[maven-release-plugin] prepare release v0.7.0

While there, tweak the usage message of both `apply-error-prone-suggestions.sh`
and `run-mutation-tests.sh`.

.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

@@ -7,10 +7,27 @@ permissions:
   contents: read
 jobs:
   build:
-    runs-on: ubuntu-22.04
     strategy:
       matrix:
-        jdk: [ 11.0.16, 17.0.4 ]
+        os: [ ubuntu-22.04 ]
+        jdk: [ 11.0.16, 17.0.4, 19 ]
+        distribution: [ temurin ]
+        experimental: [ false ]
+        include:
+          - os: macos-12
+            jdk: 17.0.4
+            distribution: temurin
+            experimental: false
+          - os: windows-2022
+            jdk: 17.0.4
+            distribution: temurin
+            experimental: false
+          - os: ubuntu-22.04
+            jdk: 20-ea
+            distribution: zulu
+            experimental: true
+    runs-on: ${{ matrix.os }}
+    continue-on-error: ${{ matrix.experimental }}
     steps:
         # We run the build twice for each supported JDK: once against the
         # original Error Prone release, using only Error Prone checks available
@@ -20,10 +37,10 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v3.1.0
       - name: Set up JDK
-        uses: actions/setup-java@v3.5.1
+        uses: actions/setup-java@v3.8.0
         with:
           java-version: ${{ matrix.jdk }}
-          distribution: temurin
+          distribution: ${{ matrix.distribution }}
           cache: maven
       - name: Display build environment details
         run: mvn --version

.github/workflows/deploy-website.yaml

@@ -3,25 +3,22 @@ on:
   pull_request:
   push:
     branches: [ master, website ]
-permissions:
-  contents: read
-  id-token: write
-  pages: write
 concurrency:
-  group: pages
-  cancel-in-progress: true
+  group: ${{ github.workflow }}-${{ github.ref }}
 jobs:
   build:
+    permissions:
+      contents: read
     runs-on: ubuntu-22.04
     steps:
       - name: Check out code
         uses: actions/checkout@v3.1.0
-      - uses: ruby/setup-ruby@v1.117.0
+      - uses: ruby/setup-ruby@v1.126.0
         with:
           working-directory: ./website
           bundler-cache: true
       - name: Configure Github Pages
-        uses: actions/configure-pages@v2.1.1
+        uses: actions/configure-pages@v2.1.3
       - name: Generate documentation
         run: ./generate-docs.sh
       - name: Build website with Jekyll
@@ -33,12 +30,15 @@ jobs:
         # "Refaster rules" terminology on our website and in the code.
         run: bundle exec htmlproofer --disable_external true --check-external-hash false ./_site
       - name: Upload website as artifact
-        uses: actions/upload-pages-artifact@v1.0.4
+        uses: actions/upload-pages-artifact@v1.0.5
         with:
           path: ./website/_site
   deploy:
     if: github.ref == 'refs/heads/website'
     needs: build
+    permissions:
+      id-token: write
+      pages: write
     runs-on: ubuntu-22.04
     environment:
       name: github-pages
@@ -46,4 +46,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v1.2.1
+        uses: actions/deploy-pages@v1.2.3

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

@@ -0,0 +1,37 @@
+# Performs mutation testing analysis on the files changed by a pull request and
+# uploads the results. The associated PR is subsequently updated by the
+# `pitest-update-pr.yml` workflow. See https://blog.pitest.org/oss-pitest-pr/
+# for details.
+name: "Mutation testing"
+on:
+  pull_request:
+permissions:
+  contents: read
+jobs:
+  analyze-pr:
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3.1.0
+        with:
+          fetch-depth: 2
+      - name: Set up JDK
+        uses: actions/setup-java@v3.8.0
+        with:
+          java-version: 17.0.4
+          distribution: temurin
+          cache: maven
+      - name: Run Pitest
+        # By running with features `+GIT(from[HEAD~1]), +gitci`, Pitest only
+        # analyzes lines changed in the associated pull request, as GitHub
+        # exposes the changes unique to the PR as a single commit on top of the
+        # target branch. See https://blog.pitest.org/pitest-pr-setup for
+        # details.
+        run: mvn test pitest:mutationCoverage -DargLine.xmx=2048m -Dverification.skip -Dfeatures="+GIT(from[HEAD~1]), +gitci"
+      - name: Aggregate Pitest reports
+        run: mvn pitest-git:aggregate -DkilledEmoji=":tada:" -DmutantEmoji=":zombie:" -DtrailingText="Mutation testing report by [Pitest](https://pitest.org/). Review any surviving mutants by inspecting the line comments under [_Files changed_](${{ github.event.number }}/files)."
+      - name: Upload Pitest reports as artifact
+        uses: actions/upload-artifact@v3.1.1
+        with:
+          name: pitest-reports
+          path: ./target/pit-reports-ci

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

@@ -0,0 +1,35 @@
+# Updates a pull request based on the corresponding mutation testing analysis
+# performed by the `pitest-analyze-pr.yml` workflow. See
+# https://blog.pitest.org/oss-pitest-pr/ for details.
+name: "Mutation testing: post results"
+on:
+  workflow_run:
+    workflows: ["Mutation testing"]
+    types:
+      - completed
+permissions:
+  actions: read
+  checks: write
+  contents: read
+  pull-requests: write
+jobs:
+  update-pr:
+    if: ${{ github.event.workflow_run.conclusion == 'success' }}
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3.1.0
+      - name: Set up JDK
+        uses: actions/setup-java@v3.8.0
+        with:
+          java-version: 17.0.4
+          distribution: temurin
+          cache: maven
+      - name: Download Pitest analysis artifact
+        uses: dawidd6/action-download-artifact@v2.24.2
+        with:
+          workflow: ${{ github.event.workflow_run.workflow_id }}
+          name: pitest-reports
+          path: ./target/pit-reports-ci
+      - name: Update PR
+        run: mvn -DrepoToken="${{ secrets.GITHUB_TOKEN }}" pitest-github:updatePR

.renovaterc.json

@@ -10,7 +10,7 @@
     },
     {
       "matchPackagePatterns": [
-        "^com\\.palantir\\.baseline:baseline-error-prone$"
+        "^ruby\\/setup-ruby$"
       ],
       "schedule": "* * 1 * *"
     }

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

@@ -20,6 +20,7 @@ loves Error Prone: producing high-quality and consistent Java
 code_][picnic-blog-ep-post].
 
 [![Maven Central][maven-central-badge]][maven-central-search]
+[![Reproducible Builds][reproducible-builds-badge]][reproducible-builds-report]
 [![GitHub Actions][github-actions-build-badge]][github-actions-build-master]
 [![License][license-badge]][license]
 [![PRs Welcome][pr-badge]][contributing]
@@ -119,16 +120,13 @@ code with Maven should yield two compiler warnings:
 ```sh
 $ mvn clean install
 ...
-[INFO] -------------------------------------------------------------
-[WARNING] COMPILATION WARNING :
-[INFO] -------------------------------------------------------------
-[WARNING] Example.java:[9,34] [tech.picnic.errorprone.refasterrules.BigDecimalRules.BigDecimalZero]
+[INFO] Example.java:[9,34] [Refaster Rule] BigDecimalRules.BigDecimalZero: Refactoring opportunity
+    (see https://error-prone.picnic.tech/refasterrules/BigDecimalRules#BigDecimalZero)
   Did you mean 'return BigDecimal.ZERO;'?
+...
 [WARNING] Example.java:[13,35] [IdentityConversion] This method invocation appears redundant; remove it or suppress this warning and add a comment explaining its purpose
     (see https://error-prone.picnic.tech/bugpatterns/IdentityConversion)
   Did you mean 'return set;' or '@SuppressWarnings("IdentityConversion") public ImmutableSet<Integer> getSet() {'?
-[INFO] 2 warnings
-[INFO] -------------------------------------------------------------
 ...
 ```
 
@@ -168,7 +166,7 @@ Some other commands one may find relevant:
 
 - `mvn fmt:format` formats the code using
   [`google-java-format`][google-java-format].
-- `./run-mutation-tests.sh` runs mutation tests using [PIT][pitest]. The
+- `./run-mutation-tests.sh` runs mutation tests using [Pitest][pitest]. The
   results can be reviewed by opening the respective
   `target/pit-reports/index.html` files. For more information check the [PIT
   Maven plugin][pitest-maven].
@@ -229,3 +227,5 @@ guidelines][contributing].
 [refaster]: https://errorprone.info/docs/refaster
 [refaster-rules-bigdecimal]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/BigDecimalRules.java
 [refaster-rules]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/
+[reproducible-builds-badge]: https://img.shields.io/badge/Reproducible_Builds-ok-success?labelColor=1e5b96
+[reproducible-builds-report]: https://github.com/jvm-repo-rebuild/reproducible-central/blob/master/content/tech/picnic/error-prone-support/error-prone-support/README.md

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 \

cdg-pitest-licence.txt

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

error-prone-contrib/pom.xml

@@ -5,7 +5,7 @@
     <parent>
         <groupId>tech.picnic.error-prone-support</groupId>
         <artifactId>error-prone-support</artifactId>
-        <version>0.4.0</version>
+        <version>0.7.0</version>
     </parent>
 
     <artifactId>error-prone-contrib</artifactId>
@@ -64,11 +64,6 @@
             <artifactId>auto-service-annotations</artifactId>
             <scope>provided</scope>
         </dependency>
-        <dependency>
-            <groupId>com.google.code.findbugs</groupId>
-            <artifactId>jsr305</artifactId>
-            <scope>provided</scope>
-        </dependency>
         <dependency>
             <groupId>com.google.googlejavaformat</groupId>
             <artifactId>google-java-format</artifactId>
@@ -98,6 +93,11 @@
             <artifactId>reactor-adapter</artifactId>
             <scope>provided</scope>
         </dependency>
+        <dependency>
+            <groupId>io.projectreactor.addons</groupId>
+            <artifactId>reactor-extra</artifactId>
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>io.reactivex.rxjava2</groupId>
             <artifactId>rxjava</artifactId>
@@ -146,7 +146,7 @@
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-api</artifactId>
-            <scope>test</scope>
+            <scope>provided</scope>
         </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>
@@ -173,6 +173,11 @@
             <artifactId>slf4j-api</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-context</artifactId>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-test</artifactId>

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

@@ -36,6 +36,9 @@ public final class AmbiguousJsonCreator extends BugChecker implements Annotation
   private static final Matcher<AnnotationTree> IS_JSON_CREATOR_ANNOTATION =
       isType("com.fasterxml.jackson.annotation.JsonCreator");
 
+  /** Instantiates a new {@link AmbiguousJsonCreator} instance. */
+  public AmbiguousJsonCreator() {}
+
   @Override
   public Description matchAnnotation(AnnotationTree tree, VisitorState state) {
     if (!IS_JSON_CREATOR_ANNOTATION.matches(tree, state)) {

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

@@ -44,6 +44,9 @@ public final class AssertJIsNull extends BugChecker implements MethodInvocationT
           argumentCount(1),
           argument(0, nullLiteral()));
 
+  /** Instantiates a new {@link AssertJIsNull} instance. */
+  public AssertJIsNull() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (!ASSERT_IS_EQUAL_TO_NULL.matches(tree, state)) {

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

@@ -15,7 +15,6 @@ import com.google.errorprone.BugPattern;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
-import com.google.errorprone.fixes.SuggestedFix;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.matchers.MultiMatcher;
 import com.google.errorprone.util.ASTHelpers;
@@ -24,6 +23,7 @@ import com.sun.source.tree.ClassTree;
 import com.sun.source.tree.MethodTree;
 import com.sun.source.tree.Tree;
 import java.util.List;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /** A {@link BugChecker} that flags redundant {@code @Autowired} constructor annotations. */
 @AutoService(BugChecker.class)
@@ -38,6 +38,9 @@ public final class AutowiredConstructor extends BugChecker implements ClassTreeM
   private static final MultiMatcher<Tree, AnnotationTree> AUTOWIRED_ANNOTATION =
       annotations(AT_LEAST_ONE, isType("org.springframework.beans.factory.annotation.Autowired"));
 
+  /** Instantiates a new {@link AutowiredConstructor} instance. */
+  public AutowiredConstructor() {}
+
   @Override
   public Description matchClass(ClassTree tree, VisitorState state) {
     List<MethodTree> constructors = ASTHelpers.getConstructors(tree);
@@ -59,6 +62,6 @@ public final class AutowiredConstructor extends BugChecker implements ClassTreeM
      * leave flagging the unused import to Error Prone's `RemoveUnusedImports` check.
      */
     AnnotationTree annotation = Iterables.getOnlyElement(annotations);
-    return describeMatch(annotation, SuggestedFix.delete(annotation));
+    return describeMatch(annotation, SourceCode.deleteWithTrailingWhitespace(annotation, state));
   }
 }

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

@@ -46,6 +46,9 @@ public final class CanonicalAnnotationSyntax extends BugChecker implements Annot
               CanonicalAnnotationSyntax::dropRedundantValueAttribute,
               CanonicalAnnotationSyntax::dropRedundantCurlies);
 
+  /** Instantiates a new {@link CanonicalAnnotationSyntax} instance. */
+  public CanonicalAnnotationSyntax() {}
+
   @Override
   public Description matchAnnotation(AnnotationTree tree, VisitorState state) {
     return FIX_FACTORIES.stream()

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

@@ -18,6 +18,7 @@ import com.google.errorprone.matchers.Matcher;
 import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.MethodInvocationTree;
 import java.util.stream.Collector;
+import tech.picnic.errorprone.bugpatterns.util.ThirdPartyLibrary;
 
 /**
  * A {@link BugChecker} that flags {@link Collector Collectors} that don't clearly express
@@ -45,9 +46,13 @@ public final class CollectorMutability extends BugChecker implements MethodInvoc
   private static final Matcher<ExpressionTree> SET_COLLECTOR =
       staticMethod().anyClass().named("toSet");
 
+  /** Instantiates a new {@link CollectorMutability} instance. */
+  public CollectorMutability() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
-    if (!COLLECTOR_METHOD.matches(tree, state)) {
+    if (!ThirdPartyLibrary.GUAVA.isIntroductionAllowed(state)
+        || !COLLECTOR_METHOD.matches(tree, state)) {
       return Description.NO_MATCH;
     }
 

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

@@ -14,7 +14,6 @@ import com.google.errorprone.BugPattern;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
 import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
-import com.google.errorprone.fixes.SuggestedFix;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.matchers.Matcher;
 import com.google.errorprone.util.ASTHelpers;
@@ -22,6 +21,7 @@ import com.sun.source.tree.ClassTree;
 import com.sun.source.tree.MethodTree;
 import com.sun.source.tree.Tree;
 import java.util.Optional;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /** A {@link BugChecker} that flags empty methods that seemingly can simply be deleted. */
 @AutoService(BugChecker.class)
@@ -38,6 +38,9 @@ public final class EmptyMethod extends BugChecker implements MethodTreeMatcher {
           AT_LEAST_ONE,
           anyOf(isType("java.lang.Override"), isType("org.aspectj.lang.annotation.Pointcut")));
 
+  /** Instantiates a new {@link EmptyMethod} instance. */
+  public EmptyMethod() {}
+
   @Override
   public Description matchMethod(MethodTree tree, VisitorState state) {
     if (tree.getBody() == null
@@ -52,7 +55,7 @@ public final class EmptyMethod extends BugChecker implements MethodTreeMatcher {
       return Description.NO_MATCH;
     }
 
-    return describeMatch(tree, SuggestedFix.delete(tree));
+    return describeMatch(tree, SourceCode.deleteWithTrailingWhitespace(tree, state));
   }
 
   private static boolean isInPossibleTestHelperClass(VisitorState state) {

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

@@ -72,6 +72,9 @@ public final class ErrorProneTestHelperSourceFormat extends BugChecker
           .onDescendantOf("com.google.errorprone.BugCheckerRefactoringTestHelper.ExpectOutput")
           .named("addOutputLines");
 
+  /** Instantiates a new {@link ErrorProneTestHelperSourceFormat} instance. */
+  public ErrorProneTestHelperSourceFormat() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     boolean isOutputSource = OUTPUT_SOURCE_ACCEPTING_METHOD.matches(tree, state);

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

@@ -46,6 +46,9 @@ public final class ExplicitEnumOrdering extends BugChecker implements MethodInvo
   private static final Matcher<ExpressionTree> EXPLICIT_ORDERING =
       staticMethod().onClass(Ordering.class.getName()).named("explicit");
 
+  /** Instantiates a new {@link ExplicitEnumOrdering} instance. */
+  public ExplicitEnumOrdering() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (!EXPLICIT_ORDERING.matches(tree, state)) {

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

@@ -5,6 +5,10 @@ import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
 import static com.google.errorprone.BugPattern.StandardTags.LIKELY_ERROR;
 import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
 import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.generic;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.subOf;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.type;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.unbound;
 
 import com.google.auto.service.AutoService;
 import com.google.common.collect.Iterables;
@@ -17,11 +21,14 @@ import com.google.errorprone.fixes.SuggestedFix;
 import com.google.errorprone.fixes.SuggestedFixes;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.suppliers.Supplier;
+import com.google.errorprone.suppliers.Suppliers;
+import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.MemberReferenceTree;
 import com.sun.source.tree.MethodInvocationTree;
+import com.sun.tools.javac.code.Type;
 import java.util.function.Function;
-import java.util.function.Supplier;
 import reactor.core.publisher.Flux;
 
 /**
@@ -33,11 +40,12 @@ import reactor.core.publisher.Flux;
  * former interleaves values as they are emitted, yielding nondeterministic results. In most cases
  * {@link Flux#concatMap(Function)} should be preferred, as it produces consistent results and
  * avoids potentially saturating the thread pool on which subscription happens. If {@code
- * concatMap}'s single-subscription semantics are undesirable one should invoke a {@code flatMap} or
- * {@code flatMapSequential} overload with an explicit concurrency level.
+ * concatMap}'s sequential-subscription semantics are undesirable one should invoke a {@code
+ * flatMap} or {@code flatMapSequential} overload with an explicit concurrency level.
  *
- * <p>NB: The rarely-used overload {@link Flux#flatMap(Function, Function, Supplier)} is not flagged
- * by this check because there is no clear alternative to point to.
+ * <p>NB: The rarely-used overload {@link Flux#flatMap(Function, Function,
+ * java.util.function.Supplier)} is not flagged by this check because there is no clear alternative
+ * to point to.
  */
 @AutoService(BugChecker.class)
 @BugPattern(
@@ -52,11 +60,19 @@ public final class FluxFlatMapUsage extends BugChecker
     implements MethodInvocationTreeMatcher, MemberReferenceTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final String MAX_CONCURRENCY_ARG_NAME = "MAX_CONCURRENCY";
+  private static final Supplier<Type> FLUX =
+      Suppliers.typeFromString("reactor.core.publisher.Flux");
   private static final Matcher<ExpressionTree> FLUX_FLATMAP =
       instanceMethod()
-          .onDescendantOf("reactor.core.publisher.Flux")
+          .onDescendantOf(FLUX)
           .namedAnyOf("flatMap", "flatMapSequential")
           .withParameters(Function.class.getName());
+  private static final Supplier<Type> FLUX_OF_PUBLISHERS =
+      VisitorState.memoize(
+          generic(FLUX, subOf(generic(type("org.reactivestreams.Publisher"), unbound()))));
+
+  /** Instantiates a new {@link FluxFlatMapUsage} instance. */
+  public FluxFlatMapUsage() {}
 
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
@@ -64,14 +80,27 @@ public final class FluxFlatMapUsage extends BugChecker
       return Description.NO_MATCH;
     }
 
-    return buildDescription(tree)
-        .addFix(SuggestedFixes.renameMethodInvocation(tree, "concatMap", state))
-        .addFix(
-            SuggestedFix.builder()
-                .postfixWith(
-                    Iterables.getOnlyElement(tree.getArguments()), ", " + MAX_CONCURRENCY_ARG_NAME)
-                .build())
-        .build();
+    SuggestedFix serializationFix = SuggestedFixes.renameMethodInvocation(tree, "concatMap", state);
+    SuggestedFix concurrencyCapFix =
+        SuggestedFix.builder()
+            .postfixWith(
+                Iterables.getOnlyElement(tree.getArguments()), ", " + MAX_CONCURRENCY_ARG_NAME)
+            .build();
+
+    Description.Builder description = buildDescription(tree);
+
+    if (state.getTypes().isSubtype(ASTHelpers.getType(tree), FLUX_OF_PUBLISHERS.get(state))) {
+      /*
+       * Nested publishers may need to be subscribed to eagerly in order to avoid a deadlock, e.g.
+       * if they are produced by `Flux#groupBy`. In this case we suggest specifying an explicit
+       * concurrently bound, in favour of sequential subscriptions using `Flux#concatMap`.
+       */
+      description.addFix(concurrencyCapFix).addFix(serializationFix);
+    } else {
+      description.addFix(serializationFix).addFix(concurrencyCapFix);
+    }
+
+    return description.build();
   }
 
   @Override

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 javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
@@ -129,6 +129,9 @@ public final class FormatStringConcatenation extends BugChecker
           .onDescendantOf("org.slf4j.Logger")
           .namedAnyOf("debug", "error", "info", "trace", "warn");
 
