XXX-XXX Prefer jOOQs fetch().stream() over directly .stream()'ing

See:
- https://maven.apache.org/docs/3.8.7/release-notes.html
- https://github.com/apache/maven/releases/tag/maven-3.8.7
- https://github.com/apache/maven/compare/maven-3.8.6...maven-3.8.7

.github/ISSUE_TEMPLATE/feature_request.md

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

.github/workflows/build.yaml

@@ -37,7 +37,7 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v3.1.0
       - name: Set up JDK
-        uses: actions/setup-java@v3.7.0
+        uses: actions/setup-java@v3.8.0
         with:
           java-version: ${{ matrix.jdk }}
           distribution: ${{ matrix.distribution }}

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

@@ -16,7 +16,7 @@ jobs:
         with:
           fetch-depth: 2
       - name: Set up JDK
-        uses: actions/setup-java@v3.7.0
+        uses: actions/setup-java@v3.8.0
         with:
           java-version: 17.0.4
           distribution: temurin

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

@@ -20,7 +20,7 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v3.1.0
       - name: Set up JDK
-        uses: actions/setup-java@v3.7.0
+        uses: actions/setup-java@v3.8.0
         with:
           java-version: 17.0.4
           distribution: temurin

.mvn/maven.config

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

LICENSE.md

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

README.md

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

apply-error-prone-suggestions.sh

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

documentation-support/pom.xml

@@ -0,0 +1,87 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>tech.picnic.error-prone-support</groupId>
+        <artifactId>error-prone-support</artifactId>
+        <version>0.8.1-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>documentation-support</artifactId>
+
+    <name>Picnic :: Error Prone Support :: Documentation Support</name>
+    <description>Data extraction support for the purpose of documentation generation.</description>
+
+    <dependencies>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_annotation</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_annotations</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_check_api</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>${groupId.error-prone}</groupId>
+            <artifactId>error_prone_test_helpers</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-annotations</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>com.google.auto</groupId>
+            <artifactId>auto-common</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>com.google.auto.service</groupId>
+            <artifactId>auto-service-annotations</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.google.auto.value</groupId>
+            <artifactId>auto-value-annotations</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.jspecify</groupId>
+            <artifactId>jspecify</artifactId>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-params</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+</project>

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

@@ -0,0 +1,103 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.common.base.Verify.verify;
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static java.util.Objects.requireNonNull;
+
+import com.google.auto.common.AnnotationMirrors;
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.BugPattern.SeverityLevel;
+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 javax.lang.model.element.AnnotationValue;
+import tech.picnic.errorprone.documentation.BugPatternExtractor.BugPatternDocumentation;
+
+/**
+ * An {@link Extractor} that describes how to extract data from a {@code @BugPattern} annotation.
+ */
+@Immutable
+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");
+
+    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 boolean canExtract(ClassTree tree) {
+    return ASTHelpers.hasDirectAnnotationWithSimpleName(tree, BugPattern.class.getSimpleName());
+  }
+
+  /**
+   * Returns the fully-qualified class names of suppression annotations specified by the {@link
+   * BugPattern} annotation located on the given tree.
+   *
+   * @implNote This method cannot simply invoke {@link BugPattern#suppressionAnnotations()}, as that
+   *     will yield an "Attempt to access Class objects for TypeMirrors" exception.
+   */
+  private static ImmutableList<String> getSuppressionAnnotations(ClassTree tree) {
+    AnnotationTree annotationTree =
+        ASTHelpers.getAnnotationWithSimpleName(
+            ASTHelpers.getAnnotations(tree), BugPattern.class.getSimpleName());
+    requireNonNull(annotationTree, "BugPattern annotation must be present");
+
+    Attribute.Array types =
+        doCast(
+            AnnotationMirrors.getAnnotationValue(
+                ASTHelpers.getAnnotationMirror(annotationTree), "suppressionAnnotations"),
+            Attribute.Array.class);
+
+    return types.getValue().stream()
+        .map(v -> doCast(v, Attribute.Class.class).classType.toString())
+        .collect(toImmutableList());
+  }
+
+  @SuppressWarnings("unchecked")
+  private static <T extends AnnotationValue> T doCast(AnnotationValue value, Class<T> target) {
+    verify(target.isInstance(value), "Value '%s' is not of type '%s'", value, target);
+    return (T) value;
+  }
+
+  @AutoValue
+  abstract static class BugPatternDocumentation {
+    abstract String fullyQualifiedName();
+
+    abstract String name();
+
+    abstract ImmutableList<String> altNames();
+
+    abstract String link();
+
+    abstract ImmutableList<String> tags();
+
+    abstract String summary();
+
+    abstract String explanation();
+
+    abstract SeverityLevel severityLevel();
+
+    abstract boolean canDisable();
+
+    abstract ImmutableList<String> suppressionAnnotations();
+  }
+}

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

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

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

@@ -0,0 +1,91 @@
+package tech.picnic.errorprone.documentation;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
+import com.fasterxml.jackson.annotation.PropertyAccessor;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.util.TaskEvent;
+import com.sun.source.util.TaskEvent.Kind;
+import com.sun.source.util.TaskListener;
+import com.sun.tools.javac.api.JavacTrees;
+import com.sun.tools.javac.util.Context;
+import java.io.File;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.net.URI;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import javax.tools.JavaFileObject;
+
+/**
+ * A {@link TaskListener} that identifies and extracts relevant content for documentation generation
+ * and writes it to disk.
+ */
+// XXX: Find a better name for this class; it doesn't generate documentation per se.
+final class DocumentationGeneratorTaskListener implements TaskListener {
+  private static final ObjectMapper OBJECT_MAPPER =
+      new ObjectMapper().setVisibility(PropertyAccessor.FIELD, Visibility.ANY);
+
+  private final Context context;
+  private final Path docsPath;
+
+  DocumentationGeneratorTaskListener(Context context, Path path) {
+    this.context = context;
+    this.docsPath = path;
+  }
+
+  @Override
+  public void started(TaskEvent taskEvent) {
+    if (taskEvent.getKind() == Kind.ANALYZE) {
+      createDocsDirectory();
+    }
+  }
+
+  @Override
+  public void finished(TaskEvent taskEvent) {
+    if (taskEvent.getKind() != Kind.ANALYZE) {
+      return;
+    }
+
+    ClassTree classTree = JavacTrees.instance(context).getTree(taskEvent.getTypeElement());
+    JavaFileObject sourceFile = taskEvent.getSourceFile();
+    if (classTree == null || sourceFile == null) {
+      return;
+    }
+
+    ExtractorType.findMatchingType(classTree)
+        .ifPresent(
+            extractorType ->
+                writeToFile(
+                    extractorType.getIdentifier(),
+                    getSimpleClassName(sourceFile.toUri()),
+                    extractorType.getExtractor().extract(classTree, context)));
+  }
+
+  private void createDocsDirectory() {
+    try {
+      Files.createDirectories(docsPath);
+    } catch (IOException e) {
+      throw new IllegalStateException(
+          String.format("Error while creating directory with path '%s'", docsPath), e);
+    }
+  }
+
+  private <T> void writeToFile(String identifier, String className, T data) {
+    File file = docsPath.resolve(String.format("%s-%s.json", identifier, className)).toFile();
+
+    try (FileWriter fileWriter = new FileWriter(file, UTF_8)) {
+      OBJECT_MAPPER.writeValue(fileWriter, data);
+    } catch (IOException e) {
+      throw new UncheckedIOException(String.format("Cannot write to file '%s'", file.getPath()), e);
+    }
+  }
+
+  private static String getSimpleClassName(URI path) {
+    return Paths.get(path).getFileName().toString().replace(".java", "");
+  }
+}

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

@@ -0,0 +1,33 @@
+package tech.picnic.errorprone.documentation;
+
+import com.google.errorprone.annotations.Immutable;
+import com.sun.source.tree.ClassTree;
+import com.sun.tools.javac.util.Context;
+
+/**
+ * Interface implemented by classes that define how to extract data of some type {@link T} from a
+ * given {@link ClassTree}.
+ *
+ * @param <T> The type of data that is extracted.
+ */
+@Immutable
+interface Extractor<T> {
+  /**
+   * Extracts and returns an instance of {@link T} using the provided arguments.
+   *
+   * @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}.
+   */
+  // XXX: Drop `Context` parameter unless used.
+  T extract(ClassTree tree, Context context);
+
+  /**
+   * Tells whether this {@link Extractor} can extract documentation content from the given {@link
+   * ClassTree}.
+   *
+   * @param tree The {@link ClassTree} of interest.
+   * @return {@code true} iff data extraction is supported.
+   */
+  boolean canExtract(ClassTree tree);
+}

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

@@ -0,0 +1,35 @@
+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;
+  }
+
+  Extractor<?> getExtractor() {
+    return extractor;
+  }
+
+  static Optional<ExtractorType> findMatchingType(ClassTree tree) {
+    return TYPES.stream().filter(type -> type.getExtractor().canExtract(tree)).findFirst();
+  }
+}

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

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

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

@@ -0,0 +1,153 @@
+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.Files;
+import java.nio.file.Path;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+final class BugPatternExtractorTest {
+  @Test
+  void noBugPattern(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "TestCheckerWithoutAnnotation.java",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "public final class TestCheckerWithoutAnnotation extends BugChecker {}");
+
+    assertThat(outputDirectory.toAbsolutePath()).isEmptyDirectory();
+  }
+
+  @Test
+  void minimalBugPattern(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "MinimalBugChecker.java",
+        "package pkg;",
+        "",
+        "import com.google.errorprone.BugPattern;",
+        "import com.google.errorprone.BugPattern.SeverityLevel;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "@BugPattern(summary = \"MinimalBugChecker summary\", severity = SeverityLevel.ERROR)",
+        "public final class MinimalBugChecker extends BugChecker {}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-MinimalBugChecker.json",
+        "bugpattern-documentation-minimal.json");
+  }
+
+  @Test
+  void completeBugPattern(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "CompleteBugChecker.java",
+        "package pkg;",
+        "",
+        "import com.google.errorprone.BugPattern;",
+        "import com.google.errorprone.BugPattern.SeverityLevel;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "import org.junit.jupiter.api.Test;",
+        "",
+        "@BugPattern(",
+        "    name = \"OtherName\",",
+        "    summary = \"CompleteBugChecker summary\",",
+        "    linkType = BugPattern.LinkType.CUSTOM,",
+        "    link = \"https://error-prone.picnic.tech\",",
+        "    explanation = \"Example explanation\",",
+        "    severity = SeverityLevel.SUGGESTION,",
+        "    altNames = \"Check\",",
+        "    tags = BugPattern.StandardTags.SIMPLIFICATION,",
+        "    disableable = false,",
+        "    suppressionAnnotations = {BugPattern.class, Test.class})",
+        "public final class CompleteBugChecker extends BugChecker {}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-CompleteBugChecker.json",
+        "bugpattern-documentation-complete.json");
+  }
+
+  @Test
+  void undocumentedSuppressionBugPattern(@TempDir Path outputDirectory) throws IOException {
+    Compilation.compileWithDocumentationGenerator(
+        outputDirectory,
+        "UndocumentedSuppressionBugPattern.java",
+        "package pkg;",
+        "",
+        "import com.google.errorprone.BugPattern;",
+        "import com.google.errorprone.BugPattern.SeverityLevel;",
+        "import com.google.errorprone.bugpatterns.BugChecker;",
+        "",
+        "@BugPattern(",
+        "    summary = \"UndocumentedSuppressionBugPattern summary\",",
+        "    severity = SeverityLevel.WARNING,",
+        "    documentSuppression = false)",
+        "public final class UndocumentedSuppressionBugPattern extends BugChecker {}");
+
+    verifyFileMatchesResource(
+        outputDirectory,
+        "bugpattern-UndocumentedSuppressionBugPattern.json",
+        "bugpattern-documentation-undocumented-suppression.json");
+  }
+
+  @Test
+  void bugPatternAnnotationIsAbsent() {
+    CompilationTestHelper.newInstance(TestChecker.class, getClass())
+        .addSourceLines(
+            "TestChecker.java",
+            "import com.google.errorprone.bugpatterns.BugChecker;",
+            "",
+            "// BUG: Diagnostic contains: Can extract: false",
+            "public final class TestChecker extends BugChecker {}")
+        .doTest();
+  }
+
+  private static void verifyFileMatchesResource(
+      Path outputDirectory, String fileName, String resourceName) throws IOException {
+    assertThat(Files.readString(outputDirectory.resolve(fileName)))
+        .isEqualToIgnoringWhitespace(getResource(resourceName));
+  }
+
+  // XXX: Once we support only JDK 15+, drop this method in favour of including the resources as
+  // text blocks in this class. (This also requires renaming the `verifyFileMatchesResource`
+  // method.)
+  private static String getResource(String resourceName) throws IOException {
+    return Resources.toString(
+        Resources.getResource(BugPatternExtractorTest.class, resourceName), UTF_8);
+  }
+
+  /** A {@link BugChecker} that validates the {@link BugPatternExtractor}. */
+  @BugPattern(summary = "Validates `BugPatternExtractor` extraction", severity = ERROR)
+  public static final class TestChecker extends BugChecker implements ClassTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchClass(ClassTree tree, VisitorState state) {
+      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/Compilation.java

