheckerRefactoringTestHelper.newInstance(
+            JUnitNullaryParameterizedTestDeclaration.class, getClass())
+        .addInputLines(
+            "A.java",
+            "import org.junit.jupiter.params.ParameterizedTest;",
+            "import org.junit.jupiter.params.provider.ArgumentsProvider;",
+            "import org.junit.jupiter.params.provider.ArgumentsSource;",
+            "import org.junit.jupiter.params.provider.ArgumentsSources;",
+            "import org.junit.jupiter.params.provider.MethodSource;",
+            "import org.junit.jupiter.params.provider.ValueSource;",
+            "",
+            "class A {",
+            "  @ParameterizedTest",
+            "  void withoutArgumentSource() {}",
+            "",
+            "  @ParameterizedTest",
+            "  @ArgumentsSource(ArgumentsProvider.class)",
+            "  void withCustomArgumentSource() {}",
+            "",
+            "  @ParameterizedTest",
+            "  @ArgumentsSources({",
+            "    @ArgumentsSource(ArgumentsProvider.class),",
+            "    @ArgumentsSource(ArgumentsProvider.class)",
+            "  })",
+            "  void withCustomerArgumentSources() {}",
+            "",
+            "  /** Foo. */",
+            "  @ParameterizedTest",
+            "  @ValueSource(ints = {0, 1})",
+            "  void withValueSourceAndJavadoc() {}",
+            "",
+            "  @ParameterizedTest",
+            "  @MethodSource(\"nonexistentMethod\")",
+            "  @SuppressWarnings(\"foo\")",
+            "  void withMethodSourceAndUnrelatedAnnotation() {}",
+            "",
+            "  @org.junit.jupiter.params.ParameterizedTest",
+            "  @ArgumentsSource(ArgumentsProvider.class)",
+            "  @ValueSource(ints = {0, 1})",
+            "  @MethodSource(\"nonexistentMethod\")",
+            "  void withMultipleArgumentSourcesAndFullyQualifiedImport() {}",
+            "",
+            "  class NestedWithTestAnnotationFirst {",
+            "    @ParameterizedTest",
+            "    @ValueSource(ints = {0, 1})",
+            "    void withValueSource() {}",
+            "  }",
+            "",
+            "  class NestedWithTestAnnotationSecond {",
+            "    @ValueSource(ints = {0, 1})",
+            "    @ParameterizedTest",
+            "    void withValueSource() {}",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import org.junit.jupiter.api.Test;",
+            "import org.junit.jupiter.params.ParameterizedTest;",
+            "import org.junit.jupiter.params.provider.ArgumentsProvider;",
+            "import org.junit.jupiter.params.provider.ArgumentsSource;",
+            "import org.junit.jupiter.params.provider.ArgumentsSources;",
+            "import org.junit.jupiter.params.provider.MethodSource;",
+            "import org.junit.jupiter.params.provider.ValueSource;",
+            "",
+            "class A {",
+            "  @Test",
+            "  void withoutArgumentSource() {}",
+            "",
+            "  @Test",
+            "  void withCustomArgumentSource() {}",
+            "",
+            "  @Test",
+            "  void withCustomerArgumentSources() {}",
+            "",
+            "  /** Foo. */",
+            "  @Test",
+            "  void withValueSourceAndJavadoc() {}",
+            "",
+            "  @Test",
+            "  @SuppressWarnings(\"foo\")",
+            "  void withMethodSourceAndUnrelatedAnnotation() {}",
+            "",
+            "  @Test",
+            "  void withMultipleArgumentSourcesAndFullyQualifiedImport() {}",
+            "",
+            "  class NestedWithTestAnnotationFirst {",
+            "    @Test",
+            "    void withValueSource() {}",
+            "  }",
+            "",
+            "  class NestedWithTestAnnotationSecond {",
+            "    @Test",
+            "    void withValueSource() {}",
+            "  }",
+            "}")
+        .addInputLines(
+            "B.java",
+            "import org.junit.jupiter.params.ParameterizedTest;",
+            "",
+            "class B {",
+            "  @ParameterizedTest",
+            "  void scopeInWhichIdentifierTestIsAlreadyDeclared() {}",
+            "",
+            "  class Test {}",
+            "}")
+        .addOutputLines(
+            "B.java",
+            "import org.junit.jupiter.params.ParameterizedTest;",
+            "",
+            "class B {",
+            "  @org.junit.jupiter.api.Test",
+            "  void scopeInWhichIdentifierTestIsAlreadyDeclared() {}",
+            "",
+            "  class Test {}",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

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

@@ -0,0 +1,196 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Test;
+
+final class NonStaticImportTest {
+  @Test
+  void candidateTypesDoNotClash() {
+    assertThat(NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_TYPES)
+        .doesNotContainAnyElementsOf(StaticImport.STATIC_IMPORT_CANDIDATE_TYPES);
+  }
+
+  @Test
+  void candidateMembersAreNotRedundant() {
+    assertThat(NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_MEMBERS.keySet())
+        .doesNotContainAnyElementsOf(NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_TYPES);
+
+    assertThat(NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_MEMBERS.values())
+        .doesNotContainAnyElementsOf(NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_IDENTIFIERS);
+  }
+
+  @Test
+  void candidateMembersDoNotClash() {
+    assertThat(NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_MEMBERS.entries())
+        .doesNotContainAnyElementsOf(StaticImport.STATIC_IMPORT_CANDIDATE_MEMBERS.entries());
+  }
+
+  @Test
+  void candidateIdentifiersDoNotClash() {
+    assertThat(NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_IDENTIFIERS)
+        .doesNotContainAnyElementsOf(StaticImport.STATIC_IMPORT_CANDIDATE_MEMBERS.values());
+  }
+
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(NonStaticImport.class, getClass())
+        .addSourceLines(
+            "pkg/A.java",
+            "package pkg;",
+            "",
+            "// BUG: Diagnostic contains:",
+            "import static com.google.common.base.Strings.nullToEmpty;",
+            "// BUG: Diagnostic contains:",
+            "import static com.google.common.collect.ImmutableList.copyOf;",
+            "// BUG: Diagnostic contains:",
+            "import static java.lang.Integer.MAX_VALUE;",
+            "// BUG: Diagnostic contains:",
+            "import static java.lang.Integer.MIN_VALUE;",
+            "// BUG: Diagnostic contains:",
+            "import static java.time.Clock.systemUTC;",
+            "// BUG: Diagnostic contains:",
+            "import static java.time.Instant.MIN;",
+            "// BUG: Diagnostic contains:",
+            "import static java.time.ZoneOffset.SHORT_IDS;",
+            "import static java.time.ZoneOffset.UTC;",
+            "// BUG: Diagnostic contains:",
+            "import static java.util.Collections.min;",
+            "import static java.util.Locale.ENGLISH;",
+            "// BUG: Diagnostic contains:",
+            "import static java.util.Locale.ROOT;",
+            "// BUG: Diagnostic contains:",
+            "import static java.util.Optional.empty;",
+            "import static pkg.A.WithMethodThatIsSelectivelyFlagged.list;",
+            "",
+            "import com.google.common.collect.ImmutableList;",
+            "import com.google.common.collect.ImmutableSet;",
+            "import java.time.Instant;",
+            "import java.time.ZoneOffset;",
+            "import java.util.Locale;",
+            "import java.util.Map;",
+            "import pkg.A.Wrapper.ZERO;",
+            "",
+            "class A {",
+            "  private Integer MIN_VALUE = 12;",
+            "",
+            "  void m() {",
+            "    nullToEmpty(null);",
+            "    copyOf(ImmutableList.of());",
+            "    int max = MAX_VALUE;",
+            "    int min = MIN_VALUE;",
+            "    systemUTC();",
+            "    Instant minInstant = MIN;",
+            "    Map<String, String> shortIds = SHORT_IDS;",
+            "    ZoneOffset utc = UTC;",
+            "    min(ImmutableSet.of());",
+            "    Locale english = ENGLISH;",
+            "    Locale root = ROOT;",
+            "    empty();",
+            "",
+            "    list();",
+            "    new ZERO();",
+            "  }",
+            "",
+            "  static final class WithMethodThatIsSelectivelyFlagged {",
+            "    static ImmutableList<String> list() {",
+            "      return ImmutableList.of();",
+            "    }",
+            "  }",
+            "",
+            "  static final class Wrapper {",
+            "    static final class ZERO {}",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    BugCheckerRefactoringTestHelper.newInstance(NonStaticImport.class, getClass())
+        .addInputLines(
+            "A.java",
+            "import static com.google.common.collect.ImmutableList.copyOf;",
+            "import static com.google.common.collect.ImmutableSet.of;",
+            "import static java.time.Clock.systemUTC;",
+            "import static java.time.Instant.MAX;",
+            "import static java.time.Instant.MIN;",
+            "import static java.util.Collections.min;",
+            "import static java.util.Locale.ROOT;",
+            "import static java.util.Optional.empty;",
+            "",
+            "import com.google.common.collect.ImmutableList;",
+            "import com.google.common.collect.ImmutableSet;",
+            "import java.time.Clock;",
+            "import java.time.Instant;",
+            "import java.util.Locale;",
+            "import java.util.Optional;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    systemUTC();",
+            "    Clock.systemUTC();",
+            "",
+            "    Optional<Integer> o1 = empty();",
+            "    Optional<Integer> o2 = Optional.empty();",
+            "",
+            "    Object l1 = copyOf(ImmutableList.of());",
+            "    Object l2 = ImmutableList.copyOf(ImmutableList.of());",
+            "",
+            "    Locale lo1 = ROOT;",
+            "    Locale lo2 = Locale.ROOT;",
+            "",
+            "    Instant i1 = MIN;",
+            "    Instant i2 = MAX;",
+            "",
+            "    ImmutableSet.of(min(of()));",
+            "  }",
+            "",
+            "  private static final class WithCustomConstant {",
+            "    private static final Instant MIN = Instant.EPOCH;",
+            "    private static final Instant OTHER = MIN;",
+            "    private static final Instant OTHER_MAX = MAX;",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import com.google.common.collect.ImmutableList;",
+            "import com.google.common.collect.ImmutableSet;",
+            "import java.time.Clock;",
+            "import java.time.Instant;",
+            "import java.util.Collections;",
+            "import java.util.Locale;",
+            "import java.util.Optional;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Clock.systemUTC();",
+            "    Clock.systemUTC();",
+            "",
+            "    Optional<Integer> o1 = Optional.empty();",
+            "    Optional<Integer> o2 = Optional.empty();",
+            "",
+            "    Object l1 = ImmutableList.copyOf(ImmutableList.of());",
+            "    Object l2 = ImmutableList.copyOf(ImmutableList.of());",
+            "",
+            "    Locale lo1 = Locale.ROOT;",
+            "    Locale lo2 = Locale.ROOT;",
+            "",
+            "    Instant i1 = Instant.MIN;",
+            "    Instant i2 = Instant.MAX;",
+            "",
+            "    ImmutableSet.of(Collections.min(ImmutableSet.of()));",
+            "  }",
+            "",
+            "  private static final class WithCustomConstant {",
+            "    private static final Instant MIN = Instant.EPOCH;",
+            "    private static final Instant OTHER = MIN;",
+            "    private static final Instant OTHER_MAX = Instant.MAX;",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

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

@@ -9,21 +9,24 @@ import org.junit.jupiter.api.Test;
 
 final class StaticImportTest {
   @Test
-  void candidateMethodsAreNotRedundant() {
+  void candidateTypesDoNotClash() {
+    assertThat(StaticImport.STATIC_IMPORT_CANDIDATE_TYPES)
+        .doesNotContainAnyElementsOf(NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_TYPES);
+  }
+
+  @Test
+  void candidateMembersAreNotRedundant() {
     assertThat(StaticImport.STATIC_IMPORT_CANDIDATE_MEMBERS.keySet())
         .doesNotContainAnyElementsOf(StaticImport.STATIC_IMPORT_CANDIDATE_TYPES);
   }
 
   @Test
-  void exemptedMembersAreNotVacuous() {
-    assertThat(StaticImport.STATIC_IMPORT_EXEMPTED_MEMBERS.keySet())
-        .isSubsetOf(StaticImport.STATIC_IMPORT_CANDIDATE_TYPES);
-  }
+  void candidateMembersDoNotClash() {
+    assertThat(StaticImport.STATIC_IMPORT_CANDIDATE_MEMBERS.entries())
+        .doesNotContainAnyElementsOf(NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_MEMBERS.entries());
 
-  @Test
-  void exemptedMembersAreNotRedundant() {
-    assertThat(StaticImport.STATIC_IMPORT_EXEMPTED_MEMBERS.values())
-        .doesNotContainAnyElementsOf(StaticImport.STATIC_IMPORT_EXEMPTED_IDENTIFIERS);
+    assertThat(StaticImport.STATIC_IMPORT_CANDIDATE_MEMBERS.values())
+        .doesNotContainAnyElementsOf(NonStaticImport.NON_STATIC_IMPORT_CANDIDATE_IDENTIFIERS);
   }
 
   @Test

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

@@ -41,34 +41,19 @@ final class AssertJMapRulesTest implements RefasterRuleCollectionTestCase {
 
   void testAbstractMapAssertIsEmpty() {
     assertThat(ImmutableMap.of(1, 0)).containsExactlyEntriesOf(ImmutableMap.of());
-    assertThat(ImmutableMap.of(2, 0)).containsExactlyEntriesOf(ImmutableBiMap.of());
-    assertThat(ImmutableMap.of(3, 0)).containsExactlyEntriesOf(ImmutableSortedMap.of());
-    assertThat(ImmutableMap.of(4, 0)).containsExactlyEntriesOf(new HashMap<>());
-    assertThat(ImmutableMap.of(5, 0)).containsExactlyEntriesOf(new LinkedHashMap<>());
-    assertThat(ImmutableMap.of(6, 0)).containsExactlyEntriesOf(new TreeMap<>());
-    assertThat(ImmutableMap.of(7, 0)).hasSameSizeAs(ImmutableMap.of());
-    assertThat(ImmutableMap.of(8, 0)).hasSameSizeAs(ImmutableBiMap.of());
-    assertThat(ImmutableMap.of(9, 0)).hasSameSizeAs(ImmutableSortedMap.of());
-    assertThat(ImmutableMap.of(10, 0)).hasSameSizeAs(new HashMap<>());
-    assertThat(ImmutableMap.of(11, 0)).hasSameSizeAs(new LinkedHashMap<>());
-    assertThat(ImmutableMap.of(12, 0)).hasSameSizeAs(new TreeMap<>());
-    assertThat(ImmutableMap.of(13, 0)).isEqualTo(ImmutableMap.of());
-    assertThat(ImmutableMap.of(14, 0)).isEqualTo(ImmutableBiMap.of());
-    assertThat(ImmutableMap.of(15, 0)).isEqualTo(ImmutableSortedMap.of());
-    assertThat(ImmutableMap.of(16, 0)).isEqualTo(new HashMap<>());
-    assertThat(ImmutableMap.of(17, 0)).isEqualTo(new LinkedHashMap<>());
-    assertThat(ImmutableMap.of(18, 0)).isEqualTo(new TreeMap<>());
-    assertThat(ImmutableMap.of(19, 0)).containsOnlyKeys(ImmutableList.of());
-    assertThat(ImmutableMap.of(20, 0)).containsOnlyKeys(new ArrayList<>());
-    assertThat(ImmutableMap.of(21, 0)).containsOnlyKeys(ImmutableSet.of());
-    assertThat(ImmutableMap.of(22, 0)).containsOnlyKeys(new HashSet<>());
-    assertThat(ImmutableMap.of(23, 0)).containsOnlyKeys(ImmutableSortedSet.of());
-    assertThat(ImmutableMap.of(24, 0)).containsOnlyKeys(new TreeSet<>());
-    assertThat(ImmutableMap.of(25, 0)).containsOnlyKeys(ImmutableMultiset.of());
-    assertThat(ImmutableMap.of(26, 0)).containsOnlyKeys(ImmutableSortedMultiset.of());
-    assertThat(ImmutableMap.of(27, 0)).containsExactly();
-    assertThat(ImmutableMap.of(28, 0)).containsOnly();
-    assertThat(ImmutableMap.of(29, 0)).containsOnlyKeys();
+    assertThat(ImmutableMap.of(2, 0)).containsExactlyEntriesOf(ImmutableMap.of(1, 2));
+    assertThat(ImmutableMap.of(3, 0)).containsExactlyInAnyOrderEntriesOf(ImmutableMap.of());
+    assertThat(ImmutableMap.of(4, 0))
+        .containsExactlyInAnyOrderEntriesOf(ImmutableMap.of(1, 2, 3, 4));
+    assertThat(ImmutableMap.of(5, 0)).hasSameSizeAs(ImmutableMap.of());
+    assertThat(ImmutableMap.of(6, 0)).hasSameSizeAs(ImmutableMap.of(1, 2));
+    assertThat(ImmutableMap.of(7, 0)).isEqualTo(ImmutableMap.of());
+    assertThat(ImmutableMap.of(8, 0)).isEqualTo(ImmutableMap.of("foo", "bar"));
+    assertThat(ImmutableMap.of(9, 0)).containsOnlyKeys(ImmutableList.of());
+    assertThat(ImmutableMap.of(10, 0)).containsOnlyKeys(ImmutableList.of(1));
+    assertThat(ImmutableMap.of(11, 0)).containsExactly();
+    assertThat(ImmutableMap.of(12, 0)).containsOnly();
+    assertThat(ImmutableMap.of(13, 0)).containsOnlyKeys();
   }
 
   void testAssertThatMapIsEmpty() {
@@ -84,11 +69,7 @@ final class AssertJMapRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<MapAssert<Integer, Integer>> testAbstractMapAssertIsNotEmpty() {
     return ImmutableSet.of(
         assertThat(ImmutableMap.of(1, 0)).isNotEqualTo(ImmutableMap.of()),
-        assertThat(ImmutableMap.of(2, 0)).isNotEqualTo(ImmutableBiMap.of()),
-        assertThat(ImmutableMap.of(3, 0)).isNotEqualTo(ImmutableSortedMap.of()),
-        assertThat(ImmutableMap.of(4, 0)).isNotEqualTo(new HashMap<>()),
-        assertThat(ImmutableMap.of(5, 0)).isNotEqualTo(new LinkedHashMap<>()),
-        assertThat(ImmutableMap.of(6, 0)).isNotEqualTo(new TreeMap<>()));
+        assertThat(ImmutableMap.of(2, 0)).isNotEqualTo(ImmutableMap.of("foo", "bar")));
   }
 