+  /** Instantiates a new {@link FormatStringConcatenation} instance. */
+  public FormatStringConcatenation() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (hasNonConstantStringConcatenationArgument(tree, 0, state)) {
@@ -204,7 +207,7 @@ public final class FormatStringConcatenation extends BugChecker
   }
 
   private static class ReplacementArgumentsConstructor
-      extends SimpleTreeVisitor<Void, VisitorState> {
+      extends SimpleTreeVisitor<@Nullable Void, VisitorState> {
     private final StringBuilder formatString = new StringBuilder();
     private final List<Tree> formatArguments = new ArrayList<>();
     private final String formatSpecifier;
@@ -213,9 +216,8 @@ public final class FormatStringConcatenation extends BugChecker
       this.formatSpecifier = formatSpecifier;
     }
 
-    @Nullable
     @Override
-    public Void visitBinary(BinaryTree tree, VisitorState state) {
+    public @Nullable Void visitBinary(BinaryTree tree, VisitorState state) {
       if (tree.getKind() == Kind.PLUS && isStringTyped(tree, state)) {
         tree.getLeftOperand().accept(this, state);
         tree.getRightOperand().accept(this, state);
@@ -226,15 +228,13 @@ public final class FormatStringConcatenation extends BugChecker
       return null;
     }
 
-    @Nullable
     @Override
-    public Void visitParenthesized(ParenthesizedTree tree, VisitorState state) {
+    public @Nullable Void visitParenthesized(ParenthesizedTree tree, VisitorState state) {
       return tree.getExpression().accept(this, state);
     }
 
-    @Nullable
     @Override
-    protected Void defaultAction(Tree tree, VisitorState state) {
+    protected @Nullable Void defaultAction(Tree tree, VisitorState state) {
       appendExpression(tree);
       return null;
     }

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",
@@ -60,18 +68,17 @@ 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")
               .namedAnyOf("concat", "firstWithSignal", "from", "merge"),
           staticMethod().onClass("reactor.core.publisher.Mono").namedAnyOf("from", "fromDirect"));
 
+  /** Instantiates a new {@link IdentityConversion} instance. */
+  public IdentityConversion() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     List<? extends ExpressionTree> arguments = tree.getArguments();
@@ -92,6 +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/ImmutablesSortedSetComparator.java

@@ -67,6 +67,9 @@ public final class ImmutablesSortedSetComparator extends BugChecker implements M
                   hasAnnotation("org.immutables.value.Value.NaturalOrder"),
                   hasAnnotation("org.immutables.value.Value.ReverseOrder"))));
 
+  /** Instantiates a new {@link ImmutablesSortedSetComparator} instance. */
+  public ImmutablesSortedSetComparator() {}
+
   @Override
   public Description matchMethod(MethodTree tree, VisitorState state) {
     if (!METHOD_LACKS_ANNOTATION.matches(tree, state)) {

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

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

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

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

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

@@ -3,19 +3,19 @@ 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.JavaKeywords.isValidIdentifier;
+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;
@@ -24,19 +24,15 @@ 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.matchers.MultiMatcher;
-import com.google.errorprone.predicates.TypePredicate;
 import com.google.errorprone.util.ASTHelpers;
-import com.sun.source.tree.AnnotationTree;
-import com.sun.source.tree.ClassTree;
 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;
+import com.sun.tools.javac.code.Symbol.MethodSymbol;
+import com.sun.tools.javac.code.Type;
 import java.util.Optional;
 import javax.lang.model.element.Modifier;
-import javax.lang.model.element.Name;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /** A {@link BugChecker} that flags non-canonical JUnit method declarations. */
@@ -56,32 +52,19 @@ 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))));
-  private static final MultiMatcher<MethodTree, AnnotationTree> TEST_METHOD =
-      annotations(
-          AT_LEAST_ONE,
-          anyOf(
-              isType("org.junit.jupiter.api.Test"),
-              hasMetaAnnotation("org.junit.jupiter.api.TestTemplate")));
-  private static final MultiMatcher<MethodTree, AnnotationTree> SETUP_OR_TEARDOWN_METHOD =
-      annotations(
-          AT_LEAST_ONE,
-          anyOf(
-              isType("org.junit.jupiter.api.AfterAll"),
-              isType("org.junit.jupiter.api.AfterEach"),
-              isType("org.junit.jupiter.api.BeforeAll"),
-              isType("org.junit.jupiter.api.BeforeEach")));
+      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;
     }
 
@@ -103,10 +86,11 @@ 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)
+                findMethodRenameBlocker(symbol, newName, state)
                     .ifPresentOrElse(
                         blocker -> reportMethodRenameBlocker(tree, blocker, state),
                         () -> fixBuilder.merge(SuggestedFixes.renameMethod(tree, newName, state))));
@@ -138,30 +122,29 @@ public final class JUnitMethodDeclaration extends BugChecker implements MethodTr
    *       consideration cannot be referenced directly.)
    * </ul>
    */
-  private static Optional<String> findMethodRenameBlocker(String methodName, VisitorState state) {
-    if (isMethodInEnclosingClass(methodName, state)) {
+  private 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` already exists in this class", methodName));
+          String.format(
+              "a method named `%s` is already defined in this class or a supertype", newName));
     }
 
-    if (isSimpleNameStaticallyImported(methodName, state)) {
-      return Optional.of(String.format("`%s` is already statically imported", methodName));
+    if (isSimpleNameStaticallyImported(newName, state)) {
+      return Optional.of(String.format("`%s` is already statically imported", newName));
     }
 
-    if (isReservedKeyword(methodName)) {
-      return Optional.of(String.format("`%s` is a reserved keyword", methodName));
+    if (!isValidIdentifier(newName)) {
+      return Optional.of(String.format("`%s` is not a valid identifier", newName));
     }
 
     return Optional.empty();
   }
 
-  private static boolean isMethodInEnclosingClass(String methodName, VisitorState state) {
-    return state.findEnclosing(ClassTree.class).getMembers().stream()
-        .filter(MethodTree.class::isInstance)
-        .map(MethodTree.class::cast)
-        .map(MethodTree::getName)
-        .map(Name::toString)
-        .anyMatch(methodName::equals);
+  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) {
@@ -177,8 +160,8 @@ public final class JUnitMethodDeclaration extends BugChecker implements MethodTr
     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(Symbol symbol) {
+    return Optional.of(symbol.getQualifiedName().toString())
         .filter(name -> name.startsWith(TEST_PREFIX))
         .map(name -> name.substring(TEST_PREFIX.length()))
         .filter(not(String::isEmpty))
@@ -186,17 +169,9 @@ public final class JUnitMethodDeclaration extends BugChecker implements MethodTr
         .filter(name -> !Character.isDigit(name.charAt(0)));
   }
 
-  // XXX: Move to a `MoreMatchers` utility class.
-  private static Matcher<AnnotationTree> hasMetaAnnotation(String annotationClassName) {
-    TypePredicate typePredicate = hasAnnotation(annotationClassName);
-    return (tree, state) -> {
-      Symbol sym = ASTHelpers.getSymbol(tree);
-      return sym != null && typePredicate.apply(sym.type, state);
-    };
-  }
-
-  // XXX: Move to a `MoreTypePredicates` utility class.
-  private static TypePredicate hasAnnotation(String annotationClassName) {
-    return (type, state) -> ASTHelpers.hasAnnotation(type.tsym, annotationClassName, state);
+  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 javax.annotation.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;
 
 /**
@@ -82,7 +83,7 @@ public final class LexicographicalAnnotationAttributeListing extends BugChecker
 
   private final AnnotationAttributeMatcher matcher;
 
-  /** Instantiates the default {@link LexicographicalAnnotationAttributeListing}. */
+  /** Instantiates a default {@link LexicographicalAnnotationAttributeListing} instance. */
   public LexicographicalAnnotationAttributeListing() {
     this(ErrorProneFlags.empty());
   }
@@ -184,17 +185,15 @@ public final class LexicographicalAnnotationAttributeListing extends BugChecker
   private static ImmutableList<ImmutableList<String>> getStructure(ExpressionTree array) {
     ImmutableList.Builder<ImmutableList<String>> nodes = ImmutableList.builder();
 
-    new TreeScanner<Void, Void>() {
-      @Nullable
+    new TreeScanner<@Nullable Void, @Nullable Void>() {
       @Override
-      public Void visitIdentifier(IdentifierTree node, @Nullable Void unused) {
+      public @Nullable Void visitIdentifier(IdentifierTree node, @Nullable Void unused) {
         nodes.add(ImmutableList.of(node.getName().toString()));
         return super.visitIdentifier(node, unused);
       }
 
-      @Nullable
       @Override
-      public Void visitLiteral(LiteralTree node, @Nullable Void unused) {
+      public @Nullable Void visitLiteral(LiteralTree node, @Nullable Void unused) {
         Object value = ASTHelpers.constValue(node);
         nodes.add(
             value instanceof String
@@ -204,9 +203,8 @@ public final class LexicographicalAnnotationAttributeListing extends BugChecker
         return super.visitLiteral(node, unused);
       }
 
-      @Nullable
       @Override
-      public Void visitPrimitiveType(PrimitiveTypeTree node, @Nullable Void unused) {
+      public @Nullable Void visitPrimitiveType(PrimitiveTypeTree node, @Nullable Void unused) {
         nodes.add(ImmutableList.of(node.getPrimitiveTypeKind().toString()));
         return super.visitPrimitiveType(node, unused);
       }
@@ -223,7 +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

@@ -4,10 +4,13 @@ import static com.google.common.collect.ImmutableList.toImmutableList;
 import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
 import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
 import static com.google.errorprone.BugPattern.StandardTags.STYLE;
+import static com.sun.tools.javac.code.TypeAnnotations.AnnotationType.DECLARATION;
+import static com.sun.tools.javac.code.TypeAnnotations.AnnotationType.TYPE;
 import static java.util.Comparator.comparing;
 import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
+import com.google.common.base.VerifyException;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Streams;
 import com.google.errorprone.BugPattern;
@@ -17,10 +20,14 @@ import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
 import com.google.errorprone.fixes.Fix;
 import com.google.errorprone.fixes.SuggestedFix;
 import com.google.errorprone.matchers.Description;
+import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.AnnotationTree;
 import com.sun.source.tree.MethodTree;
+import com.sun.tools.javac.code.Symbol;
+import com.sun.tools.javac.code.TypeAnnotations.AnnotationType;
+import java.util.Comparator;
 import java.util.List;
-import java.util.Optional;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
@@ -39,6 +46,12 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 public final class LexicographicalAnnotationListing extends BugChecker
     implements MethodTreeMatcher {
   private static final long serialVersionUID = 1L;
+  private static final Comparator<@Nullable AnnotationType> BY_ANNOTATION_TYPE =
+      (a, b) ->
+          (a == null || a == DECLARATION) && b == TYPE ? -1 : a == TYPE && b == DECLARATION ? 1 : 0;
+
+  /** Instantiates a new {@link LexicographicalAnnotationListing} instance. */
+  public LexicographicalAnnotationListing() {}
 
   @Override
   public Description matchMethod(MethodTree tree, VisitorState state) {
@@ -47,26 +60,29 @@ public final class LexicographicalAnnotationListing extends BugChecker
       return Description.NO_MATCH;
     }
 
-    ImmutableList<? extends AnnotationTree> sortedAnnotations = sort(originalOrdering, state);
+    ImmutableList<? extends AnnotationTree> sortedAnnotations =
+        sort(originalOrdering, ASTHelpers.getSymbol(tree), state);
     if (originalOrdering.equals(sortedAnnotations)) {
       return Description.NO_MATCH;
     }
 
-    Optional<Fix> fix = tryFixOrdering(originalOrdering, sortedAnnotations, state);
-
-    Description.Builder description = buildDescription(originalOrdering.get(0));
-    fix.ifPresent(description::addFix);
-    return description.build();
+    return describeMatch(
+        originalOrdering.get(0), fixOrdering(originalOrdering, sortedAnnotations, state));
   }
 
   private static ImmutableList<? extends AnnotationTree> sort(
-      List<? extends AnnotationTree> annotations, VisitorState state) {
+      List<? extends AnnotationTree> annotations, Symbol symbol, VisitorState state) {
     return annotations.stream()
-        .sorted(comparing(annotation -> SourceCode.treeToString(annotation, state)))
+        .sorted(
+            comparing(
+                    (AnnotationTree annotation) ->
+                        ASTHelpers.getAnnotationType(annotation, symbol, state),
+                    BY_ANNOTATION_TYPE)
+                .thenComparing(annotation -> SourceCode.treeToString(annotation, state)))
         .collect(toImmutableList());
   }
 
-  private static Optional<Fix> tryFixOrdering(
+  private static Fix fixOrdering(
       List<? extends AnnotationTree> originalAnnotations,
       ImmutableList<? extends AnnotationTree> sortedAnnotations,
       VisitorState state) {
@@ -77,6 +93,7 @@ public final class LexicographicalAnnotationListing extends BugChecker
                 SuggestedFix.builder()
                     .replace(original, SourceCode.treeToString(replacement, state)))
         .reduce(SuggestedFix.Builder::merge)
-        .map(SuggestedFix.Builder::build);
+        .map(SuggestedFix.Builder::build)
+        .orElseThrow(() -> new VerifyException("No annotations were provided"));
   }
 }

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

@@ -37,6 +37,8 @@ import javax.lang.model.element.Name;
 
 /**
  * A {@link BugChecker} that flags lambda expressions that can be replaced with method references.
+ *
+ * @see IsInstanceLambdaUsage
  */
 // XXX: Other custom expressions we could rewrite:
 // - `a -> "str" + a` to `"str"::concat`. But only if `str` is provably non-null.
@@ -50,6 +52,9 @@ import javax.lang.model.element.Name;
 // `not(some::reference)`.
 // XXX: This check is extremely inefficient due to its reliance on `SuggestedFixes.compilesWithFix`.
 // Palantir's `LambdaMethodReference` check seems to suffer a similar issue at this time.
+// XXX: Expressions of the form `i -> SomeType.class.isInstance(i)` are not replaced; fix that using
+// a suitable generalization.
+// XXX: Consider folding the `IsInstanceLambdaUsage` check into this class.
 @AutoService(BugChecker.class)
 @BugPattern(
     summary = "Prefer method references over lambda expressions",
@@ -60,6 +65,9 @@ import javax.lang.model.element.Name;
 public final class MethodReferenceUsage extends BugChecker implements LambdaExpressionTreeMatcher {
   private static final long serialVersionUID = 1L;
 
+  /** Instantiates a new {@link MethodReferenceUsage} instance. */
+  public MethodReferenceUsage() {}
+
   @Override
   public Description matchLambdaExpression(LambdaExpressionTree tree, VisitorState state) {
     /*
@@ -122,7 +130,7 @@ public final class MethodReferenceUsage extends BugChecker implements LambdaExpr
           return Optional.empty();
         }
         Symbol sym = ASTHelpers.getSymbol(methodSelect);
-        if (!sym.isStatic()) {
+        if (!ASTHelpers.isStatic(sym)) {
           return constructFix(lambdaExpr, "this", methodSelect);
         }
         return constructFix(lambdaExpr, sym.owner, methodSelect);
@@ -192,7 +200,7 @@ public final class MethodReferenceUsage extends BugChecker implements LambdaExpr
     Name sName = target.getSimpleName();
     Optional<SuggestedFix.Builder> fix = constructFix(lambdaExpr, sName, methodName);
 
-    if (!"java.lang".equals(target.packge().toString())) {
+    if (!"java.lang".equals(ASTHelpers.enclosingPackage(target).toString())) {
       Name fqName = target.getQualifiedName();
       if (!sName.equals(fqName)) {
         return fix.map(b -> b.addImport(fqName.toString()));

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

@@ -40,6 +40,9 @@ public final class MissingRefasterAnnotation extends BugChecker implements Class
               isType("com.google.errorprone.refaster.annotation.BeforeTemplate"),
               isType("com.google.errorprone.refaster.annotation.AfterTemplate")));
 
+  /** Instantiates a new {@link MissingRefasterAnnotation} instance. */
+  public MissingRefasterAnnotation() {}
+
   @Override
   public Description matchClass(ClassTree tree, VisitorState state) {
     long methodTypes =

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

@@ -36,6 +36,9 @@ public final class MockitoStubbing extends BugChecker implements MethodInvocatio
   private static final Matcher<ExpressionTree> MOCKITO_EQ_METHOD =
       staticMethod().onClass("org.mockito.ArgumentMatchers").named("eq");
 
+  /** Instantiates a new {@link MockitoStubbing} instance. */
+  public MockitoStubbing() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     List<? extends ExpressionTree> arguments = tree.getArguments();

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

@@ -4,9 +4,11 @@ import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
 import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
 import static com.google.errorprone.BugPattern.StandardTags.FRAGILE_CODE;
 import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.generic;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.raw;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.subOf;
 
 import com.google.auto.service.AutoService;
-import com.google.common.collect.Iterables;
 import com.google.errorprone.BugPattern;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker;
@@ -16,9 +18,7 @@ import com.google.errorprone.suppliers.Supplier;
 import com.google.errorprone.suppliers.Suppliers;
 import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.MethodInvocationTree;
-import com.sun.source.tree.Tree;
 import com.sun.tools.javac.code.Type;
-import com.sun.tools.javac.util.List;
 import java.util.Optional;
 
 /** A {@link BugChecker} that flags nesting of {@link Optional Optionals}. */
@@ -33,21 +33,19 @@ import java.util.Optional;
 public final class NestedOptionals extends BugChecker implements MethodInvocationTreeMatcher {
   private static final long serialVersionUID = 1L;
   private static final Supplier<Type> OPTIONAL = Suppliers.typeFromClass(Optional.class);
+  private static final Supplier<Type> OPTIONAL_OF_OPTIONAL =
+      VisitorState.memoize(generic(OPTIONAL, subOf(raw(OPTIONAL))));
+
+  /** Instantiates a new {@link NestedOptionals} instance. */
+  public NestedOptionals() {}
 
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
-    return isOptionalOfOptional(tree, state) ? describeMatch(tree) : Description.NO_MATCH;
-  }
-
-  private static boolean isOptionalOfOptional(Tree tree, VisitorState state) {
-    Type optionalType = OPTIONAL.get(state);
-    Type type = ASTHelpers.getType(tree);
-    if (!ASTHelpers.isSubtype(type, optionalType, state)) {
-      return false;
+    Type type = OPTIONAL_OF_OPTIONAL.get(state);
+    if (type == null || !state.getTypes().isSubtype(ASTHelpers.getType(tree), type)) {
+      return Description.NO_MATCH;
     }
 
-    List<Type> typeArguments = type.getTypeArguments();
-    return !typeArguments.isEmpty()
-        && ASTHelpers.isSubtype(Iterables.getOnlyElement(typeArguments), optionalType, state);
+    return describeMatch(tree);
   }
 }

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

@@ -76,6 +76,9 @@ public final class NonEmptyMono extends BugChecker implements MethodInvocationTr
               .onDescendantOf("reactor.core.publisher.Mono")
               .namedAnyOf("defaultIfEmpty", "hasElement", "single"));
 
+  /** Instantiates a new {@link NonEmptyMono} instance. */
+  public NonEmptyMono() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (!MONO_SIZE_CHECK.matches(tree, state)) {

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

@@ -70,6 +70,9 @@ public final class PrimitiveComparison extends BugChecker implements MethodInvoc
               .named("thenComparing")
               .withParameters(Function.class.getName()));
 
+  /** Instantiates a new {@link PrimitiveComparison} instance. */
+  public PrimitiveComparison() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     boolean isStatic = STATIC_COMPARISON_METHOD.matches(tree, state);

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;
@@ -141,7 +141,7 @@ public final class RedundantStringConversion extends BugChecker
 
   private final Matcher<MethodInvocationTree> conversionMethodMatcher;
 
-  /** Instantiates the default {@link RedundantStringConversion}. */
+  /** Instantiates a default {@link RedundantStringConversion} instance. */
   public RedundantStringConversion() {
     this(ErrorProneFlags.empty());
   }
@@ -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/RefasterAnyOfUsage.java

@@ -37,6 +37,9 @@ public final class RefasterAnyOfUsage extends BugChecker implements MethodInvoca
   private static final Matcher<ExpressionTree> REFASTER_ANY_OF =
       staticMethod().onClass(Refaster.class.getName()).named("anyOf");
 
+  /** Instantiates a new {@link RefasterAnyOfUsage} instance. */
+  public RefasterAnyOfUsage() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (REFASTER_ANY_OF.matches(tree, state)) {

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

@@ -29,7 +29,7 @@ import java.util.Set;
 import javax.lang.model.element.Modifier;
 
 /**
- * A {@link BugChecker} which suggests a canonical set of modifiers for Refaster class and method
+ * A {@link BugChecker} that suggests a canonical set of modifiers for Refaster class and method
  * definitions.
  */
 @AutoService(BugChecker.class)
@@ -48,6 +48,9 @@ public final class RefasterRuleModifiers extends BugChecker
   private static final Matcher<Tree> REFASTER_METHOD =
       anyOf(BEFORE_TEMPLATE_METHOD, AFTER_TEMPLATE_METHOD, PLACEHOLDER_METHOD);
 
+  /** Instantiates a new {@link RefasterRuleModifiers} instance. */
+  public RefasterRuleModifiers() {}
+
   @Override
   public Description matchClass(ClassTree tree, VisitorState state) {
     if (!hasMatchingMember(tree, BEFORE_TEMPLATE_METHOD, state)) {

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

@@ -83,6 +83,9 @@ public final class RequestMappingAnnotation extends BugChecker implements Method
                   isSameType("org.springframework.web.util.UriBuilder"),
                   isSameType("org.springframework.web.util.UriComponentsBuilder"))));
 
+  /** Instantiates a new {@link RequestMappingAnnotation} instance. */
+  public RequestMappingAnnotation() {}
+
   @Override
   public Description matchMethod(MethodTree tree, VisitorState state) {
     // XXX: Auto-add `@RequestParam` where applicable.