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

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

@@ -0,0 +1,77 @@
+package tech.picnic.errorprone.documentation;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+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.common.collect.ImmutableSet;
+import com.google.common.collect.Sets;
+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 org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.DisabledOnOs;
+import org.junit.jupiter.api.condition.EnabledOnOs;
+import org.junit.jupiter.api.io.TempDir;
+
+final class DocumentationGeneratorTaskListenerTest {
+  @EnabledOnOs(WINDOWS)
+  @Test
+  void readOnlyFileSystemWindows(@TempDir Path outputDirectory) throws IOException {
+    AclFileAttributeView view =
+        Files.getFileAttributeView(outputDirectory, AclFileAttributeView.class);
+    view.setAcl(
+        view.getAcl().stream()
+            .map(
+                entry ->
+                    AclEntry.newBuilder(entry)
+                        .setPermissions(
+                            Sets.difference(entry.permissions(), ImmutableSet.of(ADD_SUBDIRECTORY)))
+                        .build())
+            .collect(toImmutableList()));
+
+    readOnlyFileSystemFailsToWrite(outputDirectory.resolve("nonexistent"));
+  }
+
+  @DisabledOnOs(WINDOWS)
+  @Test
+  void readOnlyFileSystemNonWindows(@TempDir Path outputDirectory) {
+    assertThat(outputDirectory.toFile().setWritable(false))
+        .describedAs("Failed to make test directory unwritable")
+        .isTrue();
+
+    readOnlyFileSystemFailsToWrite(outputDirectory.resolve("nonexistent"));
+  }
+
+  private static void readOnlyFileSystemFailsToWrite(Path outputDirectory) {
+    assertThatThrownBy(
+            () ->
+                Compilation.compileWithDocumentationGenerator(
+                    outputDirectory, "A.java", "class A {}"))
+        .hasRootCauseInstanceOf(FileSystemException.class)
+        .hasCauseInstanceOf(IllegalStateException.class)
+        .hasMessageEndingWith("Error while creating directory with path '%s'", outputDirectory);
+  }
+
+  @Test
+  void noClassNoOutput(@TempDir Path outputDirectory) {
+    Compilation.compileWithDocumentationGenerator(outputDirectory, "A.java", "package pkg;");
+
+    assertThat(outputDirectory).isEmptyDirectory();
+  }
+
+  @Test
+  void excessArguments(@TempDir Path outputDirectory) {
+    assertThatThrownBy(
+            () ->
+                Compilation.compileWithDocumentationGenerator(
+                    outputDirectory.toAbsolutePath() + " extra-arg", "A.java", "package pkg;"))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessage("Precisely one path must be provided");
+  }
+}

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

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

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

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

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

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

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

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

error-prone-contrib/pom.xml

@@ -5,7 +5,7 @@
     <parent>
         <groupId>tech.picnic.error-prone-support</groupId>
         <artifactId>error-prone-support</artifactId>
-        <version>0.5.1-SNAPSHOT</version>
+        <version>0.8.1-SNAPSHOT</version>
     </parent>
 
     <artifactId>error-prone-contrib</artifactId>
@@ -39,6 +39,14 @@
             <artifactId>error_prone_test_helpers</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>documentation-support</artifactId>
+            <!-- This dependency is declared only as a hint to Maven that
+            compilation depends on it; see the `maven-compiler-plugin`'s
+            `annotationProcessorPaths` configuration below. -->
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>${project.groupId}</groupId>
             <artifactId>refaster-support</artifactId>
@@ -138,6 +146,10 @@
             <artifactId>value-annotations</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.jooq</groupId>
+            <artifactId>jooq</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.jspecify</groupId>
             <artifactId>jspecify</artifactId>
@@ -146,7 +158,7 @@
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-api</artifactId>
-            <scope>test</scope>
+            <scope>provided</scope>
         </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>
@@ -213,6 +225,11 @@
                     <artifactId>maven-compiler-plugin</artifactId>
                     <configuration>
                         <annotationProcessorPaths combine.children="append">
+                            <path>
+                                <groupId>${project.groupId}</groupId>
+                                <artifactId>documentation-support</artifactId>
+                                <version>${project.version}</version>
+                            </path>
                             <path>
                                 <groupId>${project.groupId}</groupId>
                                 <artifactId>refaster-compiler</artifactId>
@@ -226,6 +243,7 @@
                         </annotationProcessorPaths>
                         <compilerArgs combine.children="append">
                             <arg>-Xplugin:RefasterRuleCompiler</arg>
+                            <arg>-Xplugin:DocumentationGenerator -XoutputDirectory=${project.build.directory}/docs</arg>
                         </compilerArgs>
                     </configuration>
                 </plugin>

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

@@ -49,6 +49,7 @@ import java.util.Locale;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.stream.Stream;
+import tech.picnic.errorprone.bugpatterns.util.Flags;
 import tech.picnic.errorprone.bugpatterns.util.MethodMatcherFactory;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
@@ -63,9 +64,8 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 public final class RedundantStringConversion extends BugChecker
     implements BinaryTreeMatcher, CompoundAssignmentTreeMatcher, MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
-  private static final String FLAG_PREFIX = "RedundantStringConversion:";
   private static final String EXTRA_STRING_CONVERSION_METHODS_FLAG =
-      FLAG_PREFIX + "ExtraConversionMethods";
+      "RedundantStringConversion:ExtraConversionMethods";
 
   @SuppressWarnings("UnnecessaryLambda")
   private static final Matcher<ExpressionTree> ANY_EXPR = (t, s) -> true;
@@ -374,10 +374,9 @@ public final class RedundantStringConversion extends BugChecker
       ErrorProneFlags flags) {
     // XXX: ErrorProneFlags#getList splits by comma, but method signatures may also contain commas.
     // For this class methods accepting more than one argument are not valid, but still: not nice.
-    return flags
-        .getList(EXTRA_STRING_CONVERSION_METHODS_FLAG)
-        .map(new MethodMatcherFactory()::create)
-        .map(m -> anyOf(WELL_KNOWN_STRING_CONVERSION_METHODS, m))
-        .orElse(WELL_KNOWN_STRING_CONVERSION_METHODS);
+    return anyOf(
+        WELL_KNOWN_STRING_CONVERSION_METHODS,
+        new MethodMatcherFactory()
+            .create(Flags.getList(flags, EXTRA_STRING_CONVERSION_METHODS_FLAG)));
   }
 }

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

@@ -18,7 +18,7 @@ import com.sun.source.tree.AnnotationTree;
 import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.MethodTree;
 import com.sun.source.tree.NewArrayTree;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A collection of JUnit-specific helper methods and {@link Matcher}s.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