   ImmutableSet<AbstractAssert<?, ?>> testAssertThatMapIsNotEmpty() {

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

@@ -41,34 +41,19 @@ final class AssertJMapRulesTest implements RefasterRuleCollectionTestCase {
 
   void testAbstractMapAssertIsEmpty() {
     assertThat(ImmutableMap.of(1, 0)).isEmpty();
-    assertThat(ImmutableMap.of(2, 0)).isEmpty();
+    assertThat(ImmutableMap.of(2, 0)).containsExactlyEntriesOf(ImmutableMap.of(1, 2));
     assertThat(ImmutableMap.of(3, 0)).isEmpty();
-    assertThat(ImmutableMap.of(4, 0)).isEmpty();
+    assertThat(ImmutableMap.of(4, 0))
+        .containsExactlyInAnyOrderEntriesOf(ImmutableMap.of(1, 2, 3, 4));
     assertThat(ImmutableMap.of(5, 0)).isEmpty();
-    assertThat(ImmutableMap.of(6, 0)).isEmpty();
+    assertThat(ImmutableMap.of(6, 0)).hasSameSizeAs(ImmutableMap.of(1, 2));
     assertThat(ImmutableMap.of(7, 0)).isEmpty();
-    assertThat(ImmutableMap.of(8, 0)).isEmpty();
+    assertThat(ImmutableMap.of(8, 0)).isEqualTo(ImmutableMap.of("foo", "bar"));
     assertThat(ImmutableMap.of(9, 0)).isEmpty();
-    assertThat(ImmutableMap.of(10, 0)).isEmpty();
+    assertThat(ImmutableMap.of(10, 0)).containsOnlyKeys(ImmutableList.of(1));
     assertThat(ImmutableMap.of(11, 0)).isEmpty();
     assertThat(ImmutableMap.of(12, 0)).isEmpty();
     assertThat(ImmutableMap.of(13, 0)).isEmpty();
-    assertThat(ImmutableMap.of(14, 0)).isEmpty();
-    assertThat(ImmutableMap.of(15, 0)).isEmpty();
-    assertThat(ImmutableMap.of(16, 0)).isEmpty();
-    assertThat(ImmutableMap.of(17, 0)).isEmpty();
-    assertThat(ImmutableMap.of(18, 0)).isEmpty();
-    assertThat(ImmutableMap.of(19, 0)).isEmpty();
-    assertThat(ImmutableMap.of(20, 0)).isEmpty();
-    assertThat(ImmutableMap.of(21, 0)).isEmpty();
-    assertThat(ImmutableMap.of(22, 0)).isEmpty();
-    assertThat(ImmutableMap.of(23, 0)).isEmpty();
-    assertThat(ImmutableMap.of(24, 0)).isEmpty();
-    assertThat(ImmutableMap.of(25, 0)).isEmpty();
-    assertThat(ImmutableMap.of(26, 0)).isEmpty();
-    assertThat(ImmutableMap.of(27, 0)).isEmpty();
-    assertThat(ImmutableMap.of(28, 0)).isEmpty();
-    assertThat(ImmutableMap.of(29, 0)).isEmpty();
   }
 
   void testAssertThatMapIsEmpty() {
@@ -84,11 +69,7 @@ final class AssertJMapRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<MapAssert<Integer, Integer>> testAbstractMapAssertIsNotEmpty() {
     return ImmutableSet.of(
         assertThat(ImmutableMap.of(1, 0)).isNotEmpty(),
-        assertThat(ImmutableMap.of(2, 0)).isNotEmpty(),
-        assertThat(ImmutableMap.of(3, 0)).isNotEmpty(),
-        assertThat(ImmutableMap.of(4, 0)).isNotEmpty(),
-        assertThat(ImmutableMap.of(5, 0)).isNotEmpty(),
-        assertThat(ImmutableMap.of(6, 0)).isNotEmpty());
+        assertThat(ImmutableMap.of(2, 0)).isNotEqualTo(ImmutableMap.of("foo", "bar")));
   }
 
   ImmutableSet<AbstractAssert<?, ?>> testAssertThatMapIsNotEmpty() {

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

@@ -20,4 +20,36 @@ final class BigDecimalRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<BigDecimal> testBigDecimalValueOf() {
     return ImmutableSet.of(new BigDecimal(2), new BigDecimal(2L), new BigDecimal(2.0));
   }
+
+  ImmutableSet<Boolean> testBigDecimalSignumIsZero() {
+    return ImmutableSet.of(
+        BigDecimal.valueOf(1).compareTo(BigDecimal.ZERO) == 0,
+        BigDecimal.ZERO.compareTo(BigDecimal.valueOf(2)) == 0,
+        BigDecimal.valueOf(3).compareTo(BigDecimal.ZERO) != 0,
+        BigDecimal.ZERO.compareTo(BigDecimal.valueOf(4)) != 0);
+  }
+
+  ImmutableSet<Boolean> testBigDecimalSignumIsPositive() {
+    return ImmutableSet.of(
+        BigDecimal.valueOf(1).compareTo(BigDecimal.ZERO) > 0,
+        BigDecimal.ZERO.compareTo(BigDecimal.valueOf(2)) < 0,
+        BigDecimal.valueOf(3).signum() > 0,
+        BigDecimal.valueOf(4).signum() >= 1,
+        BigDecimal.valueOf(5).compareTo(BigDecimal.ZERO) <= 0,
+        BigDecimal.ZERO.compareTo(BigDecimal.valueOf(6)) >= 0,
+        BigDecimal.valueOf(7).signum() <= 0,
+        BigDecimal.valueOf(8).signum() < 1);
+  }
+
+  ImmutableSet<Boolean> testBigDecimalSignumIsNegative() {
+    return ImmutableSet.of(
+        BigDecimal.valueOf(1).compareTo(BigDecimal.ZERO) < 0,
+        BigDecimal.ZERO.compareTo(BigDecimal.valueOf(2)) > 0,
+        BigDecimal.valueOf(3).signum() < 0,
+        BigDecimal.valueOf(4).signum() <= -1,
+        BigDecimal.valueOf(5).compareTo(BigDecimal.ZERO) >= 0,
+        BigDecimal.ZERO.compareTo(BigDecimal.valueOf(6)) <= 0,
+        BigDecimal.valueOf(7).signum() >= 0,
+        BigDecimal.valueOf(8).signum() > -1);
+  }
 }

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

@@ -20,4 +20,36 @@ final class BigDecimalRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<BigDecimal> testBigDecimalValueOf() {
     return ImmutableSet.of(BigDecimal.valueOf(2), BigDecimal.valueOf(2L), BigDecimal.valueOf(2.0));
   }
+
+  ImmutableSet<Boolean> testBigDecimalSignumIsZero() {
+    return ImmutableSet.of(
+        BigDecimal.valueOf(1).signum() == 0,
+        BigDecimal.valueOf(2).signum() == 0,
+        BigDecimal.valueOf(3).signum() != 0,
+        BigDecimal.valueOf(4).signum() != 0);
+  }
+
+  ImmutableSet<Boolean> testBigDecimalSignumIsPositive() {
+    return ImmutableSet.of(
+        BigDecimal.valueOf(1).signum() == 1,
+        BigDecimal.valueOf(2).signum() == 1,
+        BigDecimal.valueOf(3).signum() == 1,
+        BigDecimal.valueOf(4).signum() == 1,
+        BigDecimal.valueOf(5).signum() != 1,
+        BigDecimal.valueOf(6).signum() != 1,
+        BigDecimal.valueOf(7).signum() != 1,
+        BigDecimal.valueOf(8).signum() != 1);
+  }
+
+  ImmutableSet<Boolean> testBigDecimalSignumIsNegative() {
+    return ImmutableSet.of(
+        BigDecimal.valueOf(1).signum() == -1,
+        BigDecimal.valueOf(2).signum() == -1,
+        BigDecimal.valueOf(3).signum() == -1,
+        BigDecimal.valueOf(4).signum() == -1,
+        BigDecimal.valueOf(5).signum() != -1,
+        BigDecimal.valueOf(6).signum() != -1,
+        BigDecimal.valueOf(7).signum() != -1,
+        BigDecimal.valueOf(8).signum() != -1);
+  }
 }

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

@@ -4,12 +4,13 @@ import com.google.common.collect.ImmutableSet;
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers;
 import com.google.errorprone.bugpatterns.BugChecker;
+import com.sun.tools.javac.util.Convert;
 import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class BugCheckerRulesTest implements RefasterRuleCollectionTestCase {
   @Override
   public ImmutableSet<Object> elidedTypesAndStaticImports() {
-    return ImmutableSet.of(FixChoosers.class);
+    return ImmutableSet.of(Convert.class, FixChoosers.class);
   }
 
   ImmutableSet<BugCheckerRefactoringTestHelper> testBugCheckerRefactoringTestHelperIdentity() {
@@ -26,4 +27,8 @@ final class BugCheckerRulesTest implements RefasterRuleCollectionTestCase {
         .addInputLines("A.java", "class A {}")
         .addOutputLines("A.java", "class A {}");
   }
+
+  String testConstantsFormat() {
+    return String.format("\"%s\"", Convert.quote("foo"));
+  }
 }

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

@@ -4,12 +4,14 @@ import com.google.common.collect.ImmutableSet;
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers;
 import com.google.errorprone.bugpatterns.BugChecker;
+import com.sun.tools.javac.util.Constants;
+import com.sun.tools.javac.util.Convert;
 import tech.picnic.errorprone.refaster.test.RefasterRuleCollectionTestCase;
 
 final class BugCheckerRulesTest implements RefasterRuleCollectionTestCase {
   @Override
   public ImmutableSet<Object> elidedTypesAndStaticImports() {
-    return ImmutableSet.of(FixChoosers.class);
+    return ImmutableSet.of(Convert.class, FixChoosers.class);
   }
 
   ImmutableSet<BugCheckerRefactoringTestHelper> testBugCheckerRefactoringTestHelperIdentity() {
@@ -24,4 +26,8 @@ final class BugCheckerRulesTest implements RefasterRuleCollectionTestCase {
         .addInputLines("A.java", "class A {}")
         .expectUnchanged();
   }
+
+  String testConstantsFormat() {
+    return Constants.format("foo");
+  }
 }

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

@@ -31,6 +31,7 @@ final class ComparatorRulesTest implements RefasterRuleCollectionTestCase {
         String::compareTo,
         Comparator.comparing(identity()),
         Comparator.comparing(s -> s),
+        Comparator.comparing(s -> 0),
         Collections.<String>reverseOrder(reverseOrder()),
         Comparator.<String>reverseOrder().reversed());
   }
@@ -45,7 +46,8 @@ final class ComparatorRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<Comparator<String>> testCustomComparator() {
     return ImmutableSet.of(
         Comparator.comparing(identity(), Comparator.comparingInt(String::length)),
-        Comparator.comparing(s -> s, Comparator.comparingInt(String::length)));
+        Comparator.comparing(s -> s, Comparator.comparingInt(String::length)),
+        Comparator.comparing(s -> "foo", Comparator.comparingInt(String::length)));
   }
 
   Comparator<String> testThenComparing() {
@@ -86,7 +88,8 @@ final class ComparatorRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<Comparator<String>> testThenComparingNaturalOrder() {
     return ImmutableSet.of(
         Comparator.<String>naturalOrder().thenComparing(identity()),
-        Comparator.<String>naturalOrder().thenComparing(s -> s));
+        Comparator.<String>naturalOrder().thenComparing(s -> s),
+        Comparator.<String>naturalOrder().thenComparing(s -> 0));
   }
 
   ImmutableSet<Integer> testCompareTo() {

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

@@ -28,7 +28,12 @@ final class ComparatorRulesTest implements RefasterRuleCollectionTestCase {
 
   ImmutableSet<Comparator<String>> testNaturalOrder() {
     return ImmutableSet.of(
-        naturalOrder(), naturalOrder(), naturalOrder(), naturalOrder(), naturalOrder());
+        naturalOrder(),
+        naturalOrder(),
+        naturalOrder(),
+        Comparator.comparing(s -> 0),
+        naturalOrder(),
+        naturalOrder());
   }
 
   ImmutableSet<Comparator<String>> testReverseOrder() {
@@ -38,7 +43,9 @@ final class ComparatorRulesTest implements RefasterRuleCollectionTestCase {
 
   ImmutableSet<Comparator<String>> testCustomComparator() {
     return ImmutableSet.of(
-        Comparator.comparingInt(String::length), Comparator.comparingInt(String::length));
+        Comparator.comparingInt(String::length),
+        Comparator.comparingInt(String::length),
+        Comparator.comparing(s -> "foo", Comparator.comparingInt(String::length)));
   }
 
   Comparator<String> testThenComparing() {
@@ -73,7 +80,8 @@ final class ComparatorRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<Comparator<String>> testThenComparingNaturalOrder() {
     return ImmutableSet.of(
         Comparator.<String>naturalOrder().thenComparing(naturalOrder()),
-        Comparator.<String>naturalOrder().thenComparing(naturalOrder()));
+        Comparator.<String>naturalOrder().thenComparing(naturalOrder()),
+        Comparator.<String>naturalOrder().thenComparing(s -> 0));
   }
 
   ImmutableSet<Integer> testCompareTo() {

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

@@ -76,11 +76,22 @@ final class ImmutableListMultimapRulesTest implements RefasterRuleCollectionTest
 
   ImmutableSet<ImmutableListMultimap<Integer, Integer>> testIndexIterableToImmutableListMultimap() {
     return ImmutableSet.of(
-        ImmutableList.of(1).stream().collect(toImmutableListMultimap(n -> n * 2, identity())),
-        Streams.stream(ImmutableList.of(2)::iterator)
-            .collect(toImmutableListMultimap(Integer::valueOf, n -> n)),
+        Streams.stream(ImmutableList.of(1).iterator())
+            .collect(toImmutableListMultimap(n -> n * 2, identity())),
+        Streams.stream(ImmutableList.of(2).iterator())
+            .collect(toImmutableListMultimap(n -> n * 2, v -> v)),
         Streams.stream(ImmutableList.of(3).iterator())
-            .collect(toImmutableListMultimap(n -> n.intValue(), identity())));
+            .collect(toImmutableListMultimap(n -> n * 2, v -> 0)),
+        Streams.stream(ImmutableList.of(4)::iterator)
+            .collect(toImmutableListMultimap(Integer::valueOf, identity())),
+        Streams.stream(ImmutableList.of(5)::iterator)
+            .collect(toImmutableListMultimap(Integer::valueOf, v -> v)),
+        Streams.stream(ImmutableList.of(6)::iterator)
+            .collect(toImmutableListMultimap(Integer::valueOf, v -> 0)),
+        ImmutableList.of(7).stream()
+            .collect(toImmutableListMultimap(n -> n.intValue(), identity())),
+        ImmutableList.of(8).stream().collect(toImmutableListMultimap(n -> n.intValue(), v -> v)),
+        ImmutableList.of(9).stream().collect(toImmutableListMultimap(n -> n.intValue(), v -> 0)));
   }
 
   ImmutableListMultimap<String, Integer> testTransformMultimapValuesToImmutableListMultimap() {

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

@@ -64,9 +64,17 @@ final class ImmutableListMultimapRulesTest implements RefasterRuleCollectionTest
 
   ImmutableSet<ImmutableListMultimap<Integer, Integer>> testIndexIterableToImmutableListMultimap() {
     return ImmutableSet.of(
-        Multimaps.index(ImmutableList.of(1), n -> n * 2),
-        Multimaps.index(ImmutableList.of(2)::iterator, Integer::valueOf),
-        Multimaps.index(ImmutableList.of(3).iterator(), n -> n.intValue()));
+        Multimaps.index(ImmutableList.of(1).iterator(), n -> n * 2),
+        Multimaps.index(ImmutableList.of(2).iterator(), n -> n * 2),
+        Streams.stream(ImmutableList.of(3).iterator())
+            .collect(toImmutableListMultimap(n -> n * 2, v -> 0)),
+        Multimaps.index(ImmutableList.of(4)::iterator, Integer::valueOf),
+        Multimaps.index(ImmutableList.of(5)::iterator, Integer::valueOf),
+        Streams.stream(ImmutableList.of(6)::iterator)
+            .collect(toImmutableListMultimap(Integer::valueOf, v -> 0)),
+        Multimaps.index(ImmutableList.of(7), n -> n.intValue()),
+        Multimaps.index(ImmutableList.of(8), n -> n.intValue()),
+        ImmutableList.of(9).stream().collect(toImmutableListMultimap(n -> n.intValue(), v -> 0)));
   }
 
   ImmutableListMultimap<String, Integer> testTransformMultimapValuesToImmutableListMultimap() {