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;
@@ -9,38 +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";
+
+  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/ScheduledTransactionTrace.java

@@ -26,6 +26,7 @@ import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.AnnotationTree;
 import com.sun.source.tree.MethodTree;
 import com.sun.source.tree.Tree;
+import tech.picnic.errorprone.bugpatterns.util.ThirdPartyLibrary;
 
 /**
  * A {@link BugChecker} that flags methods with Spring's {@code @Scheduled} annotation that lack New
@@ -46,9 +47,13 @@ public final class ScheduledTransactionTrace extends BugChecker implements Metho
   private static final MultiMatcher<Tree, AnnotationTree> TRACE_ANNOTATION =
       annotations(AT_LEAST_ONE, isType(TRACE_ANNOTATION_FQCN));
 
+  /** Instantiates a new {@link ScheduledTransactionTrace} instance. */
+  public ScheduledTransactionTrace() {}
+
   @Override
   public Description matchMethod(MethodTree tree, VisitorState state) {
-    if (!IS_SCHEDULED.matches(tree, state)) {
+    if (!ThirdPartyLibrary.NEW_RELIC_AGENT_API.isIntroductionAllowed(state)
+        || !IS_SCHEDULED.matches(tree, state)) {
       return Description.NO_MATCH;
     }
 

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

@@ -48,6 +48,9 @@ public final class Slf4jLogStatement extends BugChecker implements MethodInvocat
           .onDescendantOf("org.slf4j.Logger")
           .namedAnyOf("trace", "debug", "info", "warn", "error");
 
+  /** Instantiates a new {@link Slf4jLogStatement} instance. */
+  public Slf4jLogStatement() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (!SLF4J_LOGGER_INVOCATION.matches(tree, state)) {

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

@@ -57,6 +57,9 @@ public final class SpringMvcAnnotation extends BugChecker implements AnnotationT
           .put("PUT", "PutMapping")
           .build();
 
+  /** Instantiates a new {@link SpringMvcAnnotation} instance. */
+  public SpringMvcAnnotation() {}
+
   @Override
   public Description matchAnnotation(AnnotationTree tree, VisitorState state) {
     // XXX: We could remove the `@RequestMapping` import if not other usages remain.

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

@@ -101,7 +101,8 @@ public final class StaticImport extends BugChecker implements MemberSelectTreeMa
           "org.springframework.http.HttpMethod",
           "org.springframework.http.MediaType",
           "org.testng.Assert",
-          "reactor.function.TupleUtils");
+          "reactor.function.TupleUtils",
+          "tech.picnic.errorprone.bugpatterns.util.MoreTypes");
 
   /** Type members that should be statically imported. */
   @VisibleForTesting
@@ -190,6 +191,9 @@ public final class StaticImport extends BugChecker implements MemberSelectTreeMa
           "of",
           "valueOf");
 
+  /** Instantiates a new {@link StaticImport} instance. */
+  public StaticImport() {}
+
   @Override
   public Description matchMemberSelect(MemberSelectTree tree, VisitorState state) {
     if (!isCandidateContext(state) || !isCandidate(tree)) {

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

@@ -1,9 +1,10 @@
 package tech.picnic.errorprone.bugpatterns;
 
-import static com.google.errorprone.BugPattern.LinkType.NONE;
+import static com.google.errorprone.BugPattern.LinkType.CUSTOM;
 import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
 import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
 import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
+import static tech.picnic.errorprone.bugpatterns.util.Documentation.BUG_PATTERNS_BASE_URL;
 
 import com.google.auto.service.AutoService;
 import com.google.common.base.Splitter;
@@ -26,12 +27,12 @@ import com.sun.tools.javac.util.Convert;
 import java.util.Formattable;
 import java.util.Iterator;
 import java.util.List;
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 
 /**
- * A {@link BugChecker} which flags {@link String#format(String, Object...)} invocations which can
- * be replaced with a {@link String#join(CharSequence, CharSequence...)} or even a {@link
+ * A {@link BugChecker} that flags {@link String#format(String, Object...)} invocations which can be
+ * replaced with a {@link String#join(CharSequence, CharSequence...)} or even a {@link
  * String#valueOf} invocation.
  */
 // XXX: What about `v1 + "sep" + v2` and similar expressions? Do we want to rewrite those to
@@ -40,7 +41,8 @@ import tech.picnic.errorprone.bugpatterns.util.SourceCode;
 @AutoService(BugChecker.class)
 @BugPattern(
     summary = "Prefer `String#join` over `String#format`",
-    linkType = NONE,
+    link = BUG_PATTERNS_BASE_URL + "StringJoin",
+    linkType = CUSTOM,
     severity = SUGGESTION,
     tags = SIMPLIFICATION)
 public final class StringJoin extends BugChecker implements MethodInvocationTreeMatcher {
@@ -52,6 +54,9 @@ public final class StringJoin extends BugChecker implements MethodInvocationTree
       Suppliers.typeFromClass(CharSequence.class);
   private static final Supplier<Type> FORMATTABLE_TYPE = Suppliers.typeFromClass(Formattable.class);
 
+  /** Instantiates a new {@link StringJoin} instance. */
+  public StringJoin() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     if (!STRING_FORMAT_INVOCATION.matches(tree, state)) {

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

@@ -26,6 +26,9 @@ import java.time.Instant;
 import java.time.LocalDate;
 import java.time.LocalDateTime;
 import java.time.LocalTime;
+import java.time.OffsetDateTime;
+import java.time.OffsetTime;
+import java.time.ZonedDateTime;
 
 /** A {@link BugChecker} that flags illegal time-zone related operations. */
 @AutoService(BugChecker.class)
@@ -58,10 +61,16 @@ public final class TimeZoneUsage extends BugChecker implements MethodInvocationT
               .onClassAny(
                   LocalDate.class.getName(),
                   LocalDateTime.class.getName(),
-                  LocalTime.class.getName())
+                  LocalTime.class.getName(),
+                  OffsetDateTime.class.getName(),
+                  OffsetTime.class.getName(),
+                  ZonedDateTime.class.getName())
               .named("now"),
           staticMethod().onClassAny(Instant.class.getName()).named("now").withNoParameters());
 
+  /** Instantiates a new {@link TimeZoneUsage} instance. */
+  public TimeZoneUsage() {}
+
   @Override
   public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
     return BANNED_TIME_METHOD.matches(tree, state)

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

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

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

@@ -21,6 +21,9 @@ public final class MethodMatcherFactory {
   private static final Pattern METHOD_SIGNATURE =
       Pattern.compile("([^\\s#(,)]+)#([^\\s#(,)]+)\\(((?:[^\\s#(,)]+(?:,[^\\s#(,)]+)*)?)\\)");
 
+  /** Instantiates a new {@link MethodMatcherFactory} instance. */
+  public MethodMatcherFactory() {}
+
   /**
    * Creates a {@link Matcher} of methods with any of the given signatures.
    *

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

@@ -0,0 +1,49 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.collect.ImmutableList.toImmutableList;
+
+import com.google.common.collect.ImmutableList;
+import com.google.errorprone.VisitorState;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.MethodTree;
+
+/**
+ * A collection of helper methods for working with the AST.
+ *
+ * <p>These methods are additions to the ones found in {@link
+ * com.google.errorprone.util.ASTHelpers}.
+ */
+public final class MoreASTHelpers {
+  private MoreASTHelpers() {}
+
+  /**
+   * Finds methods with the specified name in given the {@link VisitorState}'s current enclosing
+   * class.
+   *
+   * @param methodName The method name to search for.
+   * @param state The {@link VisitorState} from which to derive the enclosing class of interest.
+   * @return The {@link MethodTree}s of the methods with the given name in the enclosing class.
+   */
+  public static ImmutableList<MethodTree> findMethods(CharSequence methodName, VisitorState state) {
+    ClassTree clazz = state.findEnclosing(ClassTree.class);
+    checkArgument(clazz != null, "Visited node is not enclosed by a class");
+    return clazz.getMembers().stream()
+        .filter(MethodTree.class::isInstance)
+        .map(MethodTree.class::cast)
+        .filter(method -> method.getName().contentEquals(methodName))
+        .collect(toImmutableList());
+  }
+
+  /**
+   * Determines whether there are any methods with the specified name in given the {@link
+   * VisitorState}'s current enclosing class.
+   *
+   * @param methodName The method name to search for.
+   * @param state The {@link VisitorState} from which to derive the enclosing class of interest.
+   * @return Whether there are any methods with the given name in the enclosing class.
+   */
+  public static boolean methodExistsInEnclosingClass(CharSequence methodName, VisitorState state) {
+    return !findMethods(methodName, state).isEmpty();
+  }
+}

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

@@ -0,0 +1,81 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
+import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
+import static com.google.errorprone.matchers.Matchers.annotations;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.isType;
+import static java.util.Objects.requireNonNullElse;
+import static tech.picnic.errorprone.bugpatterns.util.MoreMatchers.hasMetaAnnotation;
+
+import com.google.common.base.Strings;
+import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.matchers.AnnotationMatcherUtils;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.matchers.MultiMatcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodTree;
+import com.sun.source.tree.NewArrayTree;
+import org.jspecify.annotations.Nullable;
+
+/**
+ * A collection of JUnit-specific helper methods and {@link Matcher}s.
+ *
+ * <p>These constants and methods are additions to the ones found in {@link
+ * com.google.errorprone.matchers.JUnitMatchers}.
+ */
+public final class MoreJUnitMatchers {
+  /** Matches JUnit Jupiter test methods. */
+  public static final MultiMatcher<MethodTree, AnnotationTree> TEST_METHOD =
+      annotations(
+          AT_LEAST_ONE,
+          anyOf(
+              isType("org.junit.jupiter.api.Test"),
+              hasMetaAnnotation("org.junit.jupiter.api.TestTemplate")));
+  /** Matches JUnit Jupiter setup and teardown methods. */
+  public static final MultiMatcher<MethodTree, AnnotationTree> SETUP_OR_TEARDOWN_METHOD =
+      annotations(
+          AT_LEAST_ONE,
+          anyOf(
+              isType("org.junit.jupiter.api.AfterAll"),
+              isType("org.junit.jupiter.api.AfterEach"),
+              isType("org.junit.jupiter.api.BeforeAll"),
+              isType("org.junit.jupiter.api.BeforeEach")));
+  /**
+   * Matches methods that have a {@link org.junit.jupiter.params.provider.MethodSource} annotation.
+   */
+  public static final MultiMatcher<MethodTree, AnnotationTree> HAS_METHOD_SOURCE =
+      annotations(AT_LEAST_ONE, isType("org.junit.jupiter.params.provider.MethodSource"));
+
+  private MoreJUnitMatchers() {}
+
+  /**
+   * Returns the names of the JUnit value factory methods specified by the given {@link
+   * org.junit.jupiter.params.provider.MethodSource} annotation.
+   *
+   * @param methodSourceAnnotation The annotation from which to extract value factory method names.
+   * @return One or more value factory names.
+   */
+  static ImmutableSet<String> getMethodSourceFactoryNames(
+      AnnotationTree methodSourceAnnotation, MethodTree method) {
+    String methodName = method.getName().toString();
+    ExpressionTree value = AnnotationMatcherUtils.getArgument(methodSourceAnnotation, "value");
+
+    if (!(value instanceof NewArrayTree)) {
+      return ImmutableSet.of(toMethodSourceFactoryName(value, methodName));
+    }
+
+    return ((NewArrayTree) value)
+        .getInitializers().stream()
+            .map(name -> toMethodSourceFactoryName(name, methodName))
+            .collect(toImmutableSet());
+  }
+
+  private static String toMethodSourceFactoryName(
+      @Nullable ExpressionTree tree, String annotatedMethodName) {
+    return requireNonNullElse(
+        Strings.emptyToNull(ASTHelpers.constValue(tree, String.class)), annotatedMethodName);
+  }
+}

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

@@ -0,0 +1,39 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.matchers.Matchers;
+import com.google.errorprone.predicates.TypePredicate;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.tools.javac.code.Symbol;
+
+/**
+ * A collection of general-purpose {@link Matcher}s.
+ *
+ * <p>These methods are additions to the ones found in {@link Matchers}.
+ */
+public final class MoreMatchers {
+  private MoreMatchers() {}
+
+  /**
+   * Returns a {@link Matcher} that determines whether a given {@link AnnotationTree} has a
+   * meta-annotation of the specified type.
+   *
+   * @param <T> The type of tree to match against.
+   * @param annotationType The binary type name of the annotation (e.g.
+   *     "org.jspecify.annotations.Nullable", or "some.package.OuterClassName$InnerClassName")
+   * @return A {@link Matcher} that matches trees with the specified meta-annotation.
+   */
+  public static <T extends AnnotationTree> Matcher<T> hasMetaAnnotation(String annotationType) {
+    TypePredicate typePredicate = hasAnnotation(annotationType);
+    return (tree, state) -> {
+      Symbol sym = ASTHelpers.getSymbol(tree);
+      return sym != null && typePredicate.apply(sym.type, state);
+    };
+  }
+
+  // XXX: Consider moving to a `MoreTypePredicates` utility class.
+  private static TypePredicate hasAnnotation(String annotationClassName) {
+    return (type, state) -> ASTHelpers.hasAnnotation(type.tsym, annotationClassName, state);
+  }
+}

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

@@ -0,0 +1,132 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static java.util.stream.Collectors.toCollection;
+
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.suppliers.Supplier;
+import com.google.errorprone.suppliers.Suppliers;
+import com.sun.tools.javac.code.BoundKind;
+import com.sun.tools.javac.code.Type;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.function.BiFunction;
+
+/**
+ * A set of helper methods which together define a DSL for defining {@link Type types}.
+ *
+ * <p>These methods are meant to be statically imported. Example usage:
+ *
+ * <pre>{@code
+ * Supplier<Type> type =
+ *     VisitorState.memoize(
+ *         generic(
+ *             type("reactor.core.publisher.Flux"),
+ *             subOf(generic(type("org.reactivestreams.Publisher"), unbound()))));
+ * }</pre>
+ *
+ * This statement produces a memoized supplier of the type {@code Flux<? extends Publisher<?>>}.
+ */
+public final class MoreTypes {
+  private MoreTypes() {}
+
+  /**
+   * Creates a supplier of the type with the given fully qualified name.
+   *
+   * <p>This method should only be used when building more complex types in combination with other
+   * {@link MoreTypes} methods. In other cases prefer directly calling {@link
+   * Suppliers#typeFromString(String)}.
+   *
+   * @param typeName The type of interest.
+   * @return A supplier which returns the described type if available in the given state, and {@code
+   *     null} otherwise.
+   */
+  public static Supplier<Type> type(String typeName) {
+    return Suppliers.typeFromString(typeName);
+  }
+
+  /**
+   * Creates a supplier of the described generic type.
+   *
+   * @param type The base type of interest.
+   * @param typeArgs The desired type arguments.
+   * @return A supplier which returns the described type if available in the given state, and {@code
+   *     null} otherwise.
+   */
+  // XXX: The given `type` should be a generic type, so perhaps `withParams` would be a better
+  // method name. But the DSL wouldn't look as nice that way.
+  @SafeVarargs
+  @SuppressWarnings("varargs")
+  public static Supplier<Type> generic(Supplier<Type> type, Supplier<Type>... typeArgs) {
+    return propagateNull(
+        type,
+        (state, baseType) -> {
+          List<Type> params =
+              Arrays.stream(typeArgs).map(s -> s.get(state)).collect(toCollection(ArrayList::new));
+          if (params.stream().anyMatch(Objects::isNull)) {
+            return null;
+          }
+
+          return state.getType(baseType, /* isArray= */ false, params);
+        });
+  }
+
+  /**
+   * Creates a raw (erased, non-generic) variant of the given type.
+   *
+   * @param type The base type of interest.
+   * @return A supplier which returns the described type if available in the given state, and {@code
+   *     null} otherwise.
+   */
+  public static Supplier<Type> raw(Supplier<Type> type) {
+    return propagateNull(type, (state, baseType) -> baseType.tsym.erasure(state.getTypes()));
+  }
+
+  /**
+   * Creates a {@code ? super T} wildcard type, with {@code T} bound to the given type.
+   *
+   * @param type The base type of interest.
+   * @return A supplier which returns the described type if available in the given state, and {@code
+   *     null} otherwise.
+   */
+  public static Supplier<Type> superOf(Supplier<Type> type) {
+    return propagateNull(
+        type,
+        (state, baseType) ->
+            new Type.WildcardType(baseType, BoundKind.SUPER, state.getSymtab().boundClass));
+  }
+
+  /**
+   * Creates a {@code ? extends T} wildcard type, with {@code T} bound to the given type.
+   *
+   * @param type The base type of interest.
+   * @return A supplier which returns the described type if available in the given state, and {@code
+   *     null} otherwise.
+   */
+  public static Supplier<Type> subOf(Supplier<Type> type) {
+    return propagateNull(
+        type,
+        (state, baseType) ->
+            new Type.WildcardType(
+                type.get(state), BoundKind.EXTENDS, state.getSymtab().boundClass));
+  }
+
+  /**
+   * Creates an unbound wildcard type ({@code ?}).
+   *
+   * @return A supplier which returns the described type.
+   */
+  public static Supplier<Type> unbound() {
+    return state ->
+        new Type.WildcardType(
+            state.getSymtab().objectType, BoundKind.UNBOUND, state.getSymtab().boundClass);
+  }
+
+  private static Supplier<Type> propagateNull(
+      Supplier<Type> type, BiFunction<VisitorState, Type, Type> transformer) {
+    return state ->
+        Optional.ofNullable(type.get(state)).map(t -> transformer.apply(state, t)).orElse(null);
+  }
+}

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

@@ -1,14 +1,21 @@
 package tech.picnic.errorprone.bugpatterns.util;
 
+import static com.sun.tools.javac.util.Position.NOPOS;
+
+import com.google.common.base.CharMatcher;
 import com.google.errorprone.VisitorState;
+import com.google.errorprone.fixes.SuggestedFix;
 import com.sun.source.tree.Tree;
+import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
 
 /**
  * A collection of Error Prone utility methods for dealing with the source code representation of
  * AST nodes.
  */
-// XXX: Can we locate this code in a better place? Maybe contribute it upstream?
 public final class SourceCode {
+  /** The complement of {@link CharMatcher#whitespace()}. */
+  private static final CharMatcher NON_WHITESPACE_MATCHER = CharMatcher.whitespace().negate();
+
   private SourceCode() {}
 
   /**
@@ -24,4 +31,32 @@ public final class SourceCode {
     String src = state.getSourceForNode(tree);
     return src != null ? src : tree.toString();
   }
+
+  /**
+   * Creates a {@link SuggestedFix} for the deletion of the given {@link Tree}, including any
+   * whitespace that follows it.
+   *
+   * <p>Removing trailing whitespace may prevent the introduction of an empty line at the start of a
+   * code block; such empty lines are not removed when formatting the code using Google Java Format.
+   *
+   * @param tree The AST node of interest.
+   * @param state A {@link VisitorState} describing the context in which the given {@link Tree} is
+   *     found.
+   * @return A non-{@code null} {@link SuggestedFix} similar to one produced by {@link
+   *     SuggestedFix#delete(Tree)}.
+   */
+  public static SuggestedFix deleteWithTrailingWhitespace(Tree tree, VisitorState state) {
+    CharSequence sourceCode = state.getSourceCode();
+    int endPos = state.getEndPosition(tree);
+    if (sourceCode == null || endPos == NOPOS) {
+      /* We can't identify the trailing whitespace; delete just the tree. */
+      return SuggestedFix.delete(tree);
+    }
+
+    int whitespaceEndPos = NON_WHITESPACE_MATCHER.indexIn(sourceCode, endPos);
+    return SuggestedFix.replace(
+        ((DiagnosticPosition) tree).getStartPosition(),
+        whitespaceEndPos == -1 ? sourceCode.length() : whitespaceEndPos,
+        "");
+  }
 }