@@ -0,0 +1,521 @@
+package tech.picnic.errorprone.refasterrules;
+
+import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatCode;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.assertj.core.api.Assertions.fail;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertThrowsExactly;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.annotations.DoNotCall;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import java.util.function.Supplier;
+import org.assertj.core.api.ThrowableAssert.ThrowingCallable;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.function.Executable;
+import org.junit.jupiter.api.function.ThrowingSupplier;
+import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+
+/**
+ * Refaster rules to replace JUnit assertions with AssertJ equivalents.
+ *
+ * <p>Note that, while both libraries throw an {@link AssertionError} in case of an assertion
+ * failure, the exact subtype used generally differs.
+ */
+// XXX: Not all `org.assertj.core.api.Assertions` methods have an associated Refaster rule yet;
+// expand this class.
+// XXX: Introduce a `@Matcher` on `Executable` and `ThrowingSupplier` expressions, such that they
+// are only matched if they are also compatible with the `ThrowingCallable` functional interface.
+// When implementing such a matcher, note that expressions with a non-void return type such as
+// `() -> toString()` match both `ThrowingSupplier` and `ThrowingCallable`, but `() -> "constant"`
+// is only compatible with the former.
+@OnlineDocumentation
+final class JUnitToAssertJRules {
+  private JUnitToAssertJRules() {}
+
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(
+        Assertions.class,
+        assertDoesNotThrow(() -> null),
+        assertInstanceOf(null, null),
+        assertThrows(null, null),
+        assertThrowsExactly(null, null),
+        (Runnable) () -> assertFalse(true),
+        (Runnable) () -> assertNotNull(null),
+        (Runnable) () -> assertNotSame(null, null),
+        (Runnable) () -> assertNull(null),
+        (Runnable) () -> assertSame(null, null),
+        (Runnable) () -> assertTrue(true));
+  }
+
+  static final class ThrowNewAssertionError {
+    @BeforeTemplate
+    void before() {
+      Assertions.fail();
+    }
+
+    @AfterTemplate
+    @DoNotCall
+    void after() {
+      throw new AssertionError();
+    }
+  }
+
+  static final class FailWithMessage<T> {
+    @BeforeTemplate
+    T before(String message) {
+      return Assertions.fail(message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    T after(String message) {
+      return fail(message);
+    }
+  }
+
+  static final class FailWithMessageAndThrowable<T> {
+    @BeforeTemplate
+    T before(String message, Throwable throwable) {
+      return Assertions.fail(message, throwable);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    T after(String message, Throwable throwable) {
+      return fail(message, throwable);
+    }
+  }
+
+  static final class FailWithThrowable {
+    @BeforeTemplate
+    void before(Throwable throwable) {
+      Assertions.fail(throwable);
+    }
+
+    @AfterTemplate
+    @DoNotCall
+    void after(Throwable throwable) {
+      throw new AssertionError(throwable);
+    }
+  }
+
+  static final class AssertThatIsTrue {
+    @BeforeTemplate
+    void before(boolean actual) {
+      assertTrue(actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual) {
+      assertThat(actual).isTrue();
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsTrue {
+    @BeforeTemplate
+    void before(boolean actual, String message) {
+      assertTrue(actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual, String message) {
+      assertThat(actual).withFailMessage(message).isTrue();
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsTrue {
+    @BeforeTemplate
+    void before(boolean actual, Supplier<String> supplier) {
+      assertTrue(actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isTrue();
+    }
+  }
+
+  static final class AssertThatIsFalse {
+    @BeforeTemplate
+    void before(boolean actual) {
+      assertFalse(actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual) {
+      assertThat(actual).isFalse();
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsFalse {
+    @BeforeTemplate
+    void before(boolean actual, String message) {
+      assertFalse(actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual, String message) {
+      assertThat(actual).withFailMessage(message).isFalse();
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsFalse {
+    @BeforeTemplate
+    void before(boolean actual, Supplier<String> supplier) {
+      assertFalse(actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean actual, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isFalse();
+    }
+  }
+
+  static final class AssertThatIsNull {
+    @BeforeTemplate
+    void before(Object actual) {
+      assertNull(actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual) {
+      assertThat(actual).isNull();
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsNull {
+    @BeforeTemplate
+    void before(Object actual, String message) {
+      assertNull(actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, String message) {
+      assertThat(actual).withFailMessage(message).isNull();
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsNull {
+    @BeforeTemplate
+    void before(Object actual, Supplier<String> supplier) {
+      assertNull(actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isNull();
+    }
+  }
+
+  static final class AssertThatIsNotNull {
+    @BeforeTemplate
+    void before(Object actual) {
+      assertNotNull(actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual) {
+      assertThat(actual).isNotNull();
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsNotNull {
+    @BeforeTemplate
+    void before(Object actual, String message) {
+      assertNotNull(actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, String message) {
+      assertThat(actual).withFailMessage(message).isNotNull();
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsNotNull {
+    @BeforeTemplate
+    void before(Object actual, Supplier<String> supplier) {
+      assertNotNull(actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isNotNull();
+    }
+  }
+
+  static final class AssertThatIsSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected) {
+      assertSame(expected, actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected) {
+      assertThat(actual).isSameAs(expected);
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected, String message) {
+      assertSame(expected, actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected, String message) {
+      assertThat(actual).withFailMessage(message).isSameAs(expected);
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected, Supplier<String> supplier) {
+      assertSame(expected, actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isSameAs(expected);
+    }
+  }
+
+  static final class AssertThatIsNotSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected) {
+      assertNotSame(expected, actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected) {
+      assertThat(actual).isNotSameAs(expected);
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsNotSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected, String message) {
+      assertNotSame(expected, actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected, String message) {
+      assertThat(actual).withFailMessage(message).isNotSameAs(expected);
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsNotSameAs {
+    @BeforeTemplate
+    void before(Object actual, Object expected, Supplier<String> supplier) {
+      assertNotSame(expected, actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Object expected, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isNotSameAs(expected);
+    }
+  }
+
+  static final class AssertThatThrownByIsExactlyInstanceOf<T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz) {
+      assertThrowsExactly(clazz, throwingCallable);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz) {
+      assertThatThrownBy(throwingCallable).isExactlyInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatThrownByWithFailMessageStringIsExactlyInstanceOf<
+      T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz, String message) {
+      assertThrowsExactly(clazz, throwingCallable, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz, String message) {
+      assertThatThrownBy(throwingCallable).withFailMessage(message).isExactlyInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatThrownByWithFailMessageSupplierIsExactlyInstanceOf<
+      T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz, Supplier<String> supplier) {
+      assertThrowsExactly(clazz, throwingCallable, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz, Supplier<String> supplier) {
+      assertThatThrownBy(throwingCallable).withFailMessage(supplier).isExactlyInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatThrownByIsInstanceOf<T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz) {
+      assertThrows(clazz, throwingCallable);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz) {
+      assertThatThrownBy(throwingCallable).isInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatThrownByWithFailMessageStringIsInstanceOf<T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz, String message) {
+      assertThrows(clazz, throwingCallable, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz, String message) {
+      assertThatThrownBy(throwingCallable).withFailMessage(message).isInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatThrownByWithFailMessageSupplierIsInstanceOf<T extends Throwable> {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Class<T> clazz, Supplier<String> supplier) {
+      assertThrows(clazz, throwingCallable, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Class<T> clazz, Supplier<String> supplier) {
+      assertThatThrownBy(throwingCallable).withFailMessage(supplier).isInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatCodeDoesNotThrowAnyException {
+    @BeforeTemplate
+    void before(Executable throwingCallable) {
+      assertDoesNotThrow(throwingCallable);
+    }
+
+    @BeforeTemplate
+    void before(ThrowingSupplier<?> throwingCallable) {
+      assertDoesNotThrow(throwingCallable);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable) {
+      assertThatCode(throwingCallable).doesNotThrowAnyException();
+    }
+  }
+
+  static final class AssertThatCodeWithFailMessageStringDoesNotThrowAnyException {
+    @BeforeTemplate
+    void before(Executable throwingCallable, String message) {
+      assertDoesNotThrow(throwingCallable, message);
+    }
+
+    @BeforeTemplate
+    void before(ThrowingSupplier<?> throwingCallable, String message) {
+      assertDoesNotThrow(throwingCallable, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, String message) {
+      assertThatCode(throwingCallable).withFailMessage(message).doesNotThrowAnyException();
+    }
+  }
+
+  static final class AssertThatCodeWithFailMessageSupplierDoesNotThrowAnyException {
+    @BeforeTemplate
+    void before(Executable throwingCallable, Supplier<String> supplier) {
+      assertDoesNotThrow(throwingCallable, supplier);
+    }
+
+    @BeforeTemplate
+    void before(ThrowingSupplier<?> throwingCallable, Supplier<String> supplier) {
+      assertDoesNotThrow(throwingCallable, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(ThrowingCallable throwingCallable, Supplier<String> supplier) {
+      assertThatCode(throwingCallable).withFailMessage(supplier).doesNotThrowAnyException();
+    }
+  }
+
+  static final class AssertThatIsInstanceOf<T> {
+    @BeforeTemplate
+    void before(Object actual, Class<T> clazz) {
+      assertInstanceOf(clazz, actual);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Class<T> clazz) {
+      assertThat(actual).isInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatWithFailMessageStringIsInstanceOf<T> {
+    @BeforeTemplate
+    void before(Object actual, Class<T> clazz, String message) {
+      assertInstanceOf(clazz, actual, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Class<T> clazz, String message) {
+      assertThat(actual).withFailMessage(message).isInstanceOf(clazz);
+    }
+  }
+
+  static final class AssertThatWithFailMessageSupplierIsInstanceOf<T> {
+    @BeforeTemplate
+    void before(Object actual, Class<T> clazz, Supplier<String> supplier) {
+      assertInstanceOf(clazz, actual, supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Object actual, Class<T> clazz, Supplier<String> supplier) {
+      assertThat(actual).withFailMessage(supplier).isInstanceOf(clazz);
+    }
+  }
+}

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

@@ -0,0 +1,29 @@
+package tech.picnic.errorprone.refasterrules;
+
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import java.util.stream.Stream;
+import org.jooq.Record;
+import org.jooq.ResultQuery;
+import tech.picnic.errorprone.refaster.annotation.Description;
+import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+
+@OnlineDocumentation
+final class JooqRules {
+  private JooqRules() {}
+
+  /** Prefer eagerly fetching data over (lazy) streaming to avoid potentially leaking resources. */
+  @Description(
+      "Prefer eagerly fetching data over (lazy) streaming to avoid potentially leaking resources.")
+  static final class ResultQueryFetchStream {
+    @BeforeTemplate
+    Stream<?> before(ResultQuery<? extends Record> resultQuery) {
+      return resultQuery.stream();
+    }
+
+    @AfterTemplate
+    Stream<?> after(ResultQuery<? extends Record> resultQuery) {
+      return resultQuery.fetch().stream();
+    }
+  }
+}

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

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

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

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

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

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

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

@@ -2,14 +2,18 @@ package tech.picnic.errorprone.refasterrules;
 
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 import static java.util.Objects.requireNonNullElse;
+import static java.util.Objects.requireNonNullElseGet;
 
 import com.google.common.base.MoreObjects;
+import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Predicate;
-import org.jspecify.nullness.Nullable;
+import java.util.function.Supplier;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to expressions dealing with (possibly) null values. */
@@ -43,13 +47,18 @@ final class NullRules {
     }
   }
 
-  /** Prefer {@link Objects#requireNonNullElse(Object, Object)} over the Guava alternative. */
-  // XXX: This rule is not valid in case `second` is `@Nullable`: in that case the Guava variant
-  // will return `null`, while the JDK variant will throw an NPE.
+  /**
+   * Prefer {@link Objects#requireNonNullElse(Object, Object)} over non-JDK or more contrived
+   * alternatives.
+   */
+  // XXX: This rule is not valid in case `second` is `@Nullable`: in that case the Guava and
+  // `Optional` variants will return `null`, where the `requireNonNullElse` alternative will throw
+  // an NPE.
   static final class RequireNonNullElse<T> {
     @BeforeTemplate
     T before(T first, T second) {
-      return MoreObjects.firstNonNull(first, second);
+      return Refaster.anyOf(
+          MoreObjects.firstNonNull(first, second), Optional.ofNullable(first).orElse(second));
     }
 
     @AfterTemplate
@@ -59,6 +68,26 @@ final class NullRules {
     }
   }
 
+  /**
+   * Prefer {@link Objects#requireNonNullElseGet(Object, Supplier)} over more contrived
+   * alternatives.
+   */
+  // XXX: This rule is not valid in case `supplier` yields `@Nullable` values: in that case the
+  // `Optional` variant will return `null`, where the `requireNonNullElseGet` alternative will throw
+  // an NPE.
+  static final class RequireNonNullElseGet<T, S extends T> {
+    @BeforeTemplate
+    T before(T object, Supplier<S> supplier) {
+      return Optional.ofNullable(object).orElseGet(supplier);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    T after(T object, Supplier<S> supplier) {
+      return requireNonNullElseGet(object, supplier);
+    }
+  }
+
   /** Prefer {@link Objects#isNull(Object)} over the equivalent lambda function. */
   static final class IsNullFunction<T> {
     @BeforeTemplate

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

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

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

@@ -17,6 +17,7 @@ import com.google.errorprone.refaster.annotation.NotMatches;
 import com.google.errorprone.refaster.annotation.Placeholder;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.time.Duration;
+import java.util.Comparator;
 import java.util.HashMap;
 import java.util.Optional;
 import java.util.concurrent.Callable;
@@ -26,6 +27,7 @@ import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
+import org.jspecify.annotations.Nullable;
 import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -59,6 +61,45 @@ final class ReactorRules {
     }
   }
 
