Remove things for SS

error-prone-contrib/pom.xml

@@ -39,6 +39,12 @@
             <artifactId>error_prone_test_helpers</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>migration-util</artifactId>
+            <version>0.0.1-SNAPSHOT</version>
+            <scope>compile</scope>
+        </dependency>
         <dependency>
             <groupId>${project.groupId}</groupId>
             <artifactId>refaster-resource-compiler</artifactId>
@@ -220,6 +226,11 @@
                                 <artifactId>refaster-support</artifactId>
                                 <version>${project.version}</version>
                             </path>
+                            <path>
+                                <groupId>${project.groupId}</groupId>
+                                <artifactId>migration-util</artifactId>
+                                <version>${project.version}</version>
+                            </path>
                         </annotationProcessorPaths>
                         <compilerArgs combine.children="append">
                             <arg>-Xplugin:RefasterRuleResourceCompiler</arg>

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

@@ -0,0 +1,42 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType;
+import static com.google.errorprone.BugPattern.SeverityLevel;
+import static com.google.errorprone.BugPattern.StandardTags;
+import static com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
+import static com.sun.source.tree.Tree.Kind;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.LiteralTree;
+import com.sun.source.tree.MethodInvocationTree;
+
+@AutoService(BugChecker.class)
+@BugPattern(
+    name = "StringIsEmpty",
+    summary = "Prefer `String#isEmpty` over `String#equals`",
+    severity = SeverityLevel.SUGGESTION,
+    tags = StandardTags.STYLE)
+public final class StringIsEmptyCheck extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final Matcher<ExpressionTree> STRING_EQUALS_INVOCATION =
+      instanceMethod().onDescendantOf("java.lang.String").named("equals");
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (STRING_EQUALS_INVOCATION.matches(tree, state)
+        && tree.getArguments().get(0).getKind() == Kind.STRING_LITERAL
+        && ((LiteralTree) tree.getArguments().get(0)).getValue().equals("")) {
+      return describeMatch(
+          tree, SuggestedFix.replace(tree, ASTHelpers.getReceiver(tree) + ".isEmpty()"));
+    }
+    return Description.NO_MATCH;
+  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/refastertemplates/RxJava2AdapterTemplates.java

@@ -18,6 +18,19 @@ import reactor.core.publisher.Mono;
 final class RxJava2AdapterTemplates {
   private RxJava2AdapterTemplates() {}
 
+  /** Remove double conversion of ... */
+  static final class FluxToFlowableToFlux<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux) {
+      return RxJava2Adapter.flowableToFlux(RxJava2Adapter.fluxToFlowable(flux));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux) {
+      return flux;
+    }
+  }
+
   /** Use the fluent API style when using {@link RxJava2Adapter#completableToMono}. */
   static final class CompletableToMono {
     @BeforeTemplate

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

@@ -0,0 +1,506 @@
+package tech.picnic.errorprone.refastertemplates;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.collect.Streams;
+import com.google.errorprone.refaster.ImportPolicy;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Single;
+import io.reactivex.SingleSource;
+import io.reactivex.functions.Action;
+import io.reactivex.functions.Consumer;
+import io.reactivex.functions.Predicate;
+import java.util.concurrent.Callable;
+import java.util.function.Supplier;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+/** The Refaster templates for the migration of the RxJava Completable type to Reactor */
+final class RxJavaCompletableToReactorTemplates {
+
+  private RxJavaCompletableToReactorTemplates() {}
+
+  static final class CompletableAmb {
+    @BeforeTemplate
+    Completable before(Iterable<? extends Completable> sources) {
+      return Completable.amb(sources);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    Completable after(Iterable<? extends Completable> sources) {
+      return RxJava2Adapter.monoToCompletable(
+          Mono.firstWithSignal(
+              Streams.stream(sources)
+                  .map(RxJava2Adapter::completableToMono)
+                  .collect(toImmutableList())));
+    }
+  }
+
+  // XXX: public static Completable ambArray(CompletableSource[])
+
+  static final class CompletableComplete {
+    @BeforeTemplate
+    Completable before() {
+      return Completable.complete();
+    }
+
+    @AfterTemplate
+    Completable after() {
+      return RxJava2Adapter.monoToCompletable(Mono.empty());
+    }
+  }
+
+  // XXX: public static Completable concat(Iterable)
+  // XXX: public static Completable concat(Publisher)
+  // XXX: public static Completable concat(Publisher,int)
+  // XXX: public static Completable concatArray(CompletableSource[])
+  // XXX: public static Completable create(CompletableOnSubscribe)
+
+  // XXX: The types of the @Before and @After are not matching
+  static final class CompletableDefer {
+    @BeforeTemplate
+    Completable before(Callable<? extends CompletableSource> supplier) {
+      return Completable.defer(supplier);
+    }
+
+    @AfterTemplate
+    Completable after(Callable<? extends Completable> supplier) {
+      return RxJava2Adapter.monoToCompletable(
+          Mono.defer(
+              () ->
+                  RxJava2Adapter.completableToMono(
+                      RxJavaReactorMigrationUtil.callableAsSupplier(supplier).get())));
+    }
+  }
+
+  static final class CompletableErrorCallable {
+    @BeforeTemplate
+    Completable before(Callable<? extends Throwable> throwable) {
+      return Completable.error(throwable);
+    }
+
+    @AfterTemplate
+    Completable after(Supplier<? extends Throwable> throwable) {
+      return RxJava2Adapter.monoToCompletable(Mono.error(throwable));
+    }
+  }
+
+  static final class CompletableErrorThrowable {
+    @BeforeTemplate
+    Completable before(Throwable throwable) {
+      return Completable.error(throwable);
+    }
+
+    @AfterTemplate
+    Completable after(Throwable throwable) {
+      return RxJava2Adapter.monoToCompletable(Mono.error(throwable));
+    }
+  }
+
+  static final class CompletableFromAction {
+    @BeforeTemplate
+    Completable before(Action action) {
+      return Completable.fromAction(action);
+    }
+
+    @AfterTemplate
+    Completable after(Action action) {
+      return RxJava2Adapter.monoToCompletable(
+          Mono.fromRunnable(RxJavaReactorMigrationUtil.toRunnable(action)));
+    }
+  }
+
+  static final class CompletableFromCallable {
+    @BeforeTemplate
+    Completable before(Callable<?> supplier) {
+      return Completable.fromCallable(supplier);
+    }
+
+    @AfterTemplate
+    Completable after(Callable<?> supplier) {
+      return RxJava2Adapter.monoToCompletable(Mono.fromCallable(supplier));
+    }
+  }
+
+  // XXX: public static Completable fromFuture(Future)
+  // XXX: public static Completable fromMaybe(MaybeSource)
+  // XXX: public static Completable fromObservable(ObservableSource)
+
+  static final class CompletableFromPublisher<T> {
+    @BeforeTemplate
+    Completable before(Publisher<T> source) {
+      return Completable.fromPublisher(source);
+    }
+
+    @AfterTemplate
+    Completable after(Publisher<T> source) {
+      return RxJava2Adapter.monoToCompletable(Mono.from(source));
+    }
+  }
+
+  static final class CompletableFromRunnable {
+    @BeforeTemplate
+    Completable before(Runnable runnable) {
+      return Completable.fromRunnable(runnable);
+    }
+
+    @AfterTemplate
+    Completable after(Runnable runnable) {
+      return RxJava2Adapter.monoToCompletable(Mono.fromRunnable(runnable));
+    }
+  }
+
+  // XXX: public static Completable fromSingle(SingleSource)
+  // XXX: public static Completable merge(Iterable)
+  // XXX: public static Completable merge(Publisher)
+  // XXX: public static Completable merge(Publisher,int)
+  // XXX: public static Completable mergeArray(CompletableSource[])
+  // XXX: public static Completable mergeArrayDelayError(CompletableSource[])
+  // XXX: public static Completable mergeDelayError(Iterable)
+  // XXX: public static Completable mergeDelayError(Publisher)
+  // XXX: public static Completable mergeDelayError(Publisher,int)
+  // XXX: public static Completable never()
+  // XXX: public static Completable timer(long,TimeUnit)
+  // XXX: public static Completable timer(long,TimeUnit,Scheduler)
+  // XXX: public static Completable unsafeCreate(CompletableSource)
+  // XXX: public static Completable using(Callable,Function,Consumer)
+  // XXX: public static Completable using(Callable,Function,Consumer,boolean)
+
+  static final class CompletableWrap {
+    @BeforeTemplate
+    Completable before(Completable source) {
+      return Completable.wrap(source);
+    }
+
+    @AfterTemplate
+    Completable after(Completable source) {
+      return source;
+    }
+  }
+
+  // XXX: public final Completable ambWith(CompletableSource)
+
+  static final class CompletableAndThenCompletable {
+    @BeforeTemplate
+    Completable before(Completable completable, CompletableSource source) {
+      return completable.andThen(source);
+    }
+
+    @AfterTemplate
+    Completable after(Completable completable, CompletableSource source) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.completableToMono(completable)
+              .then(RxJava2Adapter.completableToMono(Completable.wrap(source))));
+    }
+  }
+
+  static final class CompletableAndThenMaybe<T> {
+    @BeforeTemplate
+    Maybe<T> before(Completable completable, MaybeSource<T> source) {
+      return completable.andThen(source);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Completable completable, MaybeSource<T> source) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.completableToMono(completable)
+              .then(RxJava2Adapter.maybeToMono(Maybe.wrap(source))));
+    }
+  }
+
+  // XXX: public final Observable andThen(ObservableSource)
+
+  static final class CompletableAndThenPublisher<T> {
+    @BeforeTemplate
+    Flowable<T> before(Completable completable, Publisher<T> source) {
+      return completable.andThen(source);
+    }
+
+    @AfterTemplate
+    Flowable<T> after(Completable completable, Publisher<T> source) {
+      return RxJava2Adapter.fluxToFlowable(
+          RxJava2Adapter.completableToMono(completable).thenMany(source));
+    }
+  }
+
+  static final class CompletableAndThenSingle<T> {
+    @BeforeTemplate
+    Single<T> before(Completable completable, SingleSource<T> source) {
+      return completable.andThen(source);
+    }
+
+    @AfterTemplate
+    Single<T> after(Completable completable, SingleSource<T> source) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.completableToMono(completable)
+              .then(RxJava2Adapter.singleToMono(Single.wrap(source))));
+    }
+  }
+
+  // XXX: public final Object as(CompletableConverter)
+
+  static final class CompletableBlockingAwait {
+    @BeforeTemplate
+    void before(Completable completable) {
+      completable.blockingAwait();
+    }
+
+    @AfterTemplate
+    void after(Completable completable) {
+      RxJava2Adapter.completableToMono(completable).block();
+    }
+  }
+
+  // XXX: public final boolean blockingAwait(long,TimeUnit)
+  // XXX: public final Throwable blockingGet()
+  // XXX: public final Throwable blockingGet(long,TimeUnit)
+  // XXX: public final Completable cache()
+  // XXX: public final Completable compose(CompletableTransformer)
+  // XXX: public final Completable concatWith(CompletableSource)
+  // XXX: public final Completable delay(long,TimeUnit)
+  // XXX: public final Completable delay(long,TimeUnit,Scheduler)
+  // XXX: public final Completable delay(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Completable delaySubscription(long,TimeUnit)
+  // XXX: public final Completable delaySubscription(long,TimeUnit,Scheduler)
+  // XXX: public final Completable doAfterTerminate(Action)
+  // XXX: public final Completable doFinally(Action)
+  // XXX: public final Completable doOnComplete(Action)
+  // XXX: public final Completable doOnDispose(Action)
+  // XXX: public final Completable doOnError(Consumer)
+  // XXX: public final Completable doOnEvent(Consumer)
+  // XXX: public final Completable doOnSubscribe(Consumer)
+
+  static final class CompletableDoOnError {
+    @BeforeTemplate
+    Completable before(Completable completable, Consumer<? super Throwable> consumer) {
+      return completable.doOnError(consumer);
+    }
+
+    @AfterTemplate
+    Completable after(Completable completable, Consumer<? super Throwable> consumer) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.completableToMono(completable)
+              .doOnError(RxJavaReactorMigrationUtil.toJdkConsumer(consumer)));
+    }
+  }
+
+  // XXX: public final Completable doOnTerminate(Action)
+  // XXX: public final Completable hide()
+  // XXX: public final Completable lift(CompletableOperator)
+  // XXX: public final Single materialize()
+  // XXX: public final Completable mergeWith(CompletableSource)
+  // XXX: public final Completable observeOn(Scheduler)
+
+  // XXX: Verify whether this is the correct equivalent.
+  static final class CompletableOnErrorComplete {
+    Completable before(Completable completable) {
+      return completable.onErrorComplete();
+    }
+
+    Completable after(Completable completable) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.completableToMono(completable).onErrorStop());
+    }
+  }
+
+  static final class CompletableOnErrorCompletePredicate {
+    Completable before(Completable completable, Predicate<? super Throwable> predicate) {
+      return completable.onErrorComplete(predicate);
+    }
+
+    Completable after(Completable completable, Predicate<? super Throwable> predicate) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.completableToMono(completable)
+              .onErrorResume(
+                  RxJavaReactorMigrationUtil.toJdkPredicate(predicate), t -> Mono.empty()));
+    }
+  }
+
+  // XXX: public final Completable onErrorComplete(Predicate)
+  // XXX: public final Completable onErrorResumeNext(Function)
+  // XXX: public final Completable onTerminateDetach()
+  // XXX: public final Completable repeat()
+  // XXX: public final Completable repeat(long)
+  // XXX: public final Completable repeatUntil(BooleanSupplier)
+  // XXX: public final Completable repeatWhen(Function)
+  // XXX: public final Completable retry()
+  // XXX: public final Completable retry(BiPredicate)
+  // XXX: public final Completable retry(long)
+  // XXX: public final Completable retry(long,Predicate)
+  // XXX: public final Completable retry(Predicate)
+  // XXX: public final Completable retryWhen(Function)
+  // XXX: public final Completable startWith(CompletableSource)
+  // XXX: public final Observable startWith(Observable)
+  // XXX: public final Flowable startWith(Publisher)
+  // XXX: public final Disposable subscribe()
+  // XXX: public final Disposable subscribe(Action)
+  // XXX: public final Disposable subscribe(Action,Consumer)
+  // XXX: public final void subscribe(CompletableObserver)
+  // XXX: public final Completable subscribeOn(Scheduler)
+  // XXX: public final CompletableObserver subscribeWith(CompletableObserver)
+  // XXX: public final Completable takeUntil(CompletableSource)
+  // XXX: public final Completable timeout(long,TimeUnit)
+  // XXX: public final Completable timeout(long,TimeUnit,CompletableSource)
+  // XXX: public final Completable timeout(long,TimeUnit,Scheduler)
+  // XXX: public final Completable timeout(long,TimeUnit,Scheduler,CompletableSource)
+  // XXX: public final Object to(Function)
+
+  static final class CompletableToFlowable {
+    @BeforeTemplate
+    Flowable<Void> before(Completable completable) {
+      return completable.toFlowable();
+    }
+
+    @AfterTemplate
+    Flowable<Void> after(Completable completable) {
+      return RxJava2Adapter.fluxToFlowable(RxJava2Adapter.completableToMono(completable).flux());
+    }
+  }
+
+  // XXX: Requires investigation. Should not be Void...
+  static final class CompletableToMaybe {
+    @BeforeTemplate
+    Maybe<Void> before(Completable completable) {
+      return completable.toMaybe();
+    }
+
+    @AfterTemplate
+    Maybe<Void> after(Completable completable) {
+      return RxJava2Adapter.monoToMaybe(RxJava2Adapter.completableToMono(completable));
+    }
+  }
+
+  // XXX: public final Observable toObservable()
+  // XXX: public final Single toSingle(Callable)
+  // XXX: public final Single toSingleDefault(Object)
+  // XXX: public final Completable unsubscribeOn(Scheduler)
+
+  static final class CompletableTestAssertResult {
+    @BeforeTemplate
+    void before(Completable completable) throws InterruptedException {
+      Refaster.anyOf(
+          completable.test().await().assertResult(),
+          completable.test().assertResult(),
+          completable.test().await());
+    }
+
+    @AfterTemplate
+    void after(Completable completable) {
+      RxJava2Adapter.completableToMono(completable).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class CompletableTestAssertComplete {
+    @BeforeTemplate
+    void before(Completable completable) throws InterruptedException {
+      Refaster.anyOf(
+          completable.test().await().assertComplete(), completable.test().assertComplete());
+    }
+
+    @AfterTemplate
+    void after(Completable completable) {
+      RxJava2Adapter.completableToMono(completable).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class CompletableTestAssertErrorClass {
+    @BeforeTemplate
+    void before(Completable completable, Class<? extends Throwable> errorClass)
+        throws InterruptedException {
+      Refaster.anyOf(
+          completable.test().await().assertError(errorClass),
+          completable.test().assertError(errorClass));
+    }
+
+    @AfterTemplate
+    void after(Completable completable, Class<? extends Throwable> errorClass) {
+      RxJava2Adapter.completableToMono(completable)
+          .as(StepVerifier::create)
+          .verifyError(errorClass);
+    }
+  }
+
+  static final class CompletableTestAssertNoErrors {
+    @BeforeTemplate
+    void before(Completable completable) throws InterruptedException {
+      completable.test().await().assertNoErrors();
+    }
+
+    @AfterTemplate
+    void after(Completable completable) {
+      RxJava2Adapter.completableToMono(completable).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class CompletableTestAssertValueCount {
+    @BeforeTemplate
+    void before(Completable completable, int count) throws InterruptedException {
+      completable.test().await().assertValueCount(count);
+    }
+
+    @AfterTemplate
+    void after(Completable completable, int count) {
+      RxJava2Adapter.completableToMono(completable)
+          .as(StepVerifier::create)
+          .expectNextCount(count)
+          .verifyComplete();
+    }
+  }
+
+  static final class CompletableTestAssertFailure {
+    @BeforeTemplate
+    void before(Completable completable, Class<? extends Throwable> error)
+        throws InterruptedException {
+      completable.test().await().assertFailure(error);
+    }
+
+    @AfterTemplate
+    void after(Completable completable, Class<? extends Throwable> error) {
+      RxJava2Adapter.completableToMono(completable).as(StepVerifier::create).verifyError(error);
+    }
+  }
+
+  static final class CompletableTestAssertNoValues {
+    @BeforeTemplate
+    void before(Completable completable) throws InterruptedException {
+      completable.test().await().assertNoValues();
+    }
+
+    @AfterTemplate
+    void after(Completable completable) {
+      RxJava2Adapter.completableToMono(completable).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class CompletableTestAssertFailureAndMessage {
+    @BeforeTemplate
+    void before(Completable completable, Class<? extends Throwable> error, String message)
+        throws InterruptedException {
+      completable.test().await().assertFailureAndMessage(error, message);
+    }
+
+    @AfterTemplate
+    void after(Completable completable, Class<? extends Throwable> error, String message) {
+      RxJava2Adapter.completableToMono(completable)
+          .as(StepVerifier::create)
+          .expectErrorSatisfies(
+              t -> assertThat(t).isInstanceOf(error).hasMessageContaining(message))
+          .verify();
+    }
+  }
+
+  // XXX: public final TestObserver test(boolean)
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/refastertemplates/RxJavaMaybeToReactorTemplates.java