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

@@ -0,0 +1,105 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.suppliers.Supplier;
+import com.sun.tools.javac.code.ClassFinder;
+import com.sun.tools.javac.code.Symbol.CompletionFailure;
+import com.sun.tools.javac.util.Name;
+
+/**
+ * Utility class that helps decide whether it is appropriate to introduce references to (well-known)
+ * third-party libraries.
+ *
+ * <p>This class should be used by {@link BugChecker}s that may otherwise suggest the introduction
+ * of code that depends on possibly-not-present third-party libraries.
+ */
+// XXX: Consider giving users more fine-grained control. This would be beneficial in cases where a
+// dependency is on the classpath, but new usages are undesirable.
+public enum ThirdPartyLibrary {
+  /**
+   * AssertJ.
+   *
+   * @see <a href="https://assertj.github.io/doc">AssertJ documentation</a>
+   */
+  ASSERTJ("org.assertj.core.api.Assertions"),
+  /**
+   * Google's Guava.
+   *
+   * @see <a href="https://github.com/google/guava">Guava on GitHub</a>
+   */
+  GUAVA("com.google.common.collect.ImmutableList"),
+  /**
+   * New Relic's Java agent API.
+   *
+   * @see <a href="https://github.com/newrelic/newrelic-java-agent/tree/main/newrelic-api">New Relic
+   *     Java agent API on GitHub</a>
+   */
+  NEW_RELIC_AGENT_API("com.newrelic.api.agent.Agent"),
+  /**
+   * VMWare's Project Reactor.
+   *
+   * @see <a href="https://projectreactor.io">Home page</a>
+   */
+  REACTOR("reactor.core.publisher.Flux");
+
+  private static final String IGNORE_CLASSPATH_COMPAT_FLAG =
+      "ErrorProneSupport:IgnoreClasspathCompat";
+
+  @SuppressWarnings("ImmutableEnumChecker" /* Supplier is deterministic. */)
+  private final Supplier<Boolean> canUse;
+
+  /**
+   * Instantiates a {@link ThirdPartyLibrary} enum value.
+   *
+   * @param witnessFqcn The fully-qualified class name of a type that is expected to be on the
+   *     classpath iff the associated third-party library is on the classpath.
+   */
+  ThirdPartyLibrary(String witnessFqcn) {
+    this.canUse = VisitorState.memoize(state -> canIntroduceUsage(witnessFqcn, state));
+  }
+
+  /**
+   * Tells whether it is okay to introduce a dependency on this well-known third party library in
+   * the given context.
+   *
+   * @param state The context under consideration.
+   * @return {@code true} iff it is okay to assume or create a dependency on this library.
+   */
+  public boolean isIntroductionAllowed(VisitorState state) {
+    return canUse.get(state);
+  }
+
+  private static boolean canIntroduceUsage(String className, VisitorState state) {
+    return shouldIgnoreClasspath(state) || isKnownClass(className, state);
+  }
+
+  /**
+   * Attempts to determine whether a class with the given FQCN is on the classpath.
+   *
+   * <p>The {@link VisitorState}'s symbol table is consulted first. If the type has not yet been
+   * loaded, then an attempt is made to do so.
+   */
+  private static boolean isKnownClass(String className, VisitorState state) {
+    return state.getTypeFromString(className) != null || canLoadClass(className, state);
+  }
+
+  private static boolean canLoadClass(String className, VisitorState state) {
+    ClassFinder classFinder = ClassFinder.instance(state.context);
+    Name binaryName = state.binaryNameFromClassname(className);
+    try {
+      classFinder.loadClass(state.getSymtab().unnamedModule, binaryName);
+      return true;
+    } catch (CompletionFailure e) {
+      return false;
+    }
+  }
+
+  private static boolean shouldIgnoreClasspath(VisitorState state) {
+    return state
+        .errorProneOptions()
+        .getFlags()
+        .getBoolean(IGNORE_CLASSPATH_COMPAT_FLAG)
+        .orElse(Boolean.FALSE);
+  }
+}

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
-@javax.annotation.ParametersAreNonnullByDefault
+@org.jspecify.annotations.NullMarked
 package tech.picnic.errorprone.bugpatterns.util;

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

@@ -1,16 +1,148 @@
 package tech.picnic.errorprone.refasterrules;
 
+import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.collect.ImmutableBiMap;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableMultiset;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.ImmutableSortedMap;
+import com.google.common.collect.ImmutableSortedMultiset;
+import com.google.common.collect.ImmutableSortedSet;
+import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
 import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
 import java.util.Map;
+import java.util.TreeMap;
+import java.util.TreeSet;
+import org.assertj.core.api.AbstractAssert;
+import org.assertj.core.api.AbstractBooleanAssert;
 import org.assertj.core.api.AbstractMapAssert;
+import org.assertj.core.api.MapAssert;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 @OnlineDocumentation
 final class AssertJMapRules {
   private AssertJMapRules() {}
 
+  // XXX: Reduce boilerplate using a `Matcher` that identifies "empty" instances.
+  static final class AbstractMapAssertIsEmpty<K, V> {
+    @BeforeTemplate
+    @SuppressWarnings("unchecked")
+    void before(AbstractMapAssert<?, ?, K, V> mapAssert) {
+      Refaster.anyOf(
+          mapAssert.containsExactlyEntriesOf(
+              Refaster.anyOf(
+                  ImmutableMap.of(),
+                  ImmutableBiMap.of(),
+                  ImmutableSortedMap.of(),
+                  new HashMap<>(),
+                  new LinkedHashMap<>(),
+                  new TreeMap<>())),
+          mapAssert.hasSameSizeAs(
+              Refaster.anyOf(
+                  ImmutableMap.of(),
+                  ImmutableBiMap.of(),
+                  ImmutableSortedMap.of(),
+                  new HashMap<>(),
+                  new LinkedHashMap<>(),
+                  new TreeMap<>())),
+          mapAssert.isEqualTo(
+              Refaster.anyOf(
+                  ImmutableMap.of(),
+                  ImmutableBiMap.of(),
+                  ImmutableSortedMap.of(),
+                  new HashMap<>(),
+                  new LinkedHashMap<>(),
+                  new TreeMap<>())),
+          mapAssert.containsOnlyKeys(
+              Refaster.anyOf(
+                  ImmutableList.of(),
+                  new ArrayList<>(),
+                  ImmutableSet.of(),
+                  new HashSet<>(),
+                  new LinkedHashSet<>(),
+                  ImmutableSortedSet.of(),
+                  new TreeSet<>(),
+                  ImmutableMultiset.of(),
+                  ImmutableSortedMultiset.of())),
+          mapAssert.containsExactly(),
+          mapAssert.containsOnly(),
+          mapAssert.containsOnlyKeys());
+    }
+
+    @AfterTemplate
+    void after(AbstractMapAssert<?, ?, K, V> mapAssert) {
+      mapAssert.isEmpty();
+    }
+  }
+
+  static final class AssertThatMapIsEmpty<K, V> {
+    @BeforeTemplate
+    void before(Map<K, V> map) {
+      Refaster.anyOf(
+          assertThat(map).hasSize(0),
+          assertThat(map.isEmpty()).isTrue(),
+          assertThat(map.size()).isEqualTo(0L),
+          assertThat(map.size()).isNotPositive());
+    }
+
+    @BeforeTemplate
+    void before2(Map<K, V> map) {
+      assertThat(Refaster.anyOf(map.keySet(), map.values(), map.entrySet())).isEmpty();
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(Map<K, V> map) {
+      assertThat(map).isEmpty();
+    }
+  }
+
+  static final class AbstractMapAssertIsNotEmpty<K, V> {
+    @BeforeTemplate
+    AbstractMapAssert<?, ?, K, V> before(AbstractMapAssert<?, ?, K, V> mapAssert) {
+      return mapAssert.isNotEqualTo(
+          Refaster.anyOf(
+              ImmutableMap.of(),
+              ImmutableBiMap.of(),
+              ImmutableSortedMap.of(),
+              new HashMap<>(),
+              new LinkedHashMap<>(),
+              new TreeMap<>()));
+    }
+
+    @AfterTemplate
+    AbstractMapAssert<?, ?, K, V> after(AbstractMapAssert<?, ?, K, V> mapAssert) {
+      return mapAssert.isNotEmpty();
+    }
+  }
+
+  static final class AssertThatMapIsNotEmpty<K, V> {
+    @BeforeTemplate
+    AbstractAssert<?, ?> before(Map<K, V> map) {
+      return Refaster.anyOf(
+          assertThat(map.isEmpty()).isFalse(),
+          assertThat(map.size()).isNotEqualTo(0),
+          assertThat(map.size()).isPositive(),
+          assertThat(Refaster.anyOf(map.keySet(), map.values(), map.entrySet())).isNotEmpty());
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    MapAssert<K, V> after(Map<K, V> map) {
+      return assertThat(map).isNotEmpty();
+    }
+  }
+
   static final class AbstractMapAssertContainsExactlyInAnyOrderEntriesOf<K, V> {
     @BeforeTemplate
     AbstractMapAssert<?, ?, K, V> before(AbstractMapAssert<?, ?, K, V> mapAssert, Map<K, V> map) {
@@ -34,4 +166,83 @@ final class AssertJMapRules {
       return mapAssert.containsExactlyEntriesOf(ImmutableMap.of(key, value));
     }
   }
+
+  static final class AssertThatMapHasSize<K, V> {
+    @BeforeTemplate
+    AbstractAssert<?, ?> before(Map<K, V> map, int length) {
+      return Refaster.anyOf(
+          assertThat(map.size()).isEqualTo(length),
+          assertThat(Refaster.anyOf(map.keySet(), map.values(), map.entrySet())).hasSize(length));
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    MapAssert<K, V> after(Map<K, V> map, int length) {
+      return assertThat(map).hasSize(length);
+    }
+  }
+
+  static final class AbstractMapAssertHasSameSizeAs<K, V> {
+    @BeforeTemplate
+    AbstractMapAssert<?, ?, K, V> before(AbstractMapAssert<?, ?, K, V> mapAssert, Map<K, V> map) {
+      return mapAssert.hasSize(map.size());
+    }
+
+    @AfterTemplate
+    AbstractMapAssert<?, ?, K, V> after(AbstractMapAssert<?, ?, K, V> mapAssert, Map<K, V> map) {
+      return mapAssert.hasSameSizeAs(map);
+    }
+  }
+
+  static final class AssertThatMapContainsKey<K, V> {
+    @BeforeTemplate
+    AbstractBooleanAssert<?> before(Map<K, V> map, K key) {
+      return assertThat(map.containsKey(key)).isTrue();
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    MapAssert<K, V> after(Map<K, V> map, K key) {
+      return assertThat(map).containsKey(key);
+    }
+  }
+
+  static final class AssertThatMapDoesNotContainKey<K, V> {
+    @BeforeTemplate
+    AbstractBooleanAssert<?> before(Map<K, V> map, K key) {
+      return assertThat(map.containsKey(key)).isFalse();
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    MapAssert<K, V> after(Map<K, V> map, K key) {
+      return assertThat(map).doesNotContainKey(key);
+    }
+  }
+
+  static final class AssertThatMapContainsValue<K, V> {
+    @BeforeTemplate
+    AbstractBooleanAssert<?> before(Map<K, V> map, V value) {
+      return assertThat(map.containsValue(value)).isTrue();
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    MapAssert<K, V> after(Map<K, V> map, V value) {
+      return assertThat(map).containsValue(value);
+    }
+  }
+
+  static final class AssertThatMapDoesNotContainValue<K, V> {
+    @BeforeTemplate
+    AbstractBooleanAssert<?> before(Map<K, V> map, V value) {
+      return assertThat(map.containsValue(value)).isFalse();
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    MapAssert<K, V> after(Map<K, V> map, V value) {
+      return assertThat(map).doesNotContainValue(value);
+    }
+  }
 }

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/AssertJRules.java

@@ -3,12 +3,9 @@ package tech.picnic.errorprone.refasterrules;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 import static org.assertj.core.api.Assertions.assertThat;
 
-import com.google.common.collect.ImmutableBiMap;
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableMultiset;
 import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.ImmutableSortedMap;
 import com.google.common.collect.ImmutableSortedMultiset;
 import com.google.common.collect.ImmutableSortedSet;
 import com.google.common.collect.Iterables;
@@ -22,9 +19,7 @@ import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.HashMap;
 import java.util.HashSet;
-import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
@@ -32,19 +27,16 @@ import java.util.OptionalDouble;
 import java.util.OptionalInt;
 import java.util.OptionalLong;
 import java.util.Set;
-import java.util.TreeMap;
 import java.util.TreeSet;
 import java.util.function.Predicate;
 import java.util.stream.Collector;
 import java.util.stream.Stream;
 import org.assertj.core.api.AbstractAssert;
-import org.assertj.core.api.AbstractBooleanAssert;
 import org.assertj.core.api.AbstractCollectionAssert;
 import org.assertj.core.api.AbstractComparableAssert;
 import org.assertj.core.api.AbstractDoubleAssert;
 import org.assertj.core.api.AbstractIntegerAssert;
 import org.assertj.core.api.AbstractLongAssert;
-import org.assertj.core.api.AbstractMapAssert;
 import org.assertj.core.api.IterableAssert;
 import org.assertj.core.api.ListAssert;
 import org.assertj.core.api.MapAssert;
@@ -566,173 +558,8 @@ final class AssertJRules {
   // Map
   //
 
-  static final class AssertThatMapIsEmpty<K, V> {
-    @BeforeTemplate
-    @SuppressWarnings("unchecked")
-    void before(AbstractMapAssert<?, ?, K, V> mapAssert) {
-      Refaster.anyOf(
-          mapAssert.containsExactlyEntriesOf(
-              Refaster.anyOf(
-                  ImmutableMap.of(),
-                  ImmutableBiMap.of(),
-                  ImmutableSortedMap.of(),
-                  new HashMap<>(),
-                  new LinkedHashMap<>(),
-                  new TreeMap<>())),
-          mapAssert.hasSameSizeAs(
-              Refaster.anyOf(
-                  ImmutableMap.of(),
-                  ImmutableBiMap.of(),
-                  ImmutableSortedMap.of(),
-                  new HashMap<>(),
-                  new LinkedHashMap<>(),
-                  new TreeMap<>())),
-          mapAssert.isEqualTo(
-              Refaster.anyOf(
-                  ImmutableMap.of(),
-                  ImmutableBiMap.of(),
-                  ImmutableSortedMap.of(),
-                  new HashMap<>(),
-                  new LinkedHashMap<>(),
-                  new TreeMap<>())),
-          mapAssert.containsOnlyKeys(
-              Refaster.anyOf(
-                  ImmutableList.of(),
-                  new ArrayList<>(),
-                  ImmutableSet.of(),
-                  new HashSet<>(),
-                  new LinkedHashSet<>(),
-                  ImmutableSortedSet.of(),
-                  new TreeSet<>(),
-                  ImmutableMultiset.of(),
-                  ImmutableSortedMultiset.of())),
-          mapAssert.containsExactly(),
-          mapAssert.containsOnly(),
-          mapAssert.containsOnlyKeys());
-    }
-
-    @AfterTemplate
-    void after(AbstractMapAssert<?, ?, K, V> mapAssert) {
-      mapAssert.isEmpty();
-    }
-  }
-
-  // XXX: Find a better name.
-  static final class AssertThatMapIsEmpty2<K, V> {
-    @BeforeTemplate
-    void before(Map<K, V> map) {
-      Refaster.anyOf(
-          assertThat(map).hasSize(0),
-          assertThat(map.isEmpty()).isTrue(),
-          assertThat(map.size()).isEqualTo(0L),
-          assertThat(map.size()).isNotPositive());
-    }
-
-    @BeforeTemplate
-    void before2(Map<K, V> map) {
-      assertThat(Refaster.anyOf(map.keySet(), map.values())).isEmpty();
-    }
-
-    @AfterTemplate
-    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
-    void after(Map<K, V> map) {
-      assertThat(map).isEmpty();
-    }
-  }
-
-  static final class AssertThatMapIsNotEmpty<K, V> {
-    @BeforeTemplate
-    AbstractMapAssert<?, ?, K, V> before(AbstractMapAssert<?, ?, K, V> mapAssert) {
-      return mapAssert.isNotEqualTo(
-          Refaster.anyOf(
-              ImmutableMap.of(),
-              ImmutableBiMap.of(),
-              ImmutableSortedMap.of(),
-              new HashMap<>(),
-              new LinkedHashMap<>(),
-              new TreeMap<>()));
-    }
-
-    @AfterTemplate
-    AbstractMapAssert<?, ?, K, V> after(AbstractMapAssert<?, ?, K, V> mapAssert) {
-      return mapAssert.isNotEmpty();
-    }
-  }
-
-  // XXX: Find a better name.
-  static final class AssertThatMapIsNotEmpty2<K, V> {
-    @BeforeTemplate
-    AbstractAssert<?, ?> before(Map<K, V> map) {
-      return Refaster.anyOf(
-          assertThat(map.isEmpty()).isFalse(),
-          assertThat(map.size()).isNotEqualTo(0),
-          assertThat(map.size()).isPositive(),
-          assertThat(Refaster.anyOf(map.keySet(), map.values())).isNotEmpty());
-    }
-
-    @AfterTemplate
-    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
-    MapAssert<K, V> after(Map<K, V> map) {
-      return assertThat(map).isNotEmpty();
-    }
-  }
-
-  static final class AssertThatMapHasSize<K, V> {
-    @BeforeTemplate
-    AbstractAssert<?, ?> before(Map<K, V> map, int length) {
-      return Refaster.anyOf(
-          assertThat(map.size()).isEqualTo(length),
-          assertThat(Refaster.anyOf(map.keySet(), map.values())).hasSize(length));
-    }
-
-    @AfterTemplate
-    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
-    MapAssert<K, V> after(Map<K, V> map, int length) {
-      return assertThat(map).hasSize(length);
-    }
-  }
-
-  static final class AssertThatMapsHaveSameSize<K, V> {
-    @BeforeTemplate
-    AbstractAssert<?, ?> before(Map<K, V> map1, Map<K, V> map2) {
-      return assertThat(map1)
-          .hasSize(Refaster.anyOf(map2.size(), map2.keySet().size(), map2.values().size()));
-    }
-
-    @AfterTemplate
-    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
-    MapAssert<K, V> after(Map<K, V> map1, Map<K, V> map2) {
-      return assertThat(map1).hasSameSizeAs(map2);
-    }
-  }
-
-  // XXX: Should also add a rule (elsewhere) to simplify `map.keySet().contains(key)`.
-  static final class AssertThatMapContainsKey<K, V> {
-    @BeforeTemplate
-    AbstractBooleanAssert<?> before(Map<K, V> map, K key) {
-      return assertThat(map.containsKey(key)).isTrue();
-    }
-
-    @AfterTemplate
-    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
-    MapAssert<K, V> after(Map<K, V> map, K key) {
-      return assertThat(map).containsKey(key);
-    }
-  }
-
-  static final class AssertThatMapDoesNotContainKey<K, V> {
-    @BeforeTemplate
-    AbstractBooleanAssert<?> before(Map<K, V> map, K key) {
-      return assertThat(map.containsKey(key)).isFalse();
-    }
-
-    @AfterTemplate
-    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
-    MapAssert<K, V> after(Map<K, V> map, K key) {
-      return assertThat(map).doesNotContainKey(key);
-    }
-  }
-
+  // XXX: To match in all cases there'll need to be a `@BeforeTemplate` variant for each
+  // `assertThat` overload. Consider defining a `BugChecker` instead.
   static final class AssertThatMapContainsEntry<K, V> {
     @BeforeTemplate
     ObjectAssert<?> before(Map<K, V> map, K key, V value) {

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

@@ -19,15 +19,12 @@ import com.google.errorprone.refaster.annotation.BeforeTemplate;
 import com.google.errorprone.refaster.annotation.UseImportPolicy;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.EnumMap;
-import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
-import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
 import java.util.stream.Stream;
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /**
@@ -46,36 +43,30 @@ final class AssortedRules {
     }
 
     @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
     int after(int index, int size) {
       return checkIndex(index, size);
     }
   }
 
-  // XXX: We could add a rule for `new EnumMap(Map<K, ? extends V> m)`, but that constructor does
-  // not allow an empty non-EnumMap to be provided.
-  static final class CreateEnumMap<K extends Enum<K>, V> {
+  /**
+   * Prefer {@link Objects#checkIndex(int, int)} over less descriptive or more verbose alternatives.
+   *
+   * <p>If a custom error message is desired, consider using Guava's {@link
+   * com.google.common.base.Preconditions#checkElementIndex(int, int, String)}.
+   */
+  static final class CheckIndexConditional {
     @BeforeTemplate
-    Map<K, V> before() {
-      return new HashMap<>();
+    void before(int index, int size) {
+      if (index < 0 || index >= size) {
+        throw new IndexOutOfBoundsException();
+      }
     }
 
     @AfterTemplate
-    Map<K, V> after() {
-      return new EnumMap<>(Refaster.<K>clazz());
-    }
-  }
-
-  static final class MapGetOrNull<K, V, L> {
-    @BeforeTemplate
-    @Nullable
-    V before(Map<K, V> map, L key) {
-      return map.getOrDefault(key, null);
-    }
-
-    @AfterTemplate
-    @Nullable
-    V after(Map<K, V> map, L key) {
-      return map.get(key);
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(int index, int size) {
+      checkIndex(index, size);
     }
   }
 
@@ -205,32 +196,6 @@ final class AssortedRules {
     }
   }
 
-  /** Don't unnecessarily use {@link Map#entrySet()}. */
-  static final class MapKeyStream<K, V> {
-    @BeforeTemplate
-    Stream<K> before(Map<K, V> map) {
-      return map.entrySet().stream().map(Map.Entry::getKey);
-    }
-
-    @AfterTemplate
-    Stream<K> after(Map<K, V> map) {
-      return map.keySet().stream();
-    }
-  }
-
-  /** Don't unnecessarily use {@link Map#entrySet()}. */
-  static final class MapValueStream<K, V> {
-    @BeforeTemplate
-    Stream<V> before(Map<K, V> map) {
-      return map.entrySet().stream().map(Map.Entry::getValue);
-    }
-
-    @AfterTemplate
-    Stream<V> after(Map<K, V> map) {
-      return map.values().stream();
-    }
-  }
-
   /** Prefer {@link Splitter#splitToStream(CharSequence)} over less efficient alternatives. */
   static final class SplitToStream {
     @BeforeTemplate

