WIP

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

@@ -0,0 +1,91 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.LinkType.NONE;
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
+import static com.google.errorprone.matchers.Matchers.anyOf;
+import static com.google.errorprone.matchers.Matchers.instanceMethod;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+import java.util.function.BiFunction;
+import reactor.core.publisher.Mono;
+import tech.picnic.errorprone.bugpatterns.util.SourceCode;
+
+/**
+ * A {@link BugChecker} which flags {@link Mono} operations that are known to be vacuous, given that
+ * they are invoked on a {@link Mono} that is known not to complete empty.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    summary = "Avoid vacuous operations on known non-empty `Mono`s",
+    linkType = NONE,
+    severity = WARNING,
+    tags = SIMPLIFICATION)
+// XXX: This check does not simplify `someFlux.defaultIfEmpty(T).{defaultIfEmpty(T),hasElements()}`,
+// as `someFlux.defaultIfEmpty(T)` yields a `Flux` rather than a `Mono`. Consider adding support for
+// these cases.
+// XXX: Given more advanced analysis many more expressions could be flagged. Consider
+// `Mono.just(someValue)`, `Flux.just(someNonEmptySequence)`,
+// `someMono.switchIfEmpty(someProvablyNonEmptyMono)` and many other variants.
+// XXX: Consider implementing a similar check for `Publisher`s that are known to complete without
+// emitting a value (e.g. `Mono.empty()`, `someFlux.then()`, ...), or known not to complete normally
+// (`Mono.never()`, `someFlux.repeat()`, `Mono.error(...)`, ...). The latter category could
+// potentially be split out further.
+public final class NonEmptyMono extends BugChecker implements MethodInvocationTreeMatcher {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<ExpressionTree> MONO_SIZE_CHECK =
+      instanceMethod()
+          .onDescendantOf("reactor.core.publisher.Mono")
+          .namedAnyOf("defaultIfEmpty", "single", "switchIfEmpty");
+  private static final Matcher<ExpressionTree> NON_EMPTY_MONO =
+      anyOf(
+          instanceMethod()
+              .onDescendantOf("reactor.core.publisher.Flux")
+              .namedAnyOf(
+                  "all",
+                  "any",
+                  "collect",
+                  "collectList",
+                  "collectMap",
+                  "collectMultimap",
+                  "collectSortedList",
+                  "count",
+                  "elementAt",
+                  "hasElement",
+                  "hasElements",
+                  "last",
+                  "reduceWith",
+                  "single"),
+          instanceMethod()
+              .onDescendantOf("reactor.core.publisher.Flux")
+              .named("reduce")
+              .withParameters(Object.class.getName(), BiFunction.class.getName()),
+          instanceMethod()
+              .onDescendantOf("reactor.core.publisher.Mono")
+              .namedAnyOf("defaultIfEmpty", "hasElement", "single"));
+
+  @Override
+  public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+    if (!MONO_SIZE_CHECK.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    ExpressionTree receiver = ASTHelpers.getReceiver(tree);
+    if (!NON_EMPTY_MONO.matches(receiver, state)) {
+      return Description.NO_MATCH;
+    }
+
+    return describeMatch(
+        tree, SuggestedFix.replace(tree, SourceCode.treeToString(receiver, state)));
+  }
+}