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

@@ -34,11 +34,21 @@ final class ImmutableMapRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<ImmutableMap<Integer, Integer>> testIterableToImmutableMap() {
     return ImmutableSet.of(
         ImmutableList.of(1).stream().collect(toImmutableMap(identity(), n -> n * 2)),
-        Streams.stream(ImmutableList.of(2)::iterator)
-            .collect(toImmutableMap(n -> n, Integer::valueOf)),
-        Streams.stream(ImmutableList.of(3).iterator())
+        ImmutableList.of(2).stream().collect(toImmutableMap(k -> k, n -> n * 2)),
+        ImmutableList.of(3).stream().collect(toImmutableMap(k -> 0, n -> n * 2)),
+        Streams.stream(ImmutableList.of(4)::iterator)
+            .collect(toImmutableMap(identity(), Integer::valueOf)),
+        Streams.stream(ImmutableList.of(5)::iterator)
+            .collect(toImmutableMap(k -> k, Integer::valueOf)),
+        Streams.stream(ImmutableList.of(6)::iterator)
+            .collect(toImmutableMap(k -> 0, Integer::valueOf)),
+        Streams.stream(ImmutableList.of(7).iterator())
             .collect(toImmutableMap(identity(), n -> n.intValue())),
-        ImmutableMap.copyOf(Maps.asMap(ImmutableSet.of(4), Integer::valueOf)));
+        Streams.stream(ImmutableList.of(8).iterator())
+            .collect(toImmutableMap(k -> k, n -> n.intValue())),
+        Streams.stream(ImmutableList.of(9).iterator())
+            .collect(toImmutableMap(k -> 0, n -> n.intValue())),
+        ImmutableMap.copyOf(Maps.asMap(ImmutableSet.of(10), Integer::valueOf)));
   }
 
   ImmutableSet<ImmutableMap<String, Integer>> testEntryIterableToImmutableMap() {
@@ -63,10 +73,20 @@ final class ImmutableMapRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<ImmutableMap<Integer, Integer>> testIndexIterableToImmutableMap() {
     return ImmutableSet.of(
         ImmutableList.of(1).stream().collect(toImmutableMap(n -> n * 2, identity())),
-        Streams.stream(ImmutableList.of(2)::iterator)
-            .collect(toImmutableMap(Integer::valueOf, n -> n)),
-        Streams.stream(ImmutableList.of(3).iterator())
-            .collect(toImmutableMap(n -> n.intValue(), identity())));
+        ImmutableList.of(2).stream().collect(toImmutableMap(n -> n * 2, v -> v)),
+        ImmutableList.of(3).stream().collect(toImmutableMap(n -> n * 2, v -> 0)),
+        Streams.stream(ImmutableList.of(4)::iterator)
+            .collect(toImmutableMap(Integer::valueOf, identity())),
+        Streams.stream(ImmutableList.of(5)::iterator)
+            .collect(toImmutableMap(Integer::valueOf, v -> v)),
+        Streams.stream(ImmutableList.of(6)::iterator)
+            .collect(toImmutableMap(Integer::valueOf, v -> 0)),
+        Streams.stream(ImmutableList.of(7).iterator())
+            .collect(toImmutableMap(n -> n.intValue(), identity())),
+        Streams.stream(ImmutableList.of(8).iterator())
+            .collect(toImmutableMap(n -> n.intValue(), v -> v)),
+        Streams.stream(ImmutableList.of(9).iterator())
+            .collect(toImmutableMap(n -> n.intValue(), v -> 0)));
   }
 
   ImmutableSet<ImmutableMap<String, Integer>> testTransformMapValuesToImmutableMap() {

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

@@ -33,9 +33,17 @@ final class ImmutableMapRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<ImmutableMap<Integer, Integer>> testIterableToImmutableMap() {
     return ImmutableSet.of(
         Maps.toMap(ImmutableList.of(1), n -> n * 2),
-        Maps.toMap(ImmutableList.of(2)::iterator, Integer::valueOf),
-        Maps.toMap(ImmutableList.of(3).iterator(), n -> n.intValue()),
-        Maps.toMap(ImmutableSet.of(4), Integer::valueOf));
+        Maps.toMap(ImmutableList.of(2), n -> n * 2),
+        ImmutableList.of(3).stream().collect(toImmutableMap(k -> 0, n -> n * 2)),
+        Maps.toMap(ImmutableList.of(4)::iterator, Integer::valueOf),
+        Maps.toMap(ImmutableList.of(5)::iterator, Integer::valueOf),
+        Streams.stream(ImmutableList.of(6)::iterator)
+            .collect(toImmutableMap(k -> 0, Integer::valueOf)),
+        Maps.toMap(ImmutableList.of(7).iterator(), n -> n.intValue()),
+        Maps.toMap(ImmutableList.of(8).iterator(), n -> n.intValue()),
+        Streams.stream(ImmutableList.of(9).iterator())
+            .collect(toImmutableMap(k -> 0, n -> n.intValue())),
+        Maps.toMap(ImmutableSet.of(10), Integer::valueOf));
   }
 
   ImmutableSet<ImmutableMap<String, Integer>> testEntryIterableToImmutableMap() {
@@ -54,8 +62,16 @@ final class ImmutableMapRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<ImmutableMap<Integer, Integer>> testIndexIterableToImmutableMap() {
     return ImmutableSet.of(
         Maps.uniqueIndex(ImmutableList.of(1), n -> n * 2),
-        Maps.uniqueIndex(ImmutableList.of(2)::iterator, Integer::valueOf),
-        Maps.uniqueIndex(ImmutableList.of(3).iterator(), n -> n.intValue()));
+        Maps.uniqueIndex(ImmutableList.of(2), n -> n * 2),
+        ImmutableList.of(3).stream().collect(toImmutableMap(n -> n * 2, v -> 0)),
+        Maps.uniqueIndex(ImmutableList.of(4)::iterator, Integer::valueOf),
+        Maps.uniqueIndex(ImmutableList.of(5)::iterator, Integer::valueOf),
+        Streams.stream(ImmutableList.of(6)::iterator)
+            .collect(toImmutableMap(Integer::valueOf, v -> 0)),
+        Maps.uniqueIndex(ImmutableList.of(7).iterator(), n -> n.intValue()),
+        Maps.uniqueIndex(ImmutableList.of(8).iterator(), n -> n.intValue()),
+        Streams.stream(ImmutableList.of(9).iterator())
+            .collect(toImmutableMap(n -> n.intValue(), v -> 0)));
   }
 
   ImmutableSet<ImmutableMap<String, Integer>> testTransformMapValuesToImmutableMap() {

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

@@ -1,6 +1,7 @@
 package tech.picnic.errorprone.refasterrules;
 
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
@@ -29,7 +30,10 @@ final class JUnitToAssertJRulesTest implements RefasterRuleCollectionTestCase {
         (Runnable) () -> assertNotSame(null, null),
         (Runnable) () -> assertNull(null),
         (Runnable) () -> assertSame(null, null),
-        (Runnable) () -> assertTrue(true));
+        (Runnable) () -> assertTrue(true),
+        (Runnable) () -> assertEquals(0, 0),
+        (Runnable) () -> assertEquals(0, 0, "foo"),
+        (Runnable) () -> assertEquals(0, 0, () -> "foo"));
   }
 
   void testThrowNewAssertionError() {
@@ -170,4 +174,28 @@ final class JUnitToAssertJRulesTest implements RefasterRuleCollectionTestCase {
   void testAssertThatWithFailMessageSupplierIsInstanceOf() {
     assertInstanceOf(Object.class, new Object(), () -> "foo");
   }
+
+  void testAssertThatByteIsEqualTo() {
+    assertEquals((byte) 0, (byte) 0);
+  }
+
+  void testAssertThatByteWithFailMessageStringIsEqualTo() {
+    assertEquals((byte) 0, (byte) 0, "foo");
+  }
+
+  void testAssertThatByteWithFailMessageSupplierIsEqualTo() {
+    assertEquals((byte) 0, (byte) 0, () -> "foo");
+  }
+
+  void testAssertThatCharIsEqualTo() {
+    assertEquals('a', 'a');
+  }
+
+  void testAssertThatCharWithFailMessageStringIsEqualTo() {
+    assertEquals('a', 'a', "foo");
+  }
+
+  void testAssertThatCharWithFailMessageSupplierIsEqualTo() {
+    assertEquals('a', 'a', () -> "foo");
+  }
 }

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

@@ -5,6 +5,7 @@ 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.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
@@ -33,7 +34,10 @@ final class JUnitToAssertJRulesTest implements RefasterRuleCollectionTestCase {
         (Runnable) () -> assertNotSame(null, null),
         (Runnable) () -> assertNull(null),
         (Runnable) () -> assertSame(null, null),
-        (Runnable) () -> assertTrue(true));
+        (Runnable) () -> assertTrue(true),
+        (Runnable) () -> assertEquals(0, 0),
+        (Runnable) () -> assertEquals(0, 0, "foo"),
+        (Runnable) () -> assertEquals(0, 0, () -> "foo"));
   }
 
   void testThrowNewAssertionError() {
@@ -180,4 +184,28 @@ final class JUnitToAssertJRulesTest implements RefasterRuleCollectionTestCase {
   void testAssertThatWithFailMessageSupplierIsInstanceOf() {
     assertThat(new Object()).withFailMessage(() -> "foo").isInstanceOf(Object.class);
   }
+
+  void testAssertThatByteIsEqualTo() {
+    assertThat((byte) 0).isEqualTo((byte) 0);
+  }
+
+  void testAssertThatByteWithFailMessageStringIsEqualTo() {
+    assertThat((byte) 0).withFailMessage("foo").isEqualTo((byte) 0);
+  }
+
+  void testAssertThatByteWithFailMessageSupplierIsEqualTo() {
+    assertThat((byte) 0).withFailMessage(() -> "foo").isEqualTo((byte) 0);
+  }
+
+  void testAssertThatCharIsEqualTo() {
+    assertThat('a').isEqualTo('a');
+  }
+
+  void testAssertThatCharWithFailMessageStringIsEqualTo() {
+    assertThat('a').withFailMessage("foo").isEqualTo('a');
+  }
+
+  void testAssertThatCharWithFailMessageSupplierIsEqualTo() {
+    assertThat('a').withFailMessage(() -> "foo").isEqualTo('a');
+  }
 }

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

@@ -164,4 +164,30 @@ final class PrimitiveRulesTest implements RefasterRuleCollectionTestCase {
   boolean testDoubleIsFinite() {
     return Doubles.isFinite(1);
   }
+
+  ImmutableSet<Boolean> testIntegerSignumIsPositive() {
+    return ImmutableSet.of(
+        Integer.signum(1) > 0,
+        Integer.signum(2) >= 1,
+        Integer.signum(3) <= 0,
+        Integer.signum(4) < 1);
+  }
+
+  ImmutableSet<Boolean> testIntegerSignumIsNegative() {
+    return ImmutableSet.of(
+        Integer.signum(1) < 0,
+        Integer.signum(2) <= -1,
+        Integer.signum(3) >= 0,
+        Integer.signum(4) > -1);
+  }
+
+  ImmutableSet<Boolean> testLongSignumIsPositive() {
+    return ImmutableSet.of(
+        Long.signum(1L) > 0, Long.signum(2L) >= 1, Long.signum(3L) <= 0, Long.signum(4L) < 1);
+  }
+
+  ImmutableSet<Boolean> testLongSignumIsNegative() {
+    return ImmutableSet.of(
+        Long.signum(1L) < 0, Long.signum(2L) <= -1, Long.signum(3L) >= 0, Long.signum(4L) > -1);
+  }
 }

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

@@ -164,4 +164,30 @@ final class PrimitiveRulesTest implements RefasterRuleCollectionTestCase {
   boolean testDoubleIsFinite() {
     return Double.isFinite(1);
   }
+
+  ImmutableSet<Boolean> testIntegerSignumIsPositive() {
+    return ImmutableSet.of(
+        Integer.signum(1) == 1,
+        Integer.signum(2) == 1,
+        Integer.signum(3) != 1,
+        Integer.signum(4) != 1);
+  }
+
+  ImmutableSet<Boolean> testIntegerSignumIsNegative() {
+    return ImmutableSet.of(
+        Integer.signum(1) == -1,
+        Integer.signum(2) == -1,
+        Integer.signum(3) != -1,
+        Integer.signum(4) != -1);
+  }
+
+  ImmutableSet<Boolean> testLongSignumIsPositive() {
+    return ImmutableSet.of(
+        Long.signum(1L) == 1, Long.signum(2L) == 1, Long.signum(3L) != 1, Long.signum(4L) != 1);
+  }
+
+  ImmutableSet<Boolean> testLongSignumIsNegative() {
+    return ImmutableSet.of(
+        Long.signum(1L) == -1, Long.signum(2L) == -1, Long.signum(3L) != -1, Long.signum(4L) != -1);
+  }
 }

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

@@ -202,20 +202,26 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
     return ImmutableSet.of(
         Flux.just(1).flatMap(Mono::just, 1),
         Flux.just(2).flatMapSequential(Mono::just, 1),
-        Flux.just(3).map(Mono::just).concatMap(identity()));
+        Flux.just(3).map(Mono::just).concatMap(identity()),
+        Flux.just(4).map(Mono::just).concatMap(v -> v),
+        Flux.just(5).map(Mono::just).concatMap(v -> Mono.empty()));
   }
 
   ImmutableSet<Flux<Integer>> testFluxConcatMapWithPrefetch() {
     return ImmutableSet.of(
         Flux.just(1).flatMap(Mono::just, 1, 3),
         Flux.just(2).flatMapSequential(Mono::just, 1, 4),
-        Flux.just(3).map(Mono::just).concatMap(identity(), 5));
+        Flux.just(3).map(Mono::just).concatMap(identity(), 5),
+        Flux.just(4).map(Mono::just).concatMap(v -> v, 6),
+        Flux.just(5).map(Mono::just).concatMap(v -> Mono.empty(), 7));
   }
 
   ImmutableSet<Flux<Integer>> testMonoFlatMapIterable() {
     return ImmutableSet.of(
         Mono.just(1).map(ImmutableSet::of).flatMapIterable(identity()),
-        Mono.just(2).flux().concatMapIterable(ImmutableSet::of));
+        Mono.just(2).map(ImmutableSet::of).flatMapIterable(v -> v),
+        Mono.just(3).map(ImmutableSet::of).flatMapIterable(v -> ImmutableSet.of()),
+        Mono.just(4).flux().concatMapIterable(ImmutableSet::of));
   }
 
   Flux<Integer> testMonoFlatMapIterableIdentity() {
@@ -225,13 +231,17 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<Flux<Integer>> testFluxConcatMapIterable() {
     return ImmutableSet.of(
         Flux.just(1).flatMapIterable(ImmutableList::of),
-        Flux.just(2).map(ImmutableList::of).concatMapIterable(identity()));
+        Flux.just(2).map(ImmutableList::of).concatMapIterable(identity()),
+        Flux.just(3).map(ImmutableList::of).concatMapIterable(v -> v),
+        Flux.just(4).map(ImmutableList::of).concatMapIterable(v -> ImmutableSet.of()));
   }
 
   ImmutableSet<Flux<Integer>> testFluxConcatMapIterableWithPrefetch() {
     return ImmutableSet.of(
-        Flux.just(1).flatMapIterable(ImmutableList::of, 3),
-        Flux.just(2).map(ImmutableList::of).concatMapIterable(identity(), 3));
+        Flux.just(1).flatMapIterable(ImmutableList::of, 5),
+        Flux.just(2).map(ImmutableList::of).concatMapIterable(identity(), 5),
+        Flux.just(3).map(ImmutableList::of).concatMapIterable(v -> v, 5),
+        Flux.just(4).map(ImmutableList::of).concatMapIterable(v -> ImmutableSet.of(), 5));
   }
 
   Flux<String> testMonoFlatMapToFlux() {
@@ -372,25 +382,30 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
     return Flux.just(1).filter(Number.class::isInstance).cast(Number.class);
   }
 
-  Mono<String> testMonoFlatMap() {
-    return Mono.just("foo").map(Mono::just).flatMap(identity());
+  ImmutableSet<Mono<String>> testMonoFlatMap() {
+    return ImmutableSet.of(
+        Mono.just("foo").map(Mono::just).flatMap(identity()),
+        Mono.just("bar").map(Mono::just).flatMap(v -> v),
+        Mono.just("baz").map(Mono::just).flatMap(v -> Mono.empty()));
   }
 
   ImmutableSet<Flux<Integer>> testMonoFlatMapMany() {
     return ImmutableSet.of(
         Mono.just(1).map(Mono::just).flatMapMany(identity()),
-        Mono.just(2).flux().concatMap(Mono::just),
-        Mono.just(3).flux().concatMap(Mono::just, 2),
-        Mono.just(4).flux().concatMapDelayError(Mono::just),
-        Mono.just(5).flux().concatMapDelayError(Mono::just, 2),
-        Mono.just(6).flux().concatMapDelayError(Mono::just, false, 2),
-        Mono.just(7).flux().flatMap(Mono::just, 2),
-        Mono.just(8).flux().flatMap(Mono::just, 2, 3),
-        Mono.just(9).flux().flatMapDelayError(Mono::just, 2, 3),
-        Mono.just(10).flux().flatMapSequential(Mono::just, 2),
-        Mono.just(11).flux().flatMapSequential(Mono::just, 2, 3),
-        Mono.just(12).flux().flatMapSequentialDelayError(Mono::just, 2, 3),
-        Mono.just(13).flux().switchMap(Mono::just));
+        Mono.just(2).map(Mono::just).flatMapMany(v -> v),
+        Mono.just(3).map(Mono::just).flatMapMany(v -> Flux.empty()),
+        Mono.just(4).flux().concatMap(Mono::just),
+        Mono.just(5).flux().concatMap(Mono::just, 2),
+        Mono.just(6).flux().concatMapDelayError(Mono::just),
+        Mono.just(7).flux().concatMapDelayError(Mono::just, 2),
+        Mono.just(8).flux().concatMapDelayError(Mono::just, false, 2),
+        Mono.just(9).flux().flatMap(Mono::just, 2),
+        Mono.just(10).flux().flatMap(Mono::just, 2, 3),
+        Mono.just(11).flux().flatMapDelayError(Mono::just, 2, 3),
+        Mono.just(12).flux().flatMapSequential(Mono::just, 2),
+        Mono.just(13).flux().flatMapSequential(Mono::just, 2, 3),
+        Mono.just(14).flux().flatMapSequentialDelayError(Mono::just, 2, 3),
+        Mono.just(15).flux().switchMap(Mono::just));
   }
 