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/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

@@ -0,0 +1,123 @@
+package tech.picnic.errorprone.refasterrules;
+
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import java.util.EnumMap;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Stream;
+import org.jspecify.annotations.Nullable;
+import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+
+/** Refaster rules related to expressions dealing with {@link Map} instances. */
+@OnlineDocumentation
+final class MapRules {
+  private MapRules() {}
+
+  // XXX: We could add a rule for `new EnumMap(Map<K, ? extends V> m)`, but that constructor does
+  // not allow an empty non-EnumMap to be provided.
+  static final class CreateEnumMap<K extends Enum<K>, V> {
+    @BeforeTemplate
+    Map<K, V> before() {
+      return new HashMap<>();
+    }
+
+    @AfterTemplate
+    Map<K, V> after() {
+      return new EnumMap<>(Refaster.<K>clazz());
+    }
+  }
+
+  static final class MapGetOrNull<K, V, T> {
+    @BeforeTemplate
+    @Nullable
+    V before(Map<K, V> map, T key) {
+      return map.getOrDefault(key, null);
+    }
+
+    @AfterTemplate
+    @Nullable
+    V after(Map<K, V> map, T key) {
+      return map.get(key);
+    }
+  }
+
+  /** Prefer {@link Map#isEmpty()} over more contrived alternatives. */
+  static final class MapIsEmpty<K, V> {
+    @BeforeTemplate
+    boolean before(Map<K, V> map) {
+      return Refaster.anyOf(map.keySet(), map.values(), map.entrySet()).isEmpty();
+    }
+
+    @AfterTemplate
+    boolean after(Map<K, V> map) {
+      return map.isEmpty();
+    }
+  }
+
+  /** Prefer {@link Map#size()} over more contrived alternatives. */
+  static final class MapSize<K, V> {
+    @BeforeTemplate
+    int before(Map<K, V> map) {
+      return Refaster.anyOf(map.keySet(), map.values(), map.entrySet()).size();
+    }
+
+    @AfterTemplate
+    int after(Map<K, V> map) {
+      return map.size();
+    }
+  }
+
+  /** Prefer {@link Map#containsKey(Object)} over more contrived alternatives. */
+  static final class MapContainsKey<K, V, T> {
+    @BeforeTemplate
+    boolean before(Map<K, V> map, T key) {
+      return map.keySet().contains(key);
+    }
+
+    @AfterTemplate
+    boolean after(Map<K, V> map, T key) {
+      return map.containsKey(key);
+    }
+  }
+
+  /** Prefer {@link Map#containsValue(Object)} over more contrived alternatives. */
+  static final class MapContainsValue<K, V, T> {
+    @BeforeTemplate
+    boolean before(Map<K, V> map, T value) {
+      return map.values().contains(value);
+    }
+
+    @AfterTemplate
+    boolean after(Map<K, V> map, T value) {
+      return map.containsValue(value);
+    }
+  }
+
+  /** Don't unnecessarily use {@link Map#entrySet()}. */
+  static final class MapKeyStream<K, V> {
+    @BeforeTemplate
+    Stream<K> before(Map<K, V> map) {
+      return map.entrySet().stream().map(Map.Entry::getKey);
+    }
+
+    @AfterTemplate
+    Stream<K> after(Map<K, V> map) {
+      return map.keySet().stream();
+    }
+  }
+
+  /** Don't unnecessarily use {@link Map#entrySet()}. */
+  static final class MapValueStream<K, V> {
+    @BeforeTemplate
+    Stream<V> before(Map<K, V> map) {
+      return map.entrySet().stream().map(Map.Entry::getValue);
+    }
+
+    @AfterTemplate
+    Stream<V> after(Map<K, V> map) {
+      return map.values().stream();
+    }
+  }
+}

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 javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to expressions dealing with {@link Multimap}s. */

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 javax.annotation.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 javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 
 /** Refaster rules related to expressions dealing with {@link Optional}s. */
@@ -355,6 +355,42 @@ final class OptionalRules {
     }
   }
 
+  /**
+   * Avoid unnecessary {@link Optional} to {@link Stream} conversion when filtering a value of the
+   * former type.
+   */
+  static final class OptionalFilter<T> {
+    @BeforeTemplate
+    Optional<T> before(Optional<T> optional, Predicate<? super T> predicate) {
+      return Refaster.anyOf(
+          optional.stream().filter(predicate).findFirst(),
+          optional.stream().filter(predicate).findAny());
+    }
+
+    @AfterTemplate
+    Optional<T> after(Optional<T> optional, Predicate<? super T> predicate) {
+      return optional.filter(predicate);
+    }
+  }
+
+  /**
+   * Avoid unnecessary {@link Optional} to {@link Stream} conversion when mapping a value of the
+   * former type.
+   */
+  // XXX: If `StreamMapFirst` also simplifies `.findAny()` expressions, then this rule can be
+  // dropped in favour of `StreamMapFirst` and `OptionalIdentity`.
+  static final class OptionalMap<S, T> {
+    @BeforeTemplate
+    Optional<? extends T> before(Optional<S> optional, Function<? super S, ? extends T> function) {
+      return optional.stream().map(function).findAny();
+    }
+
+    @AfterTemplate
+    Optional<? extends T> after(Optional<S> optional, Function<? super S, ? extends T> function) {
+      return optional.map(function);
+    }
+  }
+
   // XXX: Add a rule for:
   // `optional.flatMap(x -> pred(x) ? Optional.empty() : Optional.of(x))` and variants.
   // (Maybe canonicalize the inner expression. Maybe we rewrite already.)

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

@@ -0,0 +1,176 @@
+package tech.picnic.errorprone.refasterrules;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkElementIndex;
+import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Preconditions.checkPositionIndex;
+import static com.google.common.base.Preconditions.checkState;
+import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
+
+import com.google.common.base.Preconditions;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+
+/** Refaster templates related to statements dealing with {@link Preconditions}. */
+@OnlineDocumentation
+final class PreconditionsRules {
+  private PreconditionsRules() {}
+
+  /** Prefer {@link Preconditions#checkArgument(boolean)} over more verbose alternatives. */
+  static final class CheckArgument {
+    @BeforeTemplate
+    void before(boolean condition) {
+      if (condition) {
+        throw new IllegalArgumentException();
+      }
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean condition) {
+      checkArgument(!condition);
+    }
+  }
+
+  /** Prefer {@link Preconditions#checkArgument(boolean, Object)} over more verbose alternatives. */
+  static final class CheckArgumentWithMessage {
+    @BeforeTemplate
+    void before(boolean condition, String message) {
+      if (condition) {
+        throw new IllegalArgumentException(message);
+      }
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean condition, String message) {
+      checkArgument(!condition, message);
+    }
+  }
+
+  /**
+   * Prefer {@link Preconditions#checkElementIndex(int, int, String)} over less descriptive or more
+   * verbose alternatives.
+   *
+   * <p>Note that the two-argument {@link Preconditions#checkElementIndex(int, int)} is better
+   * replaced with {@link java.util.Objects#checkIndex(int, int)}.
+   */
+  static final class CheckElementIndexWithMessage {
+    @BeforeTemplate
+    void before(int index, int size, String message) {
+      if (index < 0 || index >= size) {
+        throw new IndexOutOfBoundsException(message);
+      }
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(int index, int size, String message) {
+      checkElementIndex(index, size, message);
+    }
+  }
+
+  /** Prefer {@link Preconditions#checkNotNull(Object)} over more verbose alternatives. */
+  static final class CheckNotNull<T> {
+    @BeforeTemplate
+    void before(T object) {
+      if (object == null) {
+        throw new NullPointerException();
+      }
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(T object) {
+      checkNotNull(object);
+    }
+  }
+
+  /** Prefer {@link Preconditions#checkNotNull(Object, Object)} over more verbose alternatives. */
+  static final class CheckNotNullWithMessage<T> {
+    @BeforeTemplate
+    void before(T object, String message) {
+      if (object == null) {
+        throw new NullPointerException(message);
+      }
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(T object, String message) {
+      checkNotNull(object, message);
+    }
+  }
+
+  /**
+   * Prefer {@link Preconditions#checkPositionIndex(int, int)} over less descriptive or more verbose
+   * alternatives.
+   */
+  static final class CheckPositionIndex {
+    @BeforeTemplate
+    void before(int index, int size) {
+      if (index < 0 || index > size) {
+        throw new IndexOutOfBoundsException();
+      }
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(int index, int size) {
+      checkPositionIndex(index, size);
+    }
+  }
+
+  /**
+   * Prefer {@link Preconditions#checkPositionIndex(int, int, String)} over less descriptive or more
+   * verbose alternatives.
+   */
+  static final class CheckPositionIndexWithMessage {
+    @BeforeTemplate
+    void before(int index, int size, String message) {
+      if (index < 0 || index > size) {
+        throw new IndexOutOfBoundsException(message);
+      }
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(int index, int size, String message) {
+      checkPositionIndex(index, size, message);
+    }
+  }
+
+  /** Prefer {@link Preconditions#checkState(boolean)} over more verbose alternatives. */
+  static final class CheckState {
+    @BeforeTemplate
+    void before(boolean condition) {
+      if (condition) {
+        throw new IllegalStateException();
+      }
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean condition) {
+      checkState(!condition);
+    }
+  }
+
+  /** Prefer {@link Preconditions#checkState(boolean, Object)} over more verbose alternatives. */
+  static final class CheckStateWithMessage {
+    @BeforeTemplate
+    void before(boolean condition, String message) {
+      if (condition) {
+        throw new IllegalStateException(message);
+      }
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    void after(boolean condition, String message) {
+      checkState(!condition, message);
+    }
+  }
+}

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

@@ -1,10 +1,13 @@
 package tech.picnic.errorprone.refasterrules;
 
 import static com.google.common.collect.MoreCollectors.toOptional;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
 import static com.google.errorprone.refaster.ImportPolicy.STATIC_IMPORT_ALWAYS;
 import static java.util.function.Function.identity;
 import static org.assertj.core.api.Assertions.assertThat;
+import static reactor.function.TupleUtils.function;
 
+import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.MoreCollectors;
 import com.google.errorprone.refaster.Refaster;
 import com.google.errorprone.refaster.annotation.AfterTemplate;
@@ -14,18 +17,27 @@ 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;
+import java.util.function.BiConsumer;
+import java.util.function.BiFunction;
 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;
 import reactor.test.StepVerifier;
 import reactor.test.publisher.PublisherProbe;
+import reactor.util.context.Context;
+import reactor.util.function.Tuple2;
+import tech.picnic.errorprone.refaster.annotation.Description;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
+import tech.picnic.errorprone.refaster.annotation.Severity;
 import tech.picnic.errorprone.refaster.matchers.ThrowsCheckedException;
 
 /** Refaster rules related to Reactor expressions and statements. */
@@ -49,6 +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.
@@ -68,6 +119,125 @@ 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
+   * combining three or more reactive streams.
+   */
+  static final class MonoZip<T, S> {
+    @BeforeTemplate
+    Mono<Tuple2<T, S>> before(Mono<T> mono, Mono<S> other) {
+      return mono.zipWith(other);
+    }
+
+    @AfterTemplate
+    Mono<Tuple2<T, S>> after(Mono<T> mono, Mono<S> other) {
+      return Mono.zip(mono, other);
+    }
+  }
+
+  /**
+   * Prefer {@link Mono#zip(Mono, Mono)} with a chained combinator over a chained {@link
+   * Mono#zipWith(Mono, BiFunction)}, as the former better conveys that the {@link Mono}s may be
+   * subscribed to concurrently, and generalizes to combining three or more reactive streams.
+   */
+  static final class MonoZipWithCombinator<T, S, R> {
+    @BeforeTemplate
+    Mono<R> before(Mono<T> mono, Mono<S> other, BiFunction<T, S, R> combinator) {
+      return mono.zipWith(other, combinator);
+    }
+
+    @AfterTemplate
+    Mono<R> after(Mono<T> mono, Mono<S> other, BiFunction<T, S, R> combinator) {
+      return Mono.zip(mono, other).map(function(combinator));
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#zip(Publisher, Publisher)} over a chained {@link Flux#zipWith(Publisher)},
+   * as the former better conveys that the {@link Publisher}s may be subscribed to concurrently, and
+   * generalizes to combining three or more reactive streams.
+   */
+  static final class FluxZip<T, S> {
+    @BeforeTemplate
+    Flux<Tuple2<T, S>> before(Flux<T> flux, Publisher<S> other) {
+      return flux.zipWith(other);
+    }
+
+    @AfterTemplate
+    Flux<Tuple2<T, S>> after(Flux<T> flux, Publisher<S> other) {
+      return Flux.zip(flux, other);
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#zip(Publisher, Publisher)} with a chained combinator over a chained {@link
+   * Flux#zipWith(Publisher, BiFunction)}, as the former better conveys that the {@link Publisher}s
+   * may be subscribed to concurrently, and generalizes to combining three or more reactive streams.
+   */
+  static final class FluxZipWithCombinator<T, S, R> {
+    @BeforeTemplate
+    Flux<R> before(Flux<T> flux, Publisher<S> other, BiFunction<T, S, R> combinator) {
+      return flux.zipWith(other, combinator);
+    }
+
+    @AfterTemplate
+    Flux<R> after(Flux<T> flux, Publisher<S> other, BiFunction<T, S, R> combinator) {
+      return Flux.zip(flux, other).map(function(combinator));
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#zipWithIterable(Iterable)} with a chained combinator over {@link
+   * Flux#zipWithIterable(Iterable, BiFunction)}, as the former generally yields more readable code.
+   */
+  static final class FluxZipWithIterable<T, S, R> {
+    @BeforeTemplate
+    Flux<R> before(Flux<T> flux, Iterable<S> iterable, BiFunction<T, S, R> combinator) {
+      return flux.zipWithIterable(iterable, combinator);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(STATIC_IMPORT_ALWAYS)
+    Flux<R> after(Flux<T> flux, Iterable<S> iterable, BiFunction<T, S, R> combinator) {
+      return flux.zipWithIterable(iterable).map(function(combinator));
+    }
+  }
+
   /** Don't unnecessarily defer {@link Mono#error(Throwable)}. */
   static final class MonoDeferredError<T> {
     @BeforeTemplate
@@ -141,13 +311,72 @@ final class ReactorRules {
     }
   }
 
-  /** Don't unnecessarily pass an empty publisher to {@link Mono#switchIfEmpty(Mono)}. */
-  static final class MonoSwitchIfEmptyOfEmptyPublisher<T> {
+  /**
+   * Prefer {@link Flux#take(long, boolean)} over {@link Flux#take(long)}.
+   *
+   * <p>In Reactor versions prior to 3.5.0, {@code Flux#take(long)} makes an unbounded request
+   * upstream, and is equivalent to {@code Flux#take(long, false)}. In 3.5.0, the behavior of {@code
+   * Flux#take(long)} will change to that of {@code Flux#take(long, true)}.
+   *
+   * <p>The intent with this Refaster rule is to get the new behavior before upgrading to Reactor
+   * 3.5.0.
+   */
+  // XXX: Drop this rule some time after upgrading to Reactor 3.6.0, or introduce a way to apply
+  // this rule only when an older version of Reactor is on the classpath.
+  // XXX: Once Reactor 3.6.0 is out, introduce a rule that rewrites code in the opposite direction.
+  @Description(
+      "Prior to Reactor 3.5.0, `take(n)` requests and unbounded number of elements upstream.")
+  @Severity(WARNING)
+  static final class FluxTake<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, long n) {
+      return flux.take(n);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, long n) {
+      return flux.take(n, /* limitRequest= */ true);
+    }
+  }
+
+  /** Prefer {@link Mono#defaultIfEmpty(Object)} over more contrived alternatives. */
+  static final class MonoDefaultIfEmpty<T> {
+    @BeforeTemplate
+    Mono<T> before(Mono<T> mono, T object) {
+      return mono.switchIfEmpty(Mono.just(object));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<T> mono, T object) {
+      return mono.defaultIfEmpty(object);
+    }
+  }
+
+  /** Prefer {@link Flux#defaultIfEmpty(Object)} over more contrived alternatives. */
+  static final class FluxDefaultIfEmpty<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, T object) {
+      return flux.switchIfEmpty(Refaster.anyOf(Mono.just(object), Flux.just(object)));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, T object) {
+      return flux.defaultIfEmpty(object);
+    }
+  }
+
+  /** 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());
     }
 
+    @BeforeTemplate
+    Mono<@Nullable Void> before2(Mono<@Nullable Void> mono) {
+      return mono.then();
+    }
+
     @AfterTemplate
     Mono<T> after(Mono<T> mono) {
       return mono;
@@ -171,7 +400,10 @@ final class ReactorRules {
   static final class FluxConcatMap<T, S> {
     @BeforeTemplate
     Flux<S> before(Flux<T> flux, Function<? super T, ? extends Publisher<? extends S>> function) {
-      return Refaster.anyOf(flux.flatMap(function, 1), flux.flatMapSequential(function, 1));
+      return Refaster.anyOf(
+          flux.flatMap(function, 1),
+          flux.flatMapSequential(function, 1),
+          flux.map(function).concatMap(identity()));
     }
 
     @AfterTemplate
@@ -188,7 +420,9 @@ final class ReactorRules {
         Function<? super T, ? extends Publisher<? extends S>> function,
         int prefetch) {
       return Refaster.anyOf(
-          flux.flatMap(function, 1, prefetch), flux.flatMapSequential(function, 1, prefetch));
+          flux.flatMap(function, 1, prefetch),
+          flux.flatMapSequential(function, 1, prefetch),
+          flux.map(function).concatMap(identity(), prefetch));
     }
 
     @AfterTemplate
@@ -240,16 +474,195 @@ final class ReactorRules {
    */
   abstract static class MonoFlatMapToFlux<T, S> {
     @Placeholder(allowsIdentity = true)
-    abstract Mono<S> valueTransformation(@MayOptionallyUse T value);
+    abstract Mono<S> transformation(@MayOptionallyUse T value);
 
     @BeforeTemplate
     Flux<S> before(Mono<T> mono) {
-      return mono.flatMapMany(v -> valueTransformation(v));
+      return mono.flatMapMany(v -> transformation(v));
     }
 
     @AfterTemplate
     Flux<S> after(Mono<T> mono) {
-      return mono.flatMap(v -> valueTransformation(v)).flux();
+      return mono.flatMap(v -> transformation(v)).flux();
+    }
+  }
+
+  /**
+   * Prefer {@link Mono#map(Function)} over alternatives that unnecessarily require an inner
+   * subscription.
+   */
+  abstract static class MonoMap<T, S> {
+    @Placeholder(allowsIdentity = true)
+    abstract S transformation(@MayOptionallyUse T value);
+
+    @BeforeTemplate
+    Mono<S> before(Mono<T> mono) {
+      return mono.flatMap(x -> Mono.just(transformation(x)));
+    }
+
+    @AfterTemplate
+    Mono<S> after(Mono<T> mono) {
+      return mono.map(x -> transformation(x));
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#map(Function)} over alternatives that unnecessarily require an inner
+   * subscription.
+   */
+  abstract static class FluxMap<T, S> {
+    @Placeholder(allowsIdentity = true)
+    abstract S transformation(@MayOptionallyUse T value);
+
+    @BeforeTemplate
+    Flux<S> before(Flux<T> flux, boolean delayUntilEnd, int maxConcurrency, int prefetch) {
+      return Refaster.anyOf(
+          flux.concatMap(x -> Mono.just(transformation(x))),
+          flux.concatMap(x -> Flux.just(transformation(x))),
+          flux.concatMap(x -> Mono.just(transformation(x)), prefetch),
+          flux.concatMap(x -> Flux.just(transformation(x)), prefetch),
+          flux.concatMapDelayError(x -> Mono.just(transformation(x))),
+          flux.concatMapDelayError(x -> Flux.just(transformation(x))),
+          flux.concatMapDelayError(x -> Mono.just(transformation(x)), prefetch),
+          flux.concatMapDelayError(x -> Flux.just(transformation(x)), prefetch),
+          flux.concatMapDelayError(x -> Mono.just(transformation(x)), delayUntilEnd, prefetch),
+          flux.concatMapDelayError(x -> Flux.just(transformation(x)), delayUntilEnd, prefetch),
+          flux.flatMap(x -> Mono.just(transformation(x)), maxConcurrency),
+          flux.flatMap(x -> Flux.just(transformation(x)), maxConcurrency),
+          flux.flatMap(x -> Mono.just(transformation(x)), maxConcurrency, prefetch),
+          flux.flatMap(x -> Flux.just(transformation(x)), maxConcurrency, prefetch),
+          flux.flatMapDelayError(x -> Mono.just(transformation(x)), maxConcurrency, prefetch),
+          flux.flatMapDelayError(x -> Flux.just(transformation(x)), maxConcurrency, prefetch),
+          flux.flatMapSequential(x -> Mono.just(transformation(x)), maxConcurrency),
+          flux.flatMapSequential(x -> Flux.just(transformation(x)), maxConcurrency),
+          flux.flatMapSequential(x -> Mono.just(transformation(x)), maxConcurrency, prefetch),
+          flux.flatMapSequential(x -> Flux.just(transformation(x)), maxConcurrency, prefetch),
+          flux.flatMapSequentialDelayError(
+              x -> Mono.just(transformation(x)), maxConcurrency, prefetch),
+          flux.flatMapSequentialDelayError(
+              x -> Flux.just(transformation(x)), maxConcurrency, prefetch),
+          flux.switchMap(x -> Mono.just(transformation(x))),
+          flux.switchMap(x -> Flux.just(transformation(x))));
+    }
+
+    @AfterTemplate
+    Flux<S> after(Flux<T> flux) {
+      return flux.map(x -> transformation(x));
+    }
+  }
+
+  /**
+   * Prefer {@link Mono#mapNotNull(Function)} over alternatives that unnecessarily require an inner
+   * subscription.
+   */
+  abstract static class MonoMapNotNull<T, S> {
+    @Placeholder(allowsIdentity = true)
+    abstract S transformation(@MayOptionallyUse T value);
+
+    @BeforeTemplate
+    Mono<S> before(Mono<T> mono) {
+      return mono.flatMap(
+          x ->
+              Refaster.anyOf(
+                  Mono.justOrEmpty(transformation(x)), Mono.fromSupplier(() -> transformation(x))));
+    }
+
+    @AfterTemplate
+    Mono<S> after(Mono<T> mono) {
+      return mono.mapNotNull(x -> transformation(x));
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#mapNotNull(Function)} over alternatives that unnecessarily require an inner
+   * subscription.
+   */
+  abstract static class FluxMapNotNull<T, S> {
+    @Placeholder(allowsIdentity = true)
+    abstract S transformation(@MayOptionallyUse T value);
+
+    @BeforeTemplate
+    Publisher<S> before(Flux<T> flux, boolean delayUntilEnd, int maxConcurrency, int prefetch) {
+      return Refaster.anyOf(
+          flux.concatMap(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x)))),
+          flux.concatMap(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x))),
+              prefetch),
+          flux.concatMapDelayError(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x)))),
+          flux.concatMapDelayError(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x))),
+              prefetch),
+          flux.concatMapDelayError(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x))),
+              delayUntilEnd,
+              prefetch),
+          flux.flatMap(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x))),
+              maxConcurrency),
+          flux.flatMap(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x))),
+              maxConcurrency,
+              prefetch),
+          flux.flatMapDelayError(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x))),
+              maxConcurrency,
+              prefetch),
+          flux.flatMapSequential(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x))),
+              maxConcurrency),
+          flux.flatMapSequential(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x))),
+              maxConcurrency,
+              prefetch),
+          flux.flatMapSequentialDelayError(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x))),
+              maxConcurrency,
+              prefetch),
+          flux.switchMap(
+              x ->
+                  Refaster.anyOf(
+                      Mono.justOrEmpty(transformation(x)),
+                      Mono.fromSupplier(() -> transformation(x)))));
+    }
+
+    @AfterTemplate
+    Flux<S> after(Flux<T> flux) {
+      return flux.mapNotNull(x -> transformation(x));
     }
   }
 