+  /** Prefer {@link Mono#empty()} over more contrived alternatives. */
+  static final class MonoEmpty<T> {
+    @BeforeTemplate
+    Mono<T> before() {
+      return Refaster.anyOf(Mono.justOrEmpty(null), Mono.justOrEmpty(Optional.empty()));
+    }
+
+    @AfterTemplate
+    Mono<T> after() {
+      return Mono.empty();
+    }
+  }
+
+  /** Prefer {@link Mono#just(Object)} over more contrived alternatives. */
+  static final class MonoJust<T> {
+    @BeforeTemplate
+    Mono<T> before(T value) {
+      return Mono.justOrEmpty(Optional.of(value));
+    }
+
+    @AfterTemplate
+    Mono<T> after(T value) {
+      return Mono.just(value);
+    }
+  }
+
+  /** Prefer {@link Mono#justOrEmpty(Object)} over more contrived alternatives. */
+  static final class MonoJustOrEmpty<@Nullable T> {
+    @BeforeTemplate
+    Mono<T> before(T value) {
+      return Mono.justOrEmpty(Optional.ofNullable(value));
+    }
+
+    @AfterTemplate
+    Mono<T> after(T value) {
+      return Mono.justOrEmpty(value);
+    }
+  }
+
   /** Prefer {@link Mono#justOrEmpty(Optional)} over more verbose alternatives. */
   // XXX: If `optional` is a constant and effectively-final expression then the `Mono.defer` can be
   // dropped. Should look into Refaster support for identifying this.
@@ -78,6 +119,40 @@ final class ReactorRules {
     }
   }
 
+  /**
+   * Try to avoid expressions of type {@code Optional<Mono<T>>}, but if you must map an {@link
+   * Optional} to this type, prefer using {@link Mono#just(Object)}.
+   */
+  static final class OptionalMapMonoJust<T> {
+    @BeforeTemplate
+    Optional<Mono<T>> before(Optional<T> optional) {
+      return optional.map(Mono::justOrEmpty);
+    }
+
+    @AfterTemplate
+    Optional<Mono<T>> after(Optional<T> optional) {
+      return optional.map(Mono::just);
+    }
+  }
+
+  /**
+   * Prefer a {@link Mono#justOrEmpty(Optional)} and {@link Mono#switchIfEmpty(Mono)} chain over
+   * more contrived alternatives.
+   *
+   * <p>In particular, avoid mixing of the {@link Optional} and {@link Mono} APIs.
+   */
+  static final class MonoFromOptionalSwitchIfEmpty<T> {
+    @BeforeTemplate
+    Mono<T> before(Optional<T> optional, Mono<T> mono) {
+      return optional.map(Mono::just).orElse(mono);
+    }
+
+    @AfterTemplate
+    Mono<T> after(Optional<T> optional, Mono<T> mono) {
+      return Mono.justOrEmpty(optional).switchIfEmpty(mono);
+    }
+  }
+
   /**
    * Prefer {@link Mono#zip(Mono, Mono)} over a chained {@link Mono#zipWith(Mono)}, as the former
    * better conveys that the {@link Mono}s may be subscribed to concurrently, and generalizes to
@@ -290,11 +365,17 @@ final class ReactorRules {
     }
   }
 
-  /** Don't unnecessarily pass an empty publisher to {@link Mono#switchIfEmpty(Mono)}. */
-  static final class MonoSwitchIfEmptyOfEmptyPublisher<T> {
+  /** Don't unnecessarily transform a {@link Mono} to an equivalent instance. */
+  static final class MonoIdentity<T> {
     @BeforeTemplate
     Mono<T> before(Mono<T> mono) {
-      return mono.switchIfEmpty(Mono.empty());
+      return Refaster.anyOf(
+          mono.switchIfEmpty(Mono.empty()), mono.flux().next(), mono.flux().singleOrEmpty());
+    }
+
+    @BeforeTemplate
+    Mono<@Nullable Void> before2(Mono<@Nullable Void> mono) {
+      return mono.then();
     }
 
     @AfterTemplate
@@ -393,6 +474,11 @@ final class ReactorRules {
    * Flux}.
    */
   abstract static class MonoFlatMapToFlux<T, S> {
+    // XXX: It would be more expressive if this `@Placeholder` were replaced with a `Function<?
+    // super T, ? extends Mono<? extends S>>` parameter, so that compatible non-lambda expression
+    // arguments to `flatMapMany` are also matched. However, the type inferred for lambda and method
+    // reference expressions passed to `flatMapMany` appears to always be `Function<T, Publisher<?
+    // extends S>>`, which doesn't match. Find a solution.
     @Placeholder(allowsIdentity = true)
     abstract Mono<S> transformation(@MayOptionallyUse T value);
 
@@ -600,6 +686,19 @@ final class ReactorRules {
     }
   }
 
+  /** Prefer direct invocation of {@link Mono#then()}} over more contrived alternatives. */
+  static final class MonoThen<T> {
+    @BeforeTemplate
+    Mono<@Nullable Void> before(Mono<T> mono) {
+      return mono.flux().then();
+    }
+
+    @AfterTemplate
+    Mono<@Nullable Void> after(Mono<T> mono) {
+      return mono.then();
+    }
+  }
+
   /**
    * Prefer a collection using {@link MoreCollectors#toOptional()} over more contrived alternatives.
    */
@@ -988,6 +1087,38 @@ final class ReactorRules {
     }
   }
 
+  /**
+   * Apply {@link Flux#filter(Predicate)} before {@link Flux#sort()} to reduce the number of
+   * elements to sort.
+   */
+  static final class FluxFilterSort<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<? super T> predicate) {
+      return flux.sort().filter(predicate);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<? super T> predicate) {
+      return flux.filter(predicate).sort();
+    }
+  }
+
+  /**
+   * Apply {@link Flux#filter(Predicate)} before {@link Flux#sort(Comparator)} to reduce the number
+   * of elements to sort.
+   */
+  static final class FluxFilterSortWithComparator<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return flux.sort(comparator).filter(predicate);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return flux.filter(predicate).sort(comparator);
+    }
+  }
+
   /** Prefer {@link reactor.util.context.Context#empty()}} over more verbose alternatives. */
   // XXX: Consider introducing an `IsEmpty` matcher that identifies a wide range of guaranteed-empty
   // `Collection` and `Map` expressions.

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

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

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

@@ -77,6 +77,9 @@ final class StreamRules {
    * Prefer {@link Arrays#stream(Object[])} over {@link Stream#of(Object[])}, as the former is
    * clearer.
    */
+  // XXX: Introduce a `Matcher` that identifies `Refaster.asVarargs(...)` invocations and annotate
+  // the `array` parameter as `@NotMatches(IsRefasterAsVarargs.class)`. Then elsewhere
+  // `@SuppressWarnings("StreamOfArray")` annotations can be dropped.
   static final class StreamOfArray<T> {
     @BeforeTemplate
     Stream<T> before(T[] array) {
@@ -164,6 +167,40 @@ final class StreamRules {
     }
   }
 
+  /**
+   * Apply {@link Stream#filter(Predicate)} before {@link Stream#sorted()} to reduce the number of
+   * elements to sort.
+   */
+  static final class StreamFilterSorted<T> {
+    @BeforeTemplate
+    Stream<T> before(Stream<T> stream, Predicate<? super T> predicate) {
+      return stream.sorted().filter(predicate);
+    }
+
+    @AfterTemplate
+    Stream<T> after(Stream<T> stream, Predicate<? super T> predicate) {
+      return stream.filter(predicate).sorted();
+    }
+  }
+
+  /**
+   * Apply {@link Stream#filter(Predicate)} before {@link Stream#sorted(Comparator)} to reduce the
+   * number of elements to sort.
+   */
+  static final class StreamFilterSortedWithComparator<T> {
+    @BeforeTemplate
+    Stream<T> before(
+        Stream<T> stream, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return stream.sorted(comparator).filter(predicate);
+    }
+
+    @AfterTemplate
+    Stream<T> after(
+        Stream<T> stream, Predicate<? super T> predicate, Comparator<? super T> comparator) {
+      return stream.filter(predicate).sorted(comparator);
+    }
+  }
+
   /**
    * Where possible, clarify that a mapping operation will be applied only to a single stream
    * element.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

@@ -1,7 +1,5 @@
 package tech.picnic.errorprone.bugpatterns;
 
-import static com.google.errorprone.BugCheckerRefactoringTestHelper.newInstance;
-
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
@@ -9,14 +7,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class FluxFlatMapUsageTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(FluxFlatMapUsage.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      newInstance(FluxFlatMapUsage.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(FluxFlatMapUsage.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.function.BiFunction;",
@@ -73,7 +66,7 @@ final class FluxFlatMapUsageTest {
 
   @Test
   void replacementFirstSuggestedFix() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(FluxFlatMapUsage.class, getClass())
         .setFixChooser(FixChoosers.FIRST)
         .addInputLines(
             "A.java",
@@ -108,7 +101,7 @@ final class FluxFlatMapUsageTest {
 
   @Test
   void replacementSecondSuggestedFix() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(FluxFlatMapUsage.class, getClass())
         .setFixChooser(FixChoosers.SECOND)
         .addInputLines(
             "A.java",

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

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

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

@@ -7,16 +7,14 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class IdentityConversionTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(IdentityConversion.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(IdentityConversion.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(IdentityConversion.class, getClass())
         .addSourceLines(
-            "Foo.java",
+            "A.java",
+            "import static com.google.errorprone.matchers.Matchers.instanceMethod;",
+            "import static com.google.errorprone.matchers.Matchers.staticMethod;",
+            "",
             "import com.google.common.collect.ImmutableBiMap;",
             "import com.google.common.collect.ImmutableList;",
             "import com.google.common.collect.ImmutableListMultimap;",
@@ -28,12 +26,14 @@ final class IdentityConversionTest {
             "import com.google.common.collect.ImmutableSet;",
             "import com.google.common.collect.ImmutableSetMultimap;",
             "import com.google.common.collect.ImmutableTable;",
+            "import com.google.errorprone.matchers.Matcher;",
+            "import com.google.errorprone.matchers.Matchers;",
             "import reactor.adapter.rxjava.RxJava2Adapter;",
             "import reactor.core.publisher.Flux;",
             "import reactor.core.publisher.Mono;",
             "",
-            "public final class Foo {",
-            "  public void foo() {",
+            "public final class A {",
+            "  public void m() {",
             "    // BUG: Diagnostic contains:",
             "    Boolean b1 = Boolean.valueOf(Boolean.FALSE);",
             "    // BUG: Diagnostic contains:",
@@ -113,6 +113,13 @@ final class IdentityConversionTest {
             "    // BUG: Diagnostic contains:",
             "    short s4 = Short.valueOf(Short.MIN_VALUE);",
             "",
+            "    // BUG: Diagnostic contains:",
+            "    String boolStr = Boolean.valueOf(Boolean.FALSE).toString();",
+            "    int boolHash = Boolean.valueOf(false).hashCode();",
+            "    // BUG: Diagnostic contains:",
+            "    int byteHash = Byte.valueOf((Byte) Byte.MIN_VALUE).hashCode();",
+            "    String byteStr = Byte.valueOf(Byte.MIN_VALUE).toString();",
+            "",
             "    String str1 = String.valueOf(0);",
             "    // BUG: Diagnostic contains:",
             "    String str2 = String.valueOf(\"1\");",
@@ -143,7 +150,15 @@ final class IdentityConversionTest {
             "    ImmutableTable<Object, Object, Object> o11 = ImmutableTable.copyOf(ImmutableTable.of());",
             "",
             "    // BUG: Diagnostic contains:",
+            "    Matcher allOf1 = Matchers.allOf(instanceMethod());",
+            "    Matcher allOf2 = Matchers.allOf(instanceMethod(), staticMethod());",
+            "    // BUG: Diagnostic contains:",
+            "    Matcher anyOf1 = Matchers.anyOf(staticMethod());",
+            "    Matcher anyOf2 = Matchers.anyOf(instanceMethod(), staticMethod());",
+            "",
+            "    // BUG: Diagnostic contains:",
             "    Flux<Integer> flux1 = Flux.just(1).flatMap(e -> RxJava2Adapter.fluxToFlowable(Flux.just(2)));",
+            "",
             "    // BUG: Diagnostic contains:",
             "    Flux<Integer> flux2 = Flux.concat(Flux.just(1));",
             "    // BUG: Diagnostic contains:",
@@ -154,9 +169,9 @@ final class IdentityConversionTest {
             "    Flux<Integer> flux5 = Flux.merge(Flux.just(1));",
             "",
             "    // BUG: Diagnostic contains:",
-            "    Mono<Integer> m1 = Mono.from(Mono.just(1));",
+            "    Mono<Integer> mono1 = Mono.from(Mono.just(1));",
             "    // BUG: Diagnostic contains:",
-            "    Mono<Integer> m2 = Mono.fromDirect(Mono.just(1));",
+            "    Mono<Integer> mono2 = Mono.fromDirect(Mono.just(1));",
             "  }",
             "}")
         .doTest();
@@ -164,15 +179,18 @@ final class IdentityConversionTest {
 