   ImmutableSet<Flux<String>> testConcatMapIterableIdentity() {
@@ -511,7 +526,7 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
   }
 
   ImmutableSet<Context> testContextEmpty() {
-    return ImmutableSet.of(Context.of(new HashMap<>()), Context.of(ImmutableMap.of()));
+    return ImmutableSet.of(Context.of(ImmutableMap.of()), Context.of(ImmutableMap.of(1, 2)));
   }
 
   ImmutableSet<PublisherProbe<Void>> testPublisherProbeEmpty() {
@@ -528,14 +543,16 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
 
   ImmutableSet<StepVerifier.Step<Integer>> testStepVerifierStepIdentity() {
     return ImmutableSet.of(
-        StepVerifier.create(Mono.just(1)).expectNext(),
-        StepVerifier.create(Mono.just(2)).expectNextCount(0L));
+        Mono.just(1).as(StepVerifier::create).expectNext(),
+        Mono.just(2).as(StepVerifier::create).expectNextCount(0L),
+        Mono.just(3).as(StepVerifier::create).expectNextSequence(ImmutableList.of()),
+        Mono.just(4).as(StepVerifier::create).expectNextSequence(ImmutableList.of(5)));
   }
 
   ImmutableSet<StepVerifier.Step<String>> testStepVerifierStepExpectNext() {
     return ImmutableSet.of(
-        StepVerifier.create(Mono.just("foo")).expectNextMatches(s -> s.equals("bar")),
-        StepVerifier.create(Mono.just("baz")).expectNextMatches("qux"::equals));
+        Mono.just("foo").as(StepVerifier::create).expectNextMatches(s -> s.equals("bar")),
+        Mono.just("baz").as(StepVerifier::create).expectNextMatches("qux"::equals));
   }
 
   StepVerifier.Step<?> testFluxAsStepVerifierExpectNext() {
@@ -546,37 +563,40 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
   }
 
   Duration testStepVerifierLastStepVerifyComplete() {
-    return StepVerifier.create(Mono.empty()).expectComplete().verify();
+    return Mono.empty().as(StepVerifier::create).expectComplete().verify();
   }
 
   Duration testStepVerifierLastStepVerifyError() {
-    return StepVerifier.create(Mono.empty()).expectError().verify();
+    return Mono.empty().as(StepVerifier::create).expectError().verify();
   }
 
   ImmutableSet<Duration> testStepVerifierLastStepVerifyErrorClass() {
     return ImmutableSet.of(
-        StepVerifier.create(Mono.empty()).expectError(IllegalArgumentException.class).verify(),
-        StepVerifier.create(Mono.empty())
+        Mono.empty().as(StepVerifier::create).expectError(IllegalArgumentException.class).verify(),
+        Mono.empty()
+            .as(StepVerifier::create)
             .verifyErrorMatches(IllegalStateException.class::isInstance),
-        StepVerifier.create(Mono.empty())
+        Mono.empty()
+            .as(StepVerifier::create)
             .verifyErrorSatisfies(t -> assertThat(t).isInstanceOf(AssertionError.class)));
   }
 
   Duration testStepVerifierLastStepVerifyErrorMatches() {
-    return StepVerifier.create(Mono.empty())
+    return Mono.empty()
+        .as(StepVerifier::create)
         .expectErrorMatches(IllegalArgumentException.class::equals)
         .verify();
   }
 
   Duration testStepVerifierLastStepVerifyErrorSatisfies() {
-    return StepVerifier.create(Mono.empty()).expectErrorSatisfies(t -> {}).verify();
+    return Mono.empty().as(StepVerifier::create).expectErrorSatisfies(t -> {}).verify();
   }
 
   Duration testStepVerifierLastStepVerifyErrorMessage() {
-    return StepVerifier.create(Mono.empty()).expectErrorMessage("foo").verify();
+    return Mono.empty().as(StepVerifier::create).expectErrorMessage("foo").verify();
   }
 
   Duration testStepVerifierLastStepVerifyTimeout() {
-    return StepVerifier.create(Mono.empty()).expectTimeout(Duration.ZERO).verify();
+    return Mono.empty().as(StepVerifier::create).expectTimeout(Duration.ZERO).verify();
   }
 }

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

@@ -205,20 +205,26 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
     return ImmutableSet.of(
         Flux.just(1).concatMap(Mono::just),
         Flux.just(2).concatMap(Mono::just),
-        Flux.just(3).concatMap(Mono::just));
+        Flux.just(3).concatMap(Mono::just),
+        Flux.just(4).concatMap(Mono::just),
+        Flux.just(5).map(Mono::just).concatMap(v -> Mono.empty()));
   }
 
   ImmutableSet<Flux<Integer>> testFluxConcatMapWithPrefetch() {
     return ImmutableSet.of(
         Flux.just(1).concatMap(Mono::just, 3),
         Flux.just(2).concatMap(Mono::just, 4),
-        Flux.just(3).concatMap(Mono::just, 5));
+        Flux.just(3).concatMap(Mono::just, 5),
+        Flux.just(4).concatMap(Mono::just, 6),
+        Flux.just(5).map(Mono::just).concatMap(v -> Mono.empty(), 7));
   }
 
   ImmutableSet<Flux<Integer>> testMonoFlatMapIterable() {
     return ImmutableSet.of(
         Mono.just(1).flatMapIterable(ImmutableSet::of),
-        Mono.just(2).flatMapIterable(ImmutableSet::of));
+        Mono.just(2).flatMapIterable(ImmutableSet::of),
+        Mono.just(3).map(ImmutableSet::of).flatMapIterable(v -> ImmutableSet.of()),
+        Mono.just(4).flatMapIterable(ImmutableSet::of));
   }
 
   Flux<Integer> testMonoFlatMapIterableIdentity() {
@@ -228,13 +234,17 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<Flux<Integer>> testFluxConcatMapIterable() {
     return ImmutableSet.of(
         Flux.just(1).concatMapIterable(ImmutableList::of),
-        Flux.just(2).concatMapIterable(ImmutableList::of));
+        Flux.just(2).concatMapIterable(ImmutableList::of),
+        Flux.just(3).concatMapIterable(ImmutableList::of),
+        Flux.just(4).map(ImmutableList::of).concatMapIterable(v -> ImmutableSet.of()));
   }
 
   ImmutableSet<Flux<Integer>> testFluxConcatMapIterableWithPrefetch() {
     return ImmutableSet.of(
-        Flux.just(1).concatMapIterable(ImmutableList::of, 3),
-        Flux.just(2).concatMapIterable(ImmutableList::of, 3));
+        Flux.just(1).concatMapIterable(ImmutableList::of, 5),
+        Flux.just(2).concatMapIterable(ImmutableList::of, 5),
+        Flux.just(3).concatMapIterable(ImmutableList::of, 5),
+        Flux.just(4).map(ImmutableList::of).concatMapIterable(v -> ImmutableSet.of(), 5));
   }
 
   Flux<String> testMonoFlatMapToFlux() {
@@ -365,15 +375,18 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
     return Flux.just(1).ofType(Number.class);
   }
 
-  Mono<String> testMonoFlatMap() {
-    return Mono.just("foo").flatMap(Mono::just);
+  ImmutableSet<Mono<String>> testMonoFlatMap() {
+    return ImmutableSet.of(
+        Mono.just("foo").flatMap(Mono::just),
+        Mono.just("bar").flatMap(Mono::just),
+        Mono.just("baz").map(Mono::just).flatMap(v -> Mono.empty()));
   }
 
   ImmutableSet<Flux<Integer>> testMonoFlatMapMany() {
     return ImmutableSet.of(
         Mono.just(1).flatMapMany(Mono::just),
         Mono.just(2).flatMapMany(Mono::just),
-        Mono.just(3).flatMapMany(Mono::just),
+        Mono.just(3).map(Mono::just).flatMapMany(v -> Flux.empty()),
         Mono.just(4).flatMapMany(Mono::just),
         Mono.just(5).flatMapMany(Mono::just),
         Mono.just(6).flatMapMany(Mono::just),
@@ -383,7 +396,9 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
         Mono.just(10).flatMapMany(Mono::just),
         Mono.just(11).flatMapMany(Mono::just),
         Mono.just(12).flatMapMany(Mono::just),
-        Mono.just(13).flatMapMany(Mono::just));
+        Mono.just(13).flatMapMany(Mono::just),
+        Mono.just(14).flatMapMany(Mono::just),
+        Mono.just(15).flatMapMany(Mono::just));
   }
 
   ImmutableSet<Flux<String>> testConcatMapIterableIdentity() {
@@ -500,7 +515,7 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
   }
 
   ImmutableSet<Context> testContextEmpty() {
-    return ImmutableSet.of(Context.empty(), Context.empty());
+    return ImmutableSet.of(Context.empty(), Context.of(ImmutableMap.of(1, 2)));
   }
 
   ImmutableSet<PublisherProbe<Void>> testPublisherProbeEmpty() {
@@ -516,13 +531,17 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
   }
 
   ImmutableSet<StepVerifier.Step<Integer>> testStepVerifierStepIdentity() {
-    return ImmutableSet.of(StepVerifier.create(Mono.just(1)), StepVerifier.create(Mono.just(2)));
+    return ImmutableSet.of(
+        Mono.just(1).as(StepVerifier::create),
+        Mono.just(2).as(StepVerifier::create),
+        Mono.just(3).as(StepVerifier::create),
+        Mono.just(4).as(StepVerifier::create).expectNextSequence(ImmutableList.of(5)));
   }
 
   ImmutableSet<StepVerifier.Step<String>> testStepVerifierStepExpectNext() {
     return ImmutableSet.of(
-        StepVerifier.create(Mono.just("foo")).expectNext("bar"),
-        StepVerifier.create(Mono.just("baz")).expectNext("qux"));
+        Mono.just("foo").as(StepVerifier::create).expectNext("bar"),
+        Mono.just("baz").as(StepVerifier::create).expectNext("qux"));
   }
 
   StepVerifier.Step<?> testFluxAsStepVerifierExpectNext() {
@@ -530,34 +549,35 @@ final class ReactorRulesTest implements RefasterRuleCollectionTestCase {
   }
 
   Duration testStepVerifierLastStepVerifyComplete() {
-    return StepVerifier.create(Mono.empty()).verifyComplete();
+    return Mono.empty().as(StepVerifier::create).verifyComplete();
   }
 
   Duration testStepVerifierLastStepVerifyError() {
-    return StepVerifier.create(Mono.empty()).verifyError();
+    return Mono.empty().as(StepVerifier::create).verifyError();
   }
 
   ImmutableSet<Duration> testStepVerifierLastStepVerifyErrorClass() {
     return ImmutableSet.of(
-        StepVerifier.create(Mono.empty()).verifyError(IllegalArgumentException.class),
-        StepVerifier.create(Mono.empty()).verifyError(IllegalStateException.class),
-        StepVerifier.create(Mono.empty()).verifyError(AssertionError.class));
+        Mono.empty().as(StepVerifier::create).verifyError(IllegalArgumentException.class),
+        Mono.empty().as(StepVerifier::create).verifyError(IllegalStateException.class),
+        Mono.empty().as(StepVerifier::create).verifyError(AssertionError.class));
   }
 
   Duration testStepVerifierLastStepVerifyErrorMatches() {
-    return StepVerifier.create(Mono.empty())
+    return Mono.empty()
+        .as(StepVerifier::create)
         .verifyErrorMatches(IllegalArgumentException.class::equals);
   }
 
   Duration testStepVerifierLastStepVerifyErrorSatisfies() {
-    return StepVerifier.create(Mono.empty()).verifyErrorSatisfies(t -> {});
+    return Mono.empty().as(StepVerifier::create).verifyErrorSatisfies(t -> {});
   }
 
   Duration testStepVerifierLastStepVerifyErrorMessage() {
-    return StepVerifier.create(Mono.empty()).verifyErrorMessage("foo");
+    return Mono.empty().as(StepVerifier::create).verifyErrorMessage("foo");
   }
 
   Duration testStepVerifierLastStepVerifyTimeout() {
-    return StepVerifier.create(Mono.empty()).verifyTimeout(Duration.ZERO);
+    return Mono.empty().as(StepVerifier::create).verifyTimeout(Duration.ZERO);
   }
 }

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

@@ -258,7 +258,8 @@ final class StreamRulesTest implements RefasterRuleCollectionTestCase {
   ImmutableSet<Stream<Integer>> testStreamsConcat() {
     return ImmutableSet.of(
         Stream.of(Stream.of(1), Stream.of(2)).flatMap(identity()),
-        Stream.of(Stream.of(3), Stream.of(4)).flatMap(v -> v));
+        Stream.of(Stream.of(3), Stream.of(4)).flatMap(v -> v),
+        Stream.of(Stream.of(5), Stream.of(6)).flatMap(v -> Stream.empty()));
   }
 
   Stream<Integer> testStreamTakeWhile() {

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

@@ -258,7 +258,9 @@ final class StreamRulesTest implements RefasterRuleCollectionTestCase {
 
   ImmutableSet<Stream<Integer>> testStreamsConcat() {
     return ImmutableSet.of(
-        Streams.concat(Stream.of(1), Stream.of(2)), Streams.concat(Stream.of(3), Stream.of(4)));
+        Streams.concat(Stream.of(1), Stream.of(2)),
+        Streams.concat(Stream.of(3), Stream.of(4)),
+        Stream.of(Stream.of(5), Stream.of(6)).flatMap(v -> Stream.empty()));
   }
 