@@ -257,7 +670,8 @@ final class ReactorRules {
   static final class MonoFlux<T> {
     @BeforeTemplate
     Flux<T> before(Mono<T> mono) {
-      return Flux.concat(mono);
+      return Refaster.anyOf(
+          mono.flatMapMany(Mono::just), mono.flatMapMany(Flux::just), Flux.concat(mono));
     }
 
     @AfterTemplate
@@ -266,6 +680,19 @@ 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.
    */
@@ -274,9 +701,7 @@ final class ReactorRules {
   static final class MonoCollectToOptional<T> {
     @BeforeTemplate
     Mono<Optional<T>> before(Mono<T> mono) {
-      return Refaster.anyOf(
-          mono.map(Optional::of).defaultIfEmpty(Optional.empty()),
-          mono.map(Optional::of).switchIfEmpty(Mono.just(Optional.empty())));
+      return mono.map(Optional::of).defaultIfEmpty(Optional.empty());
     }
 
     @AfterTemplate
@@ -312,6 +737,32 @@ final class ReactorRules {
     }
   }
 
+  /** Prefer {@link Mono#flatMap(Function)} over more contrived alternatives. */
+  static final class MonoFlatMap<S, T> {
+    @BeforeTemplate
+    Mono<T> before(Mono<S> mono, Function<? super S, ? extends Mono<? extends T>> function) {
+      return mono.map(function).flatMap(identity());
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<S> mono, Function<? super S, ? extends Mono<? extends T>> function) {
+      return mono.flatMap(function);
+    }
+  }
+
+  /** Prefer {@link Mono#flatMapMany(Function)} over more contrived alternatives. */
+  static final class MonoFlatMapMany<S, T> {
+    @BeforeTemplate
+    Flux<T> before(Mono<S> mono, Function<? super S, ? extends Publisher<? extends T>> function) {
+      return mono.map(function).flatMapMany(identity());
+    }
+
+    @AfterTemplate
+    Flux<T> after(Mono<S> mono, Function<? super S, ? extends Publisher<? extends T>> function) {
+      return mono.flatMapMany(function);
+    }
+  }
+
   /**
    * Prefer {@link Flux#concatMapIterable(Function)} over alternatives that require an additional
    * subscription.
@@ -349,6 +800,42 @@ final class ReactorRules {
     }
   }
 
+  /**
+   * Prefer {@link Mono#doOnError(Class, Consumer)} over {@link Mono#doOnError(Predicate, Consumer)}
+   * where possible.
+   */
+  static final class MonoDoOnError<T> {
+    @BeforeTemplate
+    Mono<T> before(
+        Mono<T> mono, Class<? extends Throwable> clazz, Consumer<? super Throwable> onError) {
+      return mono.doOnError(clazz::isInstance, onError);
+    }
+
+    @AfterTemplate
+    Mono<T> after(
+        Mono<T> mono, Class<? extends Throwable> clazz, Consumer<? super Throwable> onError) {
+      return mono.doOnError(clazz, onError);
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#doOnError(Class, Consumer)} over {@link Flux#doOnError(Predicate, Consumer)}
+   * where possible.
+   */
+  static final class FluxDoOnError<T> {
+    @BeforeTemplate
+    Flux<T> before(
+        Flux<T> flux, Class<? extends Throwable> clazz, Consumer<? super Throwable> onError) {
+      return flux.doOnError(clazz::isInstance, onError);
+    }
+
+    @AfterTemplate
+    Flux<T> after(
+        Flux<T> flux, Class<? extends Throwable> clazz, Consumer<? super Throwable> onError) {
+      return flux.doOnError(clazz, onError);
+    }
+  }
+
   /** Prefer {@link Mono#onErrorComplete()} over more contrived alternatives. */
   static final class MonoOnErrorComplete<T> {
     @BeforeTemplate
@@ -375,6 +862,272 @@ final class ReactorRules {
     }
   }
 
+  /** Prefer {@link Mono#onErrorComplete(Class)}} over more contrived alternatives. */
+  static final class MonoOnErrorCompleteClass<T> {
+    @BeforeTemplate
+    Mono<T> before(Mono<T> mono, Class<? extends Throwable> clazz) {
+      return Refaster.anyOf(
+          mono.onErrorComplete(clazz::isInstance), mono.onErrorResume(clazz, e -> Mono.empty()));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<T> mono, Class<? extends Throwable> clazz) {
+      return mono.onErrorComplete(clazz);
+    }
+  }
+
+  /** Prefer {@link Flux#onErrorComplete(Class)}} over more contrived alternatives. */
+  static final class FluxOnErrorCompleteClass<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Class<? extends Throwable> clazz) {
+      return Refaster.anyOf(
+          flux.onErrorComplete(clazz::isInstance),
+          flux.onErrorResume(clazz, e -> Refaster.anyOf(Mono.empty(), Flux.empty())));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Class<? extends Throwable> clazz) {
+      return flux.onErrorComplete(clazz);
+    }
+  }
+
+  /** Prefer {@link Mono#onErrorComplete(Predicate)}} over more contrived alternatives. */
+  static final class MonoOnErrorCompletePredicate<T> {
+    @BeforeTemplate
+    Mono<T> before(Mono<T> mono, Predicate<? super Throwable> predicate) {
+      return mono.onErrorResume(predicate, e -> Mono.empty());
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<T> mono, Predicate<? super Throwable> predicate) {
+      return mono.onErrorComplete(predicate);
+    }
+  }
+
+  /** Prefer {@link Flux#onErrorComplete(Predicate)}} over more contrived alternatives. */
+  static final class FluxOnErrorCompletePredicate<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<? super Throwable> predicate) {
+      return flux.onErrorResume(predicate, e -> Refaster.anyOf(Mono.empty(), Flux.empty()));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<? super Throwable> predicate) {
+      return flux.onErrorComplete(predicate);
+    }
+  }
+
+  /**
+   * Prefer {@link Mono#onErrorContinue(Class, BiConsumer)} over {@link
+   * Mono#onErrorContinue(Predicate, BiConsumer)} where possible.
+   */
+  static final class MonoOnErrorContinue<T> {
+    @BeforeTemplate
+    Mono<T> before(
+        Mono<T> mono,
+        Class<? extends Throwable> clazz,
+        BiConsumer<Throwable, Object> errorConsumer) {
+      return mono.onErrorContinue(clazz::isInstance, errorConsumer);
+    }
+
+    @AfterTemplate
+    Mono<T> after(
+        Mono<T> mono,
+        Class<? extends Throwable> clazz,
+        BiConsumer<Throwable, Object> errorConsumer) {
+      return mono.onErrorContinue(clazz, errorConsumer);
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#onErrorContinue(Class, BiConsumer)} over {@link
+   * Flux#onErrorContinue(Predicate, BiConsumer)} where possible.
+   */
+  static final class FluxOnErrorContinue<T> {
+    @BeforeTemplate
+    Flux<T> before(
+        Flux<T> flux,
+        Class<? extends Throwable> clazz,
+        BiConsumer<Throwable, Object> errorConsumer) {
+      return flux.onErrorContinue(clazz::isInstance, errorConsumer);
+    }
+
+    @AfterTemplate
+    Flux<T> after(
+        Flux<T> flux,
+        Class<? extends Throwable> clazz,
+        BiConsumer<Throwable, Object> errorConsumer) {
+      return flux.onErrorContinue(clazz, errorConsumer);
+    }
+  }
+
+  /**
+   * Prefer {@link Mono#onErrorMap(Class, Function)} over {@link Mono#onErrorMap(Predicate,
+   * Function)} where possible.
+   */
+  static final class MonoOnErrorMap<T> {
+    @BeforeTemplate
+    Mono<T> before(
+        Mono<T> mono,
+        Class<? extends Throwable> clazz,
+        Function<? super Throwable, ? extends Throwable> mapper) {
+      return mono.onErrorMap(clazz::isInstance, mapper);
+    }
+
+    @AfterTemplate
+    Mono<T> after(
+        Mono<T> mono,
+        Class<? extends Throwable> clazz,
+        Function<? super Throwable, ? extends Throwable> mapper) {
+      return mono.onErrorMap(clazz, mapper);
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#onErrorMap(Class, Function)} over {@link Flux#onErrorMap(Predicate,
+   * Function)} where possible.
+   */
+  static final class FluxOnErrorMap<T> {
+    @BeforeTemplate
+    Flux<T> before(
+        Flux<T> flux,
+        Class<? extends Throwable> clazz,
+        Function<? super Throwable, ? extends Throwable> mapper) {
+      return flux.onErrorMap(clazz::isInstance, mapper);
+    }
+
+    @AfterTemplate
+    Flux<T> after(
+        Flux<T> flux,
+        Class<? extends Throwable> clazz,
+        Function<? super Throwable, ? extends Throwable> mapper) {
+      return flux.onErrorMap(clazz, mapper);
+    }
+  }
+
+  /**
+   * Prefer {@link Mono#onErrorResume(Class, Function)} over {@link Mono#onErrorResume(Predicate,
+   * Function)} where possible.
+   */
+  static final class MonoOnErrorResume<T> {
+    @BeforeTemplate
+    Mono<T> before(
+        Mono<T> mono,
+        Class<? extends Throwable> clazz,
+        Function<? super Throwable, ? extends Mono<? extends T>> fallback) {
+      return mono.onErrorResume(clazz::isInstance, fallback);
+    }
+
+    @AfterTemplate
+    Mono<T> after(
+        Mono<T> mono,
+        Class<? extends Throwable> clazz,
+        Function<? super Throwable, ? extends Mono<? extends T>> fallback) {
+      return mono.onErrorResume(clazz, fallback);
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#onErrorResume(Class, Function)} over {@link Flux#onErrorResume(Predicate,
+   * Function)} where possible.
+   */
+  static final class FluxOnErrorResume<T> {
+    @BeforeTemplate
+    Flux<T> before(
+        Flux<T> flux,
+        Class<? extends Throwable> clazz,
+        Function<? super Throwable, ? extends Publisher<? extends T>> fallback) {
+      return flux.onErrorResume(clazz::isInstance, fallback);
+    }
+
+    @AfterTemplate
+    Flux<T> after(
+        Flux<T> flux,
+        Class<? extends Throwable> clazz,
+        Function<? super Throwable, ? extends Publisher<? extends T>> fallback) {
+      return flux.onErrorResume(clazz, fallback);
+    }
+  }
+
+  /**
+   * Prefer {@link Mono#onErrorReturn(Class, Object)} over {@link Mono#onErrorReturn(Predicate,
+   * Object)} where possible.
+   */
+  static final class MonoOnErrorReturn<T> {
+    @BeforeTemplate
+    Mono<T> before(Mono<T> mono, Class<? extends Throwable> clazz, T fallbackValue) {
+      return mono.onErrorReturn(clazz::isInstance, fallbackValue);
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<T> mono, Class<? extends Throwable> clazz, T fallbackValue) {
+      return mono.onErrorReturn(clazz, fallbackValue);
+    }
+  }
+
+  /**
+   * Prefer {@link Flux#onErrorReturn(Class, Object)} over {@link Flux#onErrorReturn(Predicate,
+   * Object)} where possible.
+   */
+  static final class FluxOnErrorReturn<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Class<? extends Throwable> clazz, T fallbackValue) {
+      return flux.onErrorReturn(clazz::isInstance, fallbackValue);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Class<? extends Throwable> clazz, T fallbackValue) {
+      return flux.onErrorReturn(clazz, fallbackValue);
+    }
+  }
+
+  /**
+   * 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.
+  static final class ContextEmpty {
+    @BeforeTemplate
+    Context before() {
+      return Context.of(Refaster.anyOf(new HashMap<>(), ImmutableMap.of()));
+    }
+
+    @AfterTemplate
+    Context after() {
+      return Context.empty();
+    }
+  }
+
   /** Prefer {@link PublisherProbe#empty()}} over more verbose alternatives. */
   static final class PublisherProbeEmpty<T> {
     @BeforeTemplate

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) {
@@ -164,12 +167,47 @@ 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.
    */
-  // XXX: Consider whether to have a similar rule for `.findAny()`. For parallel streams it
-  // wouldn't be quite the same....
+  // XXX: Implement a similar rule for `.findAny()`. For parallel streams this wouldn't be quite the
+  // same, so such a rule requires a `Matcher` that heuristically identifies `Stream` expressions
+  // with deterministic order.
   // XXX: This change is not equivalent for `null`-returning functions, as the original code throws
   // an NPE if the first element is `null`, while the latter yields an empty `Optional`.
   static final class StreamMapFirst<T, S> {

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 javax.annotation.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/TimeRules.java

@@ -13,9 +13,11 @@ import java.time.LocalDate;
 import java.time.LocalDateTime;
 import java.time.LocalTime;
 import java.time.OffsetDateTime;
+import java.time.OffsetTime;
 import java.time.Period;
 import java.time.ZoneId;
 import java.time.ZoneOffset;
+import java.time.ZonedDateTime;
 import java.time.chrono.ChronoLocalDate;
 import java.time.chrono.ChronoLocalDateTime;
 import java.time.chrono.ChronoZonedDateTime;
@@ -64,7 +66,83 @@ final class TimeRules {
     }
   }
 
-  /** Prefer {@link Instant#atOffset(ZoneOffset)} over the more verbose alternative. */
+  /** Prefer {@link LocalDate#ofInstant(Instant, ZoneId)} over more indirect alternatives. */
+  static final class LocalDateOfInstant {
+    @BeforeTemplate
+    LocalDate before(Instant instant, ZoneId zoneId) {
+      return Refaster.anyOf(
+          instant.atZone(zoneId).toLocalDate(),
+          LocalDateTime.ofInstant(instant, zoneId).toLocalDate(),
+          OffsetDateTime.ofInstant(instant, zoneId).toLocalDate());
+    }
+
+    @BeforeTemplate
+    LocalDate before(Instant instant, ZoneOffset zoneId) {
+      return instant.atOffset(zoneId).toLocalDate();
+    }
+
+    @AfterTemplate
+    LocalDate after(Instant instant, ZoneId zoneId) {
+      return LocalDate.ofInstant(instant, zoneId);
+    }
+  }
+
+  /** Prefer {@link LocalDateTime#ofInstant(Instant, ZoneId)} over more indirect alternatives. */
+  static final class LocalDateTimeOfInstant {
+    @BeforeTemplate
+    LocalDateTime before(Instant instant, ZoneId zoneId) {
+      return Refaster.anyOf(
+          instant.atZone(zoneId).toLocalDateTime(),
+          OffsetDateTime.ofInstant(instant, zoneId).toLocalDateTime());
+    }
+
+    @BeforeTemplate
+    LocalDateTime before(Instant instant, ZoneOffset zoneId) {
+      return instant.atOffset(zoneId).toLocalDateTime();
+    }
+
+    @AfterTemplate
+    LocalDateTime after(Instant instant, ZoneId zoneId) {
+      return LocalDateTime.ofInstant(instant, zoneId);
+    }
+  }
+
+  /** Prefer {@link LocalTime#ofInstant(Instant, ZoneId)} over more indirect alternatives. */
+  static final class LocalTimeOfInstant {
+    @BeforeTemplate
+    LocalTime before(Instant instant, ZoneId zoneId) {
+      return Refaster.anyOf(
+          instant.atZone(zoneId).toLocalTime(),
+          LocalDateTime.ofInstant(instant, zoneId).toLocalTime(),
+          OffsetDateTime.ofInstant(instant, zoneId).toLocalTime(),
+          OffsetTime.ofInstant(instant, zoneId).toLocalTime());
+    }
+
+    @BeforeTemplate
+    LocalTime before(Instant instant, ZoneOffset zoneId) {
+      return instant.atOffset(zoneId).toLocalTime();
+    }
+
+    @AfterTemplate
+    LocalTime after(Instant instant, ZoneId zoneId) {
+      return LocalTime.ofInstant(instant, zoneId);
+    }
+  }
+
+  /** Prefer {@link OffsetDateTime#ofInstant(Instant, ZoneId)} over more indirect alternatives. */
+  static final class OffsetDateTimeOfInstant {
+    @BeforeTemplate
+    OffsetDateTime before(Instant instant, ZoneId zoneId) {
+      return instant.atZone(zoneId).toOffsetDateTime();
+    }
+
+    @AfterTemplate
+    OffsetDateTime after(Instant instant, ZoneId zoneId) {
+      return OffsetDateTime.ofInstant(instant, zoneId);
+    }
+  }
+
+  /** Prefer {@link Instant#atOffset(ZoneOffset)} over more verbose alternatives. */
   static final class InstantAtOffset {
     @BeforeTemplate
     OffsetDateTime before(Instant instant, ZoneOffset zoneOffset) {
@@ -77,6 +155,37 @@ final class TimeRules {
     }
   }
 
+  /** Prefer {@link OffsetTime#ofInstant(Instant, ZoneId)} over more indirect alternatives. */
+  static final class OffsetTimeOfInstant {
+    @BeforeTemplate
+    OffsetTime before(Instant instant, ZoneId zoneId) {
+      return OffsetDateTime.ofInstant(instant, zoneId).toOffsetTime();
+    }
+
+    @BeforeTemplate
+    OffsetTime before(Instant instant, ZoneOffset zoneId) {
+      return instant.atOffset(zoneId).toOffsetTime();
+    }
+
+    @AfterTemplate
+    OffsetTime after(Instant instant, ZoneId zoneId) {
+      return OffsetTime.ofInstant(instant, zoneId);
+    }
+  }
+
+  /** Prefer {@link Instant#atZone(ZoneId)} over more verbose alternatives. */
+  static final class InstantAtZone {
+    @BeforeTemplate
+    ZonedDateTime before(Instant instant, ZoneId zoneId) {
+      return ZonedDateTime.ofInstant(instant, zoneId);
+    }
+
+    @AfterTemplate
+    ZonedDateTime after(Instant instant, ZoneId zoneId) {
+      return instant.atZone(zoneId);
+    }
+  }
+
   /** Use {@link Clock#systemUTC()} when possible. */
   static final class UtcClock {
     @BeforeTemplate

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
-@javax.annotation.ParametersAreNonnullByDefault
+@org.jspecify.annotations.NullMarked
 package tech.picnic.errorprone.refasterrules;

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

@@ -94,13 +94,11 @@ final class AutowiredConstructorTest {
             "",
             "interface Container {",
             "  class A {",
-            "",
             "    @Deprecated",
             "    A() {}",
             "  }",
             "",
             "  class B {",
-            "",
             "    B(String x) {}",
             "  }",
             "}")

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

@@ -65,6 +65,23 @@ final class CollectorMutabilityTest {
         .doTest();
   }
 