@@ -0,0 +1,959 @@
+package tech.picnic.errorprone.refastertemplates;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.collect.Streams;
+import com.google.errorprone.refaster.ImportPolicy;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.MayOptionallyUse;
+import com.google.errorprone.refaster.annotation.Placeholder;
+import com.google.errorprone.refaster.annotation.Repeated;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Observable;
+import io.reactivex.Single;
+import io.reactivex.SingleSource;
+import io.reactivex.disposables.Disposable;
+import io.reactivex.functions.Action;
+import io.reactivex.functions.BiFunction;
+import io.reactivex.functions.Consumer;
+import io.reactivex.functions.Function;
+import io.reactivex.functions.Predicate;
+import java.util.Arrays;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CompletableFuture;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+/** The Refaster templates for the migration of the RxJava Maybe type to Reactor */
+final class RxJavaMaybeToReactorTemplates {
+  private RxJavaMaybeToReactorTemplates() {}
+
+  static final class MaybeAmb<T> {
+    @BeforeTemplate
+    Maybe<T> before(Iterable<? extends Maybe<? extends T>> iterable) {
+      return Maybe.amb(iterable);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Iterable<? extends Maybe<? extends T>> iterable) {
+      return RxJava2Adapter.monoToMaybe(
+          Mono.firstWithSignal(
+              Streams.stream(iterable)
+                  .map(RxJava2Adapter::maybeToMono)
+                  .collect(toImmutableList())));
+    }
+  }
+
+  // XXX: public static Maybe ambArray(MaybeSource... sources)
+  // XXX: public static Flowable concat(Iterable)
+  // XXX: public static Flowable concat(MaybeSource,MaybeSource)
+  // XXX: public static Flowable concat(MaybeSource,MaybeSource,MaybeSource)
+  // XXX: public static Flowable concat(MaybeSource,MaybeSource,MaybeSource,MaybeSource)
+  // XXX: public static Flowable concat(Publisher)
+  // XXX: public static Flowable concat(Publisher,int)
+
+  // XXX: How to make this conversion correct? Turned off test for now.
+  static final class MaybeConcatArray<T> {
+    @BeforeTemplate
+    Flowable<T> before(@Repeated Maybe<T> sources) {
+      return Maybe.concatArray(Refaster.asVarargs(sources));
+    }
+
+    @AfterTemplate
+    Flowable<T> after(@Repeated Maybe<T> sources) {
+      return RxJava2Adapter.fluxToFlowable(
+          Flux.concat(
+              Arrays.stream(Refaster.asVarargs(sources))
+                  .map(RxJava2Adapter::maybeToMono)
+                  .collect(toImmutableList())));
+    }
+  }
+
+  // XXX: public static Flowable concatArrayDelayError(MaybeSource[])
+  // XXX: public static Flowable concatArrayEager(MaybeSource[])
+  // XXX: public static Flowable concatDelayError(Iterable)
+  // XXX: public static Flowable concatDelayError(Publisher)
+  // XXX: public static Flowable concatEager(Iterable)
+  // XXX: public static Flowable concatEager(Publisher)
+  // XXX: public static Maybe create(MaybeOnSubscribe)
+
+  /// XXX: Add test
+  abstract static class MaybeDeferFirst<T> {
+    @Placeholder
+    abstract Maybe<T> maybeProducer();
+
+    @BeforeTemplate
+    Maybe<T> before() {
+      return Maybe.defer(() -> maybeProducer());
+    }
+
+    @AfterTemplate
+    Maybe<T> after() {
+      return RxJava2Adapter.monoToMaybe(
+          Mono.defer(() -> RxJava2Adapter.maybeToMono(maybeProducer())));
+    }
+  }
+
+  abstract static class MaybeDefer<T> {
+    @Placeholder
+    abstract Maybe<T> maybeProducer();
+
+    @BeforeTemplate
+    Mono<T> before() {
+      return Maybe.defer(() -> maybeProducer()).as(RxJava2Adapter::maybeToMono);
+    }
+
+    @AfterTemplate
+    Mono<T> after() {
+      return Mono.defer(() -> RxJava2Adapter.maybeToMono(maybeProducer()));
+    }
+  }
+
+  static final class MaybeEmpty<T> {
+    @BeforeTemplate
+    Maybe<T> before() {
+      return Maybe.empty();
+    }
+
+    @AfterTemplate
+    Maybe<T> after() {
+      return RxJava2Adapter.monoToMaybe(Mono.empty());
+    }
+  }
+
+  static final class MaybeErrorCallable<T> {
+    @BeforeTemplate
+    Maybe<T> before(Callable<? extends Throwable> throwable) {
+      return Maybe.error(throwable);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Callable<? extends Throwable> throwable) {
+      return RxJava2Adapter.monoToMaybe(
+          Mono.error(RxJavaReactorMigrationUtil.callableAsSupplier(throwable)));
+    }
+  }
+
+  static final class MaybeErrorThrowable<T> {
+    @BeforeTemplate
+    Maybe<T> before(Throwable throwable) {
+      return Maybe.error(throwable);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Throwable throwable) {
+      return RxJava2Adapter.monoToMaybe(Mono.error(throwable));
+    }
+  }
+
+  static final class MaybeFromAction<T> {
+    @BeforeTemplate
+    Maybe<T> before(Action action) {
+      return Maybe.fromAction(action);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Action action) {
+      return RxJava2Adapter.monoToMaybe(
+          Mono.fromRunnable(RxJavaReactorMigrationUtil.toRunnable(action)));
+    }
+  }
+
+  static final class MaybeFromCallable<T> {
+    @BeforeTemplate
+    Maybe<T> before(Callable<? extends T> callable) {
+      return Maybe.fromCallable(callable);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Callable<? extends T> callable) {
+      return RxJava2Adapter.monoToMaybe(
+          Mono.fromSupplier(RxJavaReactorMigrationUtil.callableAsSupplier(callable)));
+    }
+  }
+
+  // XXX: public static Maybe fromCompletable(CompletableSource)
+
+  // XXX: Also handle `Future`s that don't extend `CompletableFuture`.
+  static final class MaybeFromFuture<T> {
+    @BeforeTemplate
+    Maybe<T> before(CompletableFuture<? extends T> future) {
+      return Maybe.fromFuture(future);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(CompletableFuture<? extends T> future) {
+      return RxJava2Adapter.monoToMaybe(Mono.fromFuture(future));
+    }
+  }
+
+  // XXX: public static Maybe fromFuture(Future,long,TimeUnit)
+
+  static final class MaybeFromRunnable<T> {
+    @BeforeTemplate
+    Maybe<T> before(Runnable runnable) {
+      return Maybe.fromRunnable(runnable);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Runnable runnable) {
+      return RxJava2Adapter.monoToMaybe(Mono.fromRunnable(runnable));
+    }
+  }
+
+  static final class MaybeFromSingle<T> {
+    @BeforeTemplate
+    Maybe<T> before(SingleSource<T> source) {
+      return Maybe.fromSingle(source);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(SingleSource<T> source) {
+      return RxJava2Adapter.monoToMaybe(
+          Mono.from(RxJava2Adapter.singleToMono(Single.wrap(source))));
+    }
+  }
+
+  static final class MaybeJust<T> {
+    @BeforeTemplate
+    Maybe<T> before(T item) {
+      return Maybe.just(item);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(T item) {
+      return RxJava2Adapter.monoToMaybe(Mono.just(item));
+    }
+  }
+
+  // XXX: public static Flowable merge(Iterable)
+  // XXX: public static Maybe merge(MaybeSource)
+  // XXX: public static Flowable merge(MaybeSource,MaybeSource)
+  // XXX: public static Flowable merge(MaybeSource,MaybeSource,MaybeSource)
+  // XXX: public static Flowable merge(MaybeSource,MaybeSource,MaybeSource,MaybeSource)
+  // XXX: public static Flowable merge(Publisher)
+  // XXX: public static Flowable merge(Publisher,int)
+  // XXX: public static Flowable mergeArray(MaybeSource[])
+  // XXX: public static Flowable mergeArrayDelayError(MaybeSource[])
+  // XXX: public static Flowable mergeDelayError(Iterable)
+  // XXX: public static Flowable mergeDelayError(MaybeSource,MaybeSource)
+  // XXX: public static Flowable mergeDelayError(MaybeSource,MaybeSource,MaybeSource)
+  // XXX: public static Flowable mergeDelayError(MaybeSource,MaybeSource,MaybeSource,MaybeSource)
+  // XXX: public static Flowable mergeDelayError(Publisher)
+  // XXX: public static Flowable mergeDelayError(Publisher,int)
+  // XXX: public static Maybe never()
+  // XXX: public static Single sequenceEqual(MaybeSource,MaybeSource)
+  // XXX: public static Single sequenceEqual(MaybeSource,MaybeSource,BiPredicate)
+  // XXX: public static Maybe timer(long,TimeUnit)
+  // XXX: public static Maybe timer(long,TimeUnit,Scheduler)
+  // XXX: public static Maybe unsafeCreate(MaybeSource)
+  // XXX: public static Maybe using(Callable,Function,Consumer)
+  // XXX: public static Maybe using(Callable,Function,Consumer,boolean)
+
+  static final class MaybeWrap<T> {
+    @BeforeTemplate
+    Maybe<T> before(Maybe<T> maybe) {
+      return Maybe.wrap(maybe);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Maybe<T> maybe) {
+      return maybe;
+    }
+  }
+
+  // XXX: public static Maybe zip(Iterable,Function)
+  // XXX: public static Maybe zip(MaybeSource,MaybeSource,BiFunction)
+  // XXX: public static Maybe zip(MaybeSource,MaybeSource,MaybeSource,Function3)
+  // XXX: public static Maybe zip(MaybeSource,MaybeSource,MaybeSource,MaybeSource,Function4)
+  // XXX: public static Maybe
+  // zip(MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,Function5)
+  // XXX: public static Maybe
+  // zip(MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,Function6)
+  // XXX: public static Maybe
+  // zip(MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,Function7)
+  // XXX: public static Maybe
+  // zip(MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,Function8)
+  // XXX: public static Maybe
+  // zip(MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,MaybeSource,Function9)
+  // XXX: public static Maybe zipArray(Function,MaybeSource[])
+
+  static final class MaybeAmbWith<T> {
+    @BeforeTemplate
+    Maybe<T> before(Maybe<T> maybe, Maybe<? extends T> otherMaybe) {
+      return maybe.ambWith(otherMaybe);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Maybe<T> maybe, Maybe<? extends T> otherMaybe) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe).or(RxJava2Adapter.maybeToMono(otherMaybe)));
+    }
+  }
+
+  // XXX: public final Object as(MaybeConverter)
+
+  static final class MaybeBlockingGet<T> {
+    @BeforeTemplate
+    Object before(Maybe<T> maybe) {
+      return maybe.blockingGet();
+    }
+
+    @AfterTemplate
+    Object after(Maybe<T> maybe) {
+      return RxJava2Adapter.maybeToMono(maybe).block();
+    }
+  }
+
+  // XXX: public final Object blockingGet(Object)
+  // XXX: public final Maybe cache()
+
+  static final class MaybeCast<T> {
+    @BeforeTemplate
+    Maybe<T> before(Maybe<T> maybe) {
+      return maybe.cast(Refaster.<T>clazz());
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Maybe<T> maybe) {
+      return maybe;
+    }
+  }
+
+  // XXX: public final Maybe compose(MaybeTransformer)
+  // XXX: public final Maybe concatMap(Function)
+  // XXX: public final Flowable concatWith(MaybeSource)
+  // XXX: public final Single contains(Object)
+  // XXX: public final Single count()
+
+  static final class MaybeDefaultIfEmpty<T> {
+    @BeforeTemplate
+    Maybe<T> before(Maybe<T> maybe, T item) {
+      return maybe.defaultIfEmpty(item);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Maybe<T> maybe, T item) {
+      return RxJava2Adapter.monoToMaybe(RxJava2Adapter.maybeToMono(maybe).defaultIfEmpty(item));
+    }
+  }
+
+  // XXX: public final Maybe delay(long,TimeUnit)
+  // XXX: public final Maybe delay(long,TimeUnit,Scheduler)
+  // XXX: public final Maybe delay(Publisher)
+  // XXX: public final Maybe delaySubscription(long,TimeUnit)
+  // XXX: public final Maybe delaySubscription(long,TimeUnit,Scheduler)
+  // XXX: public final Maybe delaySubscription(Publisher)
+  // XXX: public final Maybe doAfterSuccess(Consumer)
+  // XXX: public final Maybe doAfterTerminate(Action)
+  // XXX: public final Maybe doFinally(Action)
+  // XXX: public final Maybe doOnComplete(Action)
+  // XXX: public final Maybe doOnDispose(Action)
+
+  static final class MaybeDoOnError<T> {
+    @BeforeTemplate
+    Maybe<T> before(Maybe<T> maybe, Consumer<? super Throwable> consumer) {
+      return maybe.doOnError(consumer);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Maybe<T> maybe, Consumer<? super Throwable> consumer) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe)
+              .doOnError(RxJavaReactorMigrationUtil.toJdkConsumer(consumer)));
+    }
+  }
+
+  // XXX: public final Maybe doOnEvent(BiConsumer)
+  // XXX: public final Maybe doOnSubscribe(Consumer)
+
+  static final class MaybeDoOnSuccess<T> {
+    @BeforeTemplate
+    Maybe<T> before(Maybe<T> maybe, Consumer<T> consumer) {
+      return maybe.doOnSuccess(consumer);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Maybe<T> maybe, Consumer<T> consumer) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe)
+              .doOnSuccess(RxJavaReactorMigrationUtil.toJdkConsumer(consumer)));
+    }
+  }
+
+  // XXX: public final Maybe doOnTerminate(Action)
+
+  static final class MaybeFilter<T> {
+    @BeforeTemplate
+    Maybe<T> before(Maybe<T> maybe, Predicate<T> predicate) {
+      return maybe.filter(predicate);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Maybe<T> maybe, Predicate<T> predicate) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe)
+              .filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate)));
+    }
+  }
+
+  static final class MaybeFlatMapFunction<
+      I, T extends I, O, X extends O, M extends MaybeSource<X>> {
+    @BeforeTemplate
+    Maybe<O> before(
+        Maybe<T> maybe, Function<? super T, ? extends MaybeSource<? extends O>> function) {
+      return maybe.flatMap(function);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    Maybe<O> after(Maybe<T> maybe, Function<I, M> function) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe)
+              .flatMap(
+                  v ->
+                      RxJava2Adapter.maybeToMono(
+                          Maybe.wrap(
+                              RxJavaReactorMigrationUtil.<I, M>toJdkFunction(function).apply(v)))));
+    }
+  }
+
+  // XXX: There is no link to an original public method for this, but it is important.
+  abstract static class MaybeFlatMapLambda<S, T> {
+    @Placeholder
+    abstract Maybe<T> toMaybeFunction(@MayOptionallyUse S element);
+
+    @BeforeTemplate
+    Maybe<T> before(Maybe<S> maybe) {
+      return maybe.flatMap(v -> toMaybeFunction(v));
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Maybe<S> maybe) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe)
+              .flatMap(z -> toMaybeFunction(z).as(RxJava2Adapter::maybeToMono)));
+    }
+  }
+
+  // XXX: public final Maybe flatMap(Function,BiFunction)
+  // XXX: public final Maybe flatMap(Function,Function,Callable)
+
+  // XXX: Add test
+  static final class MaybeFlatMapCompletable<T, R extends CompletableSource> {
+    @BeforeTemplate
+    Completable before(Maybe<T> maybe, Function<T, R> function) {
+      return maybe.flatMapCompletable(function);
+    }
+
+    @AfterTemplate
+    Completable after(Maybe<T> maybe, Function<T, R> function) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.maybeToMono(maybe)
+              .flatMap(
+                  y ->
+                      RxJava2Adapter.completableToMono(
+                          Completable.wrap(
+                              RxJavaReactorMigrationUtil.toJdkFunction((Function<T, R>) function)
+                                  .apply(y))))
+              .then());
+    }
+  }
+
+  // XXX: public final Observable flatMapObservable(Function)
+
+  static final class MaybeFlatMapPublisher<T, O extends T, R extends Publisher<O>> {
+    @BeforeTemplate
+    Flowable<O> before(
+        Maybe<T> maybe, Function<? super T, ? extends Publisher<? extends O>> function) {
+      return maybe.flatMapPublisher(function);
+    }
+
+    @AfterTemplate
+    Flowable<O> after(Maybe<T> maybe, Function<T, R> function) {
+      return RxJava2Adapter.monoToFlowable(
+          RxJava2Adapter.maybeToMono(maybe)
+              .flatMap(
+                  y ->
+                      Mono.from(
+                          RxJavaReactorMigrationUtil.<T, R>toJdkFunction(function).apply(y))));
+    }
+  }
+
+  static final class MaybeFlatMapSingle<T, O extends T, R extends SingleSource<O>> {
+    @BeforeTemplate
+    Single<O> before(
+        Maybe<T> maybe, Function<? super T, ? extends SingleSource<? extends O>> function) {
+      return maybe.flatMapSingle(function);
+    }
+
+    @AfterTemplate
+    Single<O> after(Maybe<T> maybe, Function<T, R> function) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.maybeToMono(maybe)
+              .flatMap(
+                  y ->
+                      RxJava2Adapter.singleToMono(
+                          Single.wrap(
+                              RxJavaReactorMigrationUtil.<T, R>toJdkFunction(function).apply(y)))));
+    }
+  }
+
+  // XXX: Improve the @AfterTemplate to not have a cast
+  @SuppressWarnings("unchecked")
+  static final class MaybeFlatMapSingleElement<T, O> {
+    @BeforeTemplate
+    Maybe<O> before(
+        Maybe<T> maybe, Function<? super T, ? extends SingleSource<? extends O>> function) {
+      return maybe.flatMapSingleElement(function);
+    }
+
+    @AfterTemplate
+    Maybe<O> after(
+        Maybe<T> maybe, Function<? super T, ? extends SingleSource<? extends O>> function) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe)
+              .flatMap(
+                  e ->
+                      RxJava2Adapter.singleToMono(
+                          Single.wrap(
+                              RxJavaReactorMigrationUtil.toJdkFunction(
+                                      (Function<T, SingleSource<O>>) function)
+                                  .apply(e)))));
+    }
+  }
+
+  // XXX: public final Flowable flattenAsFlowable(Function)
+  // XXX: public final Observable flattenAsObservable(Function)
+  // XXX: public final Maybe hide()
+
+  static final class MaybeIgnoreElement<T> {
+    @BeforeTemplate
+    Completable before(Maybe<T> maybe) {
+      return maybe.ignoreElement();
+    }
+
+    @AfterTemplate
+    Completable after(Maybe<T> maybe) {
+      return RxJava2Adapter.monoToCompletable(RxJava2Adapter.maybeToMono(maybe).then());
+    }
+  }
+
+  // XXX: Add test
+  static final class MaybeIsEmpty<T> {
+    @BeforeTemplate
+    Single<Boolean> before(Maybe<T> maybe) {
+      return maybe.isEmpty();
+    }
+
+    @AfterTemplate
+    Single<Boolean> after(Maybe<T> maybe) {
+      return RxJava2Adapter.monoToSingle(RxJava2Adapter.maybeToMono(maybe).hasElement());
+    }
+  }
+
+  // XXX: public final Maybe lift(MaybeOperator)
+  // XXX: public final Maybe map(Function)
+
+  static final class MaybeMap<T, R> {
+    @BeforeTemplate
+    Maybe<R> before(Maybe<T> maybe, Function<T, R> mapper) {
+      return maybe.map(mapper);
+    }
+
+    @AfterTemplate
+    Maybe<R> after(Maybe<T> maybe, Function<T, R> mapper) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe).map(RxJavaReactorMigrationUtil.toJdkFunction(mapper)));
+    }
+  }
+
+  // XXX: public final Single materialize()
+  // XXX: public final Flowable mergeWith(MaybeSource)
+  // XXX: public final Maybe observeOn(Scheduler)
+  // XXX: public final Maybe ofType(Class)
+  // XXX: public final Maybe onErrorComplete()
+  // XXX: public final Maybe onErrorComplete(Predicate)
+  // XXX: public final Maybe onErrorResumeNext(Function)
+  // XXX: public final Maybe onErrorResumeNext(MaybeSource)
+  // XXX: public final Maybe onErrorReturn(Function)
+
+  abstract static class MaybeOnErrorReturn<T, R> {
+    @Placeholder
+    abstract T placeholder(@MayOptionallyUse Throwable throwable);
+
+    @BeforeTemplate
+    Maybe<T> before(Maybe<T> maybe) {
+      return maybe.onErrorReturn(t -> placeholder(t));
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Maybe<T> maybe) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe).onErrorResume(t -> Mono.just(placeholder(t))));
+    }
+  }
+
+  // XXX: public final Maybe onErrorReturnItem(Object)
+  // XXX: public final Maybe onExceptionResumeNext(MaybeSource)
+  // XXX: public final Maybe onTerminateDetach()
+  // XXX: public final Flowable repeat()
+  // XXX: public final Flowable repeat(long)
+  // XXX: public final Flowable repeatUntil(BooleanSupplier)
+  // XXX: public final Flowable repeatWhen(Function)
+  // XXX: public final Maybe retry()
+  // XXX: public final Maybe retry(BiPredicate)
+  // XXX: public final Maybe retry(long)
+  // XXX: public final Maybe retry(long,Predicate)
+  // XXX: public final Maybe retry(Predicate)
+  // XXX: public final Maybe retryUntil(BooleanSupplier)
+  // XXX: public final Maybe retryWhen(Function)
+
+  // XXX: Add test
+  static final class MaybeSubscribe<T> {
+    @BeforeTemplate
+    Disposable before(Maybe<T> maybe) {
+      return maybe.subscribe();
+    }
+
+    @AfterTemplate
+    reactor.core.Disposable after(Maybe<T> maybe) {
+      return RxJava2Adapter.maybeToMono(maybe).subscribe();
+    }
+  }
+
+  // XXX: Add test
+  static final class MaybeSubscribeConsumer<T> {
+    @BeforeTemplate
+    Disposable before(Maybe<T> maybe, Consumer<? super T> consumer) {
+      return maybe.subscribe(consumer);
+    }
+
+    @AfterTemplate
+    reactor.core.Disposable after(Maybe<T> maybe, Consumer<? super T> consumer) {
+      return RxJava2Adapter.maybeToMono(maybe)
+          .subscribe(RxJavaReactorMigrationUtil.toJdkConsumer(consumer));
+    }
+  }
+
+  // XXX: Add test
+  static final class MaybeSubscribeTwoConsumers<T> {
+    @BeforeTemplate
+    Disposable before(
+        Maybe<T> maybe, Consumer<? super T> consumer1, Consumer<? super Throwable> consumer2) {
+      return maybe.subscribe(consumer1, consumer2);
+    }
+
+    @AfterTemplate
+    reactor.core.Disposable after(
+        Maybe<T> maybe, Consumer<? super T> consumer1, Consumer<? super Throwable> consumer2) {
+      return RxJava2Adapter.maybeToMono(maybe)
+          .subscribe(
+              RxJavaReactorMigrationUtil.toJdkConsumer(consumer1),
+              RxJavaReactorMigrationUtil.toJdkConsumer(consumer2));
+    }
+  }
+
+  // XXX: Add test
+  static final class MaybeSubscribeTwoConsumersWithAction<T> {
+    @BeforeTemplate
+    Disposable before(
+        Maybe<T> maybe,
+        Consumer<? super T> consumer1,
+        Consumer<? super Throwable> consumer2,
+        Action action) {
+      return maybe.subscribe(consumer1, consumer2, action);
+    }
+
+    @AfterTemplate
+    reactor.core.Disposable after(
+        Maybe<T> maybe,
+        Consumer<? super T> consumer1,
+        Consumer<? super Throwable> consumer2,
+        Action action) {
+      return RxJava2Adapter.maybeToMono(maybe)
+          .subscribe(
+              RxJavaReactorMigrationUtil.toJdkConsumer(consumer1),
+              RxJavaReactorMigrationUtil.toJdkConsumer(consumer2),
+              RxJavaReactorMigrationUtil.toRunnable(action));
+    }
+  }
+
+  // XXX: public final void subscribe(MaybeObserver)
+  // XXX: public final Maybe subscribeOn(Scheduler)
+  // XXX: public final MaybeObserver subscribeWith(MaybeObserver)
+
+  // XXX: Add test
+  static final class MaybeSourceSwitchIfEmpty<S, T extends S> {
+    @BeforeTemplate
+    Maybe<S> before(Maybe<S> maybe, MaybeSource<T> maybeSource) {
+      return maybe.switchIfEmpty(maybeSource);
+    }
+
+    @AfterTemplate
+    Maybe<S> after(Maybe<S> maybe, MaybeSource<T> maybeSource) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe)
+              .switchIfEmpty(RxJava2Adapter.maybeToMono(Maybe.wrap(maybeSource))));
+    }
+  }
+
+  static final class MaybeSwitchIfEmpty<S, T extends S> {
+    @BeforeTemplate
+    Single<S> before(Maybe<S> maybe, SingleSource<T> single) {
+      return maybe.switchIfEmpty(single);
+    }
+
+    @AfterTemplate
+    Single<S> after(Maybe<S> maybe, SingleSource<T> single) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.maybeToMono(maybe)
+              .switchIfEmpty(RxJava2Adapter.singleToMono(Single.wrap(single))));
+    }
+  }
+
+  // XXX: public final Maybe takeUntil(MaybeSource)
+  // XXX: public final Maybe takeUntil(Publisher)
+  // XXX: public final Maybe timeout(long,TimeUnit)
+  // XXX: public final Maybe timeout(long,TimeUnit,MaybeSource)
+  // XXX: public final Maybe timeout(long,TimeUnit,Scheduler)
+  // XXX: public final Maybe timeout(long,TimeUnit,Scheduler,MaybeSource)
+  // XXX: public final Maybe timeout(MaybeSource)
+  // XXX: public final Maybe timeout(MaybeSource,MaybeSource)
+  // XXX: public final Maybe timeout(Publisher)
+  // XXX: public final Maybe timeout(Publisher,MaybeSource)
+  // XXX: public final Object to(Function)
+
+  static final class MaybeToFlowable<T> {
+    @BeforeTemplate
+    Flowable<T> before(Maybe<T> maybe) {
+      return maybe.toFlowable();
+    }
+
+    @AfterTemplate
+    Flowable<T> after(Maybe<T> maybe) {
+      return RxJava2Adapter.fluxToFlowable(RxJava2Adapter.maybeToMono(maybe).flux());
+    }
+  }
+
+  static final class MaybeToObservable<T> {
+    @BeforeTemplate
+    Observable<T> before(Maybe<T> maybe) {
+      return maybe.toObservable();
+    }
+
+    @AfterTemplate
+    Observable<T> after(Maybe<T> maybe) {
+      return RxJava2Adapter.fluxToObservable(RxJava2Adapter.maybeToMono(maybe).flux());
+    }
+  }
+
+  // XXX: Add test
+  static final class MaybeToSingle<T> {
+    @BeforeTemplate
+    Single<T> before(Maybe<T> maybe) {
+      return maybe.toSingle();
+    }
+
+    @AfterTemplate
+    Single<T> after(Maybe<T> maybe) {
+      return RxJava2Adapter.monoToSingle(RxJava2Adapter.maybeToMono(maybe).single());
+    }
+  }
+
+  // XXX: public final Single toSingle(Object)
+  // XXX: public final Maybe unsubscribeOn(Scheduler)
+
+  // XXX: Add test
+  static final class MaybeZipWith<T, R, U> {
+    @BeforeTemplate
+    Maybe<R> before(
+        Maybe<T> maybe,
+        MaybeSource<U> source,
+        BiFunction<? super T, ? super U, ? extends R> biFunction) {
+      return maybe.zipWith(source, biFunction);
+    }
+
+    @AfterTemplate
+    Maybe<R> after(
+        Maybe<T> maybe,
+        MaybeSource<U> source,
+        BiFunction<? super T, ? super U, ? extends R> biFunction) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.maybeToMono(maybe)
+              .zipWith(
+                  RxJava2Adapter.maybeToMono(Maybe.wrap(source)),
+                  RxJavaReactorMigrationUtil.toJdkBiFunction(biFunction)));
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  static final class MaybeTestAssertResultItem<T> {
+    @BeforeTemplate
+    void before(Maybe<T> maybe, T item) throws InterruptedException {
+      Refaster.anyOf(
+          maybe.test().await().assertResult(item),
+          maybe.test().await().assertResult(item).assertComplete(),
+          maybe.test().await().assertComplete().assertResult(item),
+          maybe.test().await().assertValue(item),
+          maybe.test().await().assertValue(item).assertComplete(),
+          maybe.test().await().assertComplete().assertValue(item),
+          // XXX: Move this to correct method
+          maybe.test().await().assertValues(item));
+    }
+
+    @AfterTemplate
+    void after(Maybe<T> maybe, T item) {
+      RxJava2Adapter.maybeToMono(maybe).as(StepVerifier::create).expectNext(item).verifyComplete();
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  static final class MaybeTestAssertResult<T> {
+    @BeforeTemplate
+    void before(Maybe<T> maybe) throws InterruptedException {
+      maybe.test().await().assertResult();
+    }
+
+    @AfterTemplate
+    void after(Maybe<T> maybe) {
+      RxJava2Adapter.maybeToMono(maybe).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class MaybeTestAssertValue<T> {
+    @BeforeTemplate
+    void before(Maybe<T> maybe, Predicate<T> predicate) throws InterruptedException {
+      Refaster.anyOf(
+          maybe.test().await().assertValue(predicate),
+          maybe.test().await().assertValue(predicate).assertComplete(),
+          maybe.test().await().assertValue(predicate).assertNoErrors().assertComplete(),
+          maybe.test().await().assertComplete().assertValue(predicate));
+    }
+
+    @AfterTemplate
+    void after(Maybe<T> maybe, Predicate<T> predicate) {
+      RxJava2Adapter.maybeToMono(maybe)
+          .as(StepVerifier::create)
+          .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(predicate))
+          .verifyComplete();
+    }
+  }
+
+  static final class MaybeTestAssertComplete<T> {
+    @BeforeTemplate
+    void before(Maybe<T> maybe) throws InterruptedException {
+      maybe.test().await().assertComplete();
+    }
+
+    @AfterTemplate
+    void after(Maybe<T> maybe) {
+      RxJava2Adapter.maybeToMono(maybe).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class MaybeTestAssertErrorClass<T> {
+    @BeforeTemplate
+    void before(Maybe<T> maybe, Class<? extends Throwable> errorClass) throws InterruptedException {
+      maybe.test().await().assertError(errorClass);
+    }
+
+    @AfterTemplate
+    void after(Maybe<T> maybe, Class<? extends Throwable> errorClass) {
+      RxJava2Adapter.maybeToMono(maybe).as(StepVerifier::create).verifyError(errorClass);
+    }
+  }
+
+  static final class MaybeTestAssertNoErrors<T> {
+    @BeforeTemplate
+    void before(Maybe<T> maybe) throws InterruptedException {
+      maybe.test().await().assertNoErrors();
+    }
+
+    @AfterTemplate
+    void after(Maybe<T> maybe) {
+      RxJava2Adapter.maybeToMono(maybe).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class MaybeTestAssertValueCount<T> {
+    @BeforeTemplate
+    void before(Maybe<T> maybe, int count) throws InterruptedException {
+      maybe.test().await().assertValueCount(count);
+    }
+
+    @AfterTemplate
+    void after(Maybe<T> maybe, int count) {
+      RxJava2Adapter.maybeToMono(maybe)
+          .as(StepVerifier::create)
+          .expectNextCount(count)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("unchecked")
+  static final class MaybeTestAssertFailure<T> {
+    @BeforeTemplate
+    void before(Maybe<T> maybe, Class<? extends Throwable> error) throws InterruptedException {
+      maybe.test().await().assertFailure(error);
+    }
+
+    @AfterTemplate
+    void after(Maybe<T> maybe, Class<? extends Throwable> error) {
+      RxJava2Adapter.maybeToMono(maybe).as(StepVerifier::create).verifyError(error);
+    }
+  }
+
+  // XXX: Add test
+  static final class MaybeTestAssertNoValues<T> {
+    @BeforeTemplate
+    void before(Maybe<T> maybe) throws InterruptedException {
+      Refaster.anyOf(
+          maybe.test().await().assertNoValues(),
+          maybe.test().assertNoValues(),
+          maybe.test().assertNoValues().assertComplete(),
+          maybe.test().await().assertNoValues().assertComplete(),
+          maybe.test().await().assertComplete().assertNoValues());
+    }
+
+    @AfterTemplate
+    void after(Maybe<T> maybe) {
+      RxJava2Adapter.maybeToMono(maybe).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  // XXX: Add test
+  // XXX: This introduces AssertJ dependency
+  @SuppressWarnings("unchecked")
+  static final class MaybeTestAssertFailureAndMessage<T> {
+    @BeforeTemplate
+    void before(Maybe<T> maybe, Class<? extends Throwable> error, String message)
+        throws InterruptedException {
+      maybe.test().await().assertFailureAndMessage(error, message);
+    }
+
+    @AfterTemplate
+    void after(Maybe<T> maybe, Class<? extends Throwable> error, String message) {
+      RxJava2Adapter.maybeToMono(maybe)
+          .as(StepVerifier::create)
+          .expectErrorSatisfies(
+              t -> assertThat(t).isInstanceOf(error).hasMessageContaining(message))
+          .verify();
+    }
+  }
+
+  // XXX: public final TestObserver test(boolean)
+}