   Stream<Integer> testStreamTakeWhile() {

integration-tests/checkstyle-10.12.4-expected-warnings.txt

@@ -0,0 +1,140 @@
+src/it/java/com/google/checkstyle/test/chapter7javadoc/rule711generalform/InvalidJavadocPositionTest.java:[35,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/it/java/com/google/checkstyle/test/chapter7javadoc/rule734nonrequiredjavadoc/InvalidJavadocPositionTest.java:[35,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/it/java/com/sun/checkstyle/test/chapter5comments/rule52documentationcomments/InvalidJavadocPositionTest.java:[35,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionAbbreviationAsWordInNameTest.java:[117,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `enum` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionAbbreviationAsWordInNameTest.java:[169,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `interface` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionAbbreviationAsWordInNameTest.java:[91,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `class` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionAnnotationLocationTest.java:[104,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `enum` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionAnnotationLocationTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `class` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionAnnotationLocationTest.java:[71,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `interface` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionAnonInnerLengthTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionAvoidEscapedUnicodeCharactersTest.java:[40,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionAvoidNoArgumentSuperConstructorCallTest.java:[41,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionEqualsAvoidNullTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `equals` is already defined in this class or a supertype)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionLambdaBodyLengthTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionMissingJavadocTypeTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `class` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionMissingOverrideTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `class` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionMissingOverrideTest.java:[67,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `interface` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionNeedBracesTest.java:[40,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `do` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionOuterTypeNumberTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionUnnecessarySemicolonAfterTypeMemberDeclarationTest.java:[41,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/it/java/org/checkstyle/suppressionxpathfilter/XpathRegressionUnnecessarySemicolonInTryWithResourcesTest.java:[41,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/DetailAstImplTest.java:[597,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `toString` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/PackageNamesLoaderTest.java:[58,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/api/FilterSetTest.java:[49,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `toString` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/api/FullIdentTest.java:[41,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `toString` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/AvoidEscapedUnicodeCharactersCheckTest.java:[77,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/DescendantTokenCheckTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/OrderedPropertiesCheckTest.java:[49,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/UniquePropertiesCheckTest.java:[65,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/annotation/AnnotationLocationCheckTest.java:[193,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `class` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/annotation/AnnotationLocationCheckTest.java:[206,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `enum` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/annotation/AnnotationLocationCheckTest.java:[217,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `interface` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/annotation/AnnotationLocationCheckTest.java:[228,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `package` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/annotation/AnnotationUseStyleCheckTest.java:[103,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/blocks/EmptyBlockCheckTest.java:[49,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/blocks/EmptyCatchBlockCheckTest.java:[46,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/blocks/LeftCurlyCheckTest.java:[59,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/blocks/RightCurlyCheckTest.java:[50,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/ArrayTrailingCommaCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/AvoidDoubleBraceInitializationCheckTest.java:[37,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/AvoidInlineConditionalsCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/AvoidNoArgumentSuperConstructorCallCheckTest.java:[37,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/CovariantEqualsCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/DeclarationOrderCheckTest.java:[44,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/DefaultComesLastCheckTest.java:[55,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/ExplicitInitializationCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/FallThroughCheckTest.java:[38,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/FinalLocalVariableCheckTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/HiddenFieldCheckTest.java:[105,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/IllegalCatchCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/IllegalInstantiationCheckTest.java:[48,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/IllegalThrowsCheckTest.java:[37,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/IllegalTokenCheckTest.java:[57,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `native` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/NestedIfDepthCheckTest.java:[37,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/NestedTryDepthCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/NoArrayTrailingCommaCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/NoEnumTrailingCommaCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/OverloadMethodsDeclarationOrderCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/ParameterAssignmentCheckTest.java:[45,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/RequireThisCheckTest.java:[290,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `static` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/RequireThisCheckTest.java:[373,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `for` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/ReturnCountCheckTest.java:[48,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/UnnecessaryParenthesesCheckTest.java:[125,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `return` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/UnnecessaryParenthesesCheckTest.java:[44,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/UnnecessarySemicolonAfterOuterTypeDeclarationCheckTest.java:[40,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/UnnecessarySemicolonAfterTypeMemberDeclarationCheckTest.java:[40,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/UnnecessarySemicolonInEnumerationCheckTest.java:[38,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/coding/UnnecessarySemicolonInTryWithResourcesCheckTest.java:[38,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/design/InterfaceIsTypeCheckTest.java:[37,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/design/MutableExceptionCheckTest.java:[54,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/design/ThrowsCountCheckTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/imports/ImportControlCheckTest.java:[99,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `null` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/imports/ImportOrderCheckTest.java:[81,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/InvalidJavadocPositionCheckTest.java:[59,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/JavadocContentLocationCheckTest.java:[57,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/JavadocContentLocationCheckTest.java:[75,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `package` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/JavadocContentLocationCheckTest.java:[83,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `interface` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/JavadocNodeImplTest.java:[30,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `toString` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/JavadocTagInfoTest.java:[230,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `throws` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/JavadocTagInfoTest.java:[294,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `return` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/JavadocTagTest.java:[58,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `toString` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/JavadocTypeCheckTest.java:[83,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `protected` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/JavadocTypeCheckTest.java:[89,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `public` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/JavadocVariableCheckTest.java:[60,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/MissingJavadocTypeCheckTest.java:[102,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `public` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/MissingJavadocTypeCheckTest.java:[94,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `protected` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/javadoc/utils/InlineTagUtilTest.java:[38,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `extractInlineTags` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/metrics/ClassDataAbstractionCouplingCheckTest.java:[189,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `new` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/metrics/ClassFanOutComplexityCheckTest.java:[188,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `extends` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/metrics/ClassFanOutComplexityCheckTest.java:[196,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `implements` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/metrics/ClassFanOutComplexityCheckTest.java:[266,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `throws` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/AbbreviationAsWordInNameCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/AccessModifierOptionTest.java:[45,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `case` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/ConstantNameCheckTest.java:[67,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/LocalFinalVariableNameCheckTest.java:[48,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/LocalVariableNameCheckTest.java:[48,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/MethodNameCheckTest.java:[48,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/PackageNameCheckTest.java:[60,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/ParameterNameCheckTest.java:[48,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `catch` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/ParameterNameCheckTest.java:[78,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/PatternVariableNameCheckTest.java:[47,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/naming/TypeNameCheckTest.java:[44,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/regexp/RegexpSinglelineCheckTest.java:[120,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/regexp/RegexpSinglelineJavaCheckTest.java:[195,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/sizes/AnonInnerLengthCheckTest.java:[56,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/sizes/LambdaBodyLengthCheckTest.java:[56,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/sizes/MethodCountCheckTest.java:[94,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `enum` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/sizes/MethodLengthCheckTest.java:[93,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `abstract` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/sizes/OuterTypeNumberCheckTest.java:[73,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/sizes/ParameterNumberCheckTest.java:[58,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/sizes/RecordComponentNumberCheckTest.java:[62,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/EmptyForInitializerPadCheckTest.java:[50,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/EmptyForIteratorPadCheckTest.java:[49,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/EmptyLineSeparatorCheckTest.java:[51,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/FileTabCharacterCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/GenericWhitespaceCheckTest.java:[62,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/MethodParamPadCheckTest.java:[50,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/NoWhitespaceAfterCheckTest.java:[174,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `synchronized` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/NoWhitespaceAfterCheckTest.java:[40,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/NoWhitespaceBeforeCaseDefaultColonCheckTest.java:[38,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/NoWhitespaceBeforeCheckTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/OperatorWrapCheckTest.java:[39,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/ParenPadCheckTest.java:[44,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/TypecastParenPadCheckTest.java:[41,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/WhitespaceAfterCheckTest.java:[46,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/filters/IntMatchFilterElementTest.java:[45,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `toString` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/filters/SeverityMatchFilterTest.java:[36,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/filters/SuppressFilterElementTest.java:[185,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `equals` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/filters/SuppressWarningsFilterTest.java:[83,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/filters/SuppressWithNearbyCommentFilterTest.java:[210,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/filters/SuppressionCommentFilterTest.java:[142,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/filters/SuppressionSingleFilterTest.java:[42,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `default` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/grammar/antlr4/Antlr4AstRegressionTest.java:[34,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `package` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/grammar/comments/CommentsTest.java:[53,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `toString` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/grammar/java8/DefaultMethodsTest.java:[40,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `switch` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/gui/BaseCellEditorTest.java:[31,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `toString` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/utils/CheckUtilTest.java:[71,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that a method named `equals` is already defined in this class or a supertype)
+src/test/java/com/puppycrawl/tools/checkstyle/xpath/XpathQueryGeneratorTest.java:[205,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `package` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/xpath/XpathQueryGeneratorTest.java:[219,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `import` is not a valid identifier)
+src/test/java/com/puppycrawl/tools/checkstyle/xpath/XpathQueryGeneratorTest.java:[265,8] [JUnitMethodDeclaration] This method's name should not redundantly start with `test` (but note that `switch` is not a valid identifier)

integration-tests/checkstyle-10.12.4-init.patch

@@ -0,0 +1,185 @@
+--- a/pom.xml
++++ b/pom.xml
+@@ -334,6 +334,12 @@
+       <version>1.1.3</version>
+       <scope>test</scope>
+     </dependency>
++    <dependency>
++      <groupId>org.assertj</groupId>
++      <artifactId>assertj-core</artifactId>
++      <version>${assertj.version}</version>
++      <scope>test</scope>
++    </dependency>
+     <dependency>
+       <groupId>nl.jqno.equalsverifier</groupId>
+       <artifactId>equalsverifier</artifactId>
+@@ -2397,8 +2403,10 @@
+                     <arg>-Xpkginfo:always</arg>
+                     <arg>-XDcompilePolicy=simple</arg>
+                     <arg>
+-                      -Xplugin:ErrorProne
++                      -Xplugin:ErrorProne ${error-prone.flags}
+                     </arg>
++                    <arg>-Xmaxwarns</arg>
++                    <arg>1000000</arg>
+                   </compilerArgs>
+                   <annotationProcessorPaths>
+                     <path>
+@@ -2406,6 +2414,16 @@
+                       <artifactId>error_prone_core</artifactId>
+                       <version>${error-prone.version}</version>
+                     </path>
++                    <path>
++                      <groupId>tech.picnic.error-prone-support</groupId>
++                      <artifactId>error-prone-contrib</artifactId>
++                      <version>${error-prone-support.version}</version>
++                    </path>
++                    <path>
++                      <groupId>tech.picnic.error-prone-support</groupId>
++                      <artifactId>refaster-runner</artifactId>
++                      <version>${error-prone-support.version}</version>
++                    </path>
+                   </annotationProcessorPaths>
+                 </configuration>
+               </execution>
+@@ -2449,9 +2467,10 @@
+                     <arg>-Xpkginfo:always</arg>
+                     <arg>-XDcompilePolicy=simple</arg>
+                     <arg>
+-                      -Xplugin:ErrorProne \
+-                      -XepExcludedPaths:.*[\\/]resources[\\/].*
++                      -Xplugin:ErrorProne ${error-prone.flags}
+                     </arg>
++                    <arg>-Xmaxwarns</arg>
++                    <arg>1000000</arg>
+                   </compilerArgs>
+                   <annotationProcessorPaths>
+                     <path>
+@@ -2459,6 +2478,16 @@
+                       <artifactId>error_prone_core</artifactId>
+                       <version>${error-prone.version}</version>
+                     </path>
++                    <path>
++                      <groupId>tech.picnic.error-prone-support</groupId>
++                      <artifactId>error-prone-contrib</artifactId>
++                      <version>${error-prone-support.version}</version>
++                    </path>
++                    <path>
++                      <groupId>tech.picnic.error-prone-support</groupId>
++                      <artifactId>refaster-runner</artifactId>
++                      <version>${error-prone-support.version}</version>
++                    </path>
+                   </annotationProcessorPaths>
+                 </configuration>
+               </execution>
+--- a/src/main/java/com/puppycrawl/tools/checkstyle/DetailNodeTreeStringPrinter.java
++++ b/src/main/java/com/puppycrawl/tools/checkstyle/DetailNodeTreeStringPrinter.java
+@@ -63,6 +63,8 @@ public final class DetailNodeTreeStringPrinter {
+      * @return DetailNode tree
+      * @throws IllegalArgumentException if there is an error parsing the Javadoc.
+      */
++    // Invoking `getParseErrorMessage` requires that `status.getParseErrorMessage()` is `null`.
++    @SuppressWarnings("CheckArgumentWithMessage")
+     public static DetailNode parseJavadocAsDetailNode(DetailAST blockComment) {
+         final JavadocDetailNodeParser parser = new JavadocDetailNodeParser();
+         final ParseStatus status = parser.parseJavadocAsDetailNode(blockComment);
+--- a/src/main/java/com/puppycrawl/tools/checkstyle/Main.java
++++ b/src/main/java/com/puppycrawl/tools/checkstyle/Main.java
+@@ -626,6 +626,8 @@ public final class Main {
+             + "reported to standard out in plain format. Checkstyle requires a configuration "
+             + "XML file that configures the checks to apply.",
+             mixinStandardHelpOptions = true)
++    // XXX: Don't reorder arguments to `picocli.CommandLine.Option#names`.
++    @SuppressWarnings("LexicographicalAnnotationAttributeListing")
+     private static final class CliOptions {
+ 
+         /** Width of CLI help option. */
+--- a/src/main/java/com/puppycrawl/tools/checkstyle/SarifLogger.java
++++ b/src/main/java/com/puppycrawl/tools/checkstyle/SarifLogger.java
+@@ -139,6 +139,9 @@ public class SarifLogger extends AbstractAutomaticBean implements AuditListener
+     @Override
+     public void auditFinished(AuditEvent event) {
+         final String version = SarifLogger.class.getPackage().getImplementationVersion();
++        // Here `version` may be `null`, while `String#replace` requires non-`null` arguments.
++        // XXX: Investigate better nullness handling by `IdentityConversion`.
++        @SuppressWarnings("IdentityConversion")
+         final String rendered = report
+             .replace(VERSION_PLACEHOLDER, String.valueOf(version))
+             .replace(RESULTS_PLACEHOLDER, String.join(",\n", results));
+--- a/src/main/java/com/puppycrawl/tools/checkstyle/site/SiteUtil.java
++++ b/src/main/java/com/puppycrawl/tools/checkstyle/site/SiteUtil.java
+@@ -419,6 +419,10 @@ public final class SiteUtil {
+      * @return a set of properties for the given class.
+      */
+     public static Set<String> getPropertiesForDocumentation(Class<?> clss, Object instance) {
++        // XXX: File PR to replace `.collect(toSet())` with `.collect(toCollection(HashSet::new))`.
++        // XXX: Update `CollectorMutability` to recognize cases such as this one, where the created
++        // collection is clearly modified.
++        @SuppressWarnings("CollectorMutability")
+         final Set<String> properties =
+                 getProperties(clss).stream()
+                     .filter(prop -> {
+--- a/src/test/java/com/puppycrawl/tools/checkstyle/CheckerTest.java
++++ b/src/test/java/com/puppycrawl/tools/checkstyle/CheckerTest.java
+@@ -93,6 +93,8 @@ import de.thetaphi.forbiddenapis.SuppressForbidden;
+  * @noinspectionreason ClassWithTooManyDependencies - complex tests require a large number
+  *      of imports
+  */
++// This class is referenced from another package.
++@SuppressWarnings("JUnitClassModifiers")
+ public class CheckerTest extends AbstractModuleTestSupport {
+ 
+     @TempDir
+--- a/src/test/java/com/puppycrawl/tools/checkstyle/ConfigurationLoaderTest.java
++++ b/src/test/java/com/puppycrawl/tools/checkstyle/ConfigurationLoaderTest.java
+@@ -46,6 +46,8 @@ import com.puppycrawl.tools.checkstyle.internal.utils.TestUtil;
+ /**
+  * Unit test for ConfigurationLoader.
+  */
++// This class is referenced from another package.
++@SuppressWarnings("JUnitClassModifiers")
+ public class ConfigurationLoaderTest extends AbstractPathTestSupport {
+ 
+     @Override
+--- a/src/test/java/com/puppycrawl/tools/checkstyle/PackageObjectFactoryTest.java
++++ b/src/test/java/com/puppycrawl/tools/checkstyle/PackageObjectFactoryTest.java
+@@ -98,6 +98,8 @@ public class PackageObjectFactoryTest {
+     public void testCtorNullPackageException1() {
+         final ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
+         try {
++            // XXX: Don't suggest `ImmutableSet.of(elem)` for nullable `elem`.
++            @SuppressWarnings("ImmutableSetOf1")
+             final Object test = new PackageObjectFactory(Collections.singleton(null), classLoader);
+             assertWithMessage("Exception is expected but got " + test).fail();
+         }
+@@ -126,6 +128,8 @@ public class PackageObjectFactoryTest {
+     public void testCtorNullPackageException3() {
+         final ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
+         try {
++            // XXX: Don't suggest `ImmutableSet.of(elem)` for nullable `elem`.
++            @SuppressWarnings("ImmutableSetOf1")
+             final Object test = new PackageObjectFactory(Collections.singleton(null), classLoader,
+                     TRY_IN_ALL_REGISTERED_PACKAGES);
+             assertWithMessage("Exception is expected but got " + test).fail();
+--- a/src/test/java/com/puppycrawl/tools/checkstyle/TreeWalkerTest.java
++++ b/src/test/java/com/puppycrawl/tools/checkstyle/TreeWalkerTest.java
+@@ -79,6 +79,8 @@ import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
+  * @noinspectionreason ClassWithTooManyDependencies - complex tests require a
+  *      large number of imports
+  */
++// This class is referenced from another package.
++@SuppressWarnings("JUnitClassModifiers")
+ public class TreeWalkerTest extends AbstractModuleTestSupport {
+ 
+     @TempDir
+--- a/src/test/java/com/puppycrawl/tools/checkstyle/utils/CheckUtilTest.java
++++ b/src/test/java/com/puppycrawl/tools/checkstyle/utils/CheckUtilTest.java
+@@ -47,6 +47,8 @@ import com.puppycrawl.tools.checkstyle.checks.coding.NestedIfDepthCheck;
+ import com.puppycrawl.tools.checkstyle.checks.javadoc.JavadocMethodCheck;
+ import com.puppycrawl.tools.checkstyle.checks.naming.AccessModifierOption;
+ 
++// This class is referenced from another package.
++@SuppressWarnings("JUnitClassModifiers")
+ public class CheckUtilTest extends AbstractModuleTestSupport {
+ 
+     @Override