+  @Test
+  void identificationWithoutGuavaOnClasspath() {
+    compilationTestHelper
+        .withClasspath()
+        .addSourceLines(
+            "A.java",
+            "import java.util.stream.Collectors;",
+            "import java.util.stream.Stream;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Stream.empty().collect(Collectors.toList());",
+            "  }",
+            "}")
+        .doTest();
+  }
+
   @Test
   void replacementFirstSuggestedFix() {
     refactoringTestHelper

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

@@ -76,8 +76,18 @@ final class EmptyMethodTest {
             "  void instanceMethod() {}",
             "",
             "  static void staticMethod() {}",
+            "",
+            "  static void staticMethodWithComment() {",
+            "    /* Foo. */",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "final class A {",
+            "  static void staticMethodWithComment() {",
+            "    /* Foo. */",
+            "  }",
             "}")
-        .addOutputLines("A.java", "final class A {}")
         .doTest(TestMode.TEXT_MATCH);
   }
 }

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

@@ -4,6 +4,7 @@ import static com.google.errorprone.BugCheckerRefactoringTestHelper.newInstance;
 
 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;
 
@@ -33,6 +34,14 @@ final class FluxFlatMapUsageTest {
             "    Flux.just(1).flatMapSequential(Flux::just);",
             "    // BUG: Diagnostic contains:",
             "    Flux.just(1).<String>flatMapSequential(i -> Flux.just(String.valueOf(i)));",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1, 2).groupBy(i -> i).flatMap(Flux::just);",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1, 2).groupBy(i -> i).<String>flatMap(i -> Flux.just(String.valueOf(i)));",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1, 2).groupBy(i -> i).flatMapSequential(Flux::just);",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1, 2).groupBy(i -> i).<String>flatMapSequential(i -> Flux.just(String.valueOf(i)));",
             "",
             "    Mono.just(1).flatMap(Mono::just);",
             "    Flux.just(1).concatMap(Flux::just);",
@@ -71,9 +80,13 @@ final class FluxFlatMapUsageTest {
             "import reactor.core.publisher.Flux;",
             "",
             "class A {",
+            "  private static final int MAX_CONCURRENCY = 8;",
+            "",
             "  void m() {",
             "    Flux.just(1).flatMap(Flux::just);",
             "    Flux.just(1).flatMapSequential(Flux::just);",
+            "    Flux.just(1, 2).groupBy(i -> i).flatMap(Flux::just);",
+            "    Flux.just(1, 2).groupBy(i -> i).flatMapSequential(Flux::just);",
             "  }",
             "}")
         .addOutputLines(
@@ -81,12 +94,16 @@ final class FluxFlatMapUsageTest {
             "import reactor.core.publisher.Flux;",
             "",
             "class A {",
+            "  private static final int MAX_CONCURRENCY = 8;",
+            "",
             "  void m() {",
             "    Flux.just(1).concatMap(Flux::just);",
             "    Flux.just(1).concatMap(Flux::just);",
+            "    Flux.just(1, 2).groupBy(i -> i).flatMap(Flux::just, MAX_CONCURRENCY);",
+            "    Flux.just(1, 2).groupBy(i -> i).flatMapSequential(Flux::just, MAX_CONCURRENCY);",
             "  }",
             "}")
-        .doTest();
+        .doTest(TestMode.TEXT_MATCH);
   }
 
   @Test
@@ -103,6 +120,8 @@ final class FluxFlatMapUsageTest {
             "  void m() {",
             "    Flux.just(1).flatMap(Flux::just);",
             "    Flux.just(1).flatMapSequential(Flux::just);",
+            "    Flux.just(1, 2).groupBy(i -> i).flatMap(Flux::just);",
+            "    Flux.just(1, 2).groupBy(i -> i).flatMapSequential(Flux::just);",
             "  }",
             "}")
         .addOutputLines(
@@ -115,8 +134,10 @@ final class FluxFlatMapUsageTest {
             "  void m() {",
             "    Flux.just(1).flatMap(Flux::just, MAX_CONCURRENCY);",
             "    Flux.just(1).flatMapSequential(Flux::just, MAX_CONCURRENCY);",
+            "    Flux.just(1, 2).groupBy(i -> i).concatMap(Flux::just);",
+            "    Flux.just(1, 2).groupBy(i -> i).concatMap(Flux::just);",
             "  }",
             "}")
-        .doTest();
+        .doTest(TestMode.TEXT_MATCH);
   }
 }

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

@@ -16,7 +16,10 @@ final class IdentityConversionTest {
   void identification() {
     compilationTestHelper
         .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 +31,14 @@ 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 +118,13 @@ 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 +155,15 @@ 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 +174,9 @@ 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();
@@ -167,12 +187,15 @@ final class IdentityConversionTest {
     refactoringTestHelper
         .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 +203,8 @@ 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 +229,23 @@ 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 +253,8 @@ 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 +279,8 @@ 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)));",
             "  }",
             "",
@@ -264,14 +294,14 @@ final class IdentityConversionTest {
     refactoringTestHelper
         .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 +310,14 @@ 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/IsInstanceLambdaUsageTest.java

@@ -0,0 +1,70 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Test;
+
+final class IsInstanceLambdaUsageTest {
+  private final CompilationTestHelper compilationTestHelper =
+      CompilationTestHelper.newInstance(IsInstanceLambdaUsage.class, getClass());
+  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
+      BugCheckerRefactoringTestHelper.newInstance(IsInstanceLambdaUsage.class, getClass());
+
+  @Test
+  void identification() {
+    compilationTestHelper
+        .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(6).filter(i -> i instanceof Integer);",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    refactoringTestHelper
+        .addInputLines(
+            "A.java",
+            "import java.util.stream.Stream;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Stream.of(1).filter(i -> i instanceof Integer);",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import java.util.stream.Stream;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Stream.of(1).filter(Integer.class::isInstance);",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

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

@@ -0,0 +1,134 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Test;
+
+final class JUnitClassModifiersTest {
+  private final CompilationTestHelper compilationTestHelper =
+      CompilationTestHelper.newInstance(JUnitClassModifiers.class, getClass());
+  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
+      BugCheckerRefactoringTestHelper.newInstance(JUnitClassModifiers.class, getClass());
+
+  @Test
+  void identification() {
+    compilationTestHelper
+        .addSourceLines(
+            "Container.java",
+            "import org.junit.jupiter.api.Test;",
+            "import org.junit.jupiter.params.ParameterizedTest;",
+            "import org.springframework.boot.test.context.TestConfiguration;",
+            "import org.springframework.context.annotation.Configuration;",
+            "",
+            "class Container {",
+            "  final class FinalAndPackagePrivate {",
+            "    @Test",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  final class FinalAndPackagePrivateWithCustomTestMethod {",
+            "    @ParameterizedTest",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  public abstract class Abstract {",
+            "    @Test",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  @Configuration",
+            "  class WithConfigurationAnnotation {",
+            "    @Test",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  @TestConfiguration",
+            "  class WithConfigurationMetaAnnotation {",
+            "    @Test",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  // BUG: Diagnostic contains:",
+            "  private final class Private {",
+            "    @Test",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  // BUG: Diagnostic contains:",
+            "  protected final class Protected {",
+            "    @Test",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  // BUG: Diagnostic contains:",
+            "  public final class Public {",
+            "    @Test",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  // BUG: Diagnostic contains:",
+            "  class NonFinal {",
+            "    @Test",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  // BUG: Diagnostic contains:",
+            "  class NonFinalWithCustomTestMethod {",
+            "    @ParameterizedTest",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  @Configuration",
+            "  // BUG: Diagnostic contains:",
+            "  public class PublicWithConfigurationAnnotation {",
+            "    @Test",
+            "    void foo() {}",
+            "  }",
+            "",
+            "  @TestConfiguration",
+            "  // BUG: Diagnostic contains:",
+            "  protected class ProtectedWithConfigurationMetaAnnotation {",
+            "    @Test",
+            "    void foo() {}",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    refactoringTestHelper
+        .addInputLines(
+            "A.java",
+            "import org.junit.jupiter.api.Test;",
+            "import org.springframework.context.annotation.Configuration;",
+            "",
+            "public class A {",
+            "  @Test",
+            "  void foo() {}",
+            "",
+            "  @Configuration",
+            "  private static class B {",
+            "    @Test",
+            "    void bar() {}",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import org.junit.jupiter.api.Test;",
+            "import org.springframework.context.annotation.Configuration;",
+            "",
+            "final class A {",
+            "  @Test",
+            "  void foo() {}",
+            "",
+            "  @Configuration",
+            "  static class B {",
+            "    @Test",
+            "    void bar() {}",
+            "  }",
+            "}")
+        .doTest(TestMode.TEXT_MATCH);
+  }
+}

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

@@ -91,6 +91,9 @@ final class JUnitMethodDeclarationTest {
             "  private void tearDown8() {}",
             "",
             "  @Test",
+            "  void test() {}",
+            "",
+            "  @Test",
             "  void method1() {}",
             "",
             "  @Test",
@@ -144,8 +147,13 @@ 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 +163,20 @@ 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 +238,10 @@ final class JUnitMethodDeclarationTest {
             "",
             "  @Override",
             "  @Test",
+            "  void test() {}",
+            "",
+            "  @Override",
+            "  @Test",
             "  void method1() {}",
             "",
             "  @Override",
@@ -267,6 +291,10 @@ final class JUnitMethodDeclarationTest {
             "",
             "  @Override",
             "  @Test",
+            "  void testToString() {}",
+            "",
+            "  @Override",
+            "  @Test",
             "  void testOverload() {}",
             "",
             "  @Override",
@@ -279,6 +307,17 @@ final class JUnitMethodDeclarationTest {
             "  @Override",
             "  @Test",
             "  void testPublic() {}",
+            "",
+            "  @Override",
+            "  @Test",
+            "  void testNull() {}",
+            "",
+            "  @Override",
+            "  @Test",
+            "  void testRecord() {}",
+            "",
+            "  @Test",
+            "  void testMethodThatIsOverriddenWithoutOverrideAnnotation() {}",
             "}")
         .addSourceLines(
             "C.java",
@@ -352,6 +391,9 @@ final class JUnitMethodDeclarationTest {
             "  protected void quux() {}",
             "",
             "  @Test",
+            "  public void testToString() {}",
+            "",
+            "  @Test",
             "  public void testOverload() {}",
             "",
             "  void overload() {}",
@@ -361,6 +403,9 @@ final class JUnitMethodDeclarationTest {
             "",
             "  @Test",
             "  private void testClass() {}",
+            "",
+            "  @Test",
+            "  private void testTrue() {}",
             "}")
         .addOutputLines(
             "A.java",
@@ -407,6 +452,9 @@ final class JUnitMethodDeclarationTest {
             "  void quux() {}",
             "",
             "  @Test",
+            "  void testToString() {}",
+            "",
+            "  @Test",
             "  void testOverload() {}",
             "",
             "  void overload() {}",
@@ -416,6 +464,9 @@ final class JUnitMethodDeclarationTest {
             "",
             "  @Test",
             "  void testClass() {}",
+            "",
+            "  @Test",
+            "  void testTrue() {}",
             "}")
         .doTest(TestMode.TEXT_MATCH);
   }

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

@@ -1,7 +1,5 @@
 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;
@@ -9,9 +7,7 @@ import org.junit.jupiter.api.Test;
 
 final class LexicographicalAnnotationListingTest {
   private final CompilationTestHelper compilationTestHelper =
-      CompilationTestHelper.newInstance(LexicographicalAnnotationListing.class, getClass())
-          .expectErrorMessage(
-              "X", containsPattern("Sort annotations lexicographically where possible"));
+      CompilationTestHelper.newInstance(LexicographicalAnnotationListing.class, getClass());
   private final BugCheckerRefactoringTestHelper refactoringTestHelper =
       BugCheckerRefactoringTestHelper.newInstance(
           LexicographicalAnnotationListing.class, getClass());
@@ -21,7 +17,9 @@ final class LexicographicalAnnotationListingTest {
     compilationTestHelper
         .addSourceLines(
             "A.java",
+            "import java.lang.annotation.ElementType;",
             "import java.lang.annotation.Repeatable;",
+            "import java.lang.annotation.Target;",
             "",
             "interface A {",
             "  @Repeatable(Foos.class)",
@@ -33,6 +31,7 @@ final class LexicographicalAnnotationListingTest {
             "    Bar[] anns() default {};",
             "  }",
             "",
+            "  @Target(ElementType.METHOD)",
             "  @interface Bar {",
             "    String[] value() default {};",
             "  }",
@@ -45,11 +44,21 @@ final class LexicographicalAnnotationListingTest {
             "    Foo[] value();",
             "  }",
             "",
-            "  // BUG: Diagnostic matches: X",
+            "  @Target(ElementType.TYPE_USE)",
+            "  @interface FooTypeUse {",
+            "    String[] value() default {};",
+            "  }",
+            "",
+            "  @Target(ElementType.TYPE_USE)",
+            "  @interface BarTypeUse {",
+            "    String[] value() default {};",
+            "  }",
+            "",
+            "  // BUG: Diagnostic contains:",
             "  @Foo",
             "  @Bar",
             "  A unsortedSimpleCase();",
-            "  // BUG: Diagnostic matches: X",
+            "  // BUG: Diagnostic contains:",
             "  @Foo()",
             "  @Bar()",
             "  A unsortedWithParens();",
@@ -61,12 +70,12 @@ final class LexicographicalAnnotationListingTest {
             "  @Foo()",
             "  A sortedAnnotationsOneWithParens();",
             "",
-            "  // BUG: Diagnostic matches: X",
+            "  // BUG: Diagnostic contains:",
             "  @Foo",
             "  @Baz",
             "  @Bar",
             "  A threeUnsortedAnnotationsSameInitialLetter();",
-            "  // BUG: Diagnostic matches: X",
+            "  // BUG: Diagnostic contains:",
             "  @Bar",
             "  @Foo()",
             "  @Baz",
@@ -77,16 +86,16 @@ final class LexicographicalAnnotationListingTest {
             "  @Foo()",
             "  A threeSortedAnnotations();",
             "",
-            "  // BUG: Diagnostic matches: X",
+            "  // BUG: Diagnostic contains:",
             "  @Foo({\"b\"})",
             "  @Bar({\"a\"})",
             "  A unsortedWithStringAttributes();",
-            "  // BUG: Diagnostic matches: X",
+            "  // BUG: Diagnostic contains:",
             "  @Baz(str = {\"a\", \"b\"})",
             "  @Foo(ints = {1, 0})",
             "  @Bar",
             "  A unsortedWithAttributes();",
-            "  // BUG: Diagnostic matches: X",
+            "  // BUG: Diagnostic contains:",
             "  @Bar",
             "  @Foo(anns = {@Bar(\"b\"), @Bar(\"a\")})",
             "  @Baz",
@@ -101,11 +110,23 @@ final class LexicographicalAnnotationListingTest {
             "  @Foo(ints = {1, 2})",
             "  @Foo({\"b\"})",
             "  A sortedRepeatableAnnotation();",
-            "  // BUG: Diagnostic matches: X",
+            "  // BUG: Diagnostic contains:",
             "  @Foo(anns = {@Bar(\"b\"), @Bar(\"a\")})",
             "  @Bar",
             "  @Foo(ints = {1, 2})",
             "  A unsortedRepeatableAnnotation();",
+            "",
+            "  // BUG: Diagnostic contains:",
+            "  default @FooTypeUse @BarTypeUse A unsortedTypeAnnotations() {",
+            "    return null;",
+            "  }",
+            "",
+            "  // BUG: Diagnostic contains:",
+            "  @Baz",
+            "  @Bar",
+            "  default @FooTypeUse @BarTypeUse A unsortedTypeUseAndOtherAnnotations() {",
+            "    return null;",
+            "  }",
             "}")
         .doTest();
   }
@@ -115,7 +136,9 @@ final class LexicographicalAnnotationListingTest {
     refactoringTestHelper
         .addInputLines(
             "A.java",
+            "import java.lang.annotation.ElementType;",
             "import java.lang.annotation.Repeatable;",
+            "import java.lang.annotation.Target;",
             "",
             "interface A {",
             "  @Repeatable(Foos.class)",
@@ -127,6 +150,7 @@ final class LexicographicalAnnotationListingTest {
             "    Bar[] anns() default {};",
             "  }",
             "",
+            "  @Target(ElementType.METHOD)",
             "  @interface Bar {",
             "    String[] value() default {};",
             "  }",
@@ -139,6 +163,16 @@ final class LexicographicalAnnotationListingTest {
             "    Foo[] value();",
             "  }",
             "",
+            "  @Target(ElementType.TYPE_USE)",
+            "  @interface FooTypeUse {",
+            "    String[] value() default {};",
+            "  }",
+            "",
+            "  @Target(ElementType.TYPE_USE)",
+            "  @interface BarTypeUse {",
+            "    String[] value() default {};",
+            "  }",
+            "",
             "  @Bar",
             "  A singleAnnotation();",
             "",
@@ -174,10 +208,18 @@ final class LexicographicalAnnotationListingTest {
             "  @Bar",
             "  @Foo(ints = {1, 2})",
             "  A unsortedRepeatableAnnotation();",
+            "",
+            "  @Baz",
+            "  @Bar",
+            "  default @FooTypeUse @BarTypeUse A unsortedWithTypeUseAnnotations() {",
+            "    return null;",
+            "  }",
             "}")
         .addOutputLines(
             "A.java",
+            "import java.lang.annotation.ElementType;",
             "import java.lang.annotation.Repeatable;",
+            "import java.lang.annotation.Target;",
             "",
             "interface A {",
             "  @Repeatable(Foos.class)",
@@ -189,6 +231,7 @@ final class LexicographicalAnnotationListingTest {
             "    Bar[] anns() default {};",
             "  }",
             "",
+            "  @Target(ElementType.METHOD)",
             "  @interface Bar {",
             "    String[] value() default {};",
             "  }",
@@ -201,6 +244,16 @@ final class LexicographicalAnnotationListingTest {
             "    Foo[] value();",
             "  }",
             "",
+            "  @Target(ElementType.TYPE_USE)",
+            "  @interface FooTypeUse {",
+            "    String[] value() default {};",
+            "  }",
+            "",
+            "  @Target(ElementType.TYPE_USE)",
+            "  @interface BarTypeUse {",
+            "    String[] value() default {};",
+            "  }",
+            "",
             "  @Bar",
             "  A singleAnnotation();",
             "",
@@ -236,6 +289,12 @@ final class LexicographicalAnnotationListingTest {
             "  @Foo(anns = {@Bar(\"b\"), @Bar(\"a\")})",
             "  @Foo(ints = {1, 2})",
             "  A unsortedRepeatableAnnotation();",
+            "",
+            "  @Bar",
+            "  @Baz",
+            "  default @BarTypeUse @FooTypeUse A unsortedWithTypeUseAnnotations() {",
+            "    return null;",
+            "  }",
             "}")
         .doTest(TestMode.TEXT_MATCH);
   }

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

@@ -39,4 +39,19 @@ final class NestedOptionalsTest {
             "}")
         .doTest();
   }
+
+  @Test
+  void identificationOptionalTypeNotLoaded() {
+    compilationTestHelper
+        .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/RequestParamTypeTest.java

@@ -6,6 +6,10 @@ import org.junit.jupiter.api.Test;
 final class RequestParamTypeTest {
   private final CompilationTestHelper compilationTestHelper =
       CompilationTestHelper.newInstance(RequestParamType.class, getClass());
+  private final CompilationTestHelper restrictedCompilationTestHelper =
+      CompilationTestHelper.newInstance(RequestParamType.class, getClass())
+          .setArgs(
+              "-XepOpt:RequestParamType:SupportedCustomTypes=com.google.common.collect.ImmutableSet,com.google.common.collect.ImmutableSortedMultiset");
 
   @Test
   void identification() {
@@ -19,7 +23,7 @@ final class RequestParamTypeTest {
             "import java.util.List;",
             "import java.util.Map;",
             "import java.util.Set;",
-            "import javax.annotation.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 +67,53 @@ final class RequestParamTypeTest {
             "}")
         .doTest();
   }
+
+  @Test
+  void identificationRestricted() {
+    restrictedCompilationTestHelper
+        .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

@@ -4,6 +4,7 @@ import com.google.errorprone.BugCheckerRefactoringTestHelper;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
 import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
+import org.springframework.scheduling.annotation.Scheduled;
 
 final class ScheduledTransactionTraceTest {
   private final CompilationTestHelper compilationTestHelper =
@@ -43,6 +44,21 @@ final class ScheduledTransactionTraceTest {
         .doTest();
   }
 
+  @Test
+  void identificationWithoutNewRelicAgentApiOnClasspath() {
+    compilationTestHelper
+        .withClasspath(Scheduled.class)
+        .addSourceLines(
+            "A.java",
+            "import org.springframework.scheduling.annotation.Scheduled;",
+            "",
+            "class A {",
+            "  @Scheduled(fixedDelay = 1)",
+            "  void scheduledButNotTraced() {}",
+            "}")
+        .doTest();
+  }
+
   @Test
   void replacement() {
     refactoringTestHelper

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

@@ -0,0 +1,132 @@
+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;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Test;
+
+final class StringCaseLocaleUsageTest {
+  private final CompilationTestHelper compilationTestHelper =
+      CompilationTestHelper.newInstance(StringCaseLocaleUsage.class, getClass());
+  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
+      newInstance(StringCaseLocaleUsage.class, getClass());
+
+  @Test
+  void identification() {
+    compilationTestHelper
+        .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() {
+    refactoringTestHelper
+        .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() {
+    refactoringTestHelper
+        .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/TimeZoneUsageTest.java