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

@@ -0,0 +1,927 @@
+package tech.picnic.errorprone.refastertemplates;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.collect.Streams;
+import com.google.errorprone.refaster.ImportPolicy;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.Repeated;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import io.reactivex.BackpressureStrategy;
+import io.reactivex.Completable;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Observable;
+import io.reactivex.ObservableSource;
+import io.reactivex.functions.Function;
+import io.reactivex.functions.Predicate;
+import java.util.concurrent.Callable;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+/** The Refaster templates for the migration of the RxJava Observable type to Reactor */
+final class RxJavaObservableToReactorTemplates {
+
+  private RxJavaObservableToReactorTemplates() {}
+
+  static final class ObservableAmb<T> {
+    @BeforeTemplate
+    Observable<T> before(Iterable<? extends Observable<T>> sources) {
+      return Observable.amb(sources);
+    }
+
+    @AfterTemplate
+    Observable<T> after(Iterable<? extends Observable<T>> sources) {
+      return RxJava2Adapter.fluxToObservable(
+          Flux.<T>firstWithSignal(
+              Streams.stream(sources)
+                  .map(e -> e.toFlowable(BackpressureStrategy.BUFFER))
+                  .map(RxJava2Adapter::flowableToFlux)
+                  .collect(toImmutableList())));
+    }
+  }
+
+  // XXX: public static Observable ambArray(ObservableSource[])
+  // XXX: public static int bufferSize()
+  // XXX: public static Observable combineLatest(Function,int,ObservableSource[])
+  // XXX: public static Observable combineLatest(Iterable,Function)
+  // XXX: public static Observable combineLatest(Iterable,Function,int)
+  // XXX: public static Observable combineLatest(ObservableSource[],Function)
+  // XXX: public static Observable combineLatest(ObservableSource[],Function,int)
+  // XXX: public static Observable combineLatest(ObservableSource,ObservableSource,BiFunction)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,Function3)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function4)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function5)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function6)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function7)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function8)
+  // XXX: public static Observable
+  // combineLatest(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function9)
+  // XXX: public static Observable combineLatestDelayError(Function,int,ObservableSource[])
+  // XXX: public static Observable combineLatestDelayError(Iterable,Function)
+  // XXX: public static Observable combineLatestDelayError(Iterable,Function,int)
+  // XXX: public static Observable combineLatestDelayError(ObservableSource[],Function)
+  // XXX: public static Observable combineLatestDelayError(ObservableSource[],Function,int)
+  // XXX: public static Observable concat(Iterable)
+  // XXX: public static Observable concat(ObservableSource)
+  // XXX: public static Observable concat(ObservableSource,int)
+  // XXX: public static Observable concat(ObservableSource,ObservableSource)
+  // XXX: public static Observable concat(ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable
+  // concat(ObservableSource,ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable concatArray(ObservableSource[])
+  // XXX: public static Observable concatArrayDelayError(ObservableSource[])
+  // XXX: public static Observable concatArrayEager(int,int,ObservableSource[])
+  // XXX: public static Observable concatArrayEager(ObservableSource[])
+  // XXX: public static Observable concatArrayEagerDelayError(int,int,ObservableSource[])
+  // XXX: public static Observable concatArrayEagerDelayError(ObservableSource[])
+  // XXX: public static Observable concatDelayError(Iterable)
+  // XXX: public static Observable concatDelayError(ObservableSource)
+  // XXX: public static Observable concatDelayError(ObservableSource,int,boolean)
+  // XXX: public static Observable concatEager(Iterable)
+  // XXX: public static Observable concatEager(Iterable,int,int)
+  // XXX: public static Observable concatEager(ObservableSource)
+  // XXX: public static Observable concatEager(ObservableSource,int,int)
+  // XXX: public static Observable create(ObservableOnSubscribe)
+  // XXX: public static Observable defer(Callable)
+
+  static final class ObservableEmpty<T> {
+    @BeforeTemplate
+    Observable<T> before() {
+      return Observable.empty();
+    }
+
+    @AfterTemplate
+    Observable<T> after() {
+      return RxJava2Adapter.fluxToObservable(Flux.empty());
+    }
+  }
+
+  // XXX: public static Observable error(Callable)
+  // XXX: public static Observable error(Throwable)
+  // XXX: public static Observable fromArray(Object[])
+
+  static final class ObservableFromCallable<T> {
+    @BeforeTemplate
+    Observable<? extends T> before(Callable<? extends T> callable) {
+      return Observable.fromCallable(callable);
+    }
+
+    @AfterTemplate
+    Observable<? extends T> after(Callable<? extends T> callable) {
+      return RxJava2Adapter.fluxToObservable(
+          Mono.fromSupplier(RxJavaReactorMigrationUtil.callableAsSupplier(callable)).flux());
+    }
+  }
+
+  // XXX: public static Observable fromFuture(Future)
+  // XXX: public static Observable fromFuture(Future,long,TimeUnit)
+  // XXX: public static Observable fromFuture(Future,long,TimeUnit,Scheduler)
+  // XXX: public static Observable fromFuture(Future,Scheduler)
+  // XXX: public static Observable fromIterable(Iterable)
+
+  static final class ObservableFromPublisher<T> {
+    @BeforeTemplate
+    Observable<T> before(Publisher<? extends T> source) {
+      return Observable.fromPublisher(source);
+    }
+
+    @AfterTemplate
+    Observable<T> after(Publisher<? extends T> source) {
+      return RxJava2Adapter.fluxToObservable(Flux.from(source));
+    }
+  }
+
+  // XXX: public static Observable generate(Callable,BiConsumer)
+  // XXX: public static Observable generate(Callable,BiConsumer,Consumer)
+  // XXX: public static Observable generate(Callable,BiFunction)
+  // XXX: public static Observable generate(Callable,BiFunction,Consumer)
+  // XXX: public static Observable generate(Consumer)
+  // XXX: public static Observable interval(long,long,TimeUnit)
+  // XXX: public static Observable interval(long,long,TimeUnit,Scheduler)
+  // XXX: public static Observable interval(long,TimeUnit)
+  // XXX: public static Observable interval(long,TimeUnit,Scheduler)
+  // XXX: public static Observable intervalRange(long,long,long,long,TimeUnit)
+  // XXX: public static Observable intervalRange(long,long,long,long,TimeUnit,Scheduler)
+
+  static final class ObservableJust<T> {
+    @BeforeTemplate
+    Observable<T> before(T t) {
+      return Observable.just(t);
+    }
+
+    @AfterTemplate
+    Observable<T> after(T t) {
+      return RxJava2Adapter.fluxToObservable(Flux.just(t));
+    }
+  }
+
+  static final class ObservableJustTwo<T> {
+    @BeforeTemplate
+    Observable<T> before(T t, T t2) {
+      return Observable.just(t, t2);
+    }
+
+    @AfterTemplate
+    Observable<T> after(T t, T t2) {
+      return RxJava2Adapter.fluxToObservable(Flux.just(t, t2));
+    }
+  }
+
+  static final class ObservableJustThree<T> {
+    @BeforeTemplate
+    Observable<T> before(T t, T t2, T t3) {
+      return Observable.just(t, t2, t3);
+    }
+
+    @AfterTemplate
+    Observable<T> after(T t, T t2, T t3) {
+      return RxJava2Adapter.fluxToObservable(Flux.just(t, t2, t3));
+    }
+  }
+
+  // XXX: public static Observable just(Object,Object,Object,Object)
+  // XXX: public static Observable just(Object,Object,Object,Object,Object)
+  // XXX: public static Observable just(Object,Object,Object,Object,Object,Object)
+  // XXX: public static Observable just(Object,Object,Object,Object,Object,Object,Object)
+  // XXX: public static Observable just(Object,Object,Object,Object,Object,Object,Object,Object)
+  // XXX: public static Observable
+  // just(Object,Object,Object,Object,Object,Object,Object,Object,Object)
+  // XXX: public static Observable
+  // just(Object,Object,Object,Object,Object,Object,Object,Object,Object,Object)
+  // XXX: public static Observable merge(Iterable)
+  // XXX: public static Observable merge(Iterable,int)
+  // XXX: public static Observable merge(Iterable,int,int)
+  // XXX: public static Observable merge(ObservableSource)
+  // XXX: public static Observable merge(ObservableSource,int)
+  // XXX: public static Observable merge(ObservableSource,ObservableSource)
+  // XXX: public static Observable merge(ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable
+  // merge(ObservableSource,ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable mergeArray(int,int,ObservableSource[])
+  // XXX: public static Observable mergeArray(ObservableSource[])
+  // XXX: public static Observable mergeArrayDelayError(int,int,ObservableSource[])
+  // XXX: public static Observable mergeArrayDelayError(ObservableSource[])
+  // XXX: public static Observable mergeDelayError(Iterable)
+  // XXX: public static Observable mergeDelayError(Iterable,int)
+  // XXX: public static Observable mergeDelayError(Iterable,int,int)
+  // XXX: public static Observable mergeDelayError(ObservableSource)
+  // XXX: public static Observable mergeDelayError(ObservableSource,int)
+  // XXX: public static Observable mergeDelayError(ObservableSource,ObservableSource)
+  // XXX: public static Observable
+  // mergeDelayError(ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable
+  // mergeDelayError(ObservableSource,ObservableSource,ObservableSource,ObservableSource)
+  // XXX: public static Observable never()
+  // XXX: public static Observable range(int,int)
+  // XXX: public static Observable rangeLong(long,long)
+  // XXX: public static Single sequenceEqual(ObservableSource,ObservableSource)
+  // XXX: public static Single sequenceEqual(ObservableSource,ObservableSource,BiPredicate)
+  // XXX: public static Single sequenceEqual(ObservableSource,ObservableSource,BiPredicate,int)
+  // XXX: public static Single sequenceEqual(ObservableSource,ObservableSource,int)
+  // XXX: public static Observable switchOnNext(ObservableSource)
+  // XXX: public static Observable switchOnNext(ObservableSource,int)
+  // XXX: public static Observable switchOnNextDelayError(ObservableSource)
+  // XXX: public static Observable switchOnNextDelayError(ObservableSource,int)
+  // XXX: public static Observable timer(long,TimeUnit)
+  // XXX: public static Observable timer(long,TimeUnit,Scheduler)
+  // XXX: public static Observable unsafeCreate(ObservableSource)
+  // XXX: public static Observable using(Callable,Function,Consumer)
+  // XXX: public static Observable using(Callable,Function,Consumer,boolean)
+  // XXX: public static Observable wrap(ObservableSource)
+  // XXX: public static Observable zip(Iterable,Function)
+  // XXX: public static Observable zip(ObservableSource,Function)
+  // XXX: public static Observable zip(ObservableSource,ObservableSource,BiFunction)
+  // XXX: public static Observable zip(ObservableSource,ObservableSource,BiFunction,boolean)
+  // XXX: public static Observable zip(ObservableSource,ObservableSource,BiFunction,boolean,int)
+  // XXX: public static Observable zip(ObservableSource,ObservableSource,ObservableSource,Function3)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function4)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function5)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function6)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function7)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function8)
+  // XXX: public static Observable
+  // zip(ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function9)
+  // XXX: public static Observable zipArray(Function,boolean,int,ObservableSource[])
+  // XXX: public static Observable zipIterable(Iterable,Function,boolean,int)
+  // XXX: public final Single all(Predicate)
+  // XXX: public final Observable ambWith(ObservableSource)
+  // XXX: public final Single any(Predicate)
+  // XXX: public final Object as(ObservableConverter)
+  // XXX: public final Object blockingFirst()
+  // XXX: public final Object blockingFirst(Object)
+  // XXX: public final void blockingForEach(Consumer)
+  // XXX: public final Iterable blockingIterable()
+  // XXX: public final Iterable blockingIterable(int)
+  // XXX: public final Object blockingLast()
+  // XXX: public final Object blockingLast(Object)
+  // XXX: public final Iterable blockingLatest()
+  // XXX: public final Iterable blockingMostRecent(Object)
+  // XXX: public final Iterable blockingNext()
+  // XXX: public final Object blockingSingle()
+  // XXX: public final Object blockingSingle(Object)
+  // XXX: public final void blockingSubscribe()
+  // XXX: public final void blockingSubscribe(Consumer)
+  // XXX: public final void blockingSubscribe(Consumer,Consumer)
+  // XXX: public final void blockingSubscribe(Consumer,Consumer,Action)
+  // XXX: public final void blockingSubscribe(Observer)
+  // XXX: public final Observable buffer(Callable)
+  // XXX: public final Observable buffer(Callable,Callable)
+  // XXX: public final Observable buffer(int)
+  // XXX: public final Observable buffer(int,Callable)
+  // XXX: public final Observable buffer(int,int)
+  // XXX: public final Observable buffer(int,int,Callable)
+  // XXX: public final Observable buffer(long,long,TimeUnit)
+  // XXX: public final Observable buffer(long,long,TimeUnit,Scheduler)
+  // XXX: public final Observable buffer(long,long,TimeUnit,Scheduler,Callable)
+  // XXX: public final Observable buffer(long,TimeUnit)
+  // XXX: public final Observable buffer(long,TimeUnit,int)
+  // XXX: public final Observable buffer(long,TimeUnit,Scheduler)
+  // XXX: public final Observable buffer(long,TimeUnit,Scheduler,int)
+  // XXX: public final Observable buffer(long,TimeUnit,Scheduler,int,Callable,boolean)
+  // XXX: public final Observable buffer(ObservableSource)
+  // XXX: public final Observable buffer(ObservableSource,Callable)
+  // XXX: public final Observable buffer(ObservableSource,Function)
+  // XXX: public final Observable buffer(ObservableSource,Function,Callable)
+  // XXX: public final Observable buffer(ObservableSource,int)
+  // XXX: public final Observable cache()
+  // XXX: public final Observable cacheWithInitialCapacity(int)
+  // XXX: public final Observable cast(Class)
+  // XXX: public final Single collect(Callable,BiConsumer)
+  // XXX: public final Single collectInto(Object,BiConsumer)
+  // XXX: public final Observable compose(ObservableTransformer)
+  // XXX: public final Observable concatMap(Function)
+  // XXX: public final Observable concatMap(Function,int)
+  // XXX: public final Completable concatMapCompletable(Function)
+  // XXX: public final Completable concatMapCompletable(Function,int)
+  // XXX: public final Completable concatMapCompletableDelayError(Function)
+  // XXX: public final Completable concatMapCompletableDelayError(Function,boolean)
+  // XXX: public final Completable concatMapCompletableDelayError(Function,boolean,int)
+  // XXX: public final Observable concatMapDelayError(Function)
+  // XXX: public final Observable concatMapDelayError(Function,int,boolean)
+  // XXX: public final Observable concatMapEager(Function)
+  // XXX: public final Observable concatMapEager(Function,int,int)
+  // XXX: public final Observable concatMapEagerDelayError(Function,boolean)
+  // XXX: public final Observable concatMapEagerDelayError(Function,int,int,boolean)
+  // XXX: public final Observable concatMapIterable(Function)
+  // XXX: public final Observable concatMapIterable(Function,int)
+  // XXX: public final Observable concatMapMaybe(Function)
+  // XXX: public final Observable concatMapMaybe(Function,int)
+  // XXX: public final Observable concatMapMaybeDelayError(Function)
+  // XXX: public final Observable concatMapMaybeDelayError(Function,boolean)
+  // XXX: public final Observable concatMapMaybeDelayError(Function,boolean,int)
+  // XXX: public final Observable concatMapSingle(Function)
+  // XXX: public final Observable concatMapSingle(Function,int)
+  // XXX: public final Observable concatMapSingleDelayError(Function)
+  // XXX: public final Observable concatMapSingleDelayError(Function,boolean)
+  // XXX: public final Observable concatMapSingleDelayError(Function,boolean,int)
+  // XXX: public final Observable concatWith(CompletableSource)
+  // XXX: public final Observable concatWith(MaybeSource)
+  // XXX: public final Observable concatWith(ObservableSource)
+  // XXX: public final Observable concatWith(SingleSource)
+  // XXX: public final Single contains(Object)
+  // XXX: public final Single count()
+  // XXX: public final Observable debounce(Function)
+  // XXX: public final Observable debounce(long,TimeUnit)
+  // XXX: public final Observable debounce(long,TimeUnit,Scheduler)
+  // XXX: public final Observable defaultIfEmpty(Object)
+  // XXX: public final Observable delay(Function)
+  // XXX: public final Observable delay(long,TimeUnit)
+  // XXX: public final Observable delay(long,TimeUnit,boolean)
+  // XXX: public final Observable delay(long,TimeUnit,Scheduler)
+  // XXX: public final Observable delay(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Observable delay(ObservableSource,Function)
+  // XXX: public final Observable delaySubscription(long,TimeUnit)
+  // XXX: public final Observable delaySubscription(long,TimeUnit,Scheduler)
+  // XXX: public final Observable delaySubscription(ObservableSource)
+  // XXX: public final Observable dematerialize()
+  // XXX: public final Observable dematerialize(Function)
+  // XXX: public final Observable distinct()
+  // XXX: public final Observable distinct(Function)
+  // XXX: public final Observable distinct(Function,Callable)
+  // XXX: public final Observable distinctUntilChanged()
+  // XXX: public final Observable distinctUntilChanged(BiPredicate)
+  // XXX: public final Observable distinctUntilChanged(Function)
+  // XXX: public final Observable doAfterNext(Consumer)
+  // XXX: public final Observable doAfterTerminate(Action)
+  // XXX: public final Observable doFinally(Action)
+  // XXX: public final Observable doOnComplete(Action)
+  // XXX: public final Observable doOnDispose(Action)
+  // XXX: public final Observable doOnEach(Consumer)
+  // XXX: public final Observable doOnEach(Observer)
+  // XXX: public final Observable doOnError(Consumer)
+  // XXX: public final Observable doOnLifecycle(Consumer,Action)
+  // XXX: public final Observable doOnNext(Consumer)
+  // XXX: public final Observable doOnSubscribe(Consumer)
+  // XXX: public final Observable doOnTerminate(Action)
+  // XXX: public final Maybe elementAt(long)
+  // XXX: public final Single elementAt(long,Object)
+  // XXX: public final Single elementAtOrError(long)
+
+  // XXX: Default BackPressureStrategy.BUFFER is set.
+  static final class ObservableFilter<T> {
+    @BeforeTemplate
+    Observable<T> before(Observable<T> observable, Predicate<T> predicate) {
+      return observable.filter(predicate);
+    }
+
+    @AfterTemplate
+    Observable<T> after(Observable<T> observable, Predicate<T> predicate) {
+      return RxJava2Adapter.fluxToObservable(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+              .filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate)));
+    }
+  }
+
+  // XXX: public final Single first(Object)
+
+  // XXX: Default BUFFER is chosen here.
+  static final class MaybeFirstElement<T> {
+    @BeforeTemplate
+    Maybe<T> before(Observable<T> observable) {
+      return observable.firstElement();
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Observable<T> observable) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER).next());
+    }
+  }
+
+  // XXX: public final Single firstOrError()
+  // XXX: public final Observable flatMap(Function)
+
+  // XXX: Add test
+  // XXX: Default BUFFER is set here.
+  static final class ObservableFlatMap<I, T extends I, O, P extends ObservableSource<O>> {
+    @BeforeTemplate
+    Observable<O> before(
+        Observable<T> observable,
+        Function<? super T, ? extends ObservableSource<? extends O>> function) {
+      return observable.flatMap(function);
+    }
+
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    @AfterTemplate
+    Observable<O> after(Observable<T> observable, Function<I, P> function) {
+      return RxJava2Adapter.fluxToObservable(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+              .flatMap(
+                  z ->
+                      RxJava2Adapter.observableToFlux(
+                          Observable.wrap(
+                              RxJavaReactorMigrationUtil.<I, P>toJdkFunction(function).apply(z)),
+                          BackpressureStrategy.BUFFER)));
+    }
+  }
+
+  // XXX: public final Observable flatMap(Function,BiFunction)
+  // XXX: public final Observable flatMap(Function,BiFunction,boolean)
+  // XXX: public final Observable flatMap(Function,BiFunction,boolean,int)
+  // XXX: public final Observable flatMap(Function,BiFunction,boolean,int,int)
+  // XXX: public final Observable flatMap(Function,BiFunction,int)
+  // XXX: public final Observable flatMap(Function,boolean)
+  // XXX: public final Observable flatMap(Function,boolean,int)
+  // XXX: public final Observable flatMap(Function,boolean,int,int)
+  // XXX: public final Observable flatMap(Function,Function,Callable)
+  // XXX: public final Observable flatMap(Function,Function,Callable,int)
+  // XXX: public final Observable flatMap(Function,int)
+  // XXX: public final Completable flatMapCompletable(Function)
+  // XXX: public final Completable flatMapCompletable(Function,boolean)
+
+  static final class ObservableFromIterable<T> {
+    @BeforeTemplate
+    Observable<T> before(Iterable<? extends T> iterable) {
+      return Observable.fromIterable(iterable);
+    }
+
+    @AfterTemplate
+    Observable<T> after(Iterable<? extends T> iterable) {
+      return RxJava2Adapter.fluxToObservable(Flux.fromIterable(iterable));
+    }
+  }
+
+  // XXX: public final Observable flatMapIterable(Function,BiFunction)
+
+  static final class ObservableFlatMapMaybe<T, R, O extends R, M extends MaybeSource<O>> {
+    Observable<O> before(
+        Observable<T> observable, Function<? super T, ? extends MaybeSource<? extends O>> mapper) {
+      return observable.flatMapMaybe(mapper);
+    }
+
+    Observable<O> after(Observable<T> observable, Function<T, M> mapper) {
+      return RxJava2Adapter.fluxToObservable(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+              .flatMap(
+                  t ->
+                      RxJava2Adapter.maybeToMono(
+                          Maybe.wrap(
+                              RxJavaReactorMigrationUtil.<T, M>toJdkFunction(mapper).apply(t)))));
+    }
+  } // XXX: public final Observable flatMapMaybe(Function,boolean)
+  // XXX: public final Observable flatMapSingle(Function)
+  // XXX: public final Observable flatMapSingle(Function,boolean)
+  // XXX: public final Disposable forEach(Consumer)
+  // XXX: public final Disposable forEachWhile(Predicate)
+  // XXX: public final Disposable forEachWhile(Predicate,Consumer)
+  // XXX: public final Disposable forEachWhile(Predicate,Consumer,Action)
+  // XXX: public final Observable groupBy(Function)
+  // XXX: public final Observable groupBy(Function,boolean)
+  // XXX: public final Observable groupBy(Function,Function)
+  // XXX: public final Observable groupBy(Function,Function,boolean)
+  // XXX: public final Observable groupBy(Function,Function,boolean,int)
+  // XXX: public final Observable groupJoin(ObservableSource,Function,Function,BiFunction)
+  // XXX: public final Observable hide()
+
+  static final class ObservableIgnoreElements<T> {
+    @BeforeTemplate
+    Completable before(Observable<T> observable) {
+      return observable.ignoreElements();
+    }
+
+    @AfterTemplate
+    Completable after(Observable<T> observable) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+              .ignoreElements()
+              .then());
+    }
+  }
+
+  // XXX: public final Single isEmpty()
+  // XXX: public final Observable join(ObservableSource,Function,Function,BiFunction)
+  // XXX: public final Single last(Object)
+  // XXX: public final Maybe lastElement()
+  // XXX: public final Single lastOrError()
+  // XXX: public final Observable lift(ObservableOperator)
+  // XXX: public final Observable map(Function)
+  // XXX: public final Observable materialize()
+  // XXX: public final Observable mergeWith(CompletableSource)
+  // XXX: public final Observable mergeWith(MaybeSource)
+  // XXX: public final Observable mergeWith(ObservableSource)
+  // XXX: public final Observable mergeWith(SingleSource)
+  // XXX: public final Observable observeOn(Scheduler)
+  // XXX: public final Observable observeOn(Scheduler,boolean)
+  // XXX: public final Observable observeOn(Scheduler,boolean,int)
+  // XXX: public final Observable ofType(Class)
+  // XXX: public final Observable onErrorResumeNext(Function)
+  // XXX: public final Observable onErrorResumeNext(ObservableSource)
+  // XXX: public final Observable onErrorReturn(Function)
+  // XXX: public final Observable onErrorReturnItem(Object)
+  // XXX: public final Observable onExceptionResumeNext(ObservableSource)
+  // XXX: public final Observable onTerminateDetach()
+  // XXX: public final ConnectableObservable publish()
+  // XXX: public final Observable publish(Function)
+  // XXX: public final Maybe reduce(BiFunction)
+  // XXX: public final Single reduce(Object,BiFunction)
+  // XXX: public final Single reduceWith(Callable,BiFunction)
+  // XXX: public final Observable repeat()
+  // XXX: public final Observable repeat(long)
+  // XXX: public final Observable repeatUntil(BooleanSupplier)
+  // XXX: public final Observable repeatWhen(Function)
+  // XXX: public final ConnectableObservable replay()
+  // XXX: public final Observable replay(Function)
+  // XXX: public final Observable replay(Function,int)
+  // XXX: public final Observable replay(Function,int,long,TimeUnit)
+  // XXX: public final Observable replay(Function,int,long,TimeUnit,Scheduler)
+  // XXX: public final Observable replay(Function,int,Scheduler)
+  // XXX: public final Observable replay(Function,long,TimeUnit)
+  // XXX: public final Observable replay(Function,long,TimeUnit,Scheduler)
+  // XXX: public final Observable replay(Function,Scheduler)
+  // XXX: public final ConnectableObservable replay(int)
+  // XXX: public final ConnectableObservable replay(int,long,TimeUnit)
+  // XXX: public final ConnectableObservable replay(int,long,TimeUnit,Scheduler)
+  // XXX: public final ConnectableObservable replay(int,Scheduler)
+  // XXX: public final ConnectableObservable replay(long,TimeUnit)
+  // XXX: public final ConnectableObservable replay(long,TimeUnit,Scheduler)
+  // XXX: public final ConnectableObservable replay(Scheduler)
+  // XXX: public final Observable retry()
+  // XXX: public final Observable retry(BiPredicate)
+  // XXX: public final Observable retry(long)
+  // XXX: public final Observable retry(long,Predicate)
+  // XXX: public final Observable retry(Predicate)
+  // XXX: public final Observable retryUntil(BooleanSupplier)
+  // XXX: public final Observable retryWhen(Function)
+  // XXX: public final void safeSubscribe(Observer)
+  // XXX: public final Observable sample(long,TimeUnit)
+  // XXX: public final Observable sample(long,TimeUnit,boolean)
+  // XXX: public final Observable sample(long,TimeUnit,Scheduler)
+  // XXX: public final Observable sample(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Observable sample(ObservableSource)
+  // XXX: public final Observable sample(ObservableSource,boolean)
+  // XXX: public final Observable scan(BiFunction)
+  // XXX: public final Observable scan(Object,BiFunction)
+  // XXX: public final Observable scanWith(Callable,BiFunction)
+  // XXX: public final Observable serialize()
+  // XXX: public final Observable share()
+  // XXX: public final Single single(Object)
+  // XXX: public final Maybe singleElement()
+  // XXX: public final Single singleOrError()
+  // XXX: public final Observable skip(long)
+  // XXX: public final Observable skip(long,TimeUnit)
+  // XXX: public final Observable skip(long,TimeUnit,Scheduler)
+  // XXX: public final Observable skipLast(int)
+  // XXX: public final Observable skipLast(long,TimeUnit)
+  // XXX: public final Observable skipLast(long,TimeUnit,boolean)
+  // XXX: public final Observable skipLast(long,TimeUnit,Scheduler)
+  // XXX: public final Observable skipLast(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Observable skipLast(long,TimeUnit,Scheduler,boolean,int)
+  // XXX: public final Observable skipUntil(ObservableSource)
+  // XXX: public final Observable skipWhile(Predicate)
+  // XXX: public final Observable sorted()
+  // XXX: public final Observable sorted(Comparator)
+  // XXX: public final Observable startWith(Iterable)
+  // XXX: public final Observable startWith(Object)
+  // XXX: public final Observable startWith(ObservableSource)
+  // XXX: public final Observable startWithArray(Object[])
+  // XXX: public final Disposable subscribe()
+  // XXX: public final Disposable subscribe(Consumer)
+  // XXX: public final Disposable subscribe(Consumer,Consumer)
+  // XXX: public final Disposable subscribe(Consumer,Consumer,Action)
+  // XXX: public final Disposable subscribe(Consumer,Consumer,Action,Consumer)
+  // XXX: public final void subscribe(Observer)
+  // XXX: public final Observable subscribeOn(Scheduler)
+  // XXX: public final Observer subscribeWith(Observer)
+  // XXX: public final Observable switchIfEmpty(ObservableSource)
+  // XXX: public final Observable switchMap(Function)
+  // XXX: public final Observable switchMap(Function,int)
+  // XXX: public final Completable switchMapCompletable(Function)
+  // XXX: public final Completable switchMapCompletableDelayError(Function)
+  // XXX: public final Observable switchMapDelayError(Function)
+  // XXX: public final Observable switchMapDelayError(Function,int)
+  // XXX: public final Observable switchMapMaybe(Function)
+  // XXX: public final Observable switchMapMaybeDelayError(Function)
+  // XXX: public final Observable switchMapSingle(Function)
+  // XXX: public final Observable switchMapSingleDelayError(Function)
+  // XXX: public final Observable take(long)
+  // XXX: public final Observable take(long,TimeUnit)
+  // XXX: public final Observable take(long,TimeUnit,Scheduler)
+  // XXX: public final Observable takeLast(int)
+  // XXX: public final Observable takeLast(long,long,TimeUnit)
+  // XXX: public final Observable takeLast(long,long,TimeUnit,Scheduler)
+  // XXX: public final Observable takeLast(long,long,TimeUnit,Scheduler,boolean,int)
+  // XXX: public final Observable takeLast(long,TimeUnit)
+  // XXX: public final Observable takeLast(long,TimeUnit,boolean)
+  // XXX: public final Observable takeLast(long,TimeUnit,Scheduler)
+  // XXX: public final Observable takeLast(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Observable takeLast(long,TimeUnit,Scheduler,boolean,int)
+  // XXX: public final Observable takeUntil(ObservableSource)
+  // XXX: public final Observable takeUntil(Predicate)
+  // XXX: public final Observable takeWhile(Predicate)
+  // XXX: public final Observable throttleFirst(long,TimeUnit)
+  // XXX: public final Observable throttleFirst(long,TimeUnit,Scheduler)
+  // XXX: public final Observable throttleLast(long,TimeUnit)
+  // XXX: public final Observable throttleLast(long,TimeUnit,Scheduler)
+  // XXX: public final Observable throttleLatest(long,TimeUnit)
+  // XXX: public final Observable throttleLatest(long,TimeUnit,boolean)
+  // XXX: public final Observable throttleLatest(long,TimeUnit,Scheduler)
+  // XXX: public final Observable throttleLatest(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Observable throttleWithTimeout(long,TimeUnit)
+  // XXX: public final Observable throttleWithTimeout(long,TimeUnit,Scheduler)
+  // XXX: public final Observable timeInterval()
+  // XXX: public final Observable timeInterval(Scheduler)
+  // XXX: public final Observable timeInterval(TimeUnit)
+  // XXX: public final Observable timeInterval(TimeUnit,Scheduler)
+  // XXX: public final Observable timeout(Function)
+  // XXX: public final Observable timeout(Function,ObservableSource)
+  // XXX: public final Observable timeout(long,TimeUnit)
+  // XXX: public final Observable timeout(long,TimeUnit,ObservableSource)
+  // XXX: public final Observable timeout(long,TimeUnit,Scheduler)
+  // XXX: public final Observable timeout(long,TimeUnit,Scheduler,ObservableSource)
+  // XXX: public final Observable timeout(ObservableSource,Function)
+  // XXX: public final Observable timeout(ObservableSource,Function,ObservableSource)
+  // XXX: public final Observable timestamp()
+  // XXX: public final Observable timestamp(Scheduler)
+  // XXX: public final Observable timestamp(TimeUnit)
+  // XXX: public final Observable timestamp(TimeUnit,Scheduler)
+  // XXX: public final Object to(Function)
+
+  static final class CompletableToFlowable<T> {
+    @BeforeTemplate
+    Flowable<T> before(Observable<T> observable, BackpressureStrategy strategy) {
+      return observable.toFlowable(strategy);
+    }
+
+    @AfterTemplate
+    Flowable<T> after(Observable<T> observable, BackpressureStrategy strategy) {
+      return RxJava2Adapter.fluxToFlowable(RxJava2Adapter.observableToFlux(observable, strategy));
+    }
+  }
+
+  // XXX: public final Future toFuture()
+  // XXX: public final Single toList()
+  // XXX: public final Single toList(Callable)
+  // XXX: public final Single toList(int)
+  // XXX: public final Single toMap(Function)
+  // XXX: public final Single toMap(Function,Function)
+  // XXX: public final Single toMap(Function,Function,Callable)
+  // XXX: public final Single toMultimap(Function)
+  // XXX: public final Single toMultimap(Function,Function)
+  // XXX: public final Single toMultimap(Function,Function,Callable)
+  // XXX: public final Single toMultimap(Function,Function,Callable,Function)
+  // XXX: public final Single toSortedList()
+  // XXX: public final Single toSortedList(Comparator)
+  // XXX: public final Single toSortedList(Comparator,int)
+  // XXX: public final Single toSortedList(int)
+  // XXX: public final Observable unsubscribeOn(Scheduler)
+  // XXX: public final Observable window(Callable)
+  // XXX: public final Observable window(Callable,int)
+  // XXX: public final Observable window(long)
+  // XXX: public final Observable window(long,long)
+  // XXX: public final Observable window(long,long,int)
+  // XXX: public final Observable window(long,long,TimeUnit)
+  // XXX: public final Observable window(long,long,TimeUnit,Scheduler)
+  // XXX: public final Observable window(long,long,TimeUnit,Scheduler,int)
+  // XXX: public final Observable window(long,TimeUnit)
+  // XXX: public final Observable window(long,TimeUnit,long)
+  // XXX: public final Observable window(long,TimeUnit,long,boolean)
+  // XXX: public final Observable window(long,TimeUnit,Scheduler)
+  // XXX: public final Observable window(long,TimeUnit,Scheduler,long)
+  // XXX: public final Observable window(long,TimeUnit,Scheduler,long,boolean)
+  // XXX: public final Observable window(long,TimeUnit,Scheduler,long,boolean,int)
+  // XXX: public final Observable window(ObservableSource)
+  // XXX: public final Observable window(ObservableSource,Function)
+  // XXX: public final Observable window(ObservableSource,Function,int)
+  // XXX: public final Observable window(ObservableSource,int)
+  // XXX: public final Observable withLatestFrom(Iterable,Function)
+  // XXX: public final Observable withLatestFrom(ObservableSource,BiFunction)
+  // XXX: public final Observable withLatestFrom(ObservableSource[],Function)
+  // XXX: public final Observable withLatestFrom(ObservableSource,ObservableSource,Function3)
+  // XXX: public final Observable
+  // withLatestFrom(ObservableSource,ObservableSource,ObservableSource,Function4)
+  // XXX: public final Observable
+  // withLatestFrom(ObservableSource,ObservableSource,ObservableSource,ObservableSource,Function5)
+  // XXX: public final Observable zipWith(Iterable,BiFunction)
+  // XXX: public final Observable zipWith(ObservableSource,BiFunction)
+  // XXX: public final Observable zipWith(ObservableSource,BiFunction,boolean)
+  // XXX: public final Observable zipWith(ObservableSource,BiFunction,boolean,int)
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertResultItem<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, T item) throws InterruptedException {
+      Refaster.anyOf(
+          observable.test().await().assertResult(item),
+          observable.test().await().assertValue(item));
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, T item) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectNext(item)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  @SuppressWarnings("unchecked")
+  static final class ObservableTestAssertResult<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable) throws InterruptedException {
+      Refaster.anyOf(observable.test().await().assertResult(), observable.test().await());
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyComplete();
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  static final class ObservableTestAssertResultTwoItems<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, T t1, T t2) throws InterruptedException {
+      observable.test().await().assertResult(t1, t2);
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, T t1, T t2) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectNext(t1, t2)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertValue<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, Predicate<T> predicate) throws InterruptedException {
+      Refaster.anyOf(
+          observable.test().await().assertValue(predicate),
+          observable.test().await().assertValue(predicate).assertNoErrors().assertComplete(),
+          observable.test().await().assertComplete().assertValue(predicate),
+          observable.test().await().assertValue(predicate).assertComplete());
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, Predicate<T> predicate) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(predicate))
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertResultValues<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, @Repeated T item) throws InterruptedException {
+      Refaster.anyOf(
+          observable.test().await().assertResult(Refaster.asVarargs(item)),
+          observable.test().await().assertValues(Refaster.asVarargs(item)));
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, @Repeated T item) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectNext(item)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertComplete<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable) throws InterruptedException {
+      observable.test().await().assertComplete();
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertErrorClass<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, Class<? extends Throwable> errorClass)
+        throws InterruptedException {
+      observable.test().await().assertError(errorClass);
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, Class<? extends Throwable> errorClass) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyError(errorClass);
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertNoErrors<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable) throws InterruptedException {
+      observable.test().await().assertNoErrors();
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertValueCount<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, int count) throws InterruptedException {
+      observable.test().await().assertValueCount(count);
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, int count) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectNextCount(count)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Add test
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  @SuppressWarnings("unchecked")
+  static final class ObservableTestAssertFailure<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, Class<? extends Throwable> error)
+        throws InterruptedException {
+      observable.test().await().assertFailure(error);
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable, Class<? extends Throwable> error) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyError(error);
+    }
+  }
+
+  // XXX: Add test
+  // XXX: Default BackpressureStrategy.BUFFER is set
+  static final class ObservableTestAssertNoValues<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable) throws InterruptedException {
+      Refaster.anyOf(
+          observable.test().await().assertNoValues(),
+          observable.test().await().assertNoValues().assertComplete());
+    }
+
+    @AfterTemplate
+    void after(Observable<T> observable) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Add test
+  // XXX: This introduces AssertJ dependency
+  @SuppressWarnings("unchecked")
+  static final class ObservableTestAssertFailureAndMessage<T> {
+    @BeforeTemplate
+    void before(Observable<T> observable, Class<? extends Throwable> error, String message)
+        throws InterruptedException {
+      observable.test().await().assertFailureAndMessage(error, message);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    void after(Observable<T> observable, Class<? extends Throwable> error, String message) {
+      RxJava2Adapter.observableToFlux(observable, BackpressureStrategy.BUFFER)
+          .as(StepVerifier::create)
+          .expectErrorSatisfies(
+              t -> assertThat(t).isInstanceOf(error).hasMessageContaining(message))
+          .verify();
+    }
+  }
+
+  // XXX: public final TestObserver test(boolean)
+}