integration-tests/checkstyle-10.12.4.sh

@@ -0,0 +1,183 @@
+#!/usr/bin/env bash
+
+set -e -u -o pipefail
+
+integration_test_root="$(readlink -f "$(dirname "${0}")")"
+error_prone_support_root="${integration_test_root}/.."
+repos_root="${integration_test_root}/.repos"
+
+test_name="$(basename "${0}" .sh)"
+project=checkstyle
+repository=https://github.com/checkstyle/checkstyle.git
+revision=checkstyle-10.12.4
+
+if [ "${#}" -gt 2 ] || ([ "${#}" = 2 ] && [ "${1:---sync}" != '--sync' ]); then
+  echo "Usage: ${0} [--sync] [<report_directory>]"
+  exit 1
+fi
+do_sync="$([ "${#}" = 0 ] || [ "${1:-}" != '--sync' ] || echo 1)"
+report_directory="$([ "${#}" = 0 ] || ([ -z "${do_sync}" ] && echo "${1}") || ([ "${#}" = 1 ] || echo "${2}"))"
+
+if [ -n "${report_directory}" ]; then
+  mkdir -p "${report_directory}"
+else
+  report_directory="$(mktemp -d)"
+  trap 'rm -rf -- "${report_directory}"' INT TERM HUP EXIT
+fi
+
+# XXX: Configure Renovate to manage the AssertJ version declared here.
+shared_build_flags="
+  -Perror-prone-compile,error-prone-test-compile
+  -Dassertj.version=3.24.2
+  -Derror-prone.version=$(
+    mvn -f "${error_prone_support_root}" help:evaluate -Dexpression=version.error-prone -q -DforceStdout
+  )
+  -Derror-prone-support.version=$(
+    mvn -f "${error_prone_support_root}" help:evaluate -Dexpression=project.version -q -DforceStdout
+  )
+  -DadditionalSourceDirectories=\${project.basedir}\${file.separator}src\${file.separator}it\${file.separator}java,\${project.basedir}\${file.separator}src\${file.separator}xdocs-examples\${file.separator}java
+  "
+
+# XXX: Configure Renovate to manage the fmt-maven-plugin version declared here.
+# XXX: Once GitHub actions uses Maven 3.9.2+, we can inline this variable with
+# version reference `${fmt.version}`, and `-Dfmt.version=2.21.1` added to
+# `shared_build_flags`.
+format_goal='com.spotify.fmt:fmt-maven-plugin:2.21.1:format'
+
+error_prone_shared_flags='-XepExcludedPaths:(\Q${project.basedir}${file.separator}src${file.separator}\E(it|test|xdocs-examples)\Q${file.separator}resources\E|\Q${project.build.directory}${file.separator}\E).*'
+
+error_prone_patch_flags="${error_prone_shared_flags} -XepPatchLocation:IN_PLACE -XepPatchChecks:$(
+  find "${error_prone_support_root}" -path "*/META-INF/services/com.google.errorprone.bugpatterns.BugChecker" -print0 \
+    | xargs -0 grep -hoP '[^.]+$' \
+    | paste -s -d ','
+)"
+
+error_prone_validation_flags="${error_prone_shared_flags} -XepDisableAllChecks $(
+  find "${error_prone_support_root}" -path "*/META-INF/services/com.google.errorprone.bugpatterns.BugChecker" -print0 \
+    | xargs -0 grep -hoP '[^.]+$' \
+    | sed -r 's,(.*),-Xep:\1:WARN,' \
+    | paste -s -d ' '
+)"
+
+echo "Shared build flags: ${shared_build_flags}"
+echo "Error Prone patch flags: ${error_prone_patch_flags}"
+echo "Error Prone validation flags: ${error_prone_validation_flags}"
+
+mkdir -p "${repos_root}"
+
+# Make sure that the targeted tag of the project's Git repository is checked
+# out.
+project_root="${repos_root}/${project}"
+if [ ! -d "${project_root}" ]; then
+  # The repository has not yet been cloned; create a shallow clone.
+  git clone --branch "${revision}" --depth 1 "${repository}" "${project_root}"
+else
+  # The repository does already appear to exist. Try to check out the requested
+  # tag if possible, and fetch it otherwise.
+  #
+  # Under certain circumstances this does not cause the relevant tag to be
+  # created, so if necessary we manually create it.
+  git -C "${project_root}" checkout --force "${revision}" 2>/dev/null \
+    || (
+         git -C "${project_root}" fetch --depth 1 "${repository}" "${revision}" \
+           && git -C "${project_root}" checkout --force FETCH_HEAD \
+           && (git -C "${project_root}" tag "${revision}" || true)
+       )
+fi
+
+pushd "${project_root}"
+
+# Make sure that Git is sufficiently configured to enable committing to the
+# project's Git repository.
+git config user.email || git config user.email "integration-test@example.com"
+git config user.name || git config user.name "Integration Test"
+
+# Prepare the code for analysis by (a) applying the minimal set of changes
+# required to run Error Prone with Error Prone Support and (b) formatting the
+# code using the same method by which it will be formatted after each
+# compilation round. The initial formatting operation ensures that subsequent
+# modifications can be rendered in a clean manner.
+git clean -fdx
+git apply < "${integration_test_root}/${test_name}-init.patch"
+git commit -m 'dependency: Introduce Error Prone Support' .
+mvn ${shared_build_flags} "${format_goal}"
+git commit -m 'minor: Reformat using Google Java Format' .
+diff_base="$(git rev-parse HEAD)"
+
+# Apply Error Prone Support-suggested changes until a fixed point is reached.
+function apply_patch() {
+  local extra_build_args="${1}"
+
+  mvn ${shared_build_flags} ${extra_build_args} \
+    package "${format_goal}" \
+    -Derror-prone.flags="${error_prone_patch_flags}" \
+    -DskipTests
+
+  if ! git diff --exit-code; then
+    git commit -m 'minor: Apply patches' .
+
+    # Changes were applied, so another compilation round may apply yet more
+    # changes. For performance reasons we perform incremental compilation,
+    # enabled using a misleading flag. (See
+    # https://issues.apache.org/jira/browse/MCOMPILER-209 for details.)
+    apply_patch '-Dmaven.compiler.useIncrementalCompilation=false'
+  elif [ "${extra_build_args}" != 'clean' ]; then
+    # No changes were applied. We'll attempt one more round in which all files
+    # are recompiled, because there are cases in which violations are missed
+    # during incremental compilation.
+    apply_patch 'clean'
+  fi
+}
+apply_patch ''
+
+# Run one more full build and log the output.
+#
+# By also running the tests, we validate that the (majority of) applied changes
+# are behavior preserving. Some tests are skipped:
+# - The `metadataFilesGenerationAllFiles` test is skipped because it makes line
+#   number assertions that will fail when the code is formatted or patched.
+# - The `allCheckSectionJavaDocs` test is skipped because is validates that
+#   Javadoc has certain closing tags that are removed by Google Java Format.
+validation_build_log="${report_directory}/${test_name}-validation-build-log.txt"
+mvn ${shared_build_flags} \
+      clean package \
+      -Derror-prone.flags="${error_prone_validation_flags}" \
+      -Dtest='
+        !MetadataGeneratorUtilTest#metadataFilesGenerationAllFiles,
+        !XdocsJavaDocsTest#allCheckSectionJavaDocs' \
+    | tee "${validation_build_log}" \
+  || failure=1
+
+# Collect the applied changes.
+expected_changes="${integration_test_root}/${test_name}-expected-changes.patch"
+actual_changes="${report_directory}/${test_name}-changes.patch"
+(git diff "${diff_base}"..HEAD | grep -vP '^(diff|index)' || true) > "${actual_changes}"
+
+# Collect the warnings reported by Error Prone Support checks.
+expected_warnings="${integration_test_root}/${test_name}-expected-warnings.txt"
+actual_warnings="${report_directory}/${test_name}-validation-build-warnings.txt"
+(grep -oP "(?<=^\\Q[WARNING] ${PWD}/\\E).*" "${validation_build_log}" | grep -P '\] \[' || true) | LC_ALL=C sort > "${actual_warnings}"
+
+# Persist or validate the applied changes and reported warnings.
+if [ -n "${do_sync}" ]; then
+  echo 'Saving changes...'
+  cp "${actual_changes}" "${expected_changes}"
+  cp "${actual_warnings}" "${expected_warnings}"
+else
+  echo 'Inspecting changes...'
+  # XXX: This "diff of diffs" also contains vacuous sections, introduced due to
+  # line offset differences. Try to omit those from the final output.
+  if ! diff -u "${expected_changes}" "${actual_changes}"; then
+    echo 'There are unexpected changes.'
+    failure=1
+  fi
+  echo 'Inspecting emitted warnings...'
+  if ! diff -u "${expected_warnings}" "${actual_warnings}"; then
+    echo 'Diagnostics output changed.'
+    failure=1
+  fi
+fi
+
+if [ -n "${failure:-}" ]; then
+  exit 1
+fi

pom.xml

@@ -47,9 +47,9 @@
         <module>refaster-test-support</module>
     </modules>
 
-    <scm>
+    <scm child.scm.developerConnection.inherit.append.path="false" child.scm.url.inherit.append.path="false">
         <developerConnection>scm:git:git@github.com:PicnicSupermarket/error-prone-support.git</developerConnection>
-        <tag>v0.12.0</tag>
+        <tag>HEAD</tag>
         <url>https://github.com/PicnicSupermarket/error-prone-support</url>
     </scm>
     <issueManagement>
@@ -100,6 +100,10 @@
             <!-- The test JVMs are short-running. By disabling certain
             expensive JIT optimizations we actually speed up most tests. -->
             -XX:TieredStopAtLevel=1
+            <!-- The test JVMs run in a non-interactive and generally
+            multi-core context, where the Parallel Garbage Collector generally
+            has the highest throughput. -->
+            -XX:+UseParallelGC
             <!-- We cap memory usage. This may be relevant for build agents,
             but also prevents excessive memory usage by heavily parallelized
             local builds. -->
@@ -141,7 +145,7 @@
         <groupId.error-prone>com.google.errorprone</groupId.error-prone>
         <!-- The build timestamp is derived from the most recent commit
         timestamp in support of reproducible builds. -->
-        <project.build.outputTimestamp>2023-10-04T14:40:37Z</project.build.outputTimestamp>
+        <project.build.outputTimestamp>${git.commit.time}</project.build.outputTimestamp>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <!-- Glob pattern identifying Refaster rule definition files. These
         Java classes don't contain "regular" code, and thus require special
@@ -201,16 +205,16 @@
         <version.auto-value>1.10.4</version.auto-value>
         <version.error-prone>${version.error-prone-orig}</version.error-prone>
         <version.error-prone-fork>v${version.error-prone-orig}-picnic-1</version.error-prone-fork>
-        <version.error-prone-orig>2.22.0</version.error-prone-orig>
-        <version.error-prone-slf4j>0.1.20</version.error-prone-slf4j>
+        <version.error-prone-orig>2.23.0</version.error-prone-orig>
+        <version.error-prone-slf4j>0.1.21</version.error-prone-slf4j>
         <version.guava-beta-checker>1.0</version.guava-beta-checker>
         <version.jdk>11</version.jdk>
         <version.maven>3.8.7</version.maven>
-        <version.mockito>5.6.0</version.mockito>
+        <version.mockito>5.8.0</version.mockito>
         <version.nopen-checker>1.0.1</version.nopen-checker>
-        <version.nullaway>0.10.14</version.nullaway>
-        <version.pitest-git>1.1.2</version.pitest-git>
-        <version.surefire>3.1.2</version.surefire>
+        <version.nullaway>0.10.18</version.nullaway>
+        <version.pitest-git>1.1.4</version.pitest-git>
+        <version.surefire>3.2.2</version.surefire>
     </properties>
 
     <dependencyManagement>
@@ -268,7 +272,7 @@
             <dependency>
                 <groupId>com.fasterxml.jackson</groupId>
                 <artifactId>jackson-bom</artifactId>
-                <version>2.15.2</version>
+                <version>2.16.0</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
@@ -307,7 +311,7 @@
             <dependency>
                 <groupId>com.google.guava</groupId>
                 <artifactId>guava-bom</artifactId>
-                <version>32.1.2-jre</version>
+                <version>32.1.3-jre</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
@@ -333,7 +337,7 @@
             <dependency>
                 <groupId>io.projectreactor</groupId>
                 <artifactId>reactor-bom</artifactId>
-                <version>2022.0.11</version>
+                <version>2023.0.0</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
@@ -345,12 +349,12 @@
             <dependency>
                 <groupId>io.swagger</groupId>
                 <artifactId>swagger-annotations</artifactId>
-                <version>1.6.11</version>
+                <version>1.6.12</version>
             </dependency>
             <dependency>
                 <groupId>io.swagger.core.v3</groupId>
                 <artifactId>swagger-annotations</artifactId>
-                <version>2.2.16</version>
+                <version>2.2.19</version>
             </dependency>
             <dependency>
                 <groupId>jakarta.servlet</groupId>
@@ -382,7 +386,7 @@
             <dependency>
                 <groupId>net.bytebuddy</groupId>
                 <artifactId>byte-buddy</artifactId>
-                <version>1.14.9</version>
+                <version>1.14.10</version>
             </dependency>
             <!-- Specified so that Renovate will file Maven upgrade PRs, which
             subsequently will cause `maven-enforcer-plugin` to require that
@@ -407,7 +411,7 @@
             <dependency>
                 <groupId>org.checkerframework</groupId>
                 <artifactId>checker-qual</artifactId>
-                <version>3.39.0</version>
+                <version>3.41.0</version>
             </dependency>
             <dependency>
                 <groupId>org.hamcrest</groupId>
@@ -427,7 +431,7 @@
             <dependency>
                 <groupId>org.junit</groupId>
                 <artifactId>junit-bom</artifactId>
-                <version>5.10.0</version>
+                <version>5.10.1</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
@@ -441,7 +445,7 @@
             <dependency>
                 <groupId>org.mongodb</groupId>
                 <artifactId>mongodb-driver-core</artifactId>
-                <version>4.10.2</version>
+                <version>4.11.1</version>
                 <!-- XXX: Drop this exclusion once we forgo enforcement of JDK
                 11 bytecode version compatibility. -->
                 <exclusions>
@@ -461,14 +465,14 @@
             <dependency>
                 <groupId>org.springframework</groupId>
                 <artifactId>spring-framework-bom</artifactId>
-                <version>5.3.30</version>
+                <version>5.3.31</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
             <dependency>
                 <groupId>org.springframework.boot</groupId>
                 <artifactId>spring-boot-test</artifactId>
-                <version>2.7.16</version>
+                <version>2.7.18</version>
             </dependency>
             <dependency>
                 <groupId>org.testng</groupId>
@@ -529,6 +533,14 @@
                         <forkMode>never</forkMode>
                         <failOnError>false</failOnError>
                     </configuration>
+                    <executions>
+                        <execution>
+                            <id>check-source-format</id>
+                            <goals>
+                                <goal>check</goal>
+                            </goals>
+                        </execution>
+                    </executions>
                 </plugin>
                 <plugin>
                     <groupId>de.thetaphi</groupId>
@@ -580,7 +592,7 @@
                 <plugin>
                     <groupId>io.github.git-commit-id</groupId>
                     <artifactId>git-commit-id-maven-plugin</artifactId>
-                    <version>6.0.0</version>
+                    <version>7.0.0</version>
                     <configuration>
                         <injectAllReactorProjects>true</injectAllReactorProjects>
                         <runOnlyOnce>true</runOnlyOnce>
@@ -599,7 +611,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-checkstyle-plugin</artifactId>
-                    <version>3.3.0</version>
+                    <version>3.3.1</version>
                     <configuration>
                         <checkstyleRules>
                             <!-- We only enable rules that are not enforced by
@@ -704,6 +716,10 @@
                                             <!-- Instead, please use
                                             `com.google.errorprone.annotations.Immutable`. -->
                                         </property>
+                                        <property name="illegalClasses" value="org.jetbrains.annotations.CheckReturnValue">
+                                            <!-- Instead, please use
+                                            `com.google.errorprone.annotations.CheckReturnValue`. -->
+                                        </property>
                                         <property name="illegalClasses" value="org.jetbrains.annotations.VisibleForTesting">
                                             <!-- Instead, please use
                                             `com.google.common.annotations.VisibleForTesting`. -->
@@ -810,6 +826,7 @@
                                     <module name="RedundantModifier" />
                                     <module name="SimplifyBooleanExpression" />
                                     <module name="SimplifyBooleanReturn" />
+                                    <module name="SummaryJavadoc" />
                                     <module name="SuppressWarningsHolder">
                                         <property name="aliasList" value="com.puppycrawl.tools.checkstyle.checks.coding.UnusedLocalVariableCheck=unused" />
                                     </module>
@@ -828,28 +845,21 @@
                                 <module name="io.spring.nohttp.checkstyle.check.NoHttpCheck" />
                             </module>
                         </checkstyleRules>
+                        <excludeGeneratedSources>true</excludeGeneratedSources>
                         <failOnViolation>false</failOnViolation>
                         <includeTestSourceDirectory>true</includeTestSourceDirectory>
-                        <!-- The plugin's "excludes" property accepts an Ant
-                        pattern, but does not match against the full path. So
-                        rather than explicitly excluding generated sources, we
-                        have to explicitly include "original" sources. -->
-                        <sourceDirectories>
-                            <sourceDirectory>${project.build.sourceDirectory}</sourceDirectory>
-                        </sourceDirectories>
-                        <testSourceDirectories>
-                            <testSourceDirectory>${project.build.testSourceDirectory}</testSourceDirectory>
-                            <!-- Refaster input and output test files represent
-                            valid Java code, exposed as resources on the test
-                            classpath. -->
-                            <testSourceDirectory>${basedir}/src/test/resources</testSourceDirectory>
-                        </testSourceDirectories>
+                        <resourceIncludes>**/*</resourceIncludes>
+                        <!-- XXX: The generated
+                        `target/generated-sources/license/THIRD-PARTY.txt`
+                        files are not excluded by the `excludeGeneratedSources`
+                        setting. Consider filing an issue for this. -->
+                        <resourceExcludes>THIRD-PARTY.txt</resourceExcludes>
                     </configuration>
                     <dependencies>
                         <dependency>
                             <groupId>com.puppycrawl.tools</groupId>
                             <artifactId>checkstyle</artifactId>
-                            <version>10.12.4</version>
+                            <version>10.12.5</version>
                         </dependency>
                         <dependency>
                             <groupId>io.spring.nohttp</groupId>
@@ -869,7 +879,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-clean-plugin</artifactId>
-                    <version>3.3.1</version>
+                    <version>3.3.2</version>
                 </plugin>
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
@@ -950,7 +960,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-dependency-plugin</artifactId>
-                    <version>3.6.0</version>
+                    <version>3.6.1</version>
                     <configuration>
                         <!-- XXX: Drop `ignoreAllNonTestScoped` once
                         https://issues.apache.org/jira/browse/MNG-6058 is
@@ -1033,18 +1043,7 @@
                             </requireMavenVersion>
                             <requireNoRepositories />
                             <requirePluginVersions />
-                            <requireUpperBoundDeps>
-                                <excludes>
-                                    <!-- XXX:
-                                    `com.google.errorprone:error_prone_test_helpers`
-                                    pulls in a more recent version of Truth
-                                    than
-                                    `com.google.testing.compile:compile-testing`,
-                                    but the latter is incompatible with said
-                                    never version. -->
-                                    <exclude>com.google.truth:truth</exclude>
-                                </excludes>
-                            </requireUpperBoundDeps>
+                            <requireUpperBoundDeps />
                         </rules>
                     </configuration>
                     <dependencies>
@@ -1112,7 +1111,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-javadoc-plugin</artifactId>
-                    <version>3.6.0</version>
+                    <version>3.6.3</version>
                     <configuration>
                         <additionalJOptions>
                             <additionalJOption>--add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED</additionalJOption>
@@ -1198,12 +1197,12 @@
                 <plugin>
                     <groupId>org.codehaus.mojo</groupId>
                     <artifactId>build-helper-maven-plugin</artifactId>
-                    <version>3.4.0</version>
+                    <version>3.5.0</version>
                 </plugin>
                 <plugin>
                     <groupId>org.codehaus.mojo</groupId>
                     <artifactId>license-maven-plugin</artifactId>
-                    <version>2.2.0</version>
+                    <version>2.3.0</version>
                     <configuration>
                         <includedLicenses>
                             <!-- The SPDX IDs of licenses of third-party
@@ -1302,11 +1301,19 @@
                     <groupId>org.codehaus.mojo</groupId>
                     <artifactId>tidy-maven-plugin</artifactId>
                     <version>1.2.0</version>
+                    <executions>
+                        <execution>
+                            <id>check-pom</id>
+                            <goals>
+                                <goal>check</goal>
+                            </goals>
+                        </execution>
+                    </executions>
                 </plugin>
                 <plugin>
                     <groupId>org.codehaus.mojo</groupId>
                     <artifactId>versions-maven-plugin</artifactId>
-                    <version>2.16.1</version>
+                    <version>2.16.2</version>
                     <configuration>
                         <updateBuildOutputTimestampPolicy>never</updateBuildOutputTimestampPolicy>
                     </configuration>
@@ -1345,7 +1352,7 @@
                 <plugin>
                     <groupId>org.jacoco</groupId>
                     <artifactId>jacoco-maven-plugin</artifactId>
-                    <version>0.8.10</version>
+                    <version>0.8.11</version>
                     <configuration>
                         <excludes>
                             <!-- Refaster rules are tested using a custom method
@@ -1357,7 +1364,7 @@
                 <plugin>
                     <groupId>org.pitest</groupId>
                     <artifactId>pitest-maven</artifactId>
-                    <version>1.15.1</version>
+                    <version>1.15.3</version>
                     <configuration>
                         <excludedClasses>
                             <!-- AutoValue generated classes. -->
@@ -1386,7 +1393,7 @@
                         <dependency>
                             <groupId>com.groupcdg.arcmutate</groupId>
                             <artifactId>base</artifactId>
-                            <version>1.2.1</version>
+                            <version>1.2.2</version>
                         </dependency>
                         <dependency>
                             <groupId>com.groupcdg.pitest</groupId>
@@ -1396,7 +1403,7 @@
                         <dependency>
                             <groupId>org.pitest</groupId>
                             <artifactId>pitest-junit5-plugin</artifactId>
-                            <version>1.2.0</version>
+                            <version>1.2.1</version>
                         </dependency>
                     </dependencies>
                     <executions>
@@ -1538,7 +1545,7 @@
                 `BugChecker` test code and the Refaster test files) does not
                 exhibit anti-patterns other than those associated with the
                 check/rule under test. Ideally all test cases are realistic. -->
-                <error-prone.self-check-args>-XepAllSuggestionsAsWarnings -Xep:MethodReferenceUsage:OFF</error-prone.self-check-args>
+                <error-prone.self-check-args>-Xep:MethodReferenceUsage:OFF</error-prone.self-check-args>
             </properties>
             <build>
                 <plugins>
@@ -1563,6 +1570,31 @@
                 </plugins>
             </build>
         </profile>
+        <profile>
+            <!-- A counterpart to the `disallow-warnings` profile which
+            explicitly "tones down" plugins enabled by the `build-checks`
+            profile. Necessary for dealing with plugins that default to failing
+            the build upon encountering a violation. -->
+            <id>avoid-errors</id>
+            <activation>
+                <property>
+                    <name>verification.warn</name>
+                </property>
+            </activation>
+            <build>
+                <pluginManagement>
+                    <plugins>
+                        <plugin>
+                            <groupId>org.codehaus.mojo</groupId>
+                            <artifactId>tidy-maven-plugin</artifactId>
+                            <configuration>
+                                <skip>true</skip>
+                            </configuration>
+                        </plugin>
+                    </plugins>
+                </pluginManagement>
+            </build>
+        </profile>
         <profile>
             <!-- By default, we verify various aspects of a module and the
             artifact(s) it produces. We define these checks in a profile so
@@ -1583,14 +1615,6 @@
                     <plugin>
                         <groupId>com.spotify.fmt</groupId>
                         <artifactId>fmt-maven-plugin</artifactId>
-                        <executions>
-                            <execution>
-                                <id>check-source-format</id>
-                                <goals>
-                                    <goal>check</goal>
-                                </goals>
-                            </execution>
-                        </executions>
                     </plugin>
                     <plugin>
                         <groupId>de.thetaphi</groupId>
@@ -1669,6 +1693,10 @@
                             </execution>
                         </executions>
                     </plugin>
+                    <plugin>
+                        <groupId>org.codehaus.mojo</groupId>
+                        <artifactId>tidy-maven-plugin</artifactId>
+                    </plugin>
                     <plugin>
                         <groupId>org.gaul</groupId>
                         <artifactId>modernizer-maven-plugin</artifactId>
@@ -1703,15 +1731,17 @@
                                     failing the build on the first error
                                     encountered. -->
                                     -XepAllErrorsAsWarnings
+                                    -XepAllSuggestionsAsWarnings
+                                    <!-- We want to enable almost all Error
+                                    Prone bug pattern checkers, so we enable
+                                    all and then selectively deactivate some. -->
+                                    -XepAllDisabledChecksAsWarnings
                                     <!-- Some generated classes violate Error
                                     Prone bug patterns. We cannot in all cases
                                     avoid that, so we simply tell Error Prone
                                     not to warn about generated code. -->
                                     -XepDisableWarningsInGeneratedCode
-                                    <!-- We want to enable almost all Error
-                                    Prone bug pattern checkers, so we enable
-                                    all and then selectively deactivate some. -->
-                                    -XepAllDisabledChecksAsWarnings
+                                    -XepExcludedPaths:\Q${project.build.directory}${file.separator}\E.*
                                     <!-- We don't target Android. -->
                                     -Xep:AndroidJdkLibsChecker:OFF
                                     <!-- XXX: Enable this once we open-source
@@ -1738,11 +1768,8 @@
                                     -XepOpt:NullAway:CheckOptionalEmptiness=true
                                     -XepOpt:Nullness:Conservative=false
                                     -XepOpt:StatementSwitchToExpressionSwitch:EnableAssignmentSwitchConversion=true
+                                    -XepOpt:StatementSwitchToExpressionSwitch:EnableDirectConversion=true
                                     -XepOpt:StatementSwitchToExpressionSwitch:EnableReturnSwitchConversion=true
-                                    <!-- XXX: Enable once this check respects
-                                    the compilation source version. See
-                                    https://github.com/google/error-prone/pull/3646.
-                                    -XepOpt:StatementSwitchToExpressionSwitch:EnableDirectConversion=true -->
                                     <!-- Append additional custom arguments. -->
                                     ${error-prone.patch-args}
                                     ${error-prone.self-check-args}
@@ -1775,10 +1802,10 @@
             </properties>
         </profile>
         <profile>
-            <!-- The `build-checks` and `error-prone` profiles enable a bunch
-            of additional compile checks. By default, those warnings break the
-            build. This profile allows one to collect all build warnings
-            without failing the build. -->
+            <!-- The `build-checks` and `error-prone` profiles enable numerous
+            additional validations. By default, any violations break the build.
+            This profile allows one to collect all violations without failing
+            the build. -->
             <id>disallow-warnings</id>
             <activation>
                 <property>