@@ -1,17 +1,11 @@
 package tech.picnic.errorprone.bugpatterns;
 
-import static com.google.common.base.Predicates.containsPattern;
-
 import com.google.errorprone.CompilationTestHelper;
 import org.junit.jupiter.api.Test;
 
 final class TimeZoneUsageTest {
   private final CompilationTestHelper compilationHelper =
-      CompilationTestHelper.newInstance(TimeZoneUsage.class, getClass())
-          .expectErrorMessage(
-              "X",
-              containsPattern(
-                  "Derive the current time from an existing `Clock` Spring bean, and don't rely on a `Clock`'s time zone"));
+      CompilationTestHelper.newInstance(TimeZoneUsage.class, getClass());
 
   @Test
   void identification() {
@@ -26,7 +20,10 @@ final class TimeZoneUsageTest {
             "import java.time.LocalDate;",
             "import java.time.LocalDateTime;",
             "import java.time.LocalTime;",
+            "import java.time.OffsetDateTime;",
+            "import java.time.OffsetTime;",
             "import java.time.ZoneId;",
+            "import java.time.ZonedDateTime;",
             "",
             "class A {",
             "  void m() {",
@@ -36,48 +33,69 @@ final class TimeZoneUsageTest {
             "    Clock.offset(clock, Duration.ZERO);",
             "    Clock.tick(clock, Duration.ZERO);",
             "",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    Clock.systemUTC();",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    Clock.systemDefaultZone();",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    Clock.system(UTC);",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    Clock.tickMillis(UTC);",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    Clock.tickMinutes(UTC);",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    Clock.tickSeconds(UTC);",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    clock.getZone();",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    clock.withZone(UTC);",
             "",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    Instant.now();",
             "    // This is equivalent to `clock.instant()`, which is fine.",
             "    Instant.now(clock);",
             "",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    LocalDate.now();",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    LocalDate.now(clock);",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    LocalDate.now(UTC);",
             "",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    LocalDateTime.now();",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    LocalDateTime.now(clock);",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    LocalDateTime.now(UTC);",
             "",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    LocalTime.now();",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    LocalTime.now(clock);",
-            "    // BUG: Diagnostic matches: X",
+            "    // BUG: Diagnostic contains:",
             "    LocalTime.now(UTC);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    OffsetDateTime.now();",
+            "    // BUG: Diagnostic contains:",
+            "    OffsetDateTime.now(clock);",
+            "    // BUG: Diagnostic contains:",
+            "    OffsetDateTime.now(UTC);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    OffsetTime.now();",
+            "    // BUG: Diagnostic contains:",
+            "    OffsetTime.now(clock);",
+            "    // BUG: Diagnostic contains:",
+            "    OffsetTime.now(UTC);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    ZonedDateTime.now();",
+            "    // BUG: Diagnostic contains:",
+            "    ZonedDateTime.now(clock);",
+            "    // BUG: Diagnostic contains:",
+            "    ZonedDateTime.now(UTC);",
             "  }",
             "",
             "  abstract class ForwardingClock extends Clock {",

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/MoreASTHelpersTest.java

@@ -0,0 +1,110 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Maps;
+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.sun.source.tree.MethodTree;
+import java.util.function.BiFunction;
+import org.junit.jupiter.api.Test;
+
+final class MoreASTHelpersTest {
+  @Test
+  void findMethods() {
+    CompilationTestHelper.newInstance(FindMethodsTestChecker.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "class A {",
+            "  // BUG: Diagnostic contains: {foo=1, bar=2, baz=0}",
+            "  void foo() {}",
+            "",
+            "  // BUG: Diagnostic contains: {foo=1, bar=2, baz=0}",
+            "  void bar() {}",
+            "",
+            "  // BUG: Diagnostic contains: {foo=1, bar=2, baz=0}",
+            "  void bar(int i) {}",
+            "",
+            "  static class B {",
+            "    // BUG: Diagnostic contains: {foo=0, bar=1, baz=1}",
+            "    void bar() {}",
+            "",
+            "    // BUG: Diagnostic contains: {foo=0, bar=1, baz=1}",
+            "    void baz() {}",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void methodExistsInEnclosingClass() {
+    CompilationTestHelper.newInstance(MethodExistsTestChecker.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "class A {",
+            "  // BUG: Diagnostic contains: {foo=true, bar=true, baz=false}",
+            "  void foo() {}",
+            "",
+            "  // BUG: Diagnostic contains: {foo=true, bar=true, baz=false}",
+            "  void bar() {}",
+            "",
+            "  // BUG: Diagnostic contains: {foo=true, bar=true, baz=false}",
+            "  void bar(int i) {}",
+            "",
+            "  static class B {",
+            "    // BUG: Diagnostic contains: {foo=false, bar=true, baz=true}",
+            "    void bar() {}",
+            "",
+            "    // BUG: Diagnostic contains: {foo=false, bar=true, baz=true}",
+            "    void baz() {}",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  private static String createDiagnosticsMessage(
+      BiFunction<String, VisitorState, Object> valueFunction, VisitorState state) {
+    return Maps.toMap(ImmutableSet.of("foo", "bar", "baz"), key -> valueFunction.apply(key, state))
+        .toString();
+  }
+
+  /**
+   * A {@link BugChecker} that delegates to {@link MoreASTHelpers#findMethods(CharSequence,
+   * VisitorState)}.
+   */
+  @BugPattern(summary = "Interacts with `MoreASTHelpers` for testing purposes", severity = ERROR)
+  public static final class FindMethodsTestChecker extends BugChecker implements MethodTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchMethod(MethodTree tree, VisitorState state) {
+      return buildDescription(tree)
+          .setMessage(
+              createDiagnosticsMessage(
+                  (methodName, s) -> MoreASTHelpers.findMethods(methodName, s).size(), state))
+          .build();
+    }
+  }
+
+  /**
+   * A {@link BugChecker} that delegates to {@link
+   * MoreASTHelpers#methodExistsInEnclosingClass(CharSequence, VisitorState)}.
+   */
+  @BugPattern(summary = "Interacts with `MoreASTHelpers` for testing purposes", severity = ERROR)
+  public static final class MethodExistsTestChecker extends BugChecker
+      implements MethodTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchMethod(MethodTree tree, VisitorState state) {
+      return buildDescription(tree)
+          .setMessage(createDiagnosticsMessage(MoreASTHelpers::methodExistsInEnclosingClass, state))
+          .build();
+    }
+  }
+}

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

@@ -0,0 +1,173 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+import static tech.picnic.errorprone.bugpatterns.util.MoreJUnitMatchers.HAS_METHOD_SOURCE;
+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.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Iterables;
+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.matchers.Matcher;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.MethodTree;
+import java.util.Map;
+import org.junit.jupiter.api.Test;
+
+final class MoreJUnitMatchersTest {
+  @Test
+  void methodMatchers() {
+    CompilationTestHelper.newInstance(MethodMatchersTestChecker.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import static org.junit.jupiter.params.provider.Arguments.arguments;",
+            "",
+            "import java.util.stream.Stream;",
+            "import org.junit.jupiter.api.AfterAll;",
+            "import org.junit.jupiter.api.AfterEach;",
+            "import org.junit.jupiter.api.BeforeAll;",
+            "import org.junit.jupiter.api.BeforeEach;",
+            "import org.junit.jupiter.api.RepeatedTest;",
+            "import org.junit.jupiter.api.Test;",
+            "import org.junit.jupiter.params.ParameterizedTest;",
+            "import org.junit.jupiter.params.provider.Arguments;",
+            "import org.junit.jupiter.params.provider.MethodSource;",
+            "",
+            "class A {",
+            "  @BeforeAll",
+            "  // BUG: Diagnostic contains: SETUP_OR_TEARDOWN_METHOD",
+            "  public void beforeAll() {}",
+            "",
+            "  @BeforeEach",
+            "  @Test",
+            "  // BUG: Diagnostic contains: TEST_METHOD, SETUP_OR_TEARDOWN_METHOD",
+            "  protected void beforeEachAndTest() {}",
+            "",
+            "  @AfterEach",
+            "  // BUG: Diagnostic contains: SETUP_OR_TEARDOWN_METHOD",
+            "  private void afterEach() {}",
+            "",
+            "  @AfterAll",
+            "  // BUG: Diagnostic contains: SETUP_OR_TEARDOWN_METHOD",
+            "  private void afterAll() {}",
+            "",
+            "  @Test",
+            "  // BUG: Diagnostic contains: TEST_METHOD",
+            "  void test() {}",
+            "",
+            "  private static Stream<Arguments> booleanArgs() {",
+            "    return Stream.of(arguments(false), arguments(true));",
+            "  }",
+            "",
+            "  @ParameterizedTest",
+            "  @MethodSource(\"booleanArgs\")",
+            "  // BUG: Diagnostic contains: TEST_METHOD, HAS_METHOD_SOURCE",
+            "  void parameterizedTest(boolean b) {}",
+            "",
+            "  @RepeatedTest(2)",
+            "  // BUG: Diagnostic contains: TEST_METHOD",
+            "  private void repeatedTest() {}",
+            "",
+            "  private void unannotatedMethod() {}",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void getMethodSourceFactoryNames() {
+    CompilationTestHelper.newInstance(MethodSourceFactoryNamesTestChecker.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import org.junit.jupiter.params.provider.MethodSource;",
+            "",
+            "class A {",
+            "  @MethodSource",
+            "  // BUG: Diagnostic contains: [matchingMethodSource]",
+            "  void matchingMethodSource(boolean b) {}",
+            "",
+            "  @MethodSource()",
+            "  // BUG: Diagnostic contains: [matchingMethodSourceWithParens]",
+            "  void matchingMethodSourceWithParens(boolean b) {}",
+            "",
+            "  @MethodSource(\"\")",
+            "  // BUG: Diagnostic contains: [matchingMethodSourceMadeExplicit]",
+            "  void matchingMethodSourceMadeExplicit(boolean b) {}",
+            "",
+            "  @MethodSource({\"\"})",
+            "  // BUG: Diagnostic contains: [matchingMethodSourceMadeExplicitWithParens]",
+            "  void matchingMethodSourceMadeExplicitWithParens(boolean b) {}",
+            "",
+            "  @MethodSource({})",
+            "  // BUG: Diagnostic contains: []",
+            "  void noMethodSources(boolean b) {}",
+            "",
+            "  @MethodSource(\"myValueFactory\")",
+            "  // BUG: Diagnostic contains: [myValueFactory]",
+            "  void singleCustomMethodSource(boolean b) {}",
+            "",
+            "  @MethodSource({\"firstValueFactory\", \"secondValueFactory\"})",
+            "  // BUG: Diagnostic contains: [firstValueFactory, secondValueFactory]",
+            "  void twoCustomMethodSources(boolean b) {}",
+            "",
+            "  @MethodSource({\"myValueFactory\", \"\"})",
+            "  // BUG: Diagnostic contains: [myValueFactory, customAndMatchingMethodSources]",
+            "  void customAndMatchingMethodSources(boolean b) {}",
+            "}")
+        .doTest();
+  }
+
+  /**
+   * A {@link BugChecker} that flags methods matched by {@link Matcher}s of {@link MethodTree}s
+   * exposed by {@link MoreJUnitMatchers}.
+   */
+  @BugPattern(summary = "Interacts with `MoreJUnitMatchers` for testing purposes", severity = ERROR)
+  public static final class MethodMatchersTestChecker extends BugChecker
+      implements MethodTreeMatcher {
+    private static final long serialVersionUID = 1L;
+    private static final ImmutableMap<String, Matcher<MethodTree>> METHOD_MATCHERS =
+        ImmutableMap.of(
+            "TEST_METHOD", TEST_METHOD,
+            "HAS_METHOD_SOURCE", HAS_METHOD_SOURCE,
+            "SETUP_OR_TEARDOWN_METHOD", SETUP_OR_TEARDOWN_METHOD);
+
+    @Override
+    public Description matchMethod(MethodTree tree, VisitorState state) {
+      ImmutableSet<String> matches =
+          METHOD_MATCHERS.entrySet().stream()
+              .filter(e -> e.getValue().matches(tree, state))
+              .map(Map.Entry::getKey)
+              .collect(toImmutableSet());
+
+      return matches.isEmpty()
+          ? Description.NO_MATCH
+          : buildDescription(tree).setMessage(String.join(", ", matches)).build();
+    }
+  }
+
+  /**
+   * A {@link BugChecker} that flags methods with a JUnit {@code @MethodSource} annotation by
+   * enumerating the associated value factory method names.
+   */
+  @BugPattern(summary = "Interacts with `MoreJUnitMatchers` for testing purposes", severity = ERROR)
+  public static final class MethodSourceFactoryNamesTestChecker extends BugChecker
+      implements MethodTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchMethod(MethodTree tree, VisitorState state) {
+      AnnotationTree annotation =
+          Iterables.getOnlyElement(HAS_METHOD_SOURCE.multiMatchResult(tree, state).matchingNodes());
+
+      return buildDescription(tree)
+          .setMessage(MoreJUnitMatchers.getMethodSourceFactoryNames(annotation, tree).toString())
+          .build();
+    }
+  }
+}

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

@@ -0,0 +1,62 @@
+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.AnnotationTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.sun.source.tree.AnnotationTree;
+import org.junit.jupiter.api.Test;
+
+final class MoreMatchersTest {
+  @Test
+  void hasMetaAnnotation() {
+    CompilationTestHelper.newInstance(TestMatcher.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import org.junit.jupiter.api.AfterAll;",
+            "import org.junit.jupiter.api.RepeatedTest;",
+            "import org.junit.jupiter.api.Test;",
+            "import org.junit.jupiter.api.TestTemplate;",
+            "import org.junit.jupiter.params.ParameterizedTest;",
+            "",
+            "class A {",
+            "  void negative1() {}",
+            "",
+            "  @Test",
+            "  void negative2() {}",
+            "",
+            "  @AfterAll",
+            "  void negative3() {}",
+            "",
+            "  @TestTemplate",
+            "  void negative4() {}",
+            "",
+            "  // BUG: Diagnostic contains:",
+            "  @ParameterizedTest",
+            "  void positive1() {}",
+            "",
+            "  // BUG: Diagnostic contains:",
+            "  @RepeatedTest(2)",
+            "  void positive2() {}",
+            "}")
+        .doTest();
+  }
+
+  /** A {@link BugChecker} that delegates to {@link MoreMatchers#hasMetaAnnotation(String)} . */
+  @BugPattern(summary = "Interacts with `MoreMatchers` for testing purposes", severity = ERROR)
+  public static final class TestMatcher extends BugChecker implements AnnotationTreeMatcher {
+    private static final long serialVersionUID = 1L;
+    private static final Matcher<AnnotationTree> DELEGATE =
+        MoreMatchers.hasMetaAnnotation("org.junit.jupiter.api.TestTemplate");
+
+    @Override
+    public Description matchAnnotation(AnnotationTree tree, VisitorState state) {
+      return DELEGATE.matches(tree, state) ? describeMatch(tree) : Description.NO_MATCH;
+    }
+  }
+}

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

@@ -0,0 +1,195 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.generic;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.raw;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.subOf;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.superOf;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.type;
+import static tech.picnic.errorprone.bugpatterns.util.MoreTypes.unbound;
+
+import com.google.common.collect.ImmutableSet;
+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.MethodInvocationTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.suppliers.Supplier;
+import com.google.errorprone.util.ASTHelpers;
+import com.google.errorprone.util.Signatures;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.tools.javac.code.Type;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+final class MoreTypesTest {
+  @Test
+  void matcher() {
+    CompilationTestHelper.newInstance(SubtypeFlagger.class, getClass())
+        .addSourceLines(
+            "/A.java",
+            "import java.util.Collection;",
+            "import java.util.List;",
+            "import java.util.Map;",
+            "import java.util.Optional;",
+            "import java.util.Set;",
+            "",
+            "class A<S, T> {",
+            "  void m() {",
+            "    Object object = factory();",
+            "    A a = factory();",
+            "",
+            "    // BUG: Diagnostic contains: [Number, ? super Number, Integer, ? super Integer]",
+            "    int integer = factory();",
+            "",
+            "    // BUG: Diagnostic contains: [String]",
+            "    String string = factory();",
+            "",
+            "    // BUG: Diagnostic contains: [Optional]",
+            "    Optional rawOptional = factory();",
+            "    // BUG: Diagnostic contains: [Optional, Optional<?>]",
+            "    Optional<S> optionalOfS = factory();",
+            "    // BUG: Diagnostic contains: [Optional, Optional<?>]",
+            "    Optional<T> optionalOfT = factory();",
+            "    // BUG: Diagnostic contains: [Optional, Optional<?>, Optional<Number>]",
+            "    Optional<Number> optionalOfNumber = factory();",
+            "    // BUG: Diagnostic contains: [Optional, Optional<?>]",
+            "    Optional<Integer> optionalOfInteger = factory();",
+            "",
+            "    // BUG: Diagnostic contains: [Collection]",
+            "    Collection rawCollection = factory();",
+            "    // BUG: Diagnostic contains: [Collection, Collection<?>, Collection<Number>, Collection<? super",
+            "    // Number>, Collection<? extends Number>, Collection<? super Integer>]",
+            "    Collection<Number> collectionOfNumber = factory();",
+            "    // BUG: Diagnostic contains: [Collection, Collection<?>, Collection<? extends Number>,",
+            "    // Collection<Integer>, Collection<? super Integer>, Collection<? extends Integer>]",
+            "    Collection<Integer> collectionOfInteger = factory();",
+            "    // BUG: Diagnostic contains: [Collection, Collection<?>, Collection<? extends Number>]",
+            "    Collection<Short> collectionOfShort = factory();",
+            "",
+            "    // BUG: Diagnostic contains: [Collection, List]",
+            "    List rawList = factory();",
+            "    // BUG: Diagnostic contains: [Collection, Collection<?>, Collection<Number>, Collection<? super",
+            "    // Number>, Collection<? extends Number>, Collection<? super Integer>, List, List<?>,",
+            "    // List<Number>, List<? super Number>, List<? extends Number>, List<? super Integer>]",
+            "    List<Number> listOfNumber = factory();",
+            "    // BUG: Diagnostic contains: [Collection, Collection<?>, Collection<? extends Number>,",
+            "    // Collection<Integer>, Collection<? super Integer>, Collection<? extends Integer>, List,",
+            "    // List<?>, List<? extends Number>, List<Integer>, List<? super Integer>, List<? extends",
+            "    // Integer>]",
+            "    List<Integer> listOfInteger = factory();",
+            "    // BUG: Diagnostic contains: [Collection, Collection<?>, Collection<? extends Number>, List,",
+            "    // List<?>, List<? extends Number>]",
+            "    List<Short> listOfShort = factory();",
+            "",
+            "    // BUG: Diagnostic contains: [Collection]",
+            "    Set rawSet = factory();",
+            "    // BUG: Diagnostic contains: [Collection, Collection<?>, Collection<Number>, Collection<? super",
+            "    // Number>, Collection<? extends Number>, Collection<? super Integer>]",
+            "    Set<Number> setOfNumber = factory();",
+            "    // BUG: Diagnostic contains: [Collection, Collection<?>, Collection<? extends Number>,",
+            "    // Collection<Integer>, Collection<? super Integer>, Collection<? extends Integer>]",
+            "    Set<Integer> setOfInteger = factory();",
+            "    // BUG: Diagnostic contains: [Collection, Collection<?>, Collection<? extends Number>]",
+            "    Set<Short> setOfShort = factory();",
+            "",
+            "    Map rawMap = factory();",
+            "    Map<Number, Collection<Number>> mapFromNumberToCollectionOfNumber = factory();",
+            "    Map<Number, Collection<Short>> mapFromNumberToCollectionOfShort = factory();",
+            "    Map<Number, Collection<Integer>> mapFromNumberToCollectionOfInteger = factory();",
+            "    // BUG: Diagnostic contains: [Map<String, ? extends Collection<? super Short>>]",
+            "    Map<String, Collection<Number>> mapFromStringToCollectionOfNumber = factory();",
+            "    // BUG: Diagnostic contains: [Map<String, ? extends Collection<? super Short>>]",
+            "    Map<String, Collection<Short>> mapFromStringToCollectionOfShort = factory();",
+            "    Map<String, Collection<Integer>> mapFromStringToCollectionOfInteger = factory();",
+            "    // BUG: Diagnostic contains: [Map<String, ? extends Collection<? super Short>>]",
+            "    Map<String, List<Number>> mapFromStringToListOfNumber = factory();",
+            "    // BUG: Diagnostic contains: [Map<String, ? extends Collection<? super Short>>]",
+            "    Map<String, List<Short>> mapFromStringToListOfShort = factory();",
+            "    Map<String, List<Integer>> mapFromStringToListOfInteger = factory();",
+            "  }",
+            "",
+            "  private <T> T factory() {",
+            "    return null;",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  /**
+   * 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
+      implements MethodInvocationTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+      Type treeType = ASTHelpers.getType(tree);
+
+      List<String> matches = new ArrayList<>();
+
+      for (Supplier<Type> type : getTestTypes()) {
+        Type testType = type.get(state);
+        if (testType != null && state.getTypes().isSubtype(treeType, testType)) {
+          matches.add(Signatures.prettyType(testType));
+        }
+      }
+
+      return matches.isEmpty()
+          ? 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"))))));
+    }
+  }
+}