   @Test
   void replacementFirstSuggestedFix() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(IdentityConversion.class, getClass())
         .setFixChooser(FixChoosers.FIRST)
         .addInputLines(
-            "Foo.java",
+            "A.java",
+            "import static com.google.errorprone.matchers.Matchers.staticMethod;",
             "import static org.mockito.Mockito.when;",
             "",
             "import com.google.common.collect.ImmutableCollection;",
             "import com.google.common.collect.ImmutableList;",
             "import com.google.common.collect.ImmutableSet;",
+            "import com.google.errorprone.matchers.Matcher;",
+            "import com.google.errorprone.matchers.Matchers;",
             "import java.util.ArrayList;",
             "import java.util.Collection;",
             "import org.reactivestreams.Publisher;",
@@ -180,8 +198,8 @@ final class IdentityConversionTest {
             "import reactor.core.publisher.Flux;",
             "import reactor.core.publisher.Mono;",
             "",
-            "public final class Foo {",
-            "  public void foo() {",
+            "public final class A {",
+            "  public void m() {",
             "    ImmutableSet<Object> set1 = ImmutableSet.copyOf(ImmutableSet.of());",
             "    ImmutableSet<Object> set2 = ImmutableSet.copyOf(ImmutableList.of());",
             "",
@@ -206,18 +224,23 @@ final class IdentityConversionTest {
             "    Object o1 = ImmutableSet.copyOf(ImmutableList.of());",
             "    Object o2 = ImmutableSet.copyOf(ImmutableSet.of());",
             "",
+            "    Matcher matcher = Matchers.allOf(staticMethod());",
+            "",
             "    when(\"foo\".contains(\"f\")).thenAnswer(inv -> ImmutableSet.copyOf(ImmutableList.of(1)));",
             "  }",
             "",
             "  void bar(Publisher<Integer> publisher) {}",
             "}")
         .addOutputLines(
-            "Foo.java",
+            "A.java",
+            "import static com.google.errorprone.matchers.Matchers.staticMethod;",
             "import static org.mockito.Mockito.when;",
             "",
             "import com.google.common.collect.ImmutableCollection;",
             "import com.google.common.collect.ImmutableList;",
             "import com.google.common.collect.ImmutableSet;",
+            "import com.google.errorprone.matchers.Matcher;",
+            "import com.google.errorprone.matchers.Matchers;",
             "import java.util.ArrayList;",
             "import java.util.Collection;",
             "import org.reactivestreams.Publisher;",
@@ -225,8 +248,8 @@ final class IdentityConversionTest {
             "import reactor.core.publisher.Flux;",
             "import reactor.core.publisher.Mono;",
             "",
-            "public final class Foo {",
-            "  public void foo() {",
+            "public final class A {",
+            "  public void m() {",
             "    ImmutableSet<Object> set1 = ImmutableSet.of();",
             "    ImmutableSet<Object> set2 = ImmutableSet.copyOf(ImmutableList.of());",
             "",
@@ -251,6 +274,8 @@ final class IdentityConversionTest {
             "    Object o1 = ImmutableSet.copyOf(ImmutableList.of());",
             "    Object o2 = ImmutableSet.of();",
             "",
+            "    Matcher matcher = staticMethod();",
+            "",
             "    when(\"foo\".contains(\"f\")).thenAnswer(inv -> ImmutableSet.copyOf(ImmutableList.of(1)));",
             "  }",
             "",
@@ -261,17 +286,17 @@ final class IdentityConversionTest {
 
   @Test
   void replacementSecondSuggestedFix() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(IdentityConversion.class, getClass())
         .setFixChooser(FixChoosers.SECOND)
         .addInputLines(
-            "Foo.java",
+            "A.java",
             "import com.google.common.collect.ImmutableCollection;",
             "import com.google.common.collect.ImmutableList;",
             "import com.google.common.collect.ImmutableSet;",
             "import java.util.ArrayList;",
             "",
-            "public final class Foo {",
-            "  public void foo() {",
+            "public final class A {",
+            "  public void m() {",
             "    ImmutableSet<Object> set1 = ImmutableSet.copyOf(ImmutableSet.of());",
             "    ImmutableSet<Object> set2 = ImmutableSet.copyOf(ImmutableList.of());",
             "",
@@ -280,14 +305,14 @@ final class IdentityConversionTest {
             "  }",
             "}")
         .addOutputLines(
-            "Foo.java",
+            "A.java",
             "import com.google.common.collect.ImmutableCollection;",
             "import com.google.common.collect.ImmutableList;",
             "import com.google.common.collect.ImmutableSet;",
             "import java.util.ArrayList;",
             "",
-            "public final class Foo {",
-            "  public void foo() {",
+            "public final class A {",
+            "  public void m() {",
             "    @SuppressWarnings(\"IdentityConversion\")",
             "    ImmutableSet<Object> set1 = ImmutableSet.copyOf(ImmutableSet.of());",
             "    ImmutableSet<Object> set2 = ImmutableSet.copyOf(ImmutableList.of());",

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class ImmutablesSortedSetComparatorTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(ImmutablesSortedSetComparator.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(ImmutablesSortedSetComparator.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(ImmutablesSortedSetComparator.class, getClass())
         .addSourceLines(
             "A.java",
             "import com.google.common.collect.ContiguousSet;",
@@ -109,7 +104,7 @@ final class ImmutablesSortedSetComparatorTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(ImmutablesSortedSetComparator.class, getClass())
         .addInputLines(
             "A.java",
             "import com.google.common.collect.ImmutableSortedSet;",
@@ -147,7 +142,7 @@ final class ImmutablesSortedSetComparatorTest {
 
   @Test
   void replacementWithImportClash() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(ImmutablesSortedSetComparator.class, getClass())
         .addInputLines(
             "MySpringService.java",
             "import com.google.common.collect.ImmutableSortedSet;",

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

@@ -6,23 +6,34 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class IsInstanceLambdaUsageTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(IsInstanceLambdaUsage.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(IsInstanceLambdaUsage.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(IsInstanceLambdaUsage.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.stream.Stream;",
+            "import reactor.core.publisher.Flux;",
             "",
             "class A {",
             "  void m() {",
+            "    Integer localVariable = 0;",
+            "",
+            "    Stream.of(0).map(i -> i + 1);",
+            "    Stream.of(1).filter(Integer.class::isInstance);",
+            "    Stream.of(2).filter(i -> i.getClass() instanceof Class);",
+            "    Stream.of(3).filter(i -> localVariable instanceof Integer);",
+            "    // XXX: Ideally this case is also flagged. Pick this up in the context of merging the",
+            "    // `IsInstanceLambdaUsage` and `MethodReferenceUsage` checks, or introduce a separate check that",
+            "    // simplifies unnecessary block lambda expressions.",
+            "    Stream.of(4)",
+            "        .filter(",
+            "            i -> {",
+            "              return localVariable instanceof Integer;",
+            "            });",
+            "    Flux.just(5, \"foo\").distinctUntilChanged(v -> v, (a, b) -> a instanceof Integer);",
+            "",
             "    // BUG: Diagnostic contains:",
-            "    Stream.of(1).filter(i -> i instanceof Integer);",
-            "    Stream.of(2).filter(Integer.class::isInstance);",
+            "    Stream.of(6).filter(i -> i instanceof Integer);",
             "  }",
             "}")
         .doTest();
@@ -30,7 +41,7 @@ final class IsInstanceLambdaUsageTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(IsInstanceLambdaUsage.class, getClass())
         .addInputLines(
             "A.java",
             "import java.util.stream.Stream;",

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class JUnitClassModifiersTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(JUnitClassModifiers.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(JUnitClassModifiers.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(JUnitClassModifiers.class, getClass())
         .addSourceLines(
             "Container.java",
             "import org.junit.jupiter.api.Test;",
@@ -98,7 +93,7 @@ final class JUnitClassModifiersTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(JUnitClassModifiers.class, getClass())
         .addInputLines(
             "A.java",
             "import org.junit.jupiter.api.Test;",