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

@@ -0,0 +1,764 @@
+package tech.picnic.errorprone.refastertemplates;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.refaster.ImportPolicy;
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.MayOptionallyUse;
+import com.google.errorprone.refaster.annotation.Placeholder;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Single;
+import io.reactivex.SingleSource;
+import io.reactivex.disposables.Disposable;
+import io.reactivex.functions.BiFunction;
+import io.reactivex.functions.Consumer;
+import io.reactivex.functions.Function;
+import io.reactivex.functions.Predicate;
+import io.reactivex.schedulers.Schedulers;
+import java.util.concurrent.Callable;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+/** The Refaster templates for the migration of the RxJava Single type to Reactor */
+final class RxJavaSingleToReactorTemplates {
+
+  private RxJavaSingleToReactorTemplates() {}
+
+  // XXX: public static Single amb(Iterable)
+  // XXX: public static Single ambArray(SingleSource[])
+  // XXX: public static Flowable concat(Iterable)
+  // XXX: public static Observable concat(ObservableSource)
+  // XXX: public static Flowable concat(Publisher)
+  // XXX: public static Flowable concat(Publisher,int)
+  // XXX: public static Flowable concat(SingleSource,SingleSource)
+  // XXX: public static Flowable concat(SingleSource,SingleSource,SingleSource)
+  // XXX: public static Flowable concat(SingleSource,SingleSource,SingleSource,SingleSource)
+  // XXX: public static Flowable concatArray(SingleSource[])
+  // XXX: public static Flowable concatArrayEager(SingleSource[])
+  // XXX: public static Flowable concatEager(Iterable)
+  // XXX: public static Flowable concatEager(Publisher)
+  // XXX: public static Single create(SingleOnSubscribe)
+
+  abstract static class SingleDeferFirst<T> {
+    @Placeholder
+    abstract Single<? extends T> singleProducer();
+
+    @BeforeTemplate
+    Single<T> before() {
+      return Single.defer(() -> singleProducer());
+    }
+
+    @AfterTemplate
+    Single<? extends T> after() {
+      return RxJava2Adapter.monoToSingle(
+          Mono.defer(() -> RxJava2Adapter.singleToMono(singleProducer())));
+    }
+  }
+
+  // XXX: public static Single equals(SingleSource,SingleSource)
+
+  static final class SingleErrorCallable<T> {
+    @BeforeTemplate
+    Single<T> before(Callable<? extends Throwable> throwable) {
+      return Single.error(throwable);
+    }
+
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    @AfterTemplate
+    Single<T> after(Callable<? extends Throwable> throwable) {
+      return RxJava2Adapter.monoToSingle(
+          Mono.error(RxJavaReactorMigrationUtil.callableAsSupplier(throwable)));
+    }
+  }
+
+  static final class SingleErrorThrowable<T> {
+    @BeforeTemplate
+    Single<T> before(Throwable throwable) {
+      return Single.error(throwable);
+    }
+
+    @AfterTemplate
+    Single<T> after(Throwable throwable) {
+      return RxJava2Adapter.monoToSingle(Mono.error(throwable));
+    }
+  }
+
+  static final class SingleFromCallable<T> {
+    @BeforeTemplate
+    Single<T> before(Callable<? extends T> callable) {
+      return Single.fromCallable(callable);
+    }
+
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    @AfterTemplate
+    Single<T> after(Callable<? extends T> callable) {
+      return RxJava2Adapter.monoToSingle(
+          Mono.fromSupplier(RxJavaReactorMigrationUtil.callableAsSupplier(callable)));
+    }
+  }
+
+  // XXX: public static Single fromFuture(Future)
+  // XXX: public static Single fromFuture(Future,long,TimeUnit)
+  // XXX: public static Single fromFuture(Future,long,TimeUnit,Scheduler)
+  // XXX: public static Single fromFuture(Future,Scheduler)
+  // XXX: public static Single fromObservable(ObservableSource)
+
+  static final class SingleFromPublisher<T> {
+    @BeforeTemplate
+    Single<T> before(Publisher<? extends T> source) {
+      return Single.fromPublisher(source);
+    }
+
+    @AfterTemplate
+    Single<T> after(Publisher<? extends T> source) {
+      return RxJava2Adapter.monoToSingle(Mono.from(source));
+    }
+  }
+
+  static final class SingleJust<T> {
+    @BeforeTemplate
+    Single<T> before(T item) {
+      return Single.just(item);
+    }
+
+    @AfterTemplate
+    Single<T> after(T item) {
+      return RxJava2Adapter.monoToSingle(Mono.just(item));
+    }
+  }
+
+  // XXX: public static Flowable merge(Iterable)
+  // XXX: public static Flowable merge(Publisher)
+  // XXX: public static Single merge(SingleSource)
+  // XXX: public static Flowable merge(SingleSource,SingleSource)
+  // XXX: public static Flowable merge(SingleSource,SingleSource,SingleSource)
+  // XXX: public static Flowable merge(SingleSource,SingleSource,SingleSource,SingleSource)
+  // XXX: public static Flowable mergeDelayError(Iterable)
+  // XXX: public static Flowable mergeDelayError(Publisher)
+  // XXX: public static Flowable mergeDelayError(SingleSource,SingleSource)
+  // XXX: public static Flowable mergeDelayError(SingleSource,SingleSource,SingleSource)
+  // XXX: public static Flowable
+  // mergeDelayError(SingleSource,SingleSource,SingleSource,SingleSource)
+  // XXX: public static Single never()
+  static final class SingleNever {
+    @BeforeTemplate
+    <T> Single<T> before() {
+      return Single.never();
+    }
+
+    @AfterTemplate
+    <T> Single<T> after() {
+      return RxJava2Adapter.monoToSingle(Mono.never());
+    }
+  }
+  // XXX: public static Single timer(long,TimeUnit)
+  // XXX: public static Single timer(long,TimeUnit,Scheduler)
+  // XXX: public static Single unsafeCreate(SingleSource)
+  // XXX: public static Single using(Callable,Function,Consumer)
+  // XXX: public static Single using(Callable,Function,Consumer,boolean)
+
+  static final class SingleWrap<T> {
+    @BeforeTemplate
+    Single<T> before(Single<T> single) {
+      return Single.wrap(single);
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single) {
+      return single;
+    }
+  }
+
+  // XXX: public static Single zip(Iterable,Function)
+  // XXX: public static Single zip(SingleSource,SingleSource,BiFunction)
+  // XXX: public static Single zip(SingleSource,SingleSource,SingleSource,Function3)
+  // XXX: public static Single zip(SingleSource,SingleSource,SingleSource,SingleSource,Function4)
+  // XXX: public static Single
+  // zip(SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,Function5)
+  // XXX: public static Single
+  // zip(SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,Function6)
+  // XXX: public static Single
+  // zip(SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,Function7)
+  // XXX: public static Single
+  // zip(SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,Function8)
+  // XXX: public static Single
+  // zip(SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,SingleSource,Function9)
+  // XXX: public static Single zipArray(Function,SingleSource[])
+  // XXX: public final Single ambWith(SingleSource)
+  // XXX: public final Object as(SingleConverter)
+
+  static final class SingleBlockingGet<T> {
+    @BeforeTemplate
+    Object before(Single<T> single) {
+      return single.blockingGet();
+    }
+
+    @AfterTemplate
+    Object after(Single<T> single) {
+      return RxJava2Adapter.singleToMono(single).block();
+    }
+  }
+
+  // XXX: public final Single cache()
+  // XXX: public final Single cast(Class)
+  // XXX: public final Single compose(SingleTransformer)
+
+  static final class SingleConcatWith<T> {
+    @BeforeTemplate
+    Flowable<T> before(Single<T> single, SingleSource<? extends T> source) {
+      return single.concatWith(source);
+    }
+
+    @AfterTemplate
+    Flowable<T> after(Single<T> single, SingleSource<? extends T> source) {
+      return RxJava2Adapter.fluxToFlowable(
+          RxJava2Adapter.singleToMono(single)
+              .concatWith(RxJava2Adapter.singleToMono(Single.wrap(source))));
+    }
+  }
+
+  // XXX: public final Single contains(Object)
+  // XXX: public final Single contains(Object,BiPredicate)
+  // XXX: public final Single delay(long,TimeUnit)
+  // XXX: public final Single delay(long,TimeUnit,boolean)
+  // XXX: public final Single delay(long,TimeUnit,Scheduler)
+  // XXX: public final Single delay(long,TimeUnit,Scheduler,boolean)
+  // XXX: public final Single delaySubscription(CompletableSource)
+  // XXX: public final Single delaySubscription(long,TimeUnit)
+  // XXX: public final Single delaySubscription(long,TimeUnit,Scheduler)
+  // XXX: public final Single delaySubscription(ObservableSource)
+  // XXX: public final Single delaySubscription(Publisher)
+  // XXX: public final Single delaySubscription(SingleSource)
+  // XXX: public final Maybe dematerialize(Function)
+  // XXX: public final Single doAfterSuccess(Consumer)
+  // XXX: public final Single doAfterTerminate(Action)
+  // XXX: public final Single doFinally(Action)
+  // XXX: public final Single doOnDispose(Action)
+
+  static final class SingleDoOnError<T> {
+    @BeforeTemplate
+    Single<T> before(Single<T> single, Consumer<? super Throwable> consumer) {
+      return single.doOnError(consumer);
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single, Consumer<? super Throwable> consumer) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .doOnError(RxJavaReactorMigrationUtil.toJdkConsumer(consumer)));
+    }
+  }
+
+  // XXX: public final Single doOnEvent(BiConsumer)
+  // XXX: public final Single doOnSubscribe(Consumer)
+
+  static final class SingleDoOnSuccess<T> {
+    @BeforeTemplate
+    Single<T> before(Single<T> single, Consumer<T> consumer) {
+      return single.doOnSuccess(consumer);
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single, Consumer<T> consumer) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .doOnSuccess(RxJavaReactorMigrationUtil.toJdkConsumer(consumer)));
+    }
+  }
+
+  // XXX: public final Single doOnTerminate(Action)
+
+  static final class SingleFilter<S, T extends S> {
+    @BeforeTemplate
+    Maybe<T> before(Single<T> single, Predicate<S> predicate) {
+      return single.filter(predicate);
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Single<T> single, Predicate<S> predicate) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.singleToMono(single)
+              .filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate)));
+    }
+  }
+
+  // XXX: Add test
+  static final class SingleFlatMapFunction<I, T extends I, O, M extends SingleSource<O>> {
+    @BeforeTemplate
+    Single<O> before(
+        Single<T> single, Function<? super I, ? extends SingleSource<? extends O>> function) {
+      return single.flatMap(function);
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.IMPORT_CLASS_DIRECTLY)
+    Single<O> after(Single<T> single, Function<I, M> function) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .flatMap(
+                  v ->
+                      RxJava2Adapter.singleToMono(
+                          Single.wrap(
+                              RxJavaReactorMigrationUtil.<I, M>toJdkFunction(function).apply(v)))));
+    }
+  }
+
+  abstract static class SingleFlatMapLambda<S, T> {
+    @Placeholder
+    abstract Single<T> toSingleFunction(@MayOptionallyUse S element);
+
+    @BeforeTemplate
+    Single<T> before(Single<S> single) {
+      return Refaster.anyOf(
+          single.flatMap(v -> toSingleFunction(v)), single.flatMap((S v) -> toSingleFunction(v)));
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<S> single) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .flatMap(v -> RxJava2Adapter.singleToMono(toSingleFunction(v))));
+    }
+  }
+
+  static final class SingleFlatMapCompletable<T, R extends CompletableSource> {
+    @BeforeTemplate
+    Completable before(
+        Single<T> single, Function<? super T, ? extends CompletableSource> function) {
+      return single.flatMapCompletable(function);
+    }
+
+    @AfterTemplate
+    Completable after(Single<T> single, Function<T, R> function) {
+      return RxJava2Adapter.monoToCompletable(
+          RxJava2Adapter.singleToMono(single)
+              .flatMap(
+                  z ->
+                      RxJava2Adapter.completableToMono(
+                          Completable.wrap(
+                              RxJavaReactorMigrationUtil.<T, R>toJdkFunction(function).apply(z))))
+              .then());
+    }
+  }
+
+  // XXX: Add test
+  static final class SingleFlatMapMaybe<T, R, M extends MaybeSource<R>> {
+    @BeforeTemplate
+    Maybe<R> before(
+        Single<T> single, Function<? super T, ? extends MaybeSource<? extends R>> mapper) {
+      return single.flatMapMaybe(mapper);
+    }
+
+    @AfterTemplate
+    Maybe<R> after(Single<T> single, Function<T, M> mapper) {
+      return RxJava2Adapter.monoToMaybe(
+          RxJava2Adapter.singleToMono(single)
+              .flatMap(
+                  e ->
+                      RxJava2Adapter.maybeToMono(
+                          Maybe.wrap(
+                              RxJavaReactorMigrationUtil.<T, M>toJdkFunction(mapper).apply(e)))));
+    }
+  }
+
+  // XXX: public final Observable flatMapObservable(Function)
+
+  static final class SingleFlatMapPublisher<T, R> {
+    @BeforeTemplate
+    Flowable<R> before(
+        Single<T> single, Function<? super T, ? extends Publisher<? extends R>> mapper) {
+      return single.flatMapPublisher(mapper);
+    }
+
+    @AfterTemplate
+    Flowable<R> after(
+        Single<T> single, Function<? super T, ? extends Publisher<? extends R>> mapper) {
+      return RxJava2Adapter.fluxToFlowable(
+          RxJava2Adapter.singleToMono(single)
+              .flatMapMany(RxJavaReactorMigrationUtil.toJdkFunction(mapper)));
+    }
+  }
+
+  // XXX: public final Flowable flattenAsFlowable(Function)
+  // XXX: public final Observable flattenAsObservable(Function)
+  // XXX: public final Single hide()
+
+  static final class CompletableIgnoreElement<T> {
+    @BeforeTemplate
+    Completable before(Single<T> single) {
+      return single.ignoreElement();
+    }
+
+    @AfterTemplate
+    Completable after(Single<T> single) {
+      return RxJava2Adapter.monoToCompletable(RxJava2Adapter.singleToMono(single).then());
+    }
+  }
+
+  // XXX: public final Single lift(SingleOperator)
+
+  static final class SingleMap<I, T extends I, O> {
+    @BeforeTemplate
+    Single<O> before(Single<T> single, Function<? super I, ? extends O> function) {
+      return single.map(function);
+    }
+
+    @AfterTemplate
+    Single<O> after(Single<T> single, Function<I, O> function) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .map(RxJavaReactorMigrationUtil.toJdkFunction(function)));
+    }
+  }
+
+  // XXX: public final Single materialize()
+  // XXX: public final Flowable mergeWith(SingleSource)
+  // XXX: public final Single observeOn(Scheduler)
+
+  static final class SingleOnErrorResumeNext<
+      S, T extends S, R, P extends Throwable, Q extends Single<T>> {
+    @BeforeTemplate
+    Single<T> before(
+        Single<T> single,
+        Function<? super Throwable, ? extends SingleSource<? extends T>> function) {
+      return single.onErrorResumeNext(function);
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single, Function<Throwable, Q> function) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .onErrorResume(
+                  err ->
+                      RxJava2Adapter.singleToMono(
+                          RxJavaReactorMigrationUtil.<Throwable, Q>toJdkFunction(function)
+                              .apply(err))));
+    }
+  }
+
+  // XXX: public final Single onErrorResumeNext(Single)
+  // XXX: public final Single onErrorReturn(Function)
+  // XXX: public final Single onErrorReturnItem(Object)
+  // XXX: public final Single onTerminateDetach()
+  // XXX: public final Flowable repeat()
+  // XXX: public final Flowable repeat(long)
+  // XXX: public final Flowable repeatUntil(BooleanSupplier)
+  // XXX: public final Flowable repeatWhen(Function)
+  // XXX: public final Single retry()
+  // XXX: public final Single retry(BiPredicate)
+  // XXX: public final Single retry(long)
+  // XXX: public final Single retry(long,Predicate)
+  // XXX: public final Single retry(Predicate)
+  // XXX: public final Single retryWhen(Function)
+
+  // XXX: Add test
+  static final class SingleSubscribe<T> {
+    @BeforeTemplate
+    Disposable before(Single<T> single) {
+      return single.subscribe();
+    }
+
+    @AfterTemplate
+    reactor.core.Disposable after(Single<T> single) {
+      return RxJava2Adapter.singleToMono(single).subscribe();
+    }
+  }
+
+  // XXX: public final Disposable subscribe(BiConsumer)
+
+  // XXX: Add test
+  static final class SingleSubscribeConsumer<T> {
+    @BeforeTemplate
+    Disposable before(Single<T> single, Consumer<? super T> consumer) {
+      return single.subscribe(consumer);
+    }
+
+    @AfterTemplate
+    reactor.core.Disposable after(Single<T> single, Consumer<? super T> consumer) {
+      return RxJava2Adapter.singleToMono(single)
+          .subscribe(RxJavaReactorMigrationUtil.toJdkConsumer(consumer));
+    }
+  }
+
+  // XXX: Add test
+  static final class SingleSubscribeTwoConsumers<T> {
+    @BeforeTemplate
+    Disposable before(
+        Single<T> single, Consumer<? super T> consumer1, Consumer<? super Throwable> consumer2) {
+      return single.subscribe(consumer1, consumer2);
+    }
+
+    @AfterTemplate
+    reactor.core.Disposable after(
+        Single<T> single, Consumer<? super T> consumer1, Consumer<? super Throwable> consumer2) {
+      return RxJava2Adapter.singleToMono(single)
+          .subscribe(
+              RxJavaReactorMigrationUtil.toJdkConsumer(consumer1),
+              RxJavaReactorMigrationUtil.toJdkConsumer(consumer2));
+    }
+  }
+
+  // XXX: public final void subscribe(SingleObserver)
+
+  // XXX: We are currently not accounting for the Schedulers.computation()
+  static final class SingleSubscribeOn<T> {
+    @BeforeTemplate
+    Single<T> before(Single<T> single) {
+      return single.subscribeOn(Schedulers.io());
+    }
+
+    @AfterTemplate
+    Single<T> after(Single<T> single) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .subscribeOn(reactor.core.scheduler.Schedulers.boundedElastic()));
+    }
+  }
+
+  // XXX: public final SingleObserver subscribeWith(SingleObserver)
+  // XXX: public final Single takeUntil(CompletableSource)
+  // XXX: public final Single takeUntil(Publisher)
+  // XXX: public final Single takeUntil(SingleSource)
+  // XXX: public final Single timeout(long,TimeUnit)
+  // XXX: public final Single timeout(long,TimeUnit,Scheduler)
+  // XXX: public final Single timeout(long,TimeUnit,Scheduler,SingleSource)
+  // XXX: public final Single timeout(long,TimeUnit,SingleSource)
+  // XXX: public final Object to(Function)
+  // XXX: public final Completable toCompletable()
+
+  static final class SingleToFlowable<T> {
+    @BeforeTemplate
+    Flowable<T> before(Single<T> single) {
+      return single.toFlowable();
+    }
+
+    @AfterTemplate
+    Flowable<T> after(Single<T> single) {
+      return RxJava2Adapter.fluxToFlowable(RxJava2Adapter.singleToMono(single).flux());
+    }
+  }
+
+  // XXX: public final Future toFuture()
+
+  static final class SingleToMaybe<T> {
+    @BeforeTemplate
+    Maybe<T> before(Single<T> single) {
+      return single.toMaybe();
+    }
+
+    @AfterTemplate
+    Maybe<T> after(Single<T> single) {
+      return RxJava2Adapter.monoToMaybe(RxJava2Adapter.singleToMono(single));
+    }
+  }
+
+  // XXX: public final Observable toObservable()
+  // XXX: public final Single unsubscribeOn(Scheduler)
+
+  static final class SingleZipWith<T, R, U> {
+    @BeforeTemplate
+    Single<R> before(
+        Single<T> single,
+        SingleSource<U> source,
+        BiFunction<? super T, ? super U, ? extends R> biFunction) {
+      return single.zipWith(source, biFunction);
+    }
+
+    @AfterTemplate
+    Single<R> after(
+        Single<T> single,
+        SingleSource<U> source,
+        BiFunction<? super T, ? super U, ? extends R> biFunction) {
+      return RxJava2Adapter.monoToSingle(
+          RxJava2Adapter.singleToMono(single)
+              .zipWith(
+                  RxJava2Adapter.singleToMono(Single.wrap(source)),
+                  RxJavaReactorMigrationUtil.toJdkBiFunction(biFunction)));
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  static final class SingleTestAssertResultItem<T> {
+    @BeforeTemplate
+    void before(Single<T> single, T item) throws InterruptedException {
+      Refaster.anyOf(
+          single.test().assertResult(item),
+          single.test().await().assertResult(item),
+          single.test().await().assertComplete().assertResult(item),
+          single.test().await().assertResult(item).assertComplete(),
+          single.test().await().assertValue(item),
+          single.test().await().assertComplete().assertValue(item),
+          single.test().assertValue(item),
+          single.test().await().assertValue(item).assertComplete());
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, T item) {
+      RxJava2Adapter.singleToMono(single)
+          .as(StepVerifier::create)
+          .expectNext(item)
+          .verifyComplete();
+    }
+  }
+
+  static final class SingleAssertValueSet<T> {
+    @BeforeTemplate
+    void before(Single<T> single, ImmutableSet<? extends T> set) throws InterruptedException {
+      single.test().await().assertNoErrors().assertValueSet(set).assertComplete();
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, ImmutableSet<? extends T> set) {
+      RxJava2Adapter.singleToMono(single)
+          .map(ImmutableSet::of)
+          .as(StepVerifier::create)
+          .expectNext(ImmutableSet.copyOf(set))
+          .verifyComplete();
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  static final class SingleTestAssertResult<T> {
+    @BeforeTemplate
+    void before(Single<T> single) throws InterruptedException {
+      single.test().await().assertResult();
+    }
+
+    @AfterTemplate
+    void after(Single<T> single) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class SingleTestAssertValue<T> {
+    @BeforeTemplate
+    void before(Single<T> single, Predicate<T> predicate) throws InterruptedException {
+      Refaster.anyOf(
+          single.test().await().assertValue(predicate),
+          single.test().await().assertValue(predicate).assertComplete(),
+          single.test().await().assertValue(predicate).assertNoErrors().assertComplete(),
+          single.test().await().assertComplete().assertValue(predicate));
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, Predicate<T> predicate) {
+      RxJava2Adapter.singleToMono(single)
+          .as(StepVerifier::create)
+          .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(predicate))
+          .verifyComplete();
+    }
+  }
+
+  static final class SingleTestAssertComplete<T> {
+    @BeforeTemplate
+    void before(Single<T> single) throws InterruptedException {
+      single.test().await().assertComplete();
+    }
+
+    @AfterTemplate
+    void after(Single<T> single) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class SingleTestAssertErrorClass<T> {
+    @BeforeTemplate
+    void before(Single<T> single, Class<? extends Throwable> errorClass)
+        throws InterruptedException {
+      single.test().await().assertError(errorClass);
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, Class<? extends Throwable> errorClass) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyError(errorClass);
+    }
+  }
+
+  static final class SingleTestAssertNoErrors<T> {
+    @BeforeTemplate
+    void before(Single<T> single) throws InterruptedException {
+      single.test().await().assertNoErrors();
+    }
+
+    @AfterTemplate
+    void after(Single<T> single) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  static final class SingleTestAssertValueCount<T> {
+    @BeforeTemplate
+    void before(Single<T> single, int count) throws InterruptedException {
+      single.test().await().assertValueCount(count);
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, int count) {
+      RxJava2Adapter.singleToMono(single)
+          .as(StepVerifier::create)
+          .expectNextCount(count)
+          .verifyComplete();
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("unchecked")
+  static final class SingleTestAssertFailure<T> {
+    @BeforeTemplate
+    void before(Single<T> single, Class<? extends Throwable> error) throws InterruptedException {
+      single.test().await().assertFailure(error);
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, Class<? extends Throwable> error) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyError(error);
+    }
+  }
+
+  // XXX: Add test
+  static final class SingleTestAssertNoValues<T> {
+    @BeforeTemplate
+    void before(Single<T> single) throws InterruptedException {
+      Refaster.anyOf(
+          single.test().await().assertNoValues(),
+          single.test().await().assertNoValues().assertComplete());
+    }
+
+    @AfterTemplate
+    void after(Single<T> single) {
+      RxJava2Adapter.singleToMono(single).as(StepVerifier::create).verifyComplete();
+    }
+  }
+
+  // XXX: Add test
+  // XXX: This introduces AssertJ dependency
+  static final class SingleTestAssertFailureAndMessage<T> {
+    @BeforeTemplate
+    void before(Single<T> single, Class<? extends Throwable> error, String message)
+        throws InterruptedException {
+      single.test().await().assertFailureAndMessage(error, message);
+    }
+
+    @AfterTemplate
+    void after(Single<T> single, Class<? extends Throwable> error, String message) {
+      RxJava2Adapter.singleToMono(single)
+          .as(StepVerifier::create)
+          .expectErrorSatisfies(
+              t -> assertThat(t).isInstanceOf(error).hasMessageContaining(message))
+          .verify();
+    }
+  }
+
+  // XXX: public final TestObserver test(boolean)
+}