refaster-support/pom.xml

@@ -55,6 +55,11 @@
             <groupId>com.google.guava</groupId>
             <artifactId>guava</artifactId>
         </dependency>
+        <dependency>
+            <groupId>io.projectreactor</groupId>
+            <artifactId>reactor-core</artifactId>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.assertj</groupId>
             <artifactId>assertj-core</artifactId>

refaster-support/src/main/java/tech/picnic/errorprone/refaster/matchers/IsEmpty.java

@@ -0,0 +1,151 @@
+package tech.picnic.errorprone.refaster.matchers;
+
+import static com.google.common.base.Verify.verify;
+import static com.google.errorprone.matchers.FieldMatchers.staticField;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.argumentCount;
+import static com.google.errorprone.matchers.Matchers.isPrimitiveType;
+import static com.google.errorprone.matchers.Matchers.isSameType;
+import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static com.google.errorprone.matchers.Matchers.toType;
+
+import com.google.common.collect.ImmutableCollection;
+import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableMultimap;
+import com.google.errorprone.VisitorState;
+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.NewArrayTree;
+import com.sun.source.tree.NewClassTree;
+import com.sun.source.tree.Tree;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Stack;
+import java.util.TreeMap;
+import java.util.TreeSet;
+import java.util.Vector;
+import java.util.regex.Pattern;
+import java.util.stream.Stream;
+
+/**
+ * A matcher of expressions that are guaranteed to yield "empty" instances, as defined by their
+ * respective types.
+ */
+// XXX: Also match (effectively) final variables that reference provably-empty objects.
+// XXX: Also handle `#copyOf(someEmptyInstance)`, `#sortedCopyOf(someEmptyInstance)`,
+// `Sets.immutableEnumSet(emptyIterable)` (and other `Sets` methods), `EnumSet.noneOf(...)`,
+// `emptyCollection.stream()`, `emptyStream.collect(...)`, `emptyMap.{keySet,values,entrySet}()`,
+// etc.
+// XXX: Also recognize null-hostile "container" expression types that can only reference empty
+// instances, such as `ImmutableCollection<Void>` and `Flux<Void>`.
+// XXX: Also recognize empty instances of `Optional`, `OptionalInt`, `OptionalLong`, and
+// `OptionalDouble`.
+// XXX: Also recognize empty builders and `emptyBuilder.build()` invocations.
+public final class IsEmpty implements Matcher<ExpressionTree> {
+  private static final long serialVersionUID = 1L;
+  private static final Pattern EMPTY_INSTANCE_FACTORY_METHOD_PATTERN = Pattern.compile("empty.*");
+  private static final Matcher<Tree> EMPTY_COLLECTION_CONSTRUCTOR_ARGUMENT =
+      anyOf(isPrimitiveType(), isSubtypeOf(Comparator.class));
+  // XXX: Extend this list to include additional JDK collection types with a public constructor.
+  private static final Matcher<ExpressionTree> MUTABLE_COLLECTION_TYPE =
+      anyOf(
+          isSameType(ArrayList.class),
+          isSameType(HashMap.class),
+          isSameType(HashSet.class),
+          isSameType(LinkedHashMap.class),
+          isSameType(LinkedHashSet.class),
+          isSameType(LinkedList.class),
+          isSameType(Stack.class),
+          isSameType(TreeMap.class),
+          isSameType(TreeSet.class),
+          isSameType(Vector.class));
+  private static final Matcher<ExpressionTree> EMPTY_INSTANCE_FACTORY =
+      anyOf(
+          staticField(Collections.class.getName(), "EMPTY_LIST"),
+          staticField(Collections.class.getName(), "EMPTY_MAP"),
+          staticField(Collections.class.getName(), "EMPTY_SET"),
+          toType(
+              MethodInvocationTree.class,
+              allOf(
+                  argumentCount(0),
+                  anyOf(
+                      staticMethod()
+                          .onClass(Collections.class.getName())
+                          .withNameMatching(EMPTY_INSTANCE_FACTORY_METHOD_PATTERN),
+                      staticMethod()
+                          .onDescendantOfAny(
+                              ImmutableCollection.class.getName(),
+                              ImmutableMap.class.getName(),
+                              ImmutableMultimap.class.getName(),
+                              List.class.getName(),
+                              Map.class.getName(),
+                              Set.class.getName(),
+                              Stream.class.getName())
+                          .named("of"),
+                      staticMethod()
+                          .onClassAny(
+                              Stream.class.getName(),
+                              "reactor.core.publisher.Flux",
+                              "reactor.core.publisher.Mono",
+                              "reactor.util.context.Context")
+                          .named("empty"),
+                      staticMethod()
+                          .onDescendantOf("reactor.core.publisher.Flux")
+                          .named("just")))));
+
+  /** Instantiates a new {@link IsEmpty} instance. */
+  public IsEmpty() {}
+
+  @Override
+  public boolean matches(ExpressionTree tree, VisitorState state) {
+    return isEmptyArrayCreation(tree)
+        || EMPTY_INSTANCE_FACTORY.matches(tree, state)
+        || isEmptyCollectionConstructor(tree, state);
+  }
+
+  private boolean isEmptyCollectionConstructor(ExpressionTree tree, VisitorState state) {
+    if (!(tree instanceof NewClassTree) || !MUTABLE_COLLECTION_TYPE.matches(tree, state)) {
+      return false;
+    }
+
+    List<? extends ExpressionTree> arguments = ((NewClassTree) tree).getArguments();
+    if (arguments.stream().allMatch(a -> EMPTY_COLLECTION_CONSTRUCTOR_ARGUMENT.matches(a, state))) {
+      /*
+       * This is a default constructor, or a constructor that creates an empty collection using
+       * custom (re)size/load factor parameters and/or a custom `Comparator`.
+       */
+      return true;
+    }
+
+    /*
+     * This looks like a copy constructor, in which case the resultant collection is empty if its
+     * argument is.
+     */
+    verify(arguments.size() == 1, "Unexpected %s-ary constructor", arguments.size());
+    return matches(arguments.get(0), state);
+  }
+
+  private static boolean isEmptyArrayCreation(ExpressionTree tree) {
+    if (!(tree instanceof NewArrayTree)) {
+      return false;
+    }
+
+    NewArrayTree newArray = (NewArrayTree) tree;
+    return (!newArray.getDimensions().isEmpty()
+            && ASTHelpers.constValue(newArray.getDimensions().get(0), Integer.class) == 0)
+        || (newArray.getInitializers() != null && newArray.getInitializers().isEmpty());
+  }
+}

refaster-support/src/main/java/tech/picnic/errorprone/refaster/matchers/IsIdentityOperation.java

@@ -0,0 +1,54 @@
+package tech.picnic.errorprone.refaster.matchers;
+
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+import static com.google.errorprone.matchers.Matchers.toType;
+
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.LambdaExpressionTree;
+import com.sun.source.tree.LambdaExpressionTree.BodyKind;
+import java.util.function.DoubleUnaryOperator;
+import java.util.function.Function;
+import java.util.function.IntUnaryOperator;
+import java.util.function.LongUnaryOperator;
+
+/** A matcher of expressions that represent identity operations. */
+// XXX: In selected contexts many other method invocations can be considered identity operations;
+// see the `IdentityConversion` check. Review whether those can/should be captured by this matcher
+// as well.
+public final class IsIdentityOperation implements Matcher<ExpressionTree> {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> DELEGATE =
+      anyOf(
+          staticMethod()
+              .onDescendantOfAny(
+                  DoubleUnaryOperator.class.getName(),
+                  Function.class.getName(),
+                  IntUnaryOperator.class.getName(),
+                  LongUnaryOperator.class.getName())
+              .named("identity"),
+          isIdentityLambdaExpression());
+
+  /** Instantiates a new {@link IsIdentityOperation} instance. */
+  public IsIdentityOperation() {}
+
+  @Override
+  public boolean matches(ExpressionTree tree, VisitorState state) {
+    return DELEGATE.matches(tree, state);
+  }
+
+  // XXX: Also support selected block expressions, including ones that perform a vacuous parameter
+  // transformation such as those identified by the `IdentityConversion` check.
+  private static Matcher<ExpressionTree> isIdentityLambdaExpression() {
+    return toType(
+        LambdaExpressionTree.class,
+        (tree, state) ->
+            tree.getBodyKind() == BodyKind.EXPRESSION
+                && tree.getParameters().size() == 1
+                && ASTHelpers.getSymbol(tree.getParameters().get(0))
+                    .equals(ASTHelpers.getSymbol(tree.getBody())));
+  }
+}

refaster-support/src/test/java/tech/picnic/errorprone/refaster/matchers/AbstractMatcherTestChecker.java

@@ -13,7 +13,7 @@ import com.sun.source.tree.MethodTree;
 import com.sun.source.tree.Tree;
 import com.sun.source.tree.TypeCastTree;
 import com.sun.source.util.TreePath;
-import com.sun.source.util.TreeScanner;
+import com.sun.source.util.TreePathScanner;
 import org.jspecify.annotations.Nullable;
 
 /**
@@ -34,15 +34,11 @@ abstract class AbstractMatcherTestChecker extends BugChecker implements Compilat
 
   @Override
   public Description matchCompilationUnit(CompilationUnitTree compilationUnit, VisitorState state) {
-    new TreeScanner<@Nullable Void, TreePath>() {
+    new TreePathScanner<@Nullable Void, @Nullable Void>() {
       @Override
-      public @Nullable Void scan(@Nullable Tree tree, TreePath treePath) {
-        if (tree == null) {
-          return null;
-        }
-
-        TreePath path = new TreePath(treePath, tree);
+      public @Nullable Void scan(@Nullable Tree tree, @Nullable Void unused) {
         if (tree instanceof ExpressionTree) {
+          TreePath path = new TreePath(getCurrentPath(), tree);
           ExpressionTree expressionTree = (ExpressionTree) tree;
           if (!isMethodSelect(expressionTree, path)
               && delegate.matches(expressionTree, state.withPath(path))) {
@@ -50,11 +46,11 @@ abstract class AbstractMatcherTestChecker extends BugChecker implements Compilat
           }
         }
 
-        return super.scan(tree, path);
+        return super.scan(tree, null);
       }
 