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class JUnitMethodDeclarationTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(JUnitMethodDeclaration.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(JUnitMethodDeclaration.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(JUnitMethodDeclaration.class, getClass())
         .addSourceLines(
             "A.java",
             "import static org.junit.jupiter.params.provider.Arguments.arguments;",
@@ -91,6 +86,9 @@ final class JUnitMethodDeclarationTest {
             "  private void tearDown8() {}",
             "",
             "  @Test",
+            "  void test() {}",
+            "",
+            "  @Test",
             "  void method1() {}",
             "",
             "  @Test",
@@ -144,8 +142,13 @@ final class JUnitMethodDeclarationTest {
             "  void test5() {}",
             "",
             "  @Test",
-            "  // BUG: Diagnostic contains: (but note that a method named `overload` already exists in this",
-            "  // class)",
+            "  // BUG: Diagnostic contains: (but note that a method named `toString` is already defined in this",
+            "  // class or a supertype)",
+            "  void testToString() {}",
+            "",
+            "  @Test",
+            "  // BUG: Diagnostic contains: (but note that a method named `overload` is already defined in this",
+            "  // class or a supertype)",
             "  void testOverload() {}",
             "",
             "  void overload() {}",
@@ -155,8 +158,20 @@ final class JUnitMethodDeclarationTest {
             "  void testArguments() {}",
             "",
             "  @Test",
-            "  // BUG: Diagnostic contains: (but note that `public` is a reserved keyword)",
+            "  // BUG: Diagnostic contains: (but note that `public` is not a valid identifier)",
             "  void testPublic() {}",
+            "",
+            "  @Test",
+            "  // BUG: Diagnostic contains: (but note that `null` is not a valid identifier)",
+            "  void testNull() {}",
+            "",
+            "  @Test",
+            "  // BUG: Diagnostic contains:",
+            "  void testRecord() {}",
+            "",
+            "  @Test",
+            "  // BUG: Diagnostic contains:",
+            "  void testMethodThatIsOverriddenWithoutOverrideAnnotation() {}",
             "}")
         .addSourceLines(
             "B.java",
@@ -218,6 +233,10 @@ final class JUnitMethodDeclarationTest {
             "",
             "  @Override",
             "  @Test",
+            "  void test() {}",
+            "",
+            "  @Override",
+            "  @Test",
             "  void method1() {}",
             "",
             "  @Override",
@@ -267,6 +286,10 @@ final class JUnitMethodDeclarationTest {
             "",
             "  @Override",
             "  @Test",
+            "  void testToString() {}",
+            "",
+            "  @Override",
+            "  @Test",
             "  void testOverload() {}",
             "",
             "  @Override",
@@ -279,6 +302,17 @@ final class JUnitMethodDeclarationTest {
             "  @Override",
             "  @Test",
             "  void testPublic() {}",
+            "",
+            "  @Override",
+            "  @Test",
+            "  void testNull() {}",
+            "",
+            "  @Override",
+            "  @Test",
+            "  void testRecord() {}",
+            "",
+            "  @Test",
+            "  void testMethodThatIsOverriddenWithoutOverrideAnnotation() {}",
             "}")
         .addSourceLines(
             "C.java",
@@ -306,7 +340,7 @@ final class JUnitMethodDeclarationTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(JUnitMethodDeclaration.class, getClass())
         .addInputLines(
             "A.java",
             "import static org.junit.jupiter.params.provider.Arguments.arguments;",
@@ -352,6 +386,9 @@ final class JUnitMethodDeclarationTest {
             "  protected void quux() {}",
             "",
             "  @Test",
+            "  public void testToString() {}",
+            "",
+            "  @Test",
             "  public void testOverload() {}",
             "",
             "  void overload() {}",
@@ -361,6 +398,9 @@ final class JUnitMethodDeclarationTest {
             "",
             "  @Test",
             "  private void testClass() {}",
+            "",
+            "  @Test",
+            "  private void testTrue() {}",
             "}")
         .addOutputLines(
             "A.java",
@@ -407,6 +447,9 @@ final class JUnitMethodDeclarationTest {
             "  void quux() {}",
             "",
             "  @Test",
+            "  void testToString() {}",
+            "",
+            "  @Test",
             "  void testOverload() {}",
             "",
             "  void overload() {}",
@@ -416,6 +459,9 @@ final class JUnitMethodDeclarationTest {
             "",
             "  @Test",
             "  void testClass() {}",
+            "",
+            "  @Test",
+            "  void testTrue() {}",
             "}")
         .doTest(TestMode.TEXT_MATCH);
   }

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

@@ -7,22 +7,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class LexicographicalAnnotationAttributeListingTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(
-          LexicographicalAnnotationAttributeListing.class, getClass());
-  private final CompilationTestHelper restrictedCompilationTestHelper =
-      CompilationTestHelper.newInstance(LexicographicalAnnotationAttributeListing.class, getClass())
-          .setArgs(
-              ImmutableList.of(
-                  "-XepOpt:LexicographicalAnnotationAttributeListing:Includes=pkg.A.Foo,pkg.A.Bar",
-                  "-XepOpt:LexicographicalAnnotationAttributeListing:Excludes=pkg.A.Bar#value"));
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(
-          LexicographicalAnnotationAttributeListing.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(LexicographicalAnnotationAttributeListing.class, getClass())
         .addSourceLines(
             "A.java",
             "import static java.math.RoundingMode.DOWN;",
@@ -165,7 +152,8 @@ final class LexicographicalAnnotationAttributeListingTest {
   // `CanonicalAnnotationSyntax` checker correct the situation in a subsequent run.
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(
+            LexicographicalAnnotationAttributeListing.class, getClass())
         .addInputLines(
             "A.java",
             "import static java.math.RoundingMode.DOWN;",
@@ -246,7 +234,11 @@ final class LexicographicalAnnotationAttributeListingTest {
   @Test
   void filtering() {
     /* Some violations are not flagged because they are not in- or excluded. */
-    restrictedCompilationTestHelper
+    CompilationTestHelper.newInstance(LexicographicalAnnotationAttributeListing.class, getClass())
+        .setArgs(
+            ImmutableList.of(
+                "-XepOpt:LexicographicalAnnotationAttributeListing:Includes=pkg.A.Foo,pkg.A.Bar",
+                "-XepOpt:LexicographicalAnnotationAttributeListing:Excludes=pkg.A.Bar#value"))
         .addSourceLines(
             "pkg/A.java",
             "package pkg;",

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

@@ -6,15 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class LexicographicalAnnotationListingTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(LexicographicalAnnotationListing.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(
-          LexicographicalAnnotationListing.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(LexicographicalAnnotationListing.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.lang.annotation.ElementType;",
@@ -133,7 +127,7 @@ final class LexicographicalAnnotationListingTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(LexicographicalAnnotationListing.class, getClass())
         .addInputLines(
             "A.java",
             "import java.lang.annotation.ElementType;",

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class MethodReferenceUsageTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(MethodReferenceUsage.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(MethodReferenceUsage.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(MethodReferenceUsage.class, getClass())
         .addSourceLines(
             "A.java",
             "import com.google.common.collect.Streams;",
@@ -323,7 +318,7 @@ final class MethodReferenceUsageTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(MethodReferenceUsage.class, getClass())
         .addInputLines(
             "A.java",
             "import static java.util.Collections.emptyList;",

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

@@ -6,16 +6,12 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class MissingRefasterAnnotationTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(MissingRefasterAnnotation.class, getClass())
-          .expectErrorMessage(
-              "X",
-              containsPattern(
-                  "The Refaster rule contains a method without any Refaster annotations"));
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(MissingRefasterAnnotation.class, getClass())
+        .expectErrorMessage(
+            "X",
+            containsPattern("The Refaster rule contains a method without any Refaster annotations"))
         .addSourceLines(
             "A.java",
             "import com.google.errorprone.refaster.annotation.AfterTemplate;",

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class MockitoStubbingTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(MockitoStubbing.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(MockitoStubbing.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(MockitoStubbing.class, getClass())
         .addSourceLines(
             "A.java",
             "import static org.mockito.ArgumentMatchers.eq;",
@@ -55,7 +50,7 @@ final class MockitoStubbingTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(MockitoStubbing.class, getClass())
         .addInputLines(
             "A.java",
             "import static org.mockito.ArgumentMatchers.eq;",

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

@@ -4,12 +4,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class NestedOptionalsTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(NestedOptionals.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(NestedOptionals.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.Optional;",
@@ -39,4 +36,19 @@ final class NestedOptionalsTest {
             "}")
         .doTest();
   }
+
+  @Test
+  void identificationOptionalTypeNotLoaded() {
+    CompilationTestHelper.newInstance(NestedOptionals.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import java.time.Duration;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Duration.ofSeconds(1);",
+            "  }",
+            "}")
+        .doTest();
+  }
 }

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

@@ -7,14 +7,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class NonEmptyMonoTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(NonEmptyMono.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(NonEmptyMono.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(NonEmptyMono.class, getClass())
         .addSourceLines(
             "A.java",
             "import static com.google.common.collect.ImmutableList.toImmutableList;",
@@ -111,7 +106,7 @@ final class NonEmptyMonoTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(NonEmptyMono.class, getClass())
         .addInputLines(
             "A.java",
             "import static com.google.common.collect.ImmutableList.toImmutableList;",

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

@@ -5,22 +5,21 @@ import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
 import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
+// XXX: There are no tests for multiple replacements within the same expression:
+// - Error Prone doesn't currently support this, it seems.
+// - The `BugCheckerRefactoringTestHelper` throws an exception in this case.
+// - During actual compilation only the first replacement is applied.
+// XXX: Can we perhaps work-around this by describing the fixes in reverse order?
 final class PrimitiveComparisonTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(PrimitiveComparison.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(PrimitiveComparison.class, getClass());
-
-  // XXX: There are no tests for multiple replacements within the same expression:
-  // - Error Prone doesn't currently support this, it seems.
-  // - The `BugCheckerRefactoringTestHelper` throws an exception in this case.
-  // - During actual compilation only the first replacement is applied.
-  // XXX: Can we perhaps work-around this by describing the fixes in reverse order?
-
-  // The logic for `char` and `short` is exactly analogous to the `byte` case.
+  /**
+   * Tests the identification of {@code byte} comparisons for which boxing can be avoided.
+   *
+   * @implNote The logic for {@code char} and {@code short} is exactly analogous to the {@code byte}
+   *     case.
+   */
   @Test
   void byteComparison() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.Comparator;",
@@ -120,7 +119,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void intComparison() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.Comparator;",
@@ -227,7 +226,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void longComparison() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.Comparator;",
@@ -318,7 +317,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void floatComparison() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.Comparator;",
@@ -386,7 +385,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void doubleComparison() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.Comparator;",
@@ -461,7 +460,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void stringComparison() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.util.Comparator;",
@@ -497,7 +496,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void replacementWithPrimitiveVariants() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addInputLines(
             "A.java",
             "import java.util.Comparator;",
@@ -577,7 +576,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void replacementWithBoxedVariants() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addInputLines(
             "A.java",
             "import java.util.Comparator;",
@@ -643,7 +642,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void replacementWithPrimitiveVariantsUsingStaticImports() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addInputLines(
             "A.java",
             "import static java.util.Comparator.comparing;",
@@ -682,7 +681,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void replacementWithBoxedVariantsUsingStaticImports() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addInputLines(
             "A.java",
             "import static java.util.Comparator.comparingDouble;",
@@ -723,7 +722,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void replacementWithPrimitiveVariantsInComplexSyntacticalContext() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addInputLines(
             "A.java",
             "import java.util.Comparator;",
@@ -755,7 +754,7 @@ final class PrimitiveComparisonTest {
 
   @Test
   void replacementWithBoxedVariantsInComplexSyntacticalContext() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(PrimitiveComparison.class, getClass())
         .addInputLines(
             "A.java",
             "import java.util.Comparator;",

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

@@ -12,13 +12,6 @@ import org.junit.jupiter.api.Test;
 final class RedundantStringConversionTest {
   private final CompilationTestHelper compilationTestHelper =
       CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass());
-  private final CompilationTestHelper customizedCompilationTestHelper =
-      CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass())
-          .setArgs(
-              ImmutableList.of(
-                  "-XepOpt:RedundantStringConversion:ExtraConversionMethods=java.lang.Enum#name(),A#name(),A.B#toString(int)"));
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(RedundantStringConversion.class, getClass());
 
   @Test
   void identificationOfIdentityTransformation() {
@@ -416,7 +409,10 @@ final class RedundantStringConversionTest {
 
   @Test
   void identificationOfCustomConversionMethod() {
-    customizedCompilationTestHelper
+    CompilationTestHelper.newInstance(RedundantStringConversion.class, getClass())
+        .setArgs(
+            ImmutableList.of(
+                "-XepOpt:RedundantStringConversion:ExtraConversionMethods=java.lang.Enum#name(),A#name(),A.B#toString(int)"))
         .addSourceLines(
             "A.java",
             "import java.math.RoundingMode;",
@@ -509,7 +505,7 @@ final class RedundantStringConversionTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(RedundantStringConversion.class, getClass())
         .addInputLines(
             "A.java",
             "class A {",

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class RefasterAnyOfUsageTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(RefasterAnyOfUsage.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(RefasterAnyOfUsage.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RefasterAnyOfUsage.class, getClass())
         .addSourceLines(
             "A.java",
             "import com.google.errorprone.refaster.Refaster;",
@@ -38,7 +33,7 @@ final class RefasterAnyOfUsageTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(RefasterAnyOfUsage.class, getClass())
         .addInputLines(
             "A.java",
             "import com.google.errorprone.refaster.Refaster;",