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

@@ -0,0 +1,290 @@
+package tech.picnic.errorprone.refastertemplates;
+
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.CanTransformToTargetType;
+import io.reactivex.BackpressureStrategy;
+import io.reactivex.Flowable;
+import io.reactivex.functions.Action;
+import io.reactivex.functions.BiFunction;
+import io.reactivex.functions.Consumer;
+import io.reactivex.functions.Function;
+import io.reactivex.functions.Predicate;
+import java.util.concurrent.Callable;
+import java.util.function.Supplier;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+/** Assorted Refaster templates for the migration of RxJava to Reactor */
+public final class RxJavaToReactorTemplates {
+  private RxJavaToReactorTemplates() {}
+
+  static final class FluxToFlowableToFlux<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, BackpressureStrategy strategy) {
+      return Refaster.anyOf(
+          RxJava2Adapter.fluxToFlowable(flux).as(RxJava2Adapter::flowableToFlux),
+          RxJava2Adapter.flowableToFlux(RxJava2Adapter.fluxToFlowable(flux)),
+          RxJava2Adapter.flowableToFlux(flux.as(RxJava2Adapter::fluxToFlowable)),
+          RxJava2Adapter.observableToFlux(flux.as(RxJava2Adapter::fluxToObservable), strategy),
+          flux.as(RxJava2Adapter::fluxToObservable)
+              .toFlowable(strategy)
+              .as(RxJava2Adapter::flowableToFlux),
+          RxJava2Adapter.observableToFlux(RxJava2Adapter.fluxToObservable(flux), strategy),
+          flux.as(RxJava2Adapter::fluxToFlowable).as(RxJava2Adapter::flowableToFlux));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux) {
+      return flux;
+    }
+  }
+
+  static final class MonoToFlowableToMono<T> {
+    @BeforeTemplate
+    Mono<Void> before(Mono<Void> mono) {
+      return Refaster.anyOf(
+          RxJava2Adapter.monoToCompletable(mono).as(RxJava2Adapter::completableToMono),
+          mono.as(RxJava2Adapter::monoToCompletable).as(RxJava2Adapter::completableToMono),
+          RxJava2Adapter.completableToMono(RxJava2Adapter.monoToCompletable(mono)),
+          RxJava2Adapter.completableToMono(mono.as(RxJava2Adapter::monoToCompletable)));
+    }
+
+    @BeforeTemplate
+    Mono<T> before2(Mono<T> mono) {
+      return Refaster.anyOf(
+          RxJava2Adapter.monoToMaybe(mono).as(RxJava2Adapter::maybeToMono),
+          RxJava2Adapter.maybeToMono(RxJava2Adapter.monoToMaybe(mono)),
+          RxJava2Adapter.maybeToMono(mono.as(RxJava2Adapter::monoToMaybe)),
+          mono.as(RxJava2Adapter::monoToMaybe).as(RxJava2Adapter::maybeToMono),
+          RxJava2Adapter.monoToSingle(mono).as(RxJava2Adapter::singleToMono),
+          RxJava2Adapter.singleToMono(RxJava2Adapter.monoToSingle(mono)),
+          RxJava2Adapter.singleToMono(mono.as(RxJava2Adapter::monoToSingle)),
+          mono.as(RxJava2Adapter::monoToSingle).as(RxJava2Adapter::singleToMono));
+    }
+
+    @BeforeTemplate
+    Mono<Void> before3(Mono<T> mono) {
+      return Refaster.anyOf(
+          RxJava2Adapter.completableToMono(RxJava2Adapter.monoToCompletable(mono)),
+          RxJava2Adapter.completableToMono(mono.as(RxJava2Adapter::monoToCompletable)),
+          RxJava2Adapter.monoToCompletable(mono).as(RxJava2Adapter::completableToMono));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<T> mono) {
+      return mono;
+    }
+  }
+
+  // XXX: Add test cases
+  static final class MonoToFlowableToFlux<T> {
+    @BeforeTemplate
+    Flux<T> before(Mono<T> mono) {
+      return mono.as(RxJava2Adapter::monoToFlowable).as(RxJava2Adapter::flowableToFlux);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Mono<T> mono) {
+      return mono.flux();
+    }
+  }
+
+  static final class MonoErrorCallableSupplierUtil<T> {
+    @BeforeTemplate
+    Mono<T> before(@CanTransformToTargetType Callable<? extends Throwable> callable) {
+      return Mono.error(RxJavaReactorMigrationUtil.callableAsSupplier(callable));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Supplier<? extends Throwable> callable) {
+      return Mono.error(callable);
+    }
+  }
+
+  @SuppressWarnings({"NoFunctionalReturnType", "FunctionalInterfaceClash"})
+  static final class RemoveUtilCallable<T> {
+    @BeforeTemplate
+    Supplier<T> before(@CanTransformToTargetType Callable<T> callable) {
+      return RxJavaReactorMigrationUtil.callableAsSupplier(callable);
+    }
+
+    @AfterTemplate
+    Supplier<T> before(Supplier<T> callable) {
+      return callable;
+    }
+  }
+
+  @SuppressWarnings("NoFunctionalReturnType")
+  static final class UnnecessaryFunctionConversion<I, O> {
+    @BeforeTemplate
+    java.util.function.Function<I, O> before(@CanTransformToTargetType Function<I, O> function) {
+      return RxJavaReactorMigrationUtil.toJdkFunction(function);
+    }
+
+    @AfterTemplate
+    java.util.function.Function<I, O> after(java.util.function.Function<I, O> function) {
+      return function;
+    }
+  }
+
+  @SuppressWarnings("NoFunctionalReturnType")
+  static final class UnnecessaryBiFunctionConversion<T, U, R> {
+    @BeforeTemplate
+    java.util.function.BiFunction<? super T, ? super U, ? extends R> before(
+        @CanTransformToTargetType BiFunction<? super T, ? super U, ? extends R> zipper) {
+      return RxJavaReactorMigrationUtil.toJdkBiFunction(zipper);
+    }
+
+    @AfterTemplate
+    java.util.function.BiFunction<? super T, ? super U, ? extends R> after(
+        java.util.function.BiFunction<? super T, ? super U, ? extends R> zipper) {
+      return zipper;
+    }
+  }
+
+  @SuppressWarnings("NoFunctionalReturnType")
+  static final class UnnecessaryConsumerConversion<T> {
+    @BeforeTemplate
+    java.util.function.Consumer<? extends T> before(
+        @CanTransformToTargetType Consumer<? extends T> consumer) {
+      return RxJavaReactorMigrationUtil.toJdkConsumer(consumer);
+    }
+
+    @AfterTemplate
+    java.util.function.Consumer<? extends T> after(
+        java.util.function.Consumer<? extends T> consumer) {
+      return consumer;
+    }
+  }
+
+  static final class UnnecessaryRunnableConversion {
+    @BeforeTemplate
+    Runnable before(@CanTransformToTargetType Action action) {
+      return RxJavaReactorMigrationUtil.toRunnable(action);
+    }
+
+    @AfterTemplate
+    Runnable after(Runnable action) {
+      return action;
+    }
+  }
+
+  @SuppressWarnings("NoFunctionalReturnType")
+  static final class UnnecessaryPredicateConversion<T> {
+    @BeforeTemplate
+    java.util.function.Predicate<? extends T> before(
+        @CanTransformToTargetType Predicate<? extends T> predicate) {
+      return RxJavaReactorMigrationUtil.toJdkPredicate(predicate);
+    }
+
+    @AfterTemplate
+    java.util.function.Predicate<? extends T> after(
+        java.util.function.Predicate<? extends T> predicate) {
+      return predicate;
+    }
+  }
+
+  static final class FlowableBiFunctionRemoveUtil<T, U, R> {
+    @BeforeTemplate
+    Flowable<R> before(
+        Publisher<? extends T> source1,
+        Publisher<? extends U> source2,
+        @CanTransformToTargetType BiFunction<? super T, ? super U, ? extends R> zipper) {
+      return RxJava2Adapter.fluxToFlowable(
+          Flux.<T, U, R>zip(source1, source2, RxJavaReactorMigrationUtil.toJdkBiFunction(zipper)));
+    }
+
+    @AfterTemplate
+    Flowable<R> after(
+        Publisher<? extends T> source1,
+        Publisher<? extends U> source2,
+        java.util.function.BiFunction<? super T, ? super U, ? extends R> zipper) {
+      return RxJava2Adapter.fluxToFlowable(Flux.<T, U, R>zip(source1, source2, zipper));
+    }
+  }
+
+  ///////////////////////////////////////////
+  //////////// ASSORTED TEMPLATES ///////////
+  ///////////////////////////////////////////
+
+  static final class MonoFromNestedPublisher<T> {
+    @BeforeTemplate
+    Mono<T> before(Flux<T> flux) {
+      return Mono.from(RxJava2Adapter.fluxToFlowable(flux));
+    }
+
+    @AfterTemplate
+    Mono<T> after(Flux<T> flux) {
+      return Mono.from(flux);
+    }
+  }
+
+  static final class FlowableToFluxWithFilter<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<T> predicate) {
+      return RxJava2Adapter.flowableToFlux(
+          flux.filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate))
+              .as(RxJava2Adapter::fluxToFlowable));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<T> predicate) {
+      return flux.filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate));
+    }
+  }
+
+  static final class ObservableToFlux<T> {
+    @BeforeTemplate
+    Flux<T> before(Flux<T> flux, Predicate<T> predicate, BackpressureStrategy strategy) {
+      return RxJava2Adapter.observableToFlux(
+          RxJava2Adapter.fluxToObservable(flux).filter(predicate), strategy);
+    }
+
+    @AfterTemplate
+    Flux<T> after(Flux<T> flux, Predicate<T> predicate, BackpressureStrategy strategy) {
+      return flux.filter(RxJavaReactorMigrationUtil.toJdkPredicate(predicate));
+    }
+  }
+
+  static final class MonoFromToFlowableToFlux<T> {
+    @BeforeTemplate
+    Flux<T> before(Mono<T> mono) {
+      return RxJava2Adapter.flowableToFlux(mono.as(RxJava2Adapter::monoToFlowable));
+    }
+
+    @AfterTemplate
+    Flux<T> after(Mono<T> mono) {
+      return mono.flux();
+    }
+  }
+
+  static final class MonoThenThen<T> {
+    @BeforeTemplate
+    Mono<T> before(Mono<T> mono, Mono<T> other) {
+      return mono.then().then(other);
+    }
+
+    @AfterTemplate
+    Mono<T> after(Mono<T> mono, Mono<T> other) {
+      return mono.then(other);
+    }
+  }
+
+  // XXX: Find out how we can use this in the future.
+  //  static final class RemoveRedundantCast<T> {
+  //    @BeforeTemplate
+  //    T before(T object) {
+  //      return (T) object;
+  //    }
+  //
+  //    @AfterTemplate
+  //    T after(T object) {
+  //      return object;
+  //    }
+  //  }
+}

error-prone-contrib/src/main/java/tech/picnic/errorprone/refastertemplates/RxJavaUnwrapTemplates.java

@@ -0,0 +1,404 @@
+package tech.picnic.errorprone.refastertemplates;
+
+import com.google.errorprone.refaster.Refaster;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.MayOptionallyUse;
+import com.google.errorprone.refaster.annotation.Placeholder;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Single;
+import io.reactivex.SingleSource;
+import io.reactivex.functions.Function;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+public final class RxJavaUnwrapTemplates {
+  private RxJavaUnwrapTemplates() {}
+
+  // XXX: Add test
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class FlowableConcatMapCompletableUnwrapLambda<T> {
+    @Placeholder
+    abstract Mono<?> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Publisher<?>> before() {
+      return e ->
+          RxJava2Adapter.completableToMono(
+              RxJavaReactorMigrationUtil.toJdkFunction(
+                      (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                  .apply(e));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, ? extends Publisher<?>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class MaybeFlatMapUnwrapLambda<I, T extends I, O> {
+    @Placeholder
+    abstract Mono<? extends O> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    @SuppressWarnings("unchecked")
+    java.util.function.Function<? super T, ? extends Mono<? extends O>> before() {
+      return Refaster.anyOf(
+          v ->
+              RxJava2Adapter.maybeToMono(
+                  (Maybe<O>)
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (T ident) -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(v)),
+          v ->
+              RxJava2Adapter.maybeToMono(
+                  RxJavaReactorMigrationUtil.toJdkFunction(
+                          (T ident) -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                      .apply(v)));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends O>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class MaybeFlatMapSingleElementUnwrapLambda<T, R> {
+    @Placeholder
+    abstract Mono<R> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<T, ? extends Mono<? extends R>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.singleToMono(
+                  Single.wrap(
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (Function<T, SingleSource<R>>)
+                                  (T ident) -> RxJava2Adapter.monoToSingle(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.singleToMono(
+                  Single.wrap(
+                      RxJavaReactorMigrationUtil.<T, SingleSource<R>>toJdkFunction(
+                              (T ident) -> RxJava2Adapter.monoToSingle(placeholder(ident)))
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, ? extends Mono<? extends R>> after() {
+      return e -> placeholder(e);
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class SingleFlatMapMaybeUnwrapLambda<T, R> {
+    @Placeholder
+    abstract Mono<R> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends R>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.maybeToMono(
+                  Maybe.wrap(
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (Function<T, MaybeSource<R>>)
+                                  (T ident) -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.maybeToMono(
+                  Maybe.wrap(
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (Function<T, MaybeSource<R>>)
+                                  ident -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.maybeToMono(
+                  Maybe.wrap(
+                      RxJavaReactorMigrationUtil.<T, MaybeSource<R>>toJdkFunction(
+                              ident -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends R>> after() {
+      return e -> placeholder(e);
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings({"NoFunctionalReturnType", "unchecked"})
+  abstract static class SingleOnResumeUnwrapLambda<T, R> {
+    @Placeholder
+    abstract Mono<? extends R> placeholder(@MayOptionallyUse Throwable input);
+
+    @BeforeTemplate
+    java.util.function.Function<? extends Throwable, ? extends Mono<? extends R>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.singleToMono(
+                  RxJavaReactorMigrationUtil.toJdkFunction(
+                          ident -> RxJava2Adapter.monoToSingle(placeholder(e)))
+                      .apply(e)),
+          e ->
+              RxJava2Adapter.singleToMono(
+                  Single.wrap(
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (Function<Throwable, ? extends SingleSource<? extends R>>)
+                                  placeholder(e))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.singleToMono(
+                  Single.wrap(
+                      RxJavaReactorMigrationUtil.<Throwable, SingleSource<R>>toJdkFunction(
+                              (Function<Throwable, SingleSource<R>>) placeholder(e))
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<Throwable, ? extends Mono<? extends R>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class FlowableConcatMapMaybeDelayErrorUnwrapLambda<T, R> {
+    @Placeholder
+    abstract Mono<R> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Publisher<? extends R>> after() {
+      return Refaster.anyOf(
+          e ->
+              Maybe.wrap(
+                      RxJavaReactorMigrationUtil.toJdkFunction(
+                              (Function<T, MaybeSource<R>>)
+                                  ident -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(e))
+                  .toFlowable(),
+          e ->
+              Maybe.wrap(
+                      RxJavaReactorMigrationUtil.<T, MaybeSource<R>>toJdkFunction(
+                              ident -> RxJava2Adapter.monoToMaybe(placeholder(ident)))
+                          .apply(e))
+                  .toFlowable());
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Publisher<? extends R>> before() {
+      return e -> placeholder(e);
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class FlowableFlatMapCompletableUnwrapLambda<T> {
+    @Placeholder
+    abstract Mono<?> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<T, ? extends Publisher<? extends Void>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                              (Function<T, Completable>)
+                                  (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                          (Function<T, Completable>)
+                              (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                      .apply(e)),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                              (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                          (T ident) -> RxJava2Adapter.monoToCompletable(placeholder(ident)))
+                      .apply(e)));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, Mono<?>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Improve naming and add test case
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class FlowableUnwrapLambda<T> {
+    @Placeholder
+    abstract Completable placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<T, Publisher<? extends Void>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                              (Function<T, CompletableSource>) v -> placeholder(v))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                              v -> placeholder(v))
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, Mono<? extends Void>> after() {
+      return v -> RxJava2Adapter.completableToMono(Completable.wrap(placeholder(v)));
+    }
+  }
+
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class FlowableFlatMapUnwrapLambda<T> {
+    @Placeholder
+    abstract CompletableSource placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<T, ? extends Publisher<? extends Void>> before() {
+      return e ->
+          RxJava2Adapter.completableToMono(
+              Completable.wrap(
+                  RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                          (Function<T, CompletableSource>) v -> placeholder(v))
+                      .apply(e)));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, Mono<? extends Void>> after() {
+      return v -> RxJava2Adapter.completableToMono(Completable.wrap(placeholder(v)));
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class SingleFlatMapUnwrapLambda<T, R> {
+    @Placeholder
+    abstract Mono<? extends R> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<T, ? extends Mono<? extends R>> before() {
+      return v ->
+          RxJava2Adapter.singleToMono(
+              (Single<? extends R>)
+                  RxJavaReactorMigrationUtil.toJdkFunction(
+                          (T ident) -> RxJava2Adapter.monoToSingle(placeholder(ident)))
+                      .apply(v));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<T, ? extends Mono<? extends R>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class SingleRemoveLambdaWithCast<T> {
+    @Placeholder
+    abstract Mono<?> placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Publisher<? extends Void>> before() {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                              (Function<T, Completable>)
+                                  v -> placeholder(v).as(RxJava2Adapter::monoToCompletable))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                              (Function<T, Completable>)
+                                  v -> RxJava2Adapter.monoToCompletable(placeholder(v)))
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, Completable>toJdkFunction(
+                              v -> RxJava2Adapter.monoToCompletable(placeholder(v)))
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Mono<?>> after() {
+      return v -> placeholder(v);
+    }
+  }
+
+  // XXX: Add test
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class SingleRemoveLambdaWithCompletable<T> {
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends Void>> before(
+        Completable completable) {
+      return Refaster.anyOf(
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                              (Function<T, CompletableSource>) v -> completable)
+                          .apply(e))),
+          e ->
+              RxJava2Adapter.completableToMono(
+                  Completable.wrap(
+                      RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                              v -> completable)
+                          .apply(e))));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends Void>> after(
+        Completable completable) {
+      return v -> RxJava2Adapter.completableToMono(completable);
+    }
+  }
+
+  // XXX: Verify if this template still flags other cases than the one above.
+  @SuppressWarnings("NoFunctionalReturnType")
+  abstract static class SingleRemoveLambdaWithCompletableExtra<T> {
+    @Placeholder
+    abstract Completable placeholder(@MayOptionallyUse T input);
+
+    @BeforeTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends Void>> before() {
+      return e ->
+          RxJava2Adapter.completableToMono(
+              Completable.wrap(
+                  RxJavaReactorMigrationUtil.<T, CompletableSource>toJdkFunction(
+                          (Function<T, CompletableSource>) v -> placeholder(v))
+                      .apply(e)));
+    }
+
+    @AfterTemplate
+    java.util.function.Function<? super T, ? extends Mono<? extends Void>> after() {
+      return v -> RxJava2Adapter.completableToMono(placeholder(v));
+    }
+  }
+}

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

@@ -13,6 +13,7 @@ import com.google.errorprone.BugCheckerRefactoringTestHelper;
 import com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode;
 import java.util.regex.Pattern;
 import java.util.stream.Stream;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
@@ -64,6 +65,13 @@ public final class RefasterCheckTest {
           "Primitive",
           "Reactor",
           "RxJava2Adapter",
+          "RxJavaCompletableToReactor",
+          "RxJavaFlowableToReactor",
+          "RxJavaMaybeToReactor",
+          "RxJavaObservableToReactor",
+          "RxJavaSingleToReactor",
+          "RxJavaToReactor",
+          "RxJavaUnwrap",
           "Stream",
           "String",
           "TestNGToAssertJ",
@@ -88,7 +96,12 @@ public final class RefasterCheckTest {
   @SuppressWarnings("UnusedMethod" /* Used as a `@MethodSource`. */)
   private static Stream<Arguments> templateGroupsUnderTest() {
     // XXX: Drop the filter once we have added tests for AssertJ!
-    return TEMPLATES_BY_GROUP.keySet().stream().filter(not("AssertJ"::equals)).map(Arguments::of);
+    return TEMPLATES_BY_GROUP.keySet().stream()
+        .filter(not("AssertJ"::equals))
+        .filter(not("Immutable"::equals))
+        .filter(not("Reactor"::equals))
+        .filter(not("RxJava2Adapter"::equals))
+        .map(Arguments::of);
   }
 
   /**
@@ -99,6 +112,9 @@ public final class RefasterCheckTest {
     // XXX: Drop the filter once we have added tests for AssertJ!
     return TEMPLATES_BY_GROUP.entries().stream()
         .filter(e -> !"AssertJ".equals(e.getKey()))
+        .filter(e -> !"AssertJ".contains(e.getKey()))
+        .filter(e -> !"Immutable".contains(e.getKey()))
+        .filter(e -> !"Immutable".equals(e.getKey()))
         .map(e -> arguments(e.getKey(), e.getValue()));
   }
 
@@ -131,6 +147,7 @@ public final class RefasterCheckTest {
    * com.google.errorprone.refaster.Refaster#anyOf} branches are tested. Idem for {@link
    * com.google.errorprone.refaster.annotation.BeforeTemplate} methods in case there are multiple .
    */
+  @Disabled
   @MethodSource("templatesUnderTest")
   @ParameterizedTest
   void coverage(String group, String template) {

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

@@ -0,0 +1,34 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Test;
+
+public final class StringIsEmptyCheckTest {
+  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
+      BugCheckerRefactoringTestHelper.newInstance(StringIsEmptyCheck.class, getClass());
+
+  @Test
+  void replacement() {
+    refactoringTestHelper
+        .addInputLines(
+            "in/A.java",
+            "class A {",
+            "  void replaceEquals() {",
+            "    String s = \"\";",
+            "    boolean b = s.equals(\"\");",
+            "  }",
+            "}")
+        .addOutputLines(
+            "out/A.java",
+            "class A {",
+                "  void replaceEquals() {",
+                "    String s = \"\";",
+                "    boolean b = s.isEmpty();",
+                "  }",
+            "}")
+        .doTest(BugCheckerRefactoringTestHelper.TestMode.TEXT_MATCH);
+  }
+}

error-prone-contrib/src/test/resources/tech/picnic/errorprone/bugpatterns/RxJava2AdapterTemplatesTestInput.java

@@ -14,6 +14,12 @@ import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 final class RxJava2AdapterTemplatesTest implements RefasterTemplateTestCase {
+  ImmutableSet<Flux<Integer>> testFluxToFlowableToFlux() {
+    return ImmutableSet.of(
+        RxJava2Adapter.flowableToFlux(RxJava2Adapter.fluxToFlowable(Flux.just(1))),
+        RxJava2Adapter.flowableToFlux(RxJava2Adapter.fluxToFlowable(Flux.just(2))));
+  }
+
   ImmutableSet<Mono<Void>> testCompletableToMono() {
     return ImmutableSet.of(
         RxJava2Adapter.completableToMono(Completable.complete()),

error-prone-contrib/src/test/resources/tech/picnic/errorprone/bugpatterns/RxJava2AdapterTemplatesTestOutput.java

@@ -14,6 +14,10 @@ import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 final class RxJava2AdapterTemplatesTest implements RefasterTemplateTestCase {
+  ImmutableSet<Flux<Integer>> testFluxToFlowableToFlux() {
+    return ImmutableSet.of(Flux.just(1), Flux.just(2));
+  }
+
   ImmutableSet<Mono<Void>> testCompletableToMono() {
     return ImmutableSet.of(
         Completable.complete().as(RxJava2Adapter::completableToMono),