       @Override
-      public @Nullable Void visitImport(ImportTree tree, TreePath path) {
+      public @Nullable Void visitImport(ImportTree tree, @Nullable Void unused) {
         /*
          * We're not interested in matching import statements. While components of these
          * can be `ExpressionTree`s, they will never be matched by Refaster.
@@ -63,24 +59,24 @@ abstract class AbstractMatcherTestChecker extends BugChecker implements Compilat
       }
 
       @Override
-      public @Nullable Void visitMethod(MethodTree tree, TreePath path) {
+      public @Nullable Void visitMethod(MethodTree tree, @Nullable Void unused) {
         /*
          * We're not interested in matching e.g. parameter and return type declarations. While these
          * can be `ExpressionTree`s, they will never be matched by Refaster.
          */
-        return scan(tree.getBody(), new TreePath(path, tree));
+        return scan(tree.getBody(), null);
       }
 
       @Override
-      public @Nullable Void visitTypeCast(TypeCastTree tree, TreePath path) {
+      public @Nullable Void visitTypeCast(TypeCastTree tree, @Nullable Void unused) {
         /*
          * We're not interested in matching the parenthesized type subtree that is part of a type
          * cast expression. While such trees can be `ExpressionTree`s, they will never be matched by
          * Refaster.
          */
-        return scan(tree.getExpression(), new TreePath(path, tree));
+        return scan(tree.getExpression(), null);
       }
-    }.scan(compilationUnit, state.getPath());
+    }.scan(compilationUnit, null);
 
     return Description.NO_MATCH;
   }

refaster-support/src/test/java/tech/picnic/errorprone/refaster/matchers/IsEmptyTest.java

@@ -0,0 +1,443 @@
+package tech.picnic.errorprone.refaster.matchers;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.CompilationTestHelper;
+import com.google.errorprone.bugpatterns.BugChecker;
+import org.junit.jupiter.api.Test;
+
+final class IsEmptyTest {
+  @Test
+  void matches() {
+    CompilationTestHelper.newInstance(MatcherTestChecker.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import com.google.common.collect.ImmutableList;",
+            "import com.google.common.collect.ImmutableMap;",
+            "import com.google.common.collect.ImmutableSet;",
+            "import com.google.common.collect.ImmutableSetMultimap;",
+            "import java.util.ArrayList;",
+            "import java.util.Collections;",
+            "import java.util.Comparator;",
+            "import java.util.HashMap;",
+            "import java.util.HashSet;",
+            "import java.util.LinkedHashMap;",
+            "import java.util.LinkedHashSet;",
+            "import java.util.LinkedList;",
+            "import java.util.List;",
+            "import java.util.Map;",
+            "import java.util.Random;",
+            "import java.util.Set;",
+            "import java.util.Stack;",
+            "import java.util.TreeMap;",
+            "import java.util.TreeSet;",
+            "import java.util.Vector;",
+            "import java.util.stream.Stream;",
+            "import reactor.core.publisher.Flux;",
+            "import reactor.core.publisher.Mono;",
+            "import reactor.util.context.Context;",
+            "",
+            "class A {",
+            "  int[] negative1() {",
+            "    return new int[1];",
+            "  }",
+            "",
+            "  int[][] negative2() {",
+            "    return new int[1][0];",
+            "  }",
+            "",
+            "  int[] negative3() {",
+            "    return new int[] {0};",
+            "  }",
+            "",
+            "  int[][] negative4() {",
+            "    return new int[][] {{0}};",
+            "  }",
+            "",
+            "  Random negative5() {",
+            "    return new Random();",
+            "  }",
+            "",
+            "  List<Integer> negative6() {",
+            "    return new ArrayList<>(ImmutableList.of(1));",
+            "  }",
+            "",
+            "  Map<Integer, Integer> negative7() {",
+            "    return new HashMap<>(ImmutableMap.of(1, 2));",
+            "  }",
+            "",
+            "  Set<Integer> negative8() {",
+            "    return new HashSet<>(ImmutableList.of(1));",
+            "  }",
+            "",
+            "  Map<Integer, Integer> negative9() {",
+            "    return new LinkedHashMap<>(ImmutableMap.of(1, 2));",
+            "  }",
+            "",
+            "  Set<Integer> negative10() {",
+            "    return new LinkedHashSet<>(ImmutableList.of(1));",
+            "  }",
+            "",
+            "  List<Integer> negative11() {",
+            "    return new LinkedList<>(ImmutableList.of(1));",
+            "  }",
+            "",
+            "  Map<Integer, Integer> negative12() {",
+            "    return new HashMap<>(ImmutableMap.of(1, 2));",
+            "  }",
+            "",
+            "  Set<Integer> negative13() {",
+            "    return new HashSet<>(ImmutableList.of(1));",
+            "  }",
+            "",
+            "  List<Integer> negative14() {",
+            "    return new Vector<>(ImmutableList.of(1));",
+            "  }",
+            "",
+            "  ImmutableList<Integer> negative15() {",
+            "    return ImmutableList.of(1);",
+            "  }",
+            "",
+            "  ImmutableSet<Integer> negative16() {",
+            "    return ImmutableSet.of(1);",
+            "  }",
+            "",
+            "  ImmutableMap<Integer, Integer> negative17() {",
+            "    return ImmutableMap.of(1, 2);",
+            "  }",
+            "",
+            "  ImmutableSetMultimap<Integer, Integer> negative18() {",
+            "    return ImmutableSetMultimap.of(1, 2);",
+            "  }",
+            "",
+            "  List<Integer> negative19() {",
+            "    return List.of(1);",
+            "  }",
+            "",
+            "  Map<Integer, Integer> negative20() {",
+            "    return Map.of(1, 2);",
+            "  }",
+            "",
+            "  Set<Integer> negative21() {",
+            "    return Set.of(1);",
+            "  }",
+            "",
+            "  Stream<Integer> negative22() {",
+            "    return Stream.of(1);",
+            "  }",
+            "",
+            "  int[] positive1() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new int[0];",
+            "  }",
+            "",
+            "  int[][] positive2() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new int[0][1];",
+            "  }",
+            "",
+            "  int[] positive3() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new int[] {};",
+            "  }",
+            "",
+            "  int[][] positive4() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new int[][] {};",
+            "  }",
+            "",
+            "  List<Integer> positive5() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new ArrayList<>();",
+            "  }",
+            "",
+            "  List<String> positive6() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new ArrayList<>(1);",
+            "  }",
+            "",
+            "  List<String> positive7() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new ArrayList<>(",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableList.of());",
+            "  }",
+            "",
+            "  Map<String, String> positive8() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new HashMap<>();",
+            "  }",
+            "",
+            "  Map<String, String> positive9() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new HashMap<>(1);",
+            "  }",
+            "",
+            "  Map<String, String> positive10() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new HashMap<>(1, 1.0F);",
+            "  }",
+            "",
+            "  Map<String, String> positive11() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new HashMap<>(",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableMap.of());",
+            "  }",
+            "",
+            "  Set<Integer> positive12() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new HashSet<>();",
+            "  }",
+            "",
+            "  Set<Integer> positive13() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new HashSet<>(1);",
+            "  }",
+            "",
+            "  Set<Integer> positive14() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new HashSet<>(1, 1.0F);",
+            "  }",
+            "",
+            "  Set<Integer> positive15() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new HashSet<>(",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableList.of());",
+            "  }",
+            "",
+            "  Map<String, String> positive16() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedHashMap<>();",
+            "  }",
+            "",
+            "  Map<String, String> positive17() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedHashMap<>(1);",
+            "  }",
+            "",
+            "  Map<String, String> positive18() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedHashMap<>(1, 1.0F);",
+            "  }",
+            "",
+            "  Map<String, String> positive19() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedHashMap<>(1, 1.0F, false);",
+            "  }",
+            "",
+            "  Map<String, String> positive20() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedHashMap<>(",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableMap.of());",
+            "  }",
+            "",
+            "  Set<Integer> positive21() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedHashSet<>();",
+            "  }",
+            "",
+            "  Set<Integer> positive22() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedHashSet<>(1);",
+            "  }",
+            "",
+            "  Set<Integer> positive23() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedHashSet<>(1, 1.0F);",
+            "  }",
+            "",
+            "  Set<Integer> positive24() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedHashSet<>(",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableList.of());",
+            "  }",
+            "",
+            "  List<Integer> positive25() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedList<>();",
+            "  }",
+            "",
+            "  List<String> positive26() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new LinkedList<>(",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableList.of());",
+            "  }",
+            "",
+            "  List<Integer> positive27() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new Stack<>();",
+            "  }",
+            "",
+            "  Map<String, String> positive28() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new TreeMap<>();",
+            "  }",
+            "",
+            "  Map<String, String> positive29() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new TreeMap<>(Comparator.naturalOrder());",
+            "  }",
+            "",
+            "  Map<String, String> positive30() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new TreeMap<>(",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableMap.of());",
+            "  }",
+            "",
+            "  Set<Integer> positive31() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new TreeSet<>();",
+            "  }",
+            "",
+            "  Set<Integer> positive32() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new TreeSet<>(Comparator.naturalOrder());",
+            "  }",
+            "",
+            "  Set<Integer> positive33() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new TreeSet<>(",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableList.of());",
+            "  }",
+            "",
+            "  List<Integer> positive34() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new Vector<>();",
+            "  }",
+            "",
+            "  List<Integer> positive35() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new Vector<>(1);",
+            "  }",
+            "",
+            "  List<Integer> positive36() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new Vector<>(1, 2);",
+            "  }",
+            "",
+            "  List<Integer> positive37() {",
+            "    // BUG: Diagnostic contains:",
+            "    return new Vector<>(",
+            "        // BUG: Diagnostic contains:",
+            "        ImmutableList.of());",
+            "  }",
+            "",
+            "  List<Integer> positive38() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Collections.EMPTY_LIST;",
+            "  }",
+            "",
+            "  Map<String, String> positive39() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Collections.EMPTY_MAP;",
+            "  }",
+            "",
+            "  Set<Integer> positive40() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Collections.EMPTY_SET;",
+            "  }",
+            "",
+            "  List<Integer> positive41() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Collections.emptyList();",
+            "  }",
+            "",
+            "  Map<String, String> positive42() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Collections.emptyMap();",
+            "  }",
+            "",
+            "  Set<Integer> positive43() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Collections.emptySet();",
+            "  }",
+            "",
+            "  ImmutableList<Integer> positive44() {",
+            "    // BUG: Diagnostic contains:",
+            "    return ImmutableList.of();",
+            "  }",
+            "",
+            "  ImmutableSet<Integer> positive45() {",
+            "    // BUG: Diagnostic contains:",
+            "    return ImmutableSet.of();",
+            "  }",
+            "",
+            "  ImmutableMap<String, Integer> positive46() {",
+            "    // BUG: Diagnostic contains:",
+            "    return ImmutableMap.of();",
+            "  }",
+            "",
+            "  ImmutableSetMultimap<String, Integer> positive47() {",
+            "    // BUG: Diagnostic contains:",
+            "    return ImmutableSetMultimap.of();",
+            "  }",
+            "",
+            "  List<Integer> positive48() {",
+            "    // BUG: Diagnostic contains:",
+            "    return List.of();",
+            "  }",
+            "",
+            "  Map<String, String> positive49() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Map.of();",
+            "  }",
+            "",
+            "  Set<Integer> positive50() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Set.of();",
+            "  }",
+            "",
+            "  Stream<Integer> positive51() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Stream.of();",
+            "  }",
+            "",
+            "  Stream<Integer> positive52() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Stream.empty();",
+            "  }",
+            "",
+            "  Flux<Integer> positive53() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Flux.empty();",
+            "  }",
+            "",
+            "  Mono<Integer> positive54() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Mono.empty();",
+            "  }",
+            "",
+            "  Context positive55() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Context.empty();",
+            "  }",
+            "",
+            "  Flux<Integer> positive56() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Flux.just();",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  /** A {@link BugChecker} that simply delegates to {@link IsEmpty}. */
+  @BugPattern(summary = "Flags expressions matched by `IsEmpty`", severity = ERROR)
+  public static final class MatcherTestChecker extends AbstractMatcherTestChecker {
+    private static final long serialVersionUID = 1L;
+
+    // XXX: This is a false positive reported by Checkstyle. See
+    // https://github.com/checkstyle/checkstyle/issues/10161#issuecomment-1242732120.
+    @SuppressWarnings("RedundantModifier")
+    public MatcherTestChecker() {
+      super(new IsEmpty());
+    }
+  }
+}

refaster-support/src/test/java/tech/picnic/errorprone/refaster/matchers/IsIdentityOperationTest.java

@@ -0,0 +1,77 @@
+package tech.picnic.errorprone.refaster.matchers;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.CompilationTestHelper;
+import com.google.errorprone.bugpatterns.BugChecker;
+import org.junit.jupiter.api.Test;
+
+final class IsIdentityOperationTest {
+  @Test
+  void matches() {
+    CompilationTestHelper.newInstance(MatcherTestChecker.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import java.util.function.BinaryOperator;",
+            "import java.util.function.DoubleUnaryOperator;",
+            "import java.util.function.Function;",
+            "import java.util.function.IntUnaryOperator;",
+            "import java.util.function.LongUnaryOperator;",
+            "import java.util.function.UnaryOperator;",
+            "",
+            "class A {",
+            "  BinaryOperator<String> negative1() {",
+            "    return (a, b) -> a;",
+            "  }",
+            "",
+            "  UnaryOperator<String> negative2() {",
+            "    return a -> a + a;",
+            "  }",
+            "",
+            "  DoubleUnaryOperator positive1() {",
+            "    // BUG: Diagnostic contains:",
+            "    return DoubleUnaryOperator.identity();",
+            "  }",
+            "",
+            "  Function<Integer, Integer> positive2() {",
+            "    // BUG: Diagnostic contains:",
+            "    return Function.identity();",
+            "  }",
+            "",
+            "  UnaryOperator<String> positive3() {",
+            "    // BUG: Diagnostic contains:",
+            "    return UnaryOperator.identity();",
+            "  }",
+            "",
+            "  IntUnaryOperator positive4() {",
+            "    // BUG: Diagnostic contains:",
+            "    return IntUnaryOperator.identity();",
+            "  }",
+            "",
+            "  LongUnaryOperator positive5() {",
+            "    // BUG: Diagnostic contains:",
+            "    return LongUnaryOperator.identity();",
+            "  }",
+            "",
+            "  UnaryOperator positive6() {",
+            "    // BUG: Diagnostic contains:",
+            "    return a -> a;",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  /** A {@link BugChecker} that simply delegates to {@link IsIdentityOperation}. */
+  @BugPattern(summary = "Flags expressions matched by `IsIdentityOperation`", severity = ERROR)
+  public static final class MatcherTestChecker extends AbstractMatcherTestChecker {
+    private static final long serialVersionUID = 1L;
+
+    // XXX: This is a false positive reported by Checkstyle. See
+    // https://github.com/checkstyle/checkstyle/issues/10161#issuecomment-1242732120.
+    @SuppressWarnings("RedundantModifier")
+    public MatcherTestChecker() {
+      super(new IsIdentityOperation());
+    }
+  }
+}

refaster-test-support/src/main/java/tech/picnic/errorprone/refaster/test/RefasterRuleCollection.java

@@ -4,12 +4,10 @@ import static com.google.common.base.Preconditions.checkState;
 import static com.google.common.collect.ImmutableListMultimap.toImmutableListMultimap;
 import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.common.collect.ImmutableSortedSet.toImmutableSortedSet;
-import static com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode.TEXT_MATCH;
 import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
 import static java.util.Comparator.naturalOrder;
 import static tech.picnic.errorprone.refaster.runner.Refaster.INCLUDED_RULES_PATTERN_FLAG;
 
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableListMultimap;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableRangeMap;
@@ -19,6 +17,7 @@ import com.google.common.collect.Iterables;
 import com.google.common.collect.Range;
 import com.google.common.collect.Sets;
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
 import com.google.errorprone.BugPattern;
 import com.google.errorprone.ErrorProneFlags;
 import com.google.errorprone.SubContext;
@@ -123,10 +122,12 @@ public final class RefasterRuleCollection extends BugChecker implements Compilat
     String className = clazz.getSimpleName();
 
     BugCheckerRefactoringTestHelper.newInstance(RefasterRuleCollection.class, clazz)
-        .setArgs(ImmutableList.of("-XepOpt:" + RULE_COLLECTION_FLAG + '=' + className))
+        .setArgs(
+            "--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED",
+            "-XepOpt:" + RULE_COLLECTION_FLAG + '=' + className)
         .addInput(className + "TestInput.java")
         .addOutput(className + "TestOutput.java")
-        .doTest(TEXT_MATCH);
+        .doTest(TestMode.TEXT_MATCH);
   }
 
   @Override

website/README.md

@@ -51,11 +51,11 @@ bundle install
 # Deployment
 
 The website is regenerated and deployed using the
-[`deploy-website.yaml`][error-prone-support-website-deploy-workflow] GitHub
+[`deploy-website.yml`][error-prone-support-website-deploy-workflow] GitHub
 Actions workflow any time a change is merged to `master`.
 
 [error-prone-support-website]: https://error-prone.picnic.tech
-[error-prone-support-website-deploy-workflow]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/deploy-website.yaml
+[error-prone-support-website-deploy-workflow]: https://github.com/PicnicSupermarket/error-prone-support/actions/workflows/deploy-website.yml
 [jekyll]: https://jekyllrb.com
 [jekyll-docs]: https://jekyllrb.com/docs
 [jekyll-docs-installation]: https://jekyllrb.com/docs/installation