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class RefasterRuleModifiersTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(RefasterRuleModifiers.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(RefasterRuleModifiers.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RefasterRuleModifiers.class, getClass())
         .addSourceLines(
             "A.java",
             "import com.google.errorprone.refaster.annotation.BeforeTemplate;",
@@ -136,7 +131,7 @@ final class RefasterRuleModifiersTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(RefasterRuleModifiers.class, getClass())
         .addInputLines(
             "A.java",
             "import com.google.errorprone.refaster.annotation.BeforeTemplate;",

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

@@ -4,12 +4,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class RequestMappingAnnotationTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(RequestMappingAnnotation.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RequestMappingAnnotation.class, getClass())
         .addSourceLines(
             "A.java",
             "import java.io.InputStream;",

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

@@ -4,12 +4,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class RequestParamTypeTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(RequestParamType.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(RequestParamType.class, getClass())
         .addSourceLines(
             "A.java",
             "import com.google.common.collect.ImmutableBiMap;",
@@ -19,7 +16,7 @@ final class RequestParamTypeTest {
             "import java.util.List;",
             "import java.util.Map;",
             "import java.util.Set;",
-            "import org.jspecify.nullness.Nullable;",
+            "import org.jspecify.annotations.Nullable;",
             "import org.springframework.web.bind.annotation.DeleteMapping;",
             "import org.springframework.web.bind.annotation.GetMapping;",
             "import org.springframework.web.bind.annotation.PostMapping;",
@@ -63,4 +60,55 @@ final class RequestParamTypeTest {
             "}")
         .doTest();
   }
+
+  @Test
+  void identificationRestricted() {
+    CompilationTestHelper.newInstance(RequestParamType.class, getClass())
+        .setArgs(
+            "-XepOpt:RequestParamType:SupportedCustomTypes=com.google.common.collect.ImmutableSet,com.google.common.collect.ImmutableSortedMultiset")
+        .addSourceLines(
+            "A.java",
+            "import com.google.common.collect.ImmutableBiMap;",
+            "import com.google.common.collect.ImmutableCollection;",
+            "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.ImmutableSortedMultiset;",
+            "import com.google.common.collect.ImmutableSortedSet;",
+            "import org.springframework.web.bind.annotation.GetMapping;",
+            "import org.springframework.web.bind.annotation.RequestParam;",
+            "",
+            "interface A {",
+            "  @GetMapping",
+            "  // BUG: Diagnostic contains:",
+            "  A immutableCollection(@RequestParam ImmutableCollection<String> param);",
+            "",
+            "  @GetMapping",
+            "  // BUG: Diagnostic contains:",
+            "  A immutableList(@RequestParam ImmutableList<String> param);",
+            "",
+            "  @GetMapping",
+            "  A immutableSet(@RequestParam ImmutableSet<String> param);",
+            "",
+            "  @GetMapping",
+            "  A immutableSortedSet(@RequestParam ImmutableSortedSet<String> param);",
+            "",
+            "  @GetMapping",
+            "  // BUG: Diagnostic contains:",
+            "  A immutableMultiset(@RequestParam ImmutableMultiset<String> param);",
+            "",
+            "  @GetMapping",
+            "  A immutableSortedMultiset(@RequestParam ImmutableSortedMultiset<String> param);",
+            "",
+            "  @GetMapping",
+            "  // BUG: Diagnostic contains:",
+            "  A immutableMap(@RequestParam ImmutableMap<String, String> param);",
+            "",
+            "  @GetMapping",
+            "  // BUG: Diagnostic contains:",
+            "  A immutableBiMap(@RequestParam ImmutableBiMap<String, String> param);",
+            "}")
+        .doTest();
+  }
 }

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

@@ -7,14 +7,9 @@ import org.junit.jupiter.api.Test;
 import org.springframework.scheduling.annotation.Scheduled;
 
 final class ScheduledTransactionTraceTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(ScheduledTransactionTrace.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(ScheduledTransactionTrace.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(ScheduledTransactionTrace.class, getClass())
         .addSourceLines(
             "A.java",
             "import com.newrelic.api.agent.Trace;",
@@ -46,7 +41,7 @@ final class ScheduledTransactionTraceTest {
 
   @Test
   void identificationWithoutNewRelicAgentApiOnClasspath() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(ScheduledTransactionTrace.class, getClass())
         .withClasspath(Scheduled.class)
         .addSourceLines(
             "A.java",
@@ -61,7 +56,7 @@ final class ScheduledTransactionTraceTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(ScheduledTransactionTrace.class, getClass())
         .addInputLines(
             "A.java",
             "import com.newrelic.api.agent.Trace;",

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/Slf4jLogStatementTest.java

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class Slf4jLogStatementTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(Slf4jLogStatement.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(Slf4jLogStatement.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(Slf4jLogStatement.class, getClass())
         .addSourceLines(
             "A.java",
             "import org.slf4j.Logger;",
@@ -96,7 +91,7 @@ final class Slf4jLogStatementTest {
   // XXX: Drop what's unused.
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(Slf4jLogStatement.class, getClass())
         .addInputLines(
             "A.java",
             "import org.slf4j.Logger;",

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

@@ -6,14 +6,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class SpringMvcAnnotationTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(SpringMvcAnnotation.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(SpringMvcAnnotation.class, getClass());
-
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(SpringMvcAnnotation.class, getClass())
         .addSourceLines(
             "A.java",
             "import static org.springframework.web.bind.annotation.RequestMethod.DELETE;",
@@ -85,7 +80,7 @@ final class SpringMvcAnnotationTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(SpringMvcAnnotation.class, getClass())
         .addInputLines(
             "A.java",
             "import static org.springframework.web.bind.annotation.RequestMethod.PATCH;",

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

@@ -8,11 +8,6 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class StaticImportTest {
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(StaticImport.class, getClass());
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(StaticImport.class, getClass());
-
   @Test
   void candidateMethodsAreNotRedundant() {
     assertThat(StaticImport.STATIC_IMPORT_CANDIDATE_MEMBERS.keySet())
@@ -33,7 +28,7 @@ final class StaticImportTest {
 
   @Test
   void identification() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(StaticImport.class, getClass())
         .addSourceLines(
             "A.java",
             "import static com.google.common.collect.ImmutableMap.toImmutableMap;",
@@ -118,7 +113,7 @@ final class StaticImportTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(StaticImport.class, getClass())
         .addInputLines(
             "A.java",
             "import static java.util.function.Predicate.not;",

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

@@ -0,0 +1,125 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.FixChoosers;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Test;
+
+final class StringCaseLocaleUsageTest {
+  @Test
+  void identification() {
+    CompilationTestHelper.newInstance(StringCaseLocaleUsage.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import static java.util.Locale.ROOT;",
+            "",
+            "import java.util.Locale;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    \"a\".toLowerCase(Locale.ROOT);",
+            "    \"a\".toUpperCase(Locale.ROOT);",
+            "    \"b\".toLowerCase(ROOT);",
+            "    \"b\".toUpperCase(ROOT);",
+            "    \"c\".toLowerCase(Locale.getDefault());",
+            "    \"c\".toUpperCase(Locale.getDefault());",
+            "    \"d\".toLowerCase(Locale.ENGLISH);",
+            "    \"d\".toUpperCase(Locale.ENGLISH);",
+            "    \"e\".toLowerCase(new Locale(\"foo\"));",
+            "    \"e\".toUpperCase(new Locale(\"foo\"));",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    \"f\".toLowerCase();",
+            "    // BUG: Diagnostic contains:",
+            "    \"g\".toUpperCase();",
+            "",
+            "    String h = \"h\";",
+            "    // BUG: Diagnostic contains:",
+            "    h.toLowerCase();",
+            "    String i = \"i\";",
+            "    // BUG: Diagnostic contains:",
+            "    i.toUpperCase();",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacementFirstSuggestedFix() {
+    BugCheckerRefactoringTestHelper.newInstance(StringCaseLocaleUsage.class, getClass())
+        .setFixChooser(FixChoosers.FIRST)
+        .addInputLines(
+            "A.java",
+            "class A {",
+            "  void m() {",
+            "    \"a\".toLowerCase(/* Comment with parens: (). */ );",
+            "    \"b\".toUpperCase();",
+            "    \"c\".toLowerCase().toString();",
+            "",
+            "    toString().toLowerCase();",
+            "    toString().toUpperCase /* Comment with parens: (). */();",
+            "",
+            "    this.toString().toLowerCase() /* Comment with parens: (). */;",
+            "    this.toString().toUpperCase();",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import java.util.Locale;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    \"a\".toLowerCase(/* Comment with parens: (). */ Locale.ROOT);",
+            "    \"b\".toUpperCase(Locale.ROOT);",
+            "    \"c\".toLowerCase(Locale.ROOT).toString();",
+            "",
+            "    toString().toLowerCase(Locale.ROOT);",
+            "    toString().toUpperCase /* Comment with parens: (). */(Locale.ROOT);",
+            "",
+            "    this.toString().toLowerCase(Locale.ROOT) /* Comment with parens: (). */;",
+            "    this.toString().toUpperCase(Locale.ROOT);",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+
+  @Test
+  void replacementSecondSuggestedFix() {
+    BugCheckerRefactoringTestHelper.newInstance(StringCaseLocaleUsage.class, getClass())
+        .setFixChooser(FixChoosers.SECOND)
+        .addInputLines(
+            "A.java",
+            "class A {",
+            "  void m() {",
+            "    \"a\".toLowerCase();",
+            "    \"b\".toUpperCase(/* Comment with parens: (). */ );",
+            "    \"c\".toLowerCase().toString();",
+            "",
+            "    toString().toLowerCase();",
+            "    toString().toUpperCase /* Comment with parens: (). */();",
+            "",
+            "    this.toString().toLowerCase() /* Comment with parens: (). */;",
+            "    this.toString().toUpperCase();",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import java.util.Locale;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    \"a\".toLowerCase(Locale.getDefault());",
+            "    \"b\".toUpperCase(/* Comment with parens: (). */ Locale.getDefault());",
+            "    \"c\".toLowerCase(Locale.getDefault()).toString();",
+            "",
+            "    toString().toLowerCase(Locale.getDefault());",
+            "    toString().toUpperCase /* Comment with parens: (). */(Locale.getDefault());",
+            "",
+            "    this.toString().toLowerCase(Locale.getDefault()) /* Comment with parens: (). */;",
+            "    this.toString().toUpperCase(Locale.getDefault());",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

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

@@ -8,17 +8,12 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class StringJoinTest {
-  private final CompilationTestHelper compilationHelper =
-      CompilationTestHelper.newInstance(StringJoin.class, getClass())
-          .expectErrorMessage(
-              "valueOf", containsPattern("Prefer `String#valueOf` over `String#format`"))
-          .expectErrorMessage("join", containsPattern("Prefer `String#join` over `String#format`"));
-  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
-      BugCheckerRefactoringTestHelper.newInstance(StringJoin.class, getClass());
-
   @Test
   void identification() {
-    compilationHelper
+    CompilationTestHelper.newInstance(StringJoin.class, getClass())
+        .expectErrorMessage(
+            "valueOf", containsPattern("Prefer `String#valueOf` over `String#format`"))
+        .expectErrorMessage("join", containsPattern("Prefer `String#join` over `String#format`"))
         .addSourceLines(
             "A.java",
             "import java.util.Formattable;",
@@ -63,7 +58,7 @@ final class StringJoinTest {
 