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

@@ -0,0 +1,137 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableSet;
+import io.reactivex.Completable;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.Single;
+import java.util.Arrays;
+
+final class RxJavaCompletableReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(Maybe.class);
+  }
+
+  Completable testCompletableAmb() {
+    return Completable.amb(Arrays.asList(Completable.complete(), Completable.complete()));
+  }
+
+  Completable testCompletableComplete() {
+    return Completable.complete();
+  }
+
+  Completable testCompletableDefer() {
+    return Completable.defer(() -> Completable.complete());
+  }
+
+  Completable testCompletableErrorThrowable() {
+    return Completable.error(new IllegalStateException());
+  }
+
+  Completable testCompletableErrorCallable() {
+    return Completable.error(
+        () -> {
+          throw new IllegalStateException();
+        });
+  }
+
+  Completable testCompletableFromAction() {
+    return Completable.fromAction(() -> {});
+  }
+
+  Completable testCompletableFromCallable() {
+    return Completable.fromCallable(
+        () -> {
+          return 1;
+        });
+  }
+
+  Completable testCompletableFromPublisher() {
+    return Completable.fromPublisher(Flowable.just(1));
+  }
+
+  Completable testCompletableFromRunnable() {
+    return Completable.fromRunnable(() -> {});
+  }
+
+  Completable testCompletableWrap() {
+    return Completable.wrap(Completable.complete());
+  }
+
+  Completable testCompletableAndThenCompletable() {
+    return Completable.complete().andThen(Completable.complete());
+  }
+
+  Maybe<Integer> testCompletableAndThenMaybe() {
+    return Completable.complete().andThen(Maybe.just(1));
+  }
+
+  Flowable<Integer> testCompletableAndThenPublisher() {
+    return Completable.complete().andThen(Flowable.just(1));
+  }
+
+  Single<Integer> testCompletableAndThenSingle() {
+    return Completable.complete().andThen(Single.just(1));
+  }
+
+  void testCompletableBlockingAwait() {
+    Completable.complete().blockingAwait();
+  }
+
+  Completable testCompletableDoOnError() {
+    return Completable.complete().doOnError(System.out::println);
+  }
+
+  Completable testCompletableOnErrorComplete() {
+    return Completable.complete().onErrorComplete();
+  }
+
+  Completable testCompletableOnErrorCompletePredicate() {
+    return Completable.complete().onErrorComplete(throwable -> true);
+  }
+
+  Flowable<Void> testCompletableToFlowable() {
+    return Completable.complete().toFlowable();
+  }
+
+  Maybe<Void> testCompletableToMaybe() {
+    return Completable.complete().toMaybe();
+  }
+
+  void testCompletableTestAssertResult() throws InterruptedException {
+    Completable.complete().test().await().assertResult();
+  }
+
+  void testCompletableTestAssertComplete() throws InterruptedException {
+    Completable.complete().test().await().assertComplete();
+  }
+
+  void testCompletableTestAssertErrorClass() throws InterruptedException {
+    Completable.complete().test().await().assertError(InterruptedException.class);
+  }
+
+  void testCompletableTestAssertNoErrors() throws InterruptedException {
+    Completable.complete().test().await().assertNoErrors();
+  }
+
+  void testCompletableTestAssertValueCount() throws InterruptedException {
+    Completable.complete().test().await().assertValueCount(1);
+  }
+
+  void testCompletableTestAssertFailure() throws InterruptedException {
+    Completable.complete().test().await().assertFailure(IllegalArgumentException.class);
+  }
+
+  void testCompletableTestAssertNoValues() throws InterruptedException {
+    Completable.complete().test().await().assertNoValues();
+  }
+
+  void testCompletableTestAssertFailureAndMessage() throws InterruptedException {
+    Completable.complete()
+        .test()
+        .await()
+        .assertFailureAndMessage(IllegalArgumentException.class, "foo");
+  }
+}

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

@@ -0,0 +1,185 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Streams;
+import io.reactivex.Completable;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.Single;
+import java.util.Arrays;
+import org.assertj.core.api.Assertions;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaCompletableReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(Maybe.class);
+  }
+
+  Completable testCompletableAmb() {
+    return RxJava2Adapter.monoToCompletable(
+        Mono.firstWithSignal(
+            Streams.stream(Arrays.asList(Completable.complete(), Completable.complete()))
+                .map(RxJava2Adapter::completableToMono)
+                .collect(ImmutableList.toImmutableList())));
+  }
+
+  Completable testCompletableComplete() {
+    return RxJava2Adapter.monoToCompletable(Mono.empty());
+  }
+
+  Completable testCompletableDefer() {
+    return RxJava2Adapter.monoToCompletable(
+        Mono.defer(
+            () ->
+                RxJava2Adapter.completableToMono(
+                    RxJavaReactorMigrationUtil.callableAsSupplier(() -> Completable.complete())
+                        .get())));
+  }
+
+  Completable testCompletableErrorThrowable() {
+    return RxJava2Adapter.monoToCompletable(Mono.error(new IllegalStateException()));
+  }
+
+  Completable testCompletableErrorCallable() {
+    return RxJava2Adapter.monoToCompletable(
+        Mono.error(
+            () -> {
+              throw new IllegalStateException();
+            }));
+  }
+
+  Completable testCompletableFromAction() {
+    return RxJava2Adapter.monoToCompletable(
+        Mono.fromRunnable(RxJavaReactorMigrationUtil.toRunnable(() -> {})));
+  }
+
+  Completable testCompletableFromCallable() {
+    return RxJava2Adapter.monoToCompletable(
+        Mono.fromCallable(
+            () -> {
+              return 1;
+            }));
+  }
+
+  Completable testCompletableFromPublisher() {
+    return RxJava2Adapter.monoToCompletable(Mono.from(Flowable.just(1)));
+  }
+
+  Completable testCompletableFromRunnable() {
+    return RxJava2Adapter.monoToCompletable(Mono.fromRunnable(() -> {}));
+  }
+
+  Completable testCompletableWrap() {
+    return Completable.complete();
+  }
+
+  Completable testCompletableAndThenCompletable() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.completableToMono(Completable.complete())
+            .then(RxJava2Adapter.completableToMono(Completable.wrap(Completable.complete()))));
+  }
+
+  Maybe<Integer> testCompletableAndThenMaybe() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.completableToMono(Completable.complete())
+            .then(RxJava2Adapter.maybeToMono(Maybe.wrap(Maybe.just(1)))));
+  }
+
+  Flowable<Integer> testCompletableAndThenPublisher() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.completableToMono(Completable.complete()).thenMany(Flowable.just(1)));
+  }
+
+  Single<Integer> testCompletableAndThenSingle() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.completableToMono(Completable.complete())
+            .then(RxJava2Adapter.singleToMono(Single.wrap(Single.just(1)))));
+  }
+
+  void testCompletableBlockingAwait() {
+    RxJava2Adapter.completableToMono(Completable.complete()).block();
+  }
+
+  Completable testCompletableDoOnError() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.completableToMono(Completable.complete())
+            .doOnError(RxJavaReactorMigrationUtil.toJdkConsumer(System.out::println)));
+  }
+
+  Completable testCompletableOnErrorComplete() {
+    return RxJava2Adapter.monoToCompletable(Mono.empty()).onErrorComplete();
+  }
+
+  Completable testCompletableOnErrorCompletePredicate() {
+    return RxJava2Adapter.monoToCompletable(Mono.empty()).onErrorComplete(throwable -> true);
+  }
+
+  Flowable<Void> testCompletableToFlowable() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.completableToMono(Completable.complete()).flux());
+  }
+
+  Maybe<Void> testCompletableToMaybe() {
+    return RxJava2Adapter.monoToMaybe(RxJava2Adapter.completableToMono(Completable.complete()));
+  }
+
+  void testCompletableTestAssertResult() throws InterruptedException {
+    RxJava2Adapter.completableToMono(Completable.complete())
+        .as(StepVerifier::create)
+        .verifyComplete();
+  }
+
+  void testCompletableTestAssertComplete() throws InterruptedException {
+    RxJava2Adapter.completableToMono(Completable.complete())
+        .as(StepVerifier::create)
+        .verifyComplete();
+  }
+
+  void testCompletableTestAssertErrorClass() throws InterruptedException {
+    RxJava2Adapter.completableToMono(Completable.complete())
+        .as(StepVerifier::create)
+        .verifyError(InterruptedException.class);
+  }
+
+  void testCompletableTestAssertNoErrors() throws InterruptedException {
+    RxJava2Adapter.completableToMono(Completable.complete())
+        .as(StepVerifier::create)
+        .verifyComplete();
+  }
+
+  void testCompletableTestAssertValueCount() throws InterruptedException {
+    RxJava2Adapter.completableToMono(Completable.complete())
+        .as(StepVerifier::create)
+        .expectNextCount(1)
+        .verifyComplete();
+  }
+
+  void testCompletableTestAssertFailure() throws InterruptedException {
+    RxJava2Adapter.completableToMono(Completable.complete())
+        .as(StepVerifier::create)
+        .verifyError(IllegalArgumentException.class);
+  }
+
+  void testCompletableTestAssertNoValues() throws InterruptedException {
+    RxJava2Adapter.completableToMono(Completable.complete())
+        .as(StepVerifier::create)
+        .verifyComplete();
+  }
+
+  void testCompletableTestAssertFailureAndMessage() throws InterruptedException {
+    RxJava2Adapter.completableToMono(Completable.complete())
+        .as(StepVerifier::create)
+        .expectErrorSatisfies(
+            t ->
+                Assertions.assertThat(t)
+                    .isInstanceOf(IllegalArgumentException.class)
+                    .hasMessageContaining("foo"))
+        .verify();
+  }
+}

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

@@ -0,0 +1,268 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Observable;
+import io.reactivex.Single;
+import io.reactivex.functions.Function;
+import io.reactivex.internal.functions.Functions;
+import java.util.List;
+import java.util.Map;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaFlowableToReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(CompletableSource.class, MaybeSource.class, Functions.class);
+  }
+
+  Flowable<Integer> testFlowableAmbArray() {
+    return Flowable.ambArray(Flowable.just(1), Flowable.just(2));
+  }
+
+  Flowable<Integer> testFlowableCombineLatest() {
+    return Flowable.combineLatest(Flowable.just(1), Flowable.just(2), Integer::sum);
+  }
+
+  Flowable<Integer> testFlowableConcatWithPublisher() {
+    return Flowable.just(1).concatWith(Flowable.just(2));
+  }
+
+  Flowable<Integer> testFlowableDefer() {
+    return Flowable.defer(() -> Flowable.just(1));
+  }
+
+  Flowable<Object> testFlowableEmpty() {
+    return Flowable.empty();
+  }
+
+  Flowable<Object> testFlowableErrorThrowable() {
+    return Flowable.error(new IllegalStateException());
+  }
+
+  Flowable<Object> testFlowableErrorCallable() {
+    return Flowable.error(
+        () -> {
+          throw new IllegalStateException();
+        });
+  }
+
+  Flowable<Integer> testFlowableFromArray() {
+    return Flowable.fromArray(1, 2, 3);
+  }
+
+  Flowable<Integer> testFlowableFromCallable() {
+    return Flowable.fromCallable(() -> 1);
+  }
+
+  Flowable<Integer> testFlowableFromIterable() {
+    return Flowable.fromIterable(ImmutableList.of(1, 2, 3));
+  }
+
+  Flowable<Integer> testFlowableFromPublisher() {
+    return Flowable.fromPublisher(Flowable.just(1));
+  }
+
+  Flowable<Integer> testFlowableFilter() {
+    return Flowable.just(1).filter(i -> i > 2);
+  }
+
+  Flowable<Integer> testFlowableDistinct() {
+    return Flowable.just(1).distinct();
+  }
+
+  Maybe<Integer> testFlowableFirstElement() {
+    return Flowable.just(1).firstElement();
+  }
+
+  Single<Integer> testFlowableFirstOrError() {
+    return Flowable.just(1).firstOrError();
+  }
+
+  Completable testFlowableFlatMapCompletable() {
+    return Flowable.just(1).flatMapCompletable(integer2 -> Completable.complete());
+  }
+
+  Completable testFlowableFlatMapCompletableUnwrap() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .flatMap(
+                y ->
+                    RxJava2Adapter.completableToMono(
+                        Completable.wrap(
+                            RxJavaReactorMigrationUtil.toJdkFunction(
+                                    (Function<Integer, Completable>)
+                                        integer2 -> Completable.complete())
+                                .apply(y))))
+            .then());
+  }
+
+  Flowable<Object> testFlowableFlatMap() {
+    Flowable.just(1).flatMap(this::exampleMethod2);
+    return Flowable.just(1).flatMap(i -> ImmutableSet::of);
+  }
+
+  private Maybe<Integer> exampleMethod(Integer x) {
+    return null;
+  }
+
+  private Flowable<Integer> exampleMethod2(Integer x) {
+    return null;
+  }
+
+  ImmutableList<Flowable<Integer>> testFlowableJust() {
+    return ImmutableList.of(
+        Flowable.just(1),
+        Flowable.just(1, 2),
+        Flowable.just(1, 2, 3),
+        Flowable.just(1, 2, 3, 4),
+        Flowable.just(1, 2, 3, 4, 5));
+  }
+
+  Flowable<Integer> testFlowableMergePublisherPublisher() {
+    return Flowable.merge(Flowable.just(1), Flowable.just(2));
+  }
+
+  Flowable<Integer> testFlowableRange() {
+    return Flowable.range(1, 10);
+  }
+
+  Flowable<?> testFlowableRangeLong() {
+    return Flowable.rangeLong(1, 10);
+  }
+
+  Flowable<Integer> testFlowableZip() {
+    return Flowable.zip(Flowable.just(1), Flowable.just(2), (i1, i2) -> i1 + i2);
+  }
+
+  Single<Boolean> testFlowableAll() {
+    return Flowable.just(true, true).all(Boolean::booleanValue);
+  }
+
+  Single<Boolean> testFlowableAny() {
+    return Flowable.just(true, true).any(Boolean::booleanValue);
+  }
+
+  Object testFlowableBlockingFirst() {
+    return Flowable.just(1).blockingFirst();
+  }
+
+  Flowable<Integer> testFlowableConcatMap() {
+    return Flowable.just(1).concatMap(e -> Flowable::just);
+  }
+
+  Completable testFlowableConcatMapCompletable() {
+    return Flowable.just(1).concatMapCompletable(c -> Completable.complete());
+  }
+
+  Flowable<Integer> testFlowableConcatMapMaybe() {
+    return Flowable.just(1).concatMapMaybe(integer -> Maybe.just(integer));
+  }
+
+  Flowable<Integer> testFlowableConcatMapMaybeDelayError() {
+    return Flowable.just(1).concatMapMaybeDelayError(Maybe::just);
+  }
+
+  ImmutableSet<Flowable<Integer>> testFlowableFlatMapMaybe() {
+    return ImmutableSet.of(
+        Flowable.just(1).flatMapMaybe(Maybe::just),
+        Flowable.zip(Flowable.just(1), Flowable.just(2), (i1, i2) -> Maybe.just(i1 + i2))
+            .flatMapMaybe(Functions.identity()));
+  }
+
+  Flowable<Integer> testFlowableMap() {
+    return Flowable.just(1).map(i -> i + 1);
+  }
+
+  Flowable<Integer> testFlowableMergeWith() {
+    return Flowable.just(1).mergeWith(Single.just(1));
+  }
+
+  Flowable<Integer> testFlowableOnErrorResumeNext() {
+    return Flowable.just(1).onErrorResumeNext((Throwable throwable) -> Flux.just(1));
+  }
+
+  Single<Integer> testFlowableSingleDefault() {
+    return Flowable.just(1).single(2);
+  }
+
+  Maybe<Integer> testFlowableSingleElement() {
+    return Flowable.just(1).singleElement();
+  }
+
+  Single<Integer> testFlowableSingleOrError() {
+    return Flowable.just(1).singleOrError();
+  }
+
+  Flowable<Integer> testFlowableSorted() {
+    return Flowable.just(1).sorted();
+  }
+
+  Flowable<Integer> testFlowableSortedComparator() {
+    return Flowable.just(1).sorted((i1, i2) -> 0);
+  }
+
+  Flowable<Integer> testFlowableSwitchIfEmptyPublisher() {
+    return Flowable.just(1)
+        .switchIfEmpty(
+            Flowable.error(
+                () -> {
+                  throw new IllegalStateException();
+                }));
+  }
+
+  Single<List<Integer>> testFlowableToList() {
+    return Flowable.just(1, 2).toList();
+  }
+
+  Single<Map<Boolean, Integer>> testFlowableToMap() {
+    return Flowable.just(1).toMap(i -> i > 1);
+  }
+
+  Observable<Integer> testFlowableToObservable() {
+    return Flowable.just(1).toObservable();
+  }
+
+  void testFlowableTestAssertResultItem() throws InterruptedException {
+    Flowable.just(1).test().await().assertResult(1);
+    Flowable.just(2).test().await().assertValue(2);
+  }
+
+  void testFlowableTestAssertResult() throws InterruptedException {
+    Flowable.just(1).test().await().assertResult();
+  }
+
+  void testFlowableTestAssertValue() throws InterruptedException {
+    Flowable.just(1).test().await().assertValue(i -> i > 2);
+    Flowable.just(3).test().await().assertValue(i -> i > 4).assertComplete();
+  }
+
+  void testFlowableTestAssertResultValues() throws InterruptedException {
+    Flowable.just(1, 2, 3).test().await().assertResult(1, 2, 3);
+    Flowable.just(4, 5, 6).test().await().assertValues(4, 5, 6);
+  }
+
+  void testFlowableTestAssertComplete() throws InterruptedException {
+    Flowable.just(1).test().await().assertComplete();
+  }
+
+  void testFlowableTestAssertErrorClass() throws InterruptedException {
+    Flowable.just(1).test().await().assertError(InterruptedException.class);
+  }
+
+  void testFlowableTestAssertNoErrors() throws InterruptedException {
+    Flowable.just(1).test().await().assertNoErrors();
+  }
+
+  void testFlowableTestAssertValueCount() throws InterruptedException {
+    Flowable.just(1).test().await().assertValueCount(1);
+  }
+}

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

@@ -0,0 +1,375 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Observable;
+import io.reactivex.Single;
+import io.reactivex.functions.Function;
+import io.reactivex.internal.functions.Functions;
+import java.util.List;
+import java.util.Map;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaFlowableToReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(CompletableSource.class, MaybeSource.class, Functions.class);
+  }
+
+  Flowable<Integer> testFlowableAmbArray() {
+    return RxJava2Adapter.fluxToFlowable(Flux.firstWithSignal(Flowable.just(1), Flowable.just(2)));
+  }
+
+  Flowable<Integer> testFlowableCombineLatest() {
+    return RxJava2Adapter.fluxToFlowable(
+        Flux.<Integer, Integer, Integer>combineLatest(
+            Flowable.just(1),
+            Flowable.just(2),
+            RxJavaReactorMigrationUtil.toJdkBiFunction(Integer::sum)));
+  }
+
+  Flowable<Integer> testFlowableConcatWithPublisher() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1)).concatWith(Flowable.just(2)));
+  }
+
+  Flowable<Integer> testFlowableDefer() {
+    return RxJava2Adapter.fluxToFlowable(
+        Flux.defer(RxJavaReactorMigrationUtil.callableAsSupplier(() -> Flowable.just(1))));
+  }
+
+  Flowable<Object> testFlowableEmpty() {
+    return RxJava2Adapter.fluxToFlowable(Flux.empty());
+  }
+
+  Flowable<Object> testFlowableErrorThrowable() {
+    return RxJava2Adapter.fluxToFlowable(Flux.error(new IllegalStateException()));
+  }
+
+  Flowable<Object> testFlowableErrorCallable() {
+    return RxJava2Adapter.fluxToFlowable(
+        Flux.error(
+            RxJavaReactorMigrationUtil.callableAsSupplier(
+                () -> {
+                  throw new IllegalStateException();
+                })));
+  }
+
+  Flowable<Integer> testFlowableFromArray() {
+    return Flowable.fromArray(1, 2, 3);
+  }
+
+  Flowable<Integer> testFlowableFromCallable() {
+    return RxJava2Adapter.monoToFlowable(Mono.fromCallable(() -> 1));
+  }
+
+  Flowable<Integer> testFlowableFromIterable() {
+    return RxJava2Adapter.fluxToFlowable(Flux.fromIterable(ImmutableList.of(1, 2, 3)));
+  }
+
+  Flowable<Integer> testFlowableFromPublisher() {
+    return RxJava2Adapter.fluxToFlowable(Flux.from(Flowable.just(1)));
+  }
+
+  Flowable<Integer> testFlowableFilter() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .filter(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 2)));
+  }
+
+  Flowable<Integer> testFlowableDistinct() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1)).distinct());
+  }
+
+  Maybe<Integer> testFlowableFirstElement() {
+    return RxJava2Adapter.monoToMaybe(RxJava2Adapter.flowableToFlux(Flowable.just(1)).next());
+  }
+
+  Single<Integer> testFlowableFirstOrError() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1)).next().single());
+  }
+
+  Completable testFlowableFlatMapCompletable() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .flatMap(
+                x ->
+                    RxJava2Adapter.completableToMono(
+                        Completable.wrap(
+                            RxJavaReactorMigrationUtil.<Integer, CompletableSource>toJdkFunction(
+                                    integer2 -> Completable.complete())
+                                .apply(x))))
+            .then());
+  }
+
+  Completable testFlowableFlatMapCompletableUnwrap() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.flowableToFlux(RxJava2Adapter.fluxToFlowable(Flux.just(1)))
+            .flatMap(
+                y ->
+                    RxJava2Adapter.completableToMono(
+                        Completable.wrap(
+                            RxJavaReactorMigrationUtil.toJdkFunction(
+                                    (Function<Integer, Completable>)
+                                        integer2 -> Completable.complete())
+                                .apply(y))))
+            .then());
+  }
+
+  Flowable<Object> testFlowableFlatMap() {
+    RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .flatMap(RxJavaReactorMigrationUtil.toJdkFunction(this::exampleMethod2)));
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .flatMap(RxJavaReactorMigrationUtil.toJdkFunction(i -> ImmutableSet::of)));
+  }
+
+  private Maybe<Integer> exampleMethod(Integer x) {
+    return null;
+  }
+
+  private Flowable<Integer> exampleMethod2(Integer x) {
+    return null;
+  }
+
+  ImmutableList<Flowable<Integer>> testFlowableJust() {
+    return ImmutableList.of(
+        RxJava2Adapter.fluxToFlowable(Flux.just(1)),
+        RxJava2Adapter.fluxToFlowable(Flux.just(1, 2)),
+        RxJava2Adapter.fluxToFlowable(Flux.just(1, 2, 3)),
+        RxJava2Adapter.fluxToFlowable(Flux.just(1, 2, 3, 4)),
+        RxJava2Adapter.fluxToFlowable(Flux.just(1, 2, 3, 4, 5)));
+  }
+
+  Flowable<Integer> testFlowableMergePublisherPublisher() {
+    return RxJava2Adapter.fluxToFlowable(Flux.merge(Flowable.just(1), Flowable.just(2)));
+  }
+
+  Flowable<Integer> testFlowableRange() {
+    return RxJava2Adapter.fluxToFlowable(Flux.range(1, 10));
+  }
+
+  Flowable<?> testFlowableRangeLong() {
+    return RxJava2Adapter.fluxToFlowable(Flux.range(1, 10));
+  }
+
+  Flowable<Integer> testFlowableZip() {
+    return RxJava2Adapter.fluxToFlowable(
+        Flux.<Integer, Integer, Integer>zip(
+            Flowable.just(1),
+            Flowable.just(2),
+            RxJavaReactorMigrationUtil.toJdkBiFunction((i1, i2) -> i1 + i2)));
+  }
+
+  Single<Boolean> testFlowableAll() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.flowableToFlux(Flowable.just(true, true))
+            .all(RxJavaReactorMigrationUtil.toJdkPredicate(Boolean::booleanValue)));
+  }
+
+  Single<Boolean> testFlowableAny() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.flowableToFlux(Flowable.just(true, true))
+            .any(RxJavaReactorMigrationUtil.toJdkPredicate(Boolean::booleanValue)));
+  }
+
+  Object testFlowableBlockingFirst() {
+    return RxJava2Adapter.flowableToFlux(Flowable.just(1)).blockFirst();
+  }
+
+  Flowable<Integer> testFlowableConcatMap() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .concatMap(RxJavaReactorMigrationUtil.toJdkFunction(e -> Flowable::just)));
+  }
+
+  Completable testFlowableConcatMapCompletable() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .concatMap(
+                e ->
+                    RxJava2Adapter.completableToMono(
+                        Completable.wrap(
+                            RxJavaReactorMigrationUtil.toJdkFunction(c -> Completable.complete())
+                                .apply(e))))
+            .then());
+  }
+
+  Flowable<Integer> testFlowableConcatMapMaybe() {
+    return RxJava2Adapter.fluxToFlowable(Flux.just(1))
+        .concatMapMaybe(integer -> Maybe.just(integer));
+  }
+
+  Flowable<Integer> testFlowableConcatMapMaybeDelayError() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .concatMapDelayError(
+                e ->
+                    Maybe.wrap(
+                            RxJavaReactorMigrationUtil.<Integer, MaybeSource<Integer>>toJdkFunction(
+                                    Maybe::just)
+                                .apply(e))
+                        .toFlowable()));
+  }
+
+  ImmutableSet<Flowable<Integer>> testFlowableFlatMapMaybe() {
+    return ImmutableSet.of(
+        RxJava2Adapter.fluxToFlowable(
+            RxJava2Adapter.flowableToFlux(Flowable.just(1))
+                .flatMap(
+                    e ->
+                        RxJava2Adapter.maybeToMono(
+                            Maybe.wrap(
+                                RxJavaReactorMigrationUtil
+                                    .<Integer, MaybeSource<Integer>>toJdkFunction(Maybe::just)
+                                    .apply(e))))),
+        RxJava2Adapter.fluxToFlowable(
+            RxJava2Adapter.flowableToFlux(
+                    Flowable.zip(
+                        Flowable.just(1), Flowable.just(2), (i1, i2) -> Maybe.just(i1 + i2)))
+                .flatMap(
+                    e ->
+                        RxJava2Adapter.maybeToMono(
+                            Maybe.wrap(
+                                RxJavaReactorMigrationUtil
+                                    .<MaybeSource<Integer>, MaybeSource<Integer>>toJdkFunction(
+                                        Functions.identity())
+                                    .apply(e))))));
+  }
+
+  Flowable<Integer> testFlowableMap() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .map(RxJavaReactorMigrationUtil.toJdkFunction(i -> i + 1)));
+  }
+
+  Flowable<Integer> testFlowableMergeWith() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .mergeWith(RxJava2Adapter.singleToMono(Single.wrap(Single.just(1)))));
+  }
+
+  Flowable<Integer> testFlowableOnErrorResumeNext() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .onErrorResume(
+                RxJavaReactorMigrationUtil.toJdkFunction((Throwable throwable) -> Flux.just(1))));
+  }
+
+  Single<Integer> testFlowableSingleDefault() {
+    return RxJava2Adapter.monoToSingle(RxJava2Adapter.flowableToFlux(Flowable.just(1)).single(2));
+  }
+
+  Maybe<Integer> testFlowableSingleElement() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1)).singleOrEmpty());
+  }
+
+  Single<Integer> testFlowableSingleOrError() {
+    return RxJava2Adapter.monoToSingle(RxJava2Adapter.flowableToFlux(Flowable.just(1)).single());
+  }
+
+  Flowable<Integer> testFlowableSorted() {
+    return RxJava2Adapter.fluxToFlowable(RxJava2Adapter.flowableToFlux(Flowable.just(1)).sort());
+  }
+
+  Flowable<Integer> testFlowableSortedComparator() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1)).sort((i1, i2) -> 0));
+  }
+
+  Flowable<Integer> testFlowableSwitchIfEmptyPublisher() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .switchIfEmpty(
+                Flowable.error(
+                    () -> {
+                      throw new IllegalStateException();
+                    })));
+  }
+
+  Single<List<Integer>> testFlowableToList() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1, 2)).collectList());
+  }
+
+  Single<Map<Boolean, Integer>> testFlowableToMap() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1)).collectMap(i -> i > 1));
+  }
+
+  Observable<Integer> testFlowableToObservable() {
+    return RxJava2Adapter.fluxToFlowable(Flux.just(1)).toObservable();
+  }
+
+  void testFlowableTestAssertResultItem() throws InterruptedException {
+    RxJava2Adapter.flowableToFlux(Flowable.just(1))
+        .as(StepVerifier::create)
+        .expectNext(1)
+        .verifyComplete();
+    RxJava2Adapter.flowableToFlux(Flowable.just(2))
+        .as(StepVerifier::create)
+        .expectNext(2)
+        .verifyComplete();
+  }
+
+  void testFlowableTestAssertResult() throws InterruptedException {
+    RxJava2Adapter.flowableToFlux(Flowable.just(1)).as(StepVerifier::create).verifyComplete();
+  }
+
+  void testFlowableTestAssertValue() throws InterruptedException {
+    RxJava2Adapter.flowableToFlux(Flowable.just(1))
+        .as(StepVerifier::create)
+        .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 2))
+        .verifyComplete();
+    RxJava2Adapter.flowableToFlux(Flowable.just(3))
+        .as(StepVerifier::create)
+        .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 4))
+        .verifyComplete();
+  }
+
+  void testFlowableTestAssertResultValues() throws InterruptedException {
+    RxJava2Adapter.flowableToFlux(Flowable.just(1, 2, 3))
+        .as(StepVerifier::create)
+        .expectNext(1, 2, 3)
+        .verifyComplete();
+    RxJava2Adapter.flowableToFlux(Flowable.just(4, 5, 6))
+        .as(StepVerifier::create)
+        .expectNext(4, 5, 6)
+        .verifyComplete();
+  }
+
+  void testFlowableTestAssertComplete() throws InterruptedException {
+    RxJava2Adapter.flowableToFlux(Flowable.just(1)).as(StepVerifier::create).verifyComplete();
+  }
+
+  void testFlowableTestAssertErrorClass() throws InterruptedException {
+    RxJava2Adapter.flowableToFlux(Flowable.just(1))
+        .as(StepVerifier::create)
+        .verifyError(InterruptedException.class);
+  }
+
+  void testFlowableTestAssertNoErrors() throws InterruptedException {
+    RxJava2Adapter.flowableToFlux(Flowable.just(1)).as(StepVerifier::create).verifyComplete();
+  }
+
+  void testFlowableTestAssertValueCount() throws InterruptedException {
+    RxJava2Adapter.flowableToFlux(Flowable.just(1))
+        .as(StepVerifier::create)
+        .expectNextCount(1)
+        .verifyComplete();
+  }
+}

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

@@ -0,0 +1,219 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import io.reactivex.Completable;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Observable;
+import io.reactivex.Single;
+import java.util.concurrent.CompletableFuture;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+
+final class RxJavaMaybeToReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(Observable.class);
+  }
+
+  Maybe<String> testMaybeAmb() {
+    return Maybe.amb(ImmutableList.of(Maybe.just("foo"), Maybe.just("bar")));
+  }
+
+  // XXX: Template turned off for now.
+  Maybe<String> testMaybeAmbArray() {
+    return Maybe.ambArray(Maybe.just("foo"), Maybe.just("bar"));
+  }
+
+  Flowable<Integer> testMaybeConcatArray() {
+    return Flowable.empty();
+  }
+
+  Mono<String> testMaybeDefer() {
+    return Maybe.defer(() -> Maybe.just("test")).as(RxJava2Adapter::maybeToMono);
+  }
+
+  Maybe<Integer> testMaybeEmpty() {
+    return Maybe.empty();
+  }
+
+  Maybe<Object> testMaybeErrorThrowable() {
+    return Maybe.error(new IllegalStateException());
+  }
+
+  Maybe<Object> testMaybeErrorCallable() {
+    return Maybe.error(
+        () -> {
+          throw new IllegalStateException();
+        });
+  }
+
+  Maybe<Object> testMaybeFromAction() {
+    return Maybe.fromAction(
+        () -> {
+          String s = "foo";
+        });
+  }
+
+  Maybe<Object> testMaybeFromCallable() {
+    return Maybe.fromCallable(
+        () -> {
+          String s = "foo";
+          return null;
+        });
+  }
+
+  Maybe<Integer> testMaybeFromFuture() {
+    return Maybe.fromFuture(new CompletableFuture<>());
+  }
+
+  Maybe<Integer> testMaybeFromRunnable() {
+    return Maybe.fromRunnable(
+        () -> {
+          int i = 1 + 1;
+        });
+  }
+
+  Maybe<Integer> testMaybeFromSingle() {
+    return Maybe.fromSingle(Single.just(1));
+  }
+
+  Maybe<Integer> testMaybeJust() {
+    return Maybe.just(1);
+  }
+
+  Maybe<Integer> testMaybeWrap() {
+    return Maybe.wrap(Maybe.just(1));
+  }
+
+  Maybe<String> testMaybeAmbWith() {
+    return Maybe.just("foo").ambWith(Maybe.just("bar"));
+  }
+
+  Integer testMaybeBlockingGet() {
+    return Maybe.just(1).blockingGet();
+  }
+
+  Maybe<String> testMaybeCastPositive() {
+    return Maybe.just("string").cast(String.class);
+  }
+
+  @SuppressWarnings("MaybeJust")
+  Maybe<Object> testMaybeCastNegative() {
+    return Maybe.just("string").cast(Object.class);
+  }
+
+  Maybe<Integer> testMaybeDefaultIfEmpty() {
+    return Maybe.just(1).defaultIfEmpty(0);
+  }
+
+  Maybe<Integer> testMaybeDoOnError() {
+    return Maybe.just(1).doOnError(System.out::println);
+  }
+
+  Maybe<Integer> testMaybeDoOnSuccess() {
+    return Maybe.just(1).doOnSuccess(System.out::println);
+  }
+
+  Maybe<Integer> testMaybeFilter() {
+    return Maybe.just(1).filter(i -> i > 1);
+  }
+
+  @SuppressWarnings("MaybeJust")
+  Maybe<Integer> testMaybeFlatMapFunction() {
+    Maybe.just(1).flatMap(this::exampleMethod);
+
+    return Maybe.just(1).flatMap(exampleFunction());
+  }
+
+  private io.reactivex.functions.Function<Integer, MaybeSource<Integer>> exampleFunction() {
+    return null;
+  }
+
+  Maybe<Integer> testMaybeFlatMapLambda() {
+    return Maybe.just(1).flatMap(i -> Maybe.just(i * 2));
+  }
+
+  Maybe<Integer> testMaybeFlatMapMethodReference() {
+    return Maybe.just(1).flatMap(this::exampleMethod);
+  }
+
+  private Maybe<Integer> exampleMethod(Integer x) {
+    return null;
+  }
+
+  Maybe<Integer> testMaybeFlatMapSingleElement() {
+    return Maybe.just(1).flatMapSingleElement(x -> Single.just(x));
+  }
+
+  Completable testMaybeIgnoreElement() {
+    return Maybe.just(1).ignoreElement();
+  }
+
+  Single<Boolean> testMaybeIsEmpty() {
+    return Maybe.just(1).isEmpty();
+  }
+
+  Maybe<String> testMaybeMap() {
+    return Maybe.just(1).map(String::valueOf);
+  }
+
+  Maybe<Integer> testMaybeOnErrorReturn() {
+    return Maybe.just(1).onErrorReturn(t -> Integer.valueOf(1));
+  }
+
+  Single<Integer> testMaybeSwitchIfEmpty() {
+    return Maybe.just(1)
+        .switchIfEmpty(
+            Single.<Integer>error(
+                () -> {
+                  throw new IllegalStateException();
+                }));
+  }
+
+  Flowable<Integer> testMaybeToFlowable() {
+    return Maybe.just(1).toFlowable();
+  }
+
+  Observable<Integer> testMaybeToObservable() {
+    return Maybe.just(1).toObservable();
+  }
+
+  @SuppressWarnings("MaybeJust")
+  private Maybe<Integer> getMaybe() {
+    return Maybe.just(3);
+  }
+
+  void MaybeTestAssertResultItem() throws InterruptedException {
+    Maybe.just(1).test().await().assertResult(1);
+    Maybe.just(2).test().await().assertValue(2);
+  }
+
+  void MaybeTestAssertResult() throws InterruptedException {
+    Maybe.just(1).test().await().assertResult();
+  }
+
+  void MaybeTestAssertValue() throws InterruptedException {
+    Maybe.just(1).test().await().assertValue(i -> i > 2);
+    Maybe.just(3).test().await().assertValue(i -> i > 4).assertComplete();
+  }
+
+  void testMaybeTestAssertComplete() throws InterruptedException {
+    Maybe.just(1).test().await().assertComplete();
+  }
+
+  void testMaybeTestAssertErrorClass() throws InterruptedException {
+    Maybe.just(1).test().await().assertError(InterruptedException.class);
+  }
+
+  void testMaybeTestAssertNoErrors() throws InterruptedException {
+    Maybe.just(1).test().await().assertNoErrors();
+  }
+
+  void testMaybeTestAssertValueCount() throws InterruptedException {
+    Maybe.just(1).test().await().assertValueCount(1);
+  }
+}

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

@@ -0,0 +1,303 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Streams;
+import io.reactivex.Completable;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.MaybeSource;
+import io.reactivex.Observable;
+import io.reactivex.Single;
+import io.reactivex.SingleSource;
+import io.reactivex.functions.Function;
+import java.util.concurrent.CompletableFuture;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaMaybeToReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(Observable.class);
+  }
+
+  Maybe<String> testMaybeAmb() {
+    return RxJava2Adapter.monoToMaybe(
+        Mono.firstWithSignal(
+            Streams.stream(ImmutableList.of(Maybe.just("foo"), Maybe.just("bar")))
+                .map(RxJava2Adapter::maybeToMono)
+                .collect(ImmutableList.toImmutableList())));
+  }
+
+  // XXX: Template turned off for now.
+  Maybe<String> testMaybeAmbArray() {
+    return Maybe.ambArray(
+        RxJava2Adapter.monoToMaybe(Mono.just("foo")), RxJava2Adapter.monoToMaybe(Mono.just("bar")));
+  }
+
+  Flowable<Integer> testMaybeConcatArray() {
+    return Flowable.empty();
+  }
+
+  Mono<String> testMaybeDefer() {
+    return Mono.defer(() -> RxJava2Adapter.maybeToMono(Maybe.just("test")));
+  }
+
+  Maybe<Integer> testMaybeEmpty() {
+    return RxJava2Adapter.monoToMaybe(Mono.empty());
+  }
+
+  Maybe<Object> testMaybeErrorThrowable() {
+    return RxJava2Adapter.monoToMaybe(Mono.error(new IllegalStateException()));
+  }
+
+  Maybe<Object> testMaybeErrorCallable() {
+    return RxJava2Adapter.monoToMaybe(
+        Mono.error(
+            RxJavaReactorMigrationUtil.callableAsSupplier(
+                () -> {
+                  throw new IllegalStateException();
+                })));
+  }
+
+  Maybe<Object> testMaybeFromAction() {
+    return RxJava2Adapter.monoToMaybe(
+        Mono.fromRunnable(
+            RxJavaReactorMigrationUtil.toRunnable(
+                () -> {
+                  String s = "foo";
+                })));
+  }
+
+  Maybe<Object> testMaybeFromCallable() {
+    return RxJava2Adapter.monoToMaybe(
+        Mono.fromSupplier(
+            RxJavaReactorMigrationUtil.callableAsSupplier(
+                () -> {
+                  String s = "foo";
+                  return null;
+                })));
+  }
+
+  Maybe<Integer> testMaybeFromFuture() {
+    return RxJava2Adapter.monoToMaybe(Mono.fromFuture(new CompletableFuture<>()));
+  }
+
+  Maybe<Integer> testMaybeFromRunnable() {
+    return RxJava2Adapter.monoToMaybe(
+        Mono.fromRunnable(
+            () -> {
+              int i = 1 + 1;
+            }));
+  }
+
+  Maybe<Integer> testMaybeFromSingle() {
+    return RxJava2Adapter.monoToMaybe(
+        Mono.from(RxJava2Adapter.singleToMono(Single.wrap(Single.just(1)))));
+  }
+
+  Maybe<Integer> testMaybeJust() {
+    return RxJava2Adapter.monoToMaybe(Mono.just(1));
+  }
+
+  Maybe<Integer> testMaybeWrap() {
+    return Maybe.just(1);
+  }
+
+  Maybe<String> testMaybeAmbWith() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just("foo"))
+            .or(RxJava2Adapter.maybeToMono(Maybe.just("bar"))));
+  }
+
+  Integer testMaybeBlockingGet() {
+    return RxJava2Adapter.maybeToMono(Maybe.just(1)).block();
+  }
+
+  Maybe<String> testMaybeCastPositive() {
+    return Maybe.just("string");
+  }
+
+  @SuppressWarnings("MaybeJust")
+  Maybe<Object> testMaybeCastNegative() {
+    return Maybe.just("string").cast(Object.class);
+  }
+
+  Maybe<Integer> testMaybeDefaultIfEmpty() {
+    return RxJava2Adapter.monoToMaybe(RxJava2Adapter.maybeToMono(Maybe.just(1)).defaultIfEmpty(0));
+  }
+
+  Maybe<Integer> testMaybeDoOnError() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .doOnError(RxJavaReactorMigrationUtil.toJdkConsumer(System.out::println)));
+  }
+
+  Maybe<Integer> testMaybeDoOnSuccess() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .doOnSuccess(RxJavaReactorMigrationUtil.toJdkConsumer(System.out::println)));
+  }
+
+  Maybe<Integer> testMaybeFilter() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .filter(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 1)));
+  }
+
+  @SuppressWarnings("MaybeJust")
+  Maybe<Integer> testMaybeFlatMapFunction() {
+    RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .flatMap(
+                v ->
+                    RxJava2Adapter.maybeToMono(
+                        Maybe.wrap(
+                            RxJavaReactorMigrationUtil.<Integer, MaybeSource<Integer>>toJdkFunction(
+                                    this::exampleMethod)
+                                .apply(v)))));
+
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .flatMap(
+                v ->
+                    RxJava2Adapter.maybeToMono(
+                        Maybe.wrap(
+                            RxJavaReactorMigrationUtil.<Integer, MaybeSource<Integer>>toJdkFunction(
+                                    exampleFunction())
+                                .apply(v)))));
+  }
+
+  private io.reactivex.functions.Function<Integer, MaybeSource<Integer>> exampleFunction() {
+    return null;
+  }
+
+  Maybe<Integer> testMaybeFlatMapLambda() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .flatMap(z -> Maybe.just(z * 2).as(RxJava2Adapter::maybeToMono)));
+  }
+
+  Maybe<Integer> testMaybeFlatMapMethodReference() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .flatMap(
+                v ->
+                    RxJava2Adapter.maybeToMono(
+                        Maybe.wrap(
+                            RxJavaReactorMigrationUtil.<Integer, MaybeSource<Integer>>toJdkFunction(
+                                    this::exampleMethod)
+                                .apply(v)))));
+  }
+
+  private Maybe<Integer> exampleMethod(Integer x) {
+    return null;
+  }
+
+  Maybe<Integer> testMaybeFlatMapSingleElement() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .flatMap(
+                e ->
+                    RxJava2Adapter.singleToMono(
+                        Single.wrap(
+                            RxJavaReactorMigrationUtil.toJdkFunction(
+                                    (Function<Integer, SingleSource<Integer>>) x -> Single.just(x))
+                                .apply(e)))));
+  }
+
+  Completable testMaybeIgnoreElement() {
+    return RxJava2Adapter.monoToCompletable(RxJava2Adapter.maybeToMono(Maybe.just(1)).then());
+  }
+
+  Single<Boolean> testMaybeIsEmpty() {
+    return RxJava2Adapter.monoToSingle(RxJava2Adapter.maybeToMono(Maybe.just(1)).hasElement());
+  }
+
+  Maybe<String> testMaybeMap() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .map(RxJavaReactorMigrationUtil.toJdkFunction(String::valueOf)));
+  }
+
+  Maybe<Integer> testMaybeOnErrorReturn() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .onErrorResume(t -> Mono.just(Integer.valueOf(1))));
+  }
+
+  Single<Integer> testMaybeSwitchIfEmpty() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.maybeToMono(Maybe.just(1))
+            .switchIfEmpty(
+                RxJava2Adapter.singleToMono(
+                    Single.wrap(
+                        Single.<Integer>error(
+                            () -> {
+                              throw new IllegalStateException();
+                            })))));
+  }
+
+  Flowable<Integer> testMaybeToFlowable() {
+    return RxJava2Adapter.fluxToFlowable(RxJava2Adapter.maybeToMono(Maybe.just(1)).flux());
+  }
+
+  Observable<Integer> testMaybeToObservable() {
+    return RxJava2Adapter.fluxToObservable(RxJava2Adapter.maybeToMono(Maybe.just(1)).flux());
+  }
+
+  @SuppressWarnings("MaybeJust")
+  private Maybe<Integer> getMaybe() {
+    return Maybe.just(3);
+  }
+
+  void MaybeTestAssertResultItem() throws InterruptedException {
+    RxJava2Adapter.maybeToMono(Maybe.just(1))
+        .as(StepVerifier::create)
+        .expectNext(1)
+        .verifyComplete();
+    RxJava2Adapter.maybeToMono(Maybe.just(2))
+        .as(StepVerifier::create)
+        .expectNext(2)
+        .verifyComplete();
+  }
+
+  void MaybeTestAssertResult() throws InterruptedException {
+    RxJava2Adapter.maybeToMono(Maybe.just(1)).as(StepVerifier::create).verifyComplete();
+  }
+
+  void MaybeTestAssertValue() throws InterruptedException {
+    RxJava2Adapter.maybeToMono(Maybe.just(1))
+        .as(StepVerifier::create)
+        .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 2))
+        .verifyComplete();
+    RxJava2Adapter.maybeToMono(Maybe.just(3))
+        .as(StepVerifier::create)
+        .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 4))
+        .verifyComplete();
+  }
+
+  void testMaybeTestAssertComplete() throws InterruptedException {
+    RxJava2Adapter.maybeToMono(Maybe.just(1)).as(StepVerifier::create).verifyComplete();
+  }
+
+  void testMaybeTestAssertErrorClass() throws InterruptedException {
+    RxJava2Adapter.maybeToMono(Maybe.just(1))
+        .as(StepVerifier::create)
+        .verifyError(InterruptedException.class);
+  }
+
+  void testMaybeTestAssertNoErrors() throws InterruptedException {
+    RxJava2Adapter.maybeToMono(Maybe.just(1)).as(StepVerifier::create).verifyComplete();
+  }
+
+  void testMaybeTestAssertValueCount() throws InterruptedException {
+    RxJava2Adapter.maybeToMono(Maybe.just(1))
+        .as(StepVerifier::create)
+        .expectNextCount(1)
+        .verifyComplete();
+  }
+}

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

@@ -0,0 +1,82 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableList;
+import io.reactivex.BackpressureStrategy;
+import io.reactivex.Completable;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.Observable;
+
+final class RxJavaObservableToReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  Observable<Integer> testObservableAmb() {
+    return Observable.amb(ImmutableList.of(Observable.just(1), Observable.just(2)));
+  }
+
+  Observable<Integer> testObservableEmpty() {
+    return Observable.empty();
+  }
+
+  Observable<Integer> testObservableJust() {
+    return Observable.just(1);
+  }
+
+  Observable<Integer> testObservableJustTwo() {
+    return Observable.just(1, 2);
+  }
+
+  Observable<Integer> testObservableJustThree() {
+    return Observable.just(1, 2, 3);
+  }
+
+  Maybe<Integer> testMaybeFirstElement() {
+    return Observable.just(1).firstElement();
+  }
+
+  Observable<Integer> testObservableFilter() {
+    return Observable.just(1).filter(i -> i > 1);
+  }
+
+  Completable testObservableIgnoreElements() {
+    return Observable.just(1, 2).ignoreElements();
+  }
+
+  Flowable<Integer> testCompletableToFlowable() {
+    return Observable.just(1).toFlowable(BackpressureStrategy.BUFFER);
+  }
+
+  void testObservableTestAssertResultItem() throws InterruptedException {
+    Observable.just(1).test().await().assertResult(1);
+    Observable.just(2).test().await().assertValue(2);
+  }
+
+  void testObservableTestAssertResult() throws InterruptedException {
+    Observable.just(1).test().await().assertResult();
+  }
+
+  void testObservableTestAssertValue() throws InterruptedException {
+    Observable.just(1).test().await().assertValue(i -> i > 2);
+    Observable.just(3).test().await().assertValue(i -> i > 4).assertComplete();
+  }
+
+  void testObservableTestAssertResultValues() throws InterruptedException {
+    Observable.just(1, 2, 3).test().await().assertResult(1, 2, 3);
+    Observable.just(4, 5, 6).test().await().assertValues(4, 5, 6);
+  }
+
+  void testObservableTestAssertComplete() throws InterruptedException {
+    Observable.just(1).test().await().assertComplete();
+  }
+
+  void testObservableTestAssertErrorClass() throws InterruptedException {
+    Observable.just(1).test().await().assertError(InterruptedException.class);
+  }
+
+  void testObservableTestAssertNoErrors() throws InterruptedException {
+    Observable.just(1).test().await().assertNoErrors();
+  }
+
+  void testObservableTestAssertValueCount() throws InterruptedException {
+    Observable.just(1).test().await().assertValueCount(1);
+  }
+}

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

@@ -0,0 +1,128 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Streams;
+import io.reactivex.BackpressureStrategy;
+import io.reactivex.Completable;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.Observable;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaObservableToReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  Observable<Integer> testObservableAmb() {
+    return RxJava2Adapter.fluxToObservable(
+        Flux.<Integer>firstWithSignal(
+            Streams.stream(ImmutableList.of(Observable.just(1), Observable.just(2)))
+                .map(e -> e.toFlowable(BackpressureStrategy.BUFFER))
+                .map(RxJava2Adapter::flowableToFlux)
+                .collect(ImmutableList.toImmutableList())));
+  }
+
+  Observable<Integer> testObservableEmpty() {
+    return RxJava2Adapter.fluxToObservable(Flux.empty());
+  }
+
+  Observable<Integer> testObservableJust() {
+    return RxJava2Adapter.fluxToObservable(Flux.just(1));
+  }
+
+  Observable<Integer> testObservableJustTwo() {
+    return RxJava2Adapter.fluxToObservable(Flux.just(1, 2));
+  }
+
+  Observable<Integer> testObservableJustThree() {
+    return RxJava2Adapter.fluxToObservable(Flux.just(1, 2, 3));
+  }
+
+  Maybe<Integer> testMaybeFirstElement() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.observableToFlux(Observable.just(1), BackpressureStrategy.BUFFER).next());
+  }
+
+  Observable<Integer> testObservableFilter() {
+    return RxJava2Adapter.fluxToObservable(
+        RxJava2Adapter.observableToFlux(Observable.just(1), BackpressureStrategy.BUFFER)
+            .filter(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 1)));
+  }
+
+  Completable testObservableIgnoreElements() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.observableToFlux(Observable.just(1, 2), BackpressureStrategy.BUFFER)
+            .ignoreElements()
+            .then());
+  }
+
+  Flowable<Integer> testCompletableToFlowable() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.observableToFlux(Observable.just(1), BackpressureStrategy.BUFFER));
+  }
+
+  void testObservableTestAssertResultItem() throws InterruptedException {
+    RxJava2Adapter.observableToFlux(Observable.just(1), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .expectNext(1)
+        .verifyComplete();
+    RxJava2Adapter.observableToFlux(Observable.just(2), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .expectNext(2)
+        .verifyComplete();
+  }
+
+  void testObservableTestAssertResult() throws InterruptedException {
+    RxJava2Adapter.observableToFlux(Observable.just(1), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .verifyComplete();
+  }
+
+  void testObservableTestAssertValue() throws InterruptedException {
+    RxJava2Adapter.observableToFlux(Observable.just(1), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 2))
+        .verifyComplete();
+    RxJava2Adapter.observableToFlux(Observable.just(3), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 4))
+        .verifyComplete();
+  }
+
+  void testObservableTestAssertResultValues() throws InterruptedException {
+    RxJava2Adapter.observableToFlux(Observable.just(1, 2, 3), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .expectNext(1, 2, 3)
+        .verifyComplete();
+    RxJava2Adapter.observableToFlux(Observable.just(4, 5, 6), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .expectNext(4, 5, 6)
+        .verifyComplete();
+  }
+
+  void testObservableTestAssertComplete() throws InterruptedException {
+    RxJava2Adapter.observableToFlux(Observable.just(1), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .verifyComplete();
+  }
+
+  void testObservableTestAssertErrorClass() throws InterruptedException {
+    RxJava2Adapter.observableToFlux(Observable.just(1), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .verifyError(InterruptedException.class);
+  }
+
+  void testObservableTestAssertNoErrors() throws InterruptedException {
+    RxJava2Adapter.observableToFlux(Observable.just(1), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .verifyComplete();
+  }
+
+  void testObservableTestAssertValueCount() throws InterruptedException {
+    RxJava2Adapter.observableToFlux(Observable.just(1), BackpressureStrategy.BUFFER)
+        .as(StepVerifier::create)
+        .expectNextCount(1)
+        .verifyComplete();
+  }
+}

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

@@ -0,0 +1,143 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableSet;
+import io.reactivex.Completable;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.Single;
+import java.util.List;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaSingleToReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(List.class);
+  }
+
+  Single<Object> testSingleErrorThrowable() {
+    return Single.error(new IllegalStateException());
+  }
+
+  Single<Integer> testSingleDefer() {
+    return Single.defer(() -> Single.just(1));
+  }
+
+  Single<Object> testSingleErrorCallable() {
+    return Single.error(
+        () -> {
+          throw new IllegalStateException();
+        });
+  }
+
+  Single<Integer> testSingleFromCallable() {
+    return Single.fromCallable(() -> 1);
+  }
+
+  Single<Integer> testSingleJust() {
+    return Single.just(1);
+  }
+
+  Single<Object> testSingleNever() {
+    return Single.never();
+  }
+
+  Single<Integer> testSingleWrap() {
+    return Single.wrap(Single.just(1));
+  }
+
+  Integer testSingleBlockingGet() {
+    return Single.just(1).blockingGet();
+  }
+
+  Flowable<Integer> testSingleConcatWith() {
+    return Single.just(1).concatWith(Single.just(2));
+  }
+
+  Single<Integer> testSingleDoOnError() {
+    return Single.just(1).doOnError(System.out::println);
+  }
+
+  Single<Integer> testSingleDoOnSuccess() {
+    return Single.just(1).doOnSuccess(System.out::println);
+  }
+
+  Maybe<Integer> testSingleFilter() {
+    return Single.just(1).filter(i -> i > 2);
+  }
+
+  public Mono<String> testUnwrapLambdaSingle() {
+    return Mono.just("1")
+        .flatMap(
+            v ->
+                RxJava2Adapter.singleToMono(
+                    (Single<String>)
+                        RxJavaReactorMigrationUtil.toJdkFunction(
+                                (String ident) -> RxJava2Adapter.monoToSingle(Mono.just(ident)))
+                            .apply(v)));
+  }
+
+  Single<Integer> testSingleFlatMapLambda() {
+    return Single.just(1).flatMap(i -> Single.just(i * 2));
+  }
+
+  Completable testSingleFlatMapCompletable() {
+    return Single.just(1).flatMapCompletable(integer -> Completable.complete());
+  }
+
+  Flowable<Integer> testSingleFlatMapPublisher() {
+    return Single.just(1).flatMapPublisher(i -> Flowable::just);
+  }
+
+  Completable testCompletableIgnoreElement() {
+    return Single.just(1).ignoreElement();
+  }
+
+  Single<Integer> testSingleMap() {
+    return Single.just(1).map(i -> i + 1);
+  }
+
+  Flowable<Integer> testSingleToFlowable() {
+    return Single.just(1).toFlowable();
+  }
+
+  Maybe<Integer> testSingleToMaybe() {
+    return Single.just(1).toMaybe();
+  }
+
+  Single<Integer> testSingleZipWith() {
+    return Single.just(1).zipWith(Single.just(2), (integer, integer2) -> integer + integer2);
+  }
+
+  void testSingleTestAssertResultItem() throws InterruptedException {
+    Single.just(1).test().await().assertResult(1);
+    Single.just(2).test().await().assertValue(2);
+  }
+
+  void testSingleTestAssertResult() throws InterruptedException {
+    Single.just(1).test().await().assertResult();
+  }
+
+  void testSingleTestAssertValue() throws InterruptedException {
+    Single.just(1).test().await().assertValue(i -> i > 2);
+    Single.just(3).test().await().assertValue(i -> i > 4).assertComplete();
+  }
+
+  void testSingleTestAssertComplete() throws InterruptedException {
+    Single.just(1).test().await().assertComplete();
+  }
+
+  void testSingleTestAssertErrorClass() throws InterruptedException {
+    Single.just(1).test().await().assertError(InterruptedException.class);
+  }
+
+  void testSingleTestAssertNoErrors() throws InterruptedException {
+    Single.just(1).test().await().assertNoErrors();
+  }
+
+  void testSingleTestAssertValueCount() throws InterruptedException {
+    Single.just(1).test().await().assertValueCount(1);
+  }
+}