   @Test
   void replacement() {
-    refactoringTestHelper
+    BugCheckerRefactoringTestHelper.newInstance(StringJoin.class, getClass())
         .addInputLines(
             "A.java",
             "class A {",

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

@@ -4,12 +4,9 @@ import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class TimeZoneUsageTest {
-  private final CompilationTestHelper compilationHelper =
-      CompilationTestHelper.newInstance(TimeZoneUsage.class, getClass());
-
   @Test
   void identification() {
-    compilationHelper
+    CompilationTestHelper.newInstance(TimeZoneUsage.class, getClass())
         .addSourceLines(
             "A.java",
             "import static java.time.ZoneOffset.UTC;",

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

@@ -0,0 +1,73 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+
+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.MethodTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.MethodTree;
+import com.sun.tools.javac.code.Symbol.MethodSymbol;
+import org.junit.jupiter.api.Test;
+
+final class ConflictDetectionTest {
+  @Test
+  void matcher() {
+    CompilationTestHelper.newInstance(RenameBlockerFlagger.class, getClass())
+        .addSourceLines(
+            "pkg/A.java",
+            "package pkg;",
+            "",
+            "import static pkg.A.B.method3t;",
+            "",
+            "import pkg.A.method4t;",
+            "",
+            "class A {",
+            "  void method1() {",
+            "    method3t();",
+            "    method4(method4t.class);",
+            "  }",
+            "",
+            "  // BUG: Diagnostic contains: a method named `method2t` is already defined in this class or a",
+            "  // supertype",
+            "  void method2() {}",
+            "",
+            "  void method2t() {}",
+            "",
+            "  // BUG: Diagnostic contains: `method3t` is already statically imported",
+            "  void method3() {}",
+            "",
+            "  void method4(Object o) {}",
+            "",
+            "  // BUG: Diagnostic contains: `int` is not a valid identifier",
+            "  void in() {}",
+            "",
+            "  static class B {",
+            "    static void method3t() {}",
+            "  }",
+            "",
+            "  class method4t {}",
+            "}")
+        .doTest();
+  }
+
+  /**
+   * A {@link BugChecker} that uses {@link ConflictDetection#findMethodRenameBlocker(MethodSymbol,
+   * String, VisitorState)} to flag methods of which the name cannot be suffixed with a {@code t}.
+   */
+  @BugPattern(summary = "Interacts with `ConflictDetection` for testing purposes", severity = ERROR)
+  public static final class RenameBlockerFlagger extends BugChecker implements MethodTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchMethod(MethodTree tree, VisitorState state) {
+      return ConflictDetection.findMethodRenameBlocker(
+              ASTHelpers.getSymbol(tree), tree.getName() + "t", state)
+          .map(blocker -> buildDescription(tree).setMessage(blocker).build())
+          .orElse(Description.NO_MATCH);
+    }
+  }
+}

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

@@ -0,0 +1,31 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.params.provider.Arguments.arguments;
+
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.ErrorProneOptions;
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+final class FlagsTest {
+  private static Stream<Arguments> getListTestCases() {
+    /* { args, flag, expected } */
+    return Stream.of(
+        arguments(ImmutableList.of(), "Foo", ImmutableList.of()),
+        arguments(ImmutableList.of("-XepOpt:Foo=bar,baz"), "Qux", ImmutableList.of()),
+        arguments(ImmutableList.of("-XepOpt:Foo="), "Foo", ImmutableList.of()),
+        arguments(ImmutableList.of("-XepOpt:Foo=bar"), "Foo", ImmutableList.of("bar")),
+        arguments(ImmutableList.of("-XepOpt:Foo=bar,baz"), "Foo", ImmutableList.of("bar", "baz")),
+        arguments(ImmutableList.of("-XepOpt:Foo=,"), "Foo", ImmutableList.of("", "")));
+  }
+
+  @MethodSource("getListTestCases")
+  @ParameterizedTest
+  void getList(ImmutableList<String> args, String flag, ImmutableList<String> expected) {
+    assertThat(Flags.getList(ErrorProneOptions.processArgs(args).getFlags(), flag))
+        .containsExactlyElementsOf(expected);
+  }
+}

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

@@ -0,0 +1,34 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.params.provider.Arguments.arguments;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+final class JavaKeywordsTest {
+  private static Stream<Arguments> isValidIdentifierTestCases() {
+    /* { str, expected } */
+    return Stream.of(
+        arguments("", false),
+        arguments("public", false),
+        arguments("true", false),
+        arguments("false", false),
+        arguments("null", false),
+        arguments("0", false),
+        arguments("\0", false),
+        arguments("a%\0", false),
+        arguments("a", true),
+        arguments("a0", true),
+        arguments("_a0", true),
+        arguments("test", true));
+  }
+
+  @MethodSource("isValidIdentifierTestCases")
+  @ParameterizedTest
+  void isValidIdentifier(String str, boolean expected) {
+    assertThat(JavaKeywords.isValidIdentifier(str)).isEqualTo(expected);
+  }
+}

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

@@ -40,9 +40,6 @@ final class MethodMatcherFactoryTest {
                   "com.example.A#m2(java.lang.String)",
                   "com.example.sub.B#m3(int,int)"));
 
-  private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(MatchedMethodsFlagger.class, getClass());
-
   @Test
   void createWithMalformedSignatures() {
     MethodMatcherFactory factory = new MethodMatcherFactory();
@@ -58,7 +55,7 @@ final class MethodMatcherFactoryTest {
 
   @Test
   void matcher() {
-    compilationTestHelper
+    CompilationTestHelper.newInstance(MatchedMethodsFlagger.class, getClass())
         .addSourceLines(
             "com/example/A.java",
             "package com.example;",

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

@@ -25,46 +25,6 @@ import java.util.List;
 import org.junit.jupiter.api.Test;
 
 final class MoreTypesTest {
-  private static final ImmutableSet<Supplier<Type>> TYPES =
-      ImmutableSet.of(
-          // Invalid types.
-          type("java.lang.Nonexistent"),
-          generic(type("java.util.Integer"), unbound()),
-          // Valid types.
-          type("java.lang.String"),
-          type("java.lang.Number"),
-          superOf(type("java.lang.Number")),
-          subOf(type("java.lang.Number")),
-          type("java.lang.Integer"),
-          superOf(type("java.lang.Integer")),
-          subOf(type("java.lang.Integer")),
-          type("java.util.Optional"),
-          raw(type("java.util.Optional")),
-          generic(type("java.util.Optional"), unbound()),
-          generic(type("java.util.Optional"), type("java.lang.Number")),
-          type("java.util.Collection"),
-          raw(type("java.util.Collection")),
-          generic(type("java.util.Collection"), unbound()),
-          generic(type("java.util.Collection"), type("java.lang.Number")),
-          generic(type("java.util.Collection"), superOf(type("java.lang.Number"))),
-          generic(type("java.util.Collection"), subOf(type("java.lang.Number"))),
-          generic(type("java.util.Collection"), type("java.lang.Integer")),
-          generic(type("java.util.Collection"), superOf(type("java.lang.Integer"))),
-          generic(type("java.util.Collection"), subOf(type("java.lang.Integer"))),
-          type("java.util.List"),
-          raw(type("java.util.List")),
-          generic(type("java.util.List"), unbound()),
-          generic(type("java.util.List"), type("java.lang.Number")),
-          generic(type("java.util.List"), superOf(type("java.lang.Number"))),
-          generic(type("java.util.List"), subOf(type("java.lang.Number"))),
-          generic(type("java.util.List"), type("java.lang.Integer")),
-          generic(type("java.util.List"), superOf(type("java.lang.Integer"))),
-          generic(type("java.util.List"), subOf(type("java.lang.Integer"))),
-          generic(
-              type("java.util.Map"),
-              type("java.lang.String"),
-              subOf(generic(type("java.util.Collection"), superOf(type("java.lang.Short"))))));
-
   @Test
   void matcher() {
     CompilationTestHelper.newInstance(SubtypeFlagger.class, getClass())
@@ -159,8 +119,8 @@ final class MoreTypesTest {
   }
 
   /**
-   * A {@link BugChecker} that flags method invocations that are a subtype of any type contained in
-   * {@link #TYPES}.
+   * A {@link BugChecker} that flags method invocations that are a subtype of any type defined by
+   * {@link #getTestTypes()}.
    */
   @BugPattern(summary = "Flags invocations of methods with select return types", severity = ERROR)
   public static final class SubtypeFlagger extends BugChecker
@@ -173,7 +133,7 @@ final class MoreTypesTest {
 
       List<String> matches = new ArrayList<>();
 
-      for (Supplier<Type> type : TYPES) {
+      for (Supplier<Type> type : getTestTypes()) {
         Type testType = type.get(state);
         if (testType != null && state.getTypes().isSubtype(treeType, testType)) {
           matches.add(Signatures.prettyType(testType));
@@ -184,5 +144,52 @@ final class MoreTypesTest {
           ? Description.NO_MATCH
           : buildDescription(tree).setMessage(matches.toString()).build();
     }
+
+    /**
+     * Returns the type suppliers under test.
+     *
+     * @implNote The return value of this method should not be assigned to a field, as that would
+     *     prevent mutations introduced by Pitest from being killed.
+     */
+    private static ImmutableSet<Supplier<Type>> getTestTypes() {
+      return ImmutableSet.of(
+          // Invalid types.
+          type("java.lang.Nonexistent"),
+          generic(type("java.util.Integer"), unbound()),
+          // Valid types.
+          type("java.lang.String"),
+          type("java.lang.Number"),
+          superOf(type("java.lang.Number")),
+          subOf(type("java.lang.Number")),
+          type("java.lang.Integer"),
+          superOf(type("java.lang.Integer")),
+          subOf(type("java.lang.Integer")),
+          type("java.util.Optional"),
+          raw(type("java.util.Optional")),
+          generic(type("java.util.Optional"), unbound()),
+          generic(type("java.util.Optional"), type("java.lang.Number")),
+          type("java.util.Collection"),
+          raw(type("java.util.Collection")),
+          generic(type("java.util.Collection"), unbound()),
+          generic(type("java.util.Collection"), type("java.lang.Number")),
+          generic(type("java.util.Collection"), superOf(type("java.lang.Number"))),
+          generic(type("java.util.Collection"), subOf(type("java.lang.Number"))),
+          generic(type("java.util.Collection"), type("java.lang.Integer")),
+          generic(type("java.util.Collection"), superOf(type("java.lang.Integer"))),
+          generic(type("java.util.Collection"), subOf(type("java.lang.Integer"))),
+          type("java.util.List"),
+          raw(type("java.util.List")),
+          generic(type("java.util.List"), unbound()),
+          generic(type("java.util.List"), type("java.lang.Number")),
+          generic(type("java.util.List"), superOf(type("java.lang.Number"))),
+          generic(type("java.util.List"), subOf(type("java.lang.Number"))),
+          generic(type("java.util.List"), type("java.lang.Integer")),
+          generic(type("java.util.List"), superOf(type("java.lang.Integer"))),
+          generic(type("java.util.List"), subOf(type("java.lang.Integer"))),
+          generic(
+              type("java.util.Map"),
+              type("java.lang.String"),
+              subOf(generic(type("java.util.Collection"), superOf(type("java.lang.Short"))))));
+    }
   }
 }