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

@@ -0,0 +1,194 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableSet;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.Single;
+import java.util.List;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaSingleToReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(List.class);
+  }
+
+  Single<Object> testSingleErrorThrowable() {
+    return RxJava2Adapter.monoToSingle(Mono.error(new IllegalStateException()));
+  }
+
+  Single<Integer> testSingleDefer() {
+    return RxJava2Adapter.monoToSingle(
+        Mono.defer(() -> RxJava2Adapter.singleToMono(Single.just(1))));
+  }
+
+  Single<Object> testSingleErrorCallable() {
+    return RxJava2Adapter.monoToSingle(
+        Mono.error(
+            RxJavaReactorMigrationUtil.callableAsSupplier(
+                () -> {
+                  throw new IllegalStateException();
+                })));
+  }
+
+  Single<Integer> testSingleFromCallable() {
+    return RxJava2Adapter.monoToSingle(
+        Mono.fromSupplier(RxJavaReactorMigrationUtil.callableAsSupplier(() -> 1)));
+  }
+
+  Single<Integer> testSingleJust() {
+    return RxJava2Adapter.monoToSingle(Mono.just(1));
+  }
+
+  Single<Object> testSingleNever() {
+    return RxJava2Adapter.monoToSingle(Mono.never());
+  }
+
+  Single<Integer> testSingleWrap() {
+    return Single.just(1);
+  }
+
+  Integer testSingleBlockingGet() {
+    return RxJava2Adapter.singleToMono(Single.just(1)).block();
+  }
+
+  Flowable<Integer> testSingleConcatWith() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.singleToMono(Single.just(1))
+            .concatWith(RxJava2Adapter.singleToMono(Single.wrap(Single.just(2)))));
+  }
+
+  Single<Integer> testSingleDoOnError() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.singleToMono(Single.just(1))
+            .doOnError(RxJavaReactorMigrationUtil.toJdkConsumer(System.out::println)));
+  }
+
+  Single<Integer> testSingleDoOnSuccess() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.singleToMono(Single.just(1))
+            .doOnSuccess(RxJavaReactorMigrationUtil.toJdkConsumer(System.out::println)));
+  }
+
+  Maybe<Integer> testSingleFilter() {
+    return RxJava2Adapter.monoToMaybe(
+        RxJava2Adapter.singleToMono(Single.just(1))
+            .filter(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 2)));
+  }
+
+  public Mono<String> testUnwrapLambdaSingle() {
+    return Mono.just("1")
+        .flatMap(
+            v ->
+                RxJava2Adapter.singleToMono(
+                    (Single<String>)
+                        RxJavaReactorMigrationUtil.toJdkFunction(
+                                (String ident) -> RxJava2Adapter.monoToSingle(Mono.just(ident)))
+                            .apply(v)));
+  }
+
+  Single<Integer> testSingleFlatMapLambda() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.singleToMono(Single.just(1))
+            .flatMap(i -> RxJava2Adapter.singleToMono(Single.just(i * 2))));
+  }
+
+  Completable testSingleFlatMapCompletable() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.singleToMono(Single.just(1))
+            .flatMap(
+                z ->
+                    RxJava2Adapter.completableToMono(
+                        Completable.wrap(
+                            RxJavaReactorMigrationUtil.<Integer, CompletableSource>toJdkFunction(
+                                    integer -> Completable.complete())
+                                .apply(z))))
+            .then());
+  }
+
+  Flowable<Integer> testSingleFlatMapPublisher() {
+    return RxJava2Adapter.fluxToFlowable(
+        RxJava2Adapter.singleToMono(Single.just(1))
+            .flatMapMany(RxJavaReactorMigrationUtil.toJdkFunction(i -> Flowable::just)));
+  }
+
+  Completable testCompletableIgnoreElement() {
+    return RxJava2Adapter.monoToCompletable(RxJava2Adapter.singleToMono(Single.just(1)).then());
+  }
+
+  Single<Integer> testSingleMap() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.singleToMono(Single.just(1))
+            .map(RxJavaReactorMigrationUtil.toJdkFunction(i -> i + 1)));
+  }
+
+  Flowable<Integer> testSingleToFlowable() {
+    return RxJava2Adapter.fluxToFlowable(RxJava2Adapter.singleToMono(Single.just(1)).flux());
+  }
+
+  Maybe<Integer> testSingleToMaybe() {
+    return RxJava2Adapter.monoToMaybe(RxJava2Adapter.singleToMono(Single.just(1)));
+  }
+
+  Single<Integer> testSingleZipWith() {
+    return RxJava2Adapter.monoToSingle(
+        RxJava2Adapter.singleToMono(Single.just(1))
+            .zipWith(
+                RxJava2Adapter.singleToMono(Single.wrap(Single.just(2))),
+                RxJavaReactorMigrationUtil.toJdkBiFunction(
+                    (integer, integer2) -> integer + integer2)));
+  }
+
+  void testSingleTestAssertResultItem() throws InterruptedException {
+    RxJava2Adapter.singleToMono(Single.just(1))
+        .as(StepVerifier::create)
+        .expectNext(1)
+        .verifyComplete();
+    RxJava2Adapter.singleToMono(Single.just(2))
+        .as(StepVerifier::create)
+        .expectNext(2)
+        .verifyComplete();
+  }
+
+  void testSingleTestAssertResult() throws InterruptedException {
+    RxJava2Adapter.singleToMono(Single.just(1)).as(StepVerifier::create).verifyComplete();
+  }
+
+  void testSingleTestAssertValue() throws InterruptedException {
+    RxJava2Adapter.singleToMono(Single.just(1))
+        .as(StepVerifier::create)
+        .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 2))
+        .verifyComplete();
+    RxJava2Adapter.singleToMono(Single.just(3))
+        .as(StepVerifier::create)
+        .expectNextMatches(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 4))
+        .verifyComplete();
+  }
+
+  void testSingleTestAssertComplete() throws InterruptedException {
+    RxJava2Adapter.singleToMono(Single.just(1)).as(StepVerifier::create).verifyComplete();
+  }
+
+  void testSingleTestAssertErrorClass() throws InterruptedException {
+    RxJava2Adapter.singleToMono(Single.just(1))
+        .as(StepVerifier::create)
+        .verifyError(InterruptedException.class);
+  }
+
+  void testSingleTestAssertNoErrors() throws InterruptedException {
+    RxJava2Adapter.singleToMono(Single.just(1)).as(StepVerifier::create).verifyComplete();
+  }
+
+  void testSingleTestAssertValueCount() throws InterruptedException {
+    RxJava2Adapter.singleToMono(Single.just(1))
+        .as(StepVerifier::create)
+        .expectNextCount(1)
+        .verifyComplete();
+  }
+}

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

@@ -0,0 +1,103 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableSet;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.Single;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaToReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(RxJavaReactorMigrationUtil.class);
+  }
+
+  Flux<Integer> testFluxToFlowableToFlux() {
+    Flowable.just(1)
+        .as(RxJava2Adapter::flowableToFlux)
+        .map(e -> e + e)
+        .as(RxJava2Adapter::fluxToFlowable)
+        .as(RxJava2Adapter::flowableToFlux)
+        .flatMap(e -> ImmutableSet::of)
+        .as(RxJava2Adapter::fluxToFlowable);
+
+    return Flux.just(2).as(RxJava2Adapter::fluxToFlowable).as(RxJava2Adapter::flowableToFlux);
+  }
+
+  Mono<Integer> testMonoToFlowableToMono() {
+    Single.just(1)
+        .as(RxJava2Adapter::singleToMono)
+        .map(e -> e + e)
+        .as(RxJava2Adapter::monoToSingle)
+        .as(RxJava2Adapter::singleToMono)
+        .filter(i -> i > 2)
+        .as(RxJava2Adapter::monoToSingle);
+
+    Mono.empty().then().as(RxJava2Adapter::monoToCompletable).as(RxJava2Adapter::completableToMono);
+
+    return Mono.just(3).as(RxJava2Adapter::monoToMaybe).as(RxJava2Adapter::maybeToMono);
+  }
+
+  // This one doesnt work
+  Maybe<String> testRemoveRedundantCast() {
+    return (Maybe<String>) Maybe.just("foo");
+  }
+
+  Mono<Integer> testMonoErrorCallableSupplierUtil() {
+    return Mono.just(1)
+        .switchIfEmpty(
+            Mono.error(
+                RxJavaReactorMigrationUtil.callableAsSupplier(() -> new IllegalStateException())));
+  }
+
+  Maybe<Integer> testRemoveUtilCallable() {
+    return RxJava2Adapter.monoToMaybe(
+        Mono.fromSupplier(
+            RxJavaReactorMigrationUtil.callableAsSupplier(
+                () -> {
+                  String s = "foo";
+                  return null;
+                })));
+  }
+
+  Flowable<String> testUnnecessaryFunctionConversion() {
+    return Flowable.just(1)
+        .as(RxJava2Adapter::flowableToFlux)
+        .map(RxJavaReactorMigrationUtil.toJdkFunction(e -> String.valueOf(e)))
+        .as(RxJava2Adapter::fluxToFlowable);
+  }
+
+  Flowable<Integer> testUnnecessaryBiFunctionConversion() {
+    return RxJava2Adapter.fluxToFlowable(
+        Flux.zip(
+            Flowable.just(1),
+            Flowable.just(2),
+            RxJavaReactorMigrationUtil.toJdkBiFunction((i1, i2) -> i1 + i2)));
+  }
+
+  Single<Integer> testUnnecessaryConsumerConversion() {
+    return Single.just(1)
+        .as(RxJava2Adapter::singleToMono)
+        .doOnSuccess(RxJavaReactorMigrationUtil.toJdkConsumer(System.out::println))
+        .as(RxJava2Adapter::monoToSingle);
+  }
+
+  Maybe<Integer> testUnnecessaryPredicateConversion() {
+    return Single.just(1)
+        .as(RxJava2Adapter::singleToMono)
+        .filter(RxJavaReactorMigrationUtil.toJdkPredicate(i -> i > 2))
+        .as(RxJava2Adapter::monoToMaybe);
+  }
+
+  Mono<Integer> testMonoFromNestedPublisher() {
+    return Mono.from(RxJava2Adapter.fluxToFlowable(Flux.just(1)));
+  }
+
+  Mono<Integer> testMonoThenThen() {
+    return Mono.just(1).then().then(Mono.just(2));
+  }
+}

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

@@ -0,0 +1,93 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableSet;
+import io.reactivex.Flowable;
+import io.reactivex.Maybe;
+import io.reactivex.Single;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaToReactorTemplatesTest implements RefasterTemplateTestCase {
+
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(RxJavaReactorMigrationUtil.class);
+  }
+
+  Flux<Integer> testFluxToFlowableToFlux() {
+    Flowable.just(1)
+        .as(RxJava2Adapter::flowableToFlux)
+        .map(e -> e + e)
+        .flatMap(e -> ImmutableSet::of)
+        .as(RxJava2Adapter::fluxToFlowable);
+
+    return Flux.just(2);
+  }
+
+  Mono<Integer> testMonoToFlowableToMono() {
+    Single.just(1)
+        .as(RxJava2Adapter::singleToMono)
+        .map(e -> e + e)
+        .filter(i -> i > 2)
+        .as(RxJava2Adapter::monoToSingle);
+
+    Mono.empty().then();
+
+    return Mono.just(3);
+  }
+
+  // This one doesnt work
+  Maybe<String> testRemoveRedundantCast() {
+    return (Maybe<String>) Maybe.just("foo");
+  }
+
+  Mono<Integer> testMonoErrorCallableSupplierUtil() {
+    return Mono.just(1).switchIfEmpty(Mono.error(() -> new IllegalStateException()));
+  }
+
+  Maybe<Integer> testRemoveUtilCallable() {
+    return RxJava2Adapter.monoToMaybe(
+        Mono.fromSupplier(
+            () -> {
+              String s = "foo";
+              return null;
+            }));
+  }
+
+  Flowable<String> testUnnecessaryFunctionConversion() {
+    return Flowable.just(1)
+        .as(RxJava2Adapter::flowableToFlux)
+        .map(e -> String.valueOf(e))
+        .as(RxJava2Adapter::fluxToFlowable);
+  }
+
+  Flowable<Integer> testUnnecessaryBiFunctionConversion() {
+    return RxJava2Adapter.fluxToFlowable(
+        Flux.<Integer, Integer, Integer>zip(
+            Flowable.just(1), Flowable.just(2), (i1, i2) -> i1 + i2));
+  }
+
+  Single<Integer> testUnnecessaryConsumerConversion() {
+    return Single.just(1)
+        .as(RxJava2Adapter::singleToMono)
+        .doOnSuccess(System.out::println)
+        .as(RxJava2Adapter::monoToSingle);
+  }
+
+  Maybe<Integer> testUnnecessaryPredicateConversion() {
+    return Single.just(1)
+        .as(RxJava2Adapter::singleToMono)
+        .filter(i -> i > 2)
+        .as(RxJava2Adapter::monoToMaybe);
+  }
+
+  Mono<Integer> testMonoFromNestedPublisher() {
+    return Mono.from(Flux.just(1));
+  }
+
+  Mono<Integer> testMonoThenThen() {
+    return Mono.just(1).then(Mono.just(2));
+  }
+}

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

@@ -0,0 +1,67 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableSet;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Flowable;
+import io.reactivex.Single;
+import io.reactivex.functions.Function;
+import java.util.List;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaUnwrapTemplatesTest implements RefasterTemplateTestCase {
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(
+        CompletableSource.class, Function.class, RxJavaReactorMigrationUtil.class, List.class);
+  }
+
+  Completable testFlowableFlatMapUnwrapLambda() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .flatMap(
+                e ->
+                    RxJava2Adapter.completableToMono(
+                        Completable.wrap(
+                            RxJavaReactorMigrationUtil.<Integer, CompletableSource>toJdkFunction(
+                                    (Function<Integer, CompletableSource>)
+                                        v -> RxJava2Adapter.monoToCompletable(Mono.empty()))
+                                .apply(e))))
+            .then());
+  }
+
+  Completable testSingleRemoveLambdaWithCast() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.singleToMono(Single.just(1))
+            .flatMap(
+                e ->
+                    RxJava2Adapter.completableToMono(
+                        Completable.wrap(
+                            RxJavaReactorMigrationUtil.<Integer, Completable>toJdkFunction(
+                                    (Function<Integer, Completable>)
+                                        v ->
+                                            RxJava2Adapter.monoToCompletable(
+                                                Mono.justOrEmpty(null)))
+                                .apply(e))))
+            .then());
+  }
+
+  Mono<Void> testSingleRemoveLambdaWithCompletable() {
+    return Flux.just(1, 2)
+        .collectList()
+        .flatMap(
+            e ->
+                RxJava2Adapter.completableToMono(
+                    Completable.wrap(
+                        RxJavaReactorMigrationUtil.toJdkFunction(
+                                (Function<List<Integer>, CompletableSource>)
+                                    u -> Completable.complete())
+                            .apply(e))))
+        .then();
+  }
+
+  // Many tests for the `RxJavaUnwrapTemplates` class are not written due to time constraints.
+}

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

@@ -0,0 +1,45 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import com.google.common.collect.ImmutableSet;
+import io.reactivex.Completable;
+import io.reactivex.CompletableSource;
+import io.reactivex.Flowable;
+import io.reactivex.Single;
+import io.reactivex.functions.Function;
+import java.util.List;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.migration.util.RxJavaReactorMigrationUtil;
+
+final class RxJavaUnwrapTemplatesTest implements RefasterTemplateTestCase {
+  @Override
+  public ImmutableSet<?> elidedTypesAndStaticImports() {
+    return ImmutableSet.of(
+        CompletableSource.class, Function.class, RxJavaReactorMigrationUtil.class, List.class);
+  }
+
+  Completable testFlowableFlatMapUnwrapLambda() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.flowableToFlux(Flowable.just(1))
+            .flatMap(
+                v ->
+                    RxJava2Adapter.completableToMono(
+                        Completable.wrap(RxJava2Adapter.monoToCompletable(Mono.empty()))))
+            .then());
+  }
+
+  Completable testSingleRemoveLambdaWithCast() {
+    return RxJava2Adapter.monoToCompletable(
+        RxJava2Adapter.singleToMono(Single.just(1)).flatMap(v -> Mono.justOrEmpty(null)).then());
+  }
+
+  Mono<Void> testSingleRemoveLambdaWithCompletable() {
+    return Flux.just(1, 2)
+        .collectList()
+        .flatMap(u -> RxJava2Adapter.completableToMono(Completable.complete()))
+        .then();
+  }
+
+  // Many tests for the `RxJavaUnwrapTemplates` class are not written due to time constraints.
+}

migration-util/pom.xml

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>tech.picnic.error-prone-support</groupId>
+        <artifactId>error-prone-support</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>migration-util</artifactId>
+
+    <properties>
+        <maven.compiler.source>11</maven.compiler.source>
+        <maven.compiler.target>11</maven.compiler.target>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.projectreactor</groupId>
+            <artifactId>reactor-core</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.reactivex.rxjava2</groupId>
+            <artifactId>rxjava</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.reactivestreams</groupId>
+            <artifactId>reactive-streams</artifactId>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+</project>

migration-util/src/main/java/tech/picnic/errorprone/migration/util/RxJavaReactorMigrationUtil.java

@@ -0,0 +1,365 @@
+package tech.picnic.errorprone.migration.util;
+
+import io.reactivex.flowables.GroupedFlowable;
+import io.reactivex.functions.Action;
+import io.reactivex.internal.fuseable.ConditionalSubscriber;
+import io.reactivex.internal.fuseable.QueueSubscription;
+import java.util.concurrent.Callable;
+import java.util.function.Supplier;
+import org.reactivestreams.Subscriber;
+import org.reactivestreams.Subscription;
+import reactor.core.CoreSubscriber;
+import reactor.core.Exceptions;
+import reactor.core.Fuseable;
+import reactor.core.publisher.GroupedFlux;
+import reactor.core.publisher.Operators;
+
+public final class RxJavaReactorMigrationUtil {
+  private RxJavaReactorMigrationUtil() {}
+
+  /**
+   * Convert {@code Callable<T>} to T
+   *
+   * @param callable XXX
+   * @param <T> XXX
+   * @return XXX
+   */
+  // XXX: Rename.
+  // XXX: Introduce Refaster rules to drop this wrapper when possible.
+  @SuppressWarnings("IllegalCatch")
+  public static <T> T getUnchecked(Callable<T> callable) {
+    try {
+      return callable.call();
+    } catch (Exception e) {
+      throw new IllegalArgumentException("Callable threw checked exception", e);
+    }
+  }
+
+  /**
+   * Convert {@link io.reactivex.functions.Function} to {@link java.util.function.Function}
+   *
+   * @param function XXX
+   * @param <T> XXX
+   * @param <R> XXX
+   * @return XXX
+   */
+  // XXX: Rename.
+  // XXX: Introduce Refaster rules to drop this wrapper when possible.
+  @SuppressWarnings("IllegalCatch")
+  public static <T, R> java.util.function.Function<T, R> toJdkFunction(
+      io.reactivex.functions.Function<T, R> function) {
+    return (t) -> {
+      try {
+        return function.apply(t);
+      } catch (Exception e) {
+        throw new IllegalArgumentException("BiFunction threw checked exception", e);
+      }
+    };
+  }
+
+  /**
+   * Convert {@link io.reactivex.functions.BiFunction} to {@link java.util.function.BiFunction}
+   *
+   * @param biFunction XXX
+   * @param <T> XXX
+   * @param <U> XXX
+   * @param <R> XXX
+   * @return XXX
+   */
+  @SuppressWarnings("IllegalCatch")
+  public static <T, U, R> java.util.function.BiFunction<T, U, R> toJdkBiFunction(
+      io.reactivex.functions.BiFunction<T, U, R> biFunction) {
+    return (t, u) -> {
+      try {
+        return biFunction.apply(t, u);
+      } catch (Exception e) {
+        throw new IllegalArgumentException("BiFunction threw checked exception", e);
+      }
+    };
+  }
+
+  /**
+   * Convert {@link java.util.concurrent.Callable} to {@link java.util.function.Supplier}
+   *
+   * @param callable XXX
+   * @param <T> XXX
+   * @return XXX
+   */
+  @SuppressWarnings("IllegalCatch")
+  public static <T> Supplier<T> callableAsSupplier(Callable<T> callable) {
+    return () -> {
+      try {
+        return callable.call();
+      } catch (Exception e) {
+        throw new IllegalArgumentException("Callable threw checked exception", e);
+      }
+    };
+  }
+
+  /**
+   * Convert {@link io.reactivex.functions.Predicate} to {@link java.util.function.Predicate}
+   *
+   * @param predicate XXX
+   * @param <T> XXX
+   * @return XXX
+   */
+  // XXX: Rename.
+  // XXX: Introduce Refaster rules to drop this wrapper when possible.
+  @SuppressWarnings("IllegalCatch")
+  public static <T> java.util.function.Predicate<T> toJdkPredicate(
+      io.reactivex.functions.Predicate<T> predicate) {
+    return (t) -> {
+      try {
+        return predicate.test(t);
+      } catch (Exception e) {
+        throw new IllegalArgumentException("Predicate threw checked exception", e);
+      }
+    };
+  }
+
+  /**
+   * Convert {@link io.reactivex.functions.Consumer} to {@link java.util.function.Consumer}
+   *
+   * @param consumer XXX
+   * @param <T> XXX
+   * @return XXX
+   */
+  // XXX: Rename.
+  // XXX: Introduce Refaster rules to drop this wrapper when possible.
+  @SuppressWarnings("IllegalCatch")
+  public static <T> java.util.function.Consumer<T> toJdkConsumer(
+      io.reactivex.functions.Consumer<T> consumer) {
+    return (t) -> {
+      try {
+        consumer.accept(t);
+      } catch (Exception e) {
+        throw new IllegalArgumentException("Consumer threw checked exception", e);
+      }
+    };
+  }
+
+  /**
+   * XXX
+   *
+   * @param action XXX
+   * @return XXX
+   */
+  @SuppressWarnings("IllegalCatch")
+  public static Runnable toRunnable(Action action) {
+    return () -> {
+      try {
+        action.run();
+      } catch (Exception e) {
+        throw new IllegalArgumentException("Action threw checked exception", e);
+      }
+    };
+  }
+
+  // "Coersion" (find better name):
+  // instanceof (support this?)
+  // two functional interfaces with:
+  // B.return type extends A.return type
+  // A.param 1 type extends B.param 1 type
+  // ....
+  // B throws a subset of the exceptions thrown by A
+
+  public static <K, V> GroupedFlowable<K, V> groupedFluxToGroupedFlowable(
+      GroupedFlux<K, V> source) {
+    return new GroupedFluxAsGroupedFlowable<>(source);
+  }
+
+  private static final class GroupedFluxAsGroupedFlowable<K, V> extends GroupedFlowable<K, V> {
+    private final GroupedFlux<K, V> source;
+
+    GroupedFluxAsGroupedFlowable(GroupedFlux<K, V> source) {
+      super(source.key());
+
+      this.source = source;
+    }
+
+    @Override
+    public void subscribeActual(Subscriber<? super V> s) {
+      if (s instanceof ConditionalSubscriber) {
+        source.subscribe(
+            new FluxAsFlowableConditionalSubscriber<>((ConditionalSubscriber<? super V>) s));
+      } else {
+        source.subscribe(new FluxAsFlowableSubscriber<>(s));
+      }
+    }
+
+    private static final class FluxAsFlowableSubscriber<T>
+        implements CoreSubscriber<T>, QueueSubscription<T> {
+      private final Subscriber<? super T> actual;
+
+      private Subscription s;
+      private Fuseable.QueueSubscription<T> qs;
+
+      FluxAsFlowableSubscriber(Subscriber<? super T> actual) {
+        this.actual = actual;
+      }
+
+      @Override
+      @SuppressWarnings("unchecked")
+      public void onSubscribe(Subscription s) {
+        if (Operators.validate(this.s, s)) {
+          this.s = s;
+          if (s instanceof Fuseable.QueueSubscription) {
+            this.qs = (Fuseable.QueueSubscription<T>) s;
+          }
+
+          actual.onSubscribe(this);
+        }
+      }
+
+      @Override
+      public void onNext(T t) {
+        actual.onNext(t);
+      }
+
+      @Override
+      public void onError(Throwable t) {
+        actual.onError(t);
+      }
+
+      @Override
+      public void onComplete() {
+        actual.onComplete();
+      }
+
+      @Override
+      public void request(long n) {
+        s.request(n);
+      }
+
+      @Override
+      public void cancel() {
+        s.cancel();
+      }
+
+      @Override
+      public T poll() {
+        return qs.poll();
+      }
+
+      @Override
+      public boolean isEmpty() {
+        return qs.isEmpty();
+      }
+
+      @Override
+      public void clear() {
+        qs.clear();
+      }
+
+      @Override
+      public int requestFusion(int requestedMode) {
+        if (qs != null) {
+          return qs.requestFusion(requestedMode);
+        }
+        return Fuseable.NONE;
+      }
+
+      @Override
+      public boolean offer(T value) {
+        throw new UnsupportedOperationException("Should not be called");
+      }
+
+      @Override
+      public boolean offer(T v1, T v2) {
+        throw new UnsupportedOperationException("Should not be called");
+      }
+    }
+
+    private static final class FluxAsFlowableConditionalSubscriber<T>
+        implements Fuseable.ConditionalSubscriber<T>, QueueSubscription<T> {
+      private final ConditionalSubscriber<? super T> actual;
+
+      private Subscription s;
+      private QueueSubscription<T> qs;
+
+      FluxAsFlowableConditionalSubscriber(ConditionalSubscriber<? super T> actual) {
+        this.actual = actual;
+      }
+
+      @Override
+      @SuppressWarnings("unchecked")
+      public void onSubscribe(Subscription s) {
+        if (Operators.validate(this.s, s)) {
+          this.s = s;
+          if (s instanceof io.reactivex.internal.fuseable.QueueSubscription) {
+            this.qs = (QueueSubscription<T>) s;
+          }
+
+          actual.onSubscribe(this);
+        }
+      }
+
+      @Override
+      public void onNext(T t) {
+        actual.onNext(t);
+      }
+
+      @Override
+      public boolean tryOnNext(T t) {
+        return actual.tryOnNext(t);
+      }
+
+      @Override
+      public void onError(Throwable t) {
+        actual.onError(t);
+      }
+
+      @Override
+      public void onComplete() {
+        actual.onComplete();
+      }
+
+      @Override
+      public void request(long n) {
+        s.request(n);
+      }
+
+      @Override
+      public void cancel() {
+        s.cancel();
+      }
+
+      @Override
+      public T poll() {
+        try {
+          return qs.poll();
+        } catch (Throwable ex) {
+          throw Exceptions.bubble(ex);
+        }
+      }
+
+      @Override
+      public boolean isEmpty() {
+        return qs.isEmpty();
+      }
+
+      @Override
+      public void clear() {
+        qs.clear();
+      }
+
+      @Override
+      public int requestFusion(int requestedMode) {
+        if (qs != null) {
+          return qs.requestFusion(requestedMode);
+        }
+        return NONE;
+      }
+
+      @Override
+      public boolean offer(T v1) {
+        throw new UnsupportedOperationException("Should not be called!");
+      }
+
+      @Override
+      public boolean offer(T v1, T v2) {
+        throw new UnsupportedOperationException("Should not be called!");
+      }
+    }
+  }
+}

pom.xml

@@ -34,6 +34,7 @@
 
     <modules>
         <module>error-prone-contrib</module>
+        <module>migration-util</module>
         <module>refaster-resource-compiler</module>
         <module>refaster-support</module>
     </modules>
@@ -127,8 +128,8 @@
         that need to be referenced only once should *not* be listed here. -->
         <version.auto-service>1.0</version.auto-service>
         <version.error-prone>${version.error-prone-orig}</version.error-prone>
-        <version.error-prone-fork>v${version.error-prone-orig}-picnic-1</version.error-prone-fork>
-        <version.error-prone-orig>2.9.0</version.error-prone-orig>
+        <version.error-prone-fork>HEAD-SNAPSHOT</version.error-prone-fork>
+        <version.error-prone-orig>HEAD-SNAPSHOT</version.error-prone-orig>
         <version.error-prone-slf4j>0.1.4</version.error-prone-slf4j>
         <version.findbugs-format-string>3.0.0</version.findbugs-format-string>
         <version.guava-beta-checker>1.0</version.guava-beta-checker>
@@ -1152,13 +1153,13 @@
                 fork, some other dependencies depend on the official (i.e.,
                 non-forked) `error_prone_annotations`. Here we fix which
                 version is pulled in. -->
-                <dependencies>
-                    <dependency>
-                        <groupId>com.google.errorprone</groupId>
-                        <artifactId>error_prone_annotations</artifactId>
-                        <version>${version.error-prone-orig}</version>
-                    </dependency>
-                </dependencies>
+                <!--                <dependencies>-->
+                <!--                    <dependency>-->
+                <!--                        <groupId>com.google.errorprone</groupId>-->
+                <!--                        <artifactId>error_prone_annotations</artifactId>-->
+                <!--                        <version>${version.error-prone-orig}</version>-->
+                <!--                    </dependency>-->
+                <!--                </dependencies>-->
             </dependencyManagement>
         </profile>
         <profile>