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

@@ -0,0 +1,272 @@
+package tech.picnic.errorprone.refastertemplates;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import io.reactivex.Completable;
+import io.reactivex.Flowable;
+import java.util.Arrays;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CompletableFuture;
+import java.util.function.BiFunction;
+import java.util.function.Supplier;
+import org.assertj.core.util.Streams;
+import org.reactivestreams.Publisher;
+import reactor.adapter.rxjava.RxJava2Adapter;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+/** Refaster templates which replace RxJava expressions with equivalent Reactor assertions. */
+// XXX: Document the approach and any limitations; see the `TestNGToAssertJTemplates` documentation.
+// XXX: Document that the templates use `Completable` rather than `CompletableSource`, etc.
+// XXX: Have separate files for Completable, Maybe, Single, Flowable?
+final class RxJavaToReactorTemplates {
+  private RxJavaToReactorTemplates() {}
+
+  // XXX: Handle array and varargs cases.
+  // XXX: Simplify rule with `Completable.amb(Arrays.asList(sources))`?
+  static final class CompletableAmbArray {
+    @BeforeTemplate
+    Completable before(Completable... sources) {
+      return Completable.ambArray(sources);
+    }
+
+    @AfterTemplate
+    Completable after(Completable... sources) {
+      return Mono.firstWithSignal(
+              Arrays.stream(sources)
+                  .map(RxJava2Adapter::completableToMono)
+                  .collect(toImmutableList()))
+          .as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  static final class CompletableAmb {
+    @BeforeTemplate
+    Completable before(Iterable<? extends Completable> sources) {
+      return Completable.amb(sources);
+    }
+
+    @AfterTemplate
+    Completable after(Iterable<? extends Completable> sources) {
+      return Mono.firstWithSignal(
+              Streams.stream(sources)
+                  .map(RxJava2Adapter::completableToMono)
+                  .collect(toImmutableList()))
+          .as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  static final class CompletableComplete {
+    @BeforeTemplate
+    Completable before() {
+      return Completable.complete();
+    }
+
+    @AfterTemplate
+    Completable after() {
+      return Mono.empty().as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  // XXX: Handle array and varargs cases.
+  // XXX: Simplify rule with `Completable.amb(Arrays.asList(sources))`?
+  static final class CompletableConcatArray {
+    @BeforeTemplate
+    Completable before(Completable... sources) {
+      return Completable.concatArray(sources);
+    }
+
+    @AfterTemplate
+    Completable after(Completable... sources) {
+      return Flux.concat(
+              Arrays.stream(sources)
+                  .map(RxJava2Adapter::completableToMono)
+                  .collect(toImmutableList()))
+          .then()
+          .as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  // XXX: Simplify rule with `Completable.concat(Flux.fromIterable(sources))`?
+  static final class CompletableConcatIterable {
+    @BeforeTemplate
+    Completable before(Iterable<? extends Completable> sources) {
+      return Completable.concat(sources);
+    }
+
+    @AfterTemplate
+    Completable after(Iterable<? extends Completable> sources) {
+      return Flux.concat(Flux.fromIterable(sources).map(RxJava2Adapter::completableToMono))
+          .then()
+          .as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  // XXX: Simplify rule with `Completable.concat(sources, 2)`?
+  // XXX: Arguably we should, since the Reactor prefetch is `Queues.XS_BUFFER_SIZE`.
+  static final class CompletableConcatPublisher {
+    @BeforeTemplate
+    Completable before(Publisher<? extends Completable> sources) {
+      return Completable.concat(sources);
+    }
+
+    @AfterTemplate
+    Completable after(Publisher<? extends Completable> sources) {
+      return Flux.concat(Flux.from(sources).map(RxJava2Adapter::completableToMono))
+          .then()
+          .as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  static final class CompletableConcatPublisherPrefetch {
+    @BeforeTemplate
+    Completable before(Publisher<? extends Completable> sources, int prefetch) {
+      return Completable.concat(sources, prefetch);
+    }
+
+    @AfterTemplate
+    Completable after(Publisher<? extends Completable> sources, int prefetch) {
+      return Flux.concat(Flux.from(sources).map(RxJava2Adapter::completableToMono), prefetch)
+          .then()
+          .as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  // XXX: Migrate `Completable#create(CompletableOnSubscribe)`
+
+  // XXX: Migrate `Completable#unsafeCreate(CompletableSource)`
+
+  static final class CompletableDefer {
+    @BeforeTemplate
+    Completable before(Callable<? extends Completable> completableSupplier) {
+      return Completable.defer(completableSupplier);
+    }
+
+    @AfterTemplate
+    Completable after(Callable<? extends Completable> completableSupplier) {
+      return Mono.defer(
+              () ->
+                  RxJava2ReactorMigrationUtil.getUnchecked(completableSupplier)
+                      .as(RxJava2Adapter::completableToMono))
+          .as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  static final class CompletableErrorDeferred {
+    @BeforeTemplate
+    Completable before(Callable<? extends Throwable> errorSupplier) {
+      return Completable.error(errorSupplier);
+    }
+
+    @AfterTemplate
+    Completable after(Callable<? extends Throwable> errorSupplier) {
+      return Mono.error(RxJava2ReactorMigrationUtil.callableAsSupplier(errorSupplier))
+          .as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  static final class CompletableError {
+    @BeforeTemplate
+    Completable before(Throwable error) {
+      return Completable.error(error);
+    }
+
+    @AfterTemplate
+    Completable after(Throwable error) {
+      return Mono.error(error).as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  // XXX: Migrate `Completable#fromAction(Action)`
+
+  static final class CompletableFromCallable<T> {
+    @BeforeTemplate
+    Completable before(Callable<T> callable) {
+      return Completable.fromCallable(callable);
+    }
+
+    @AfterTemplate
+    Completable after(Callable<T> callable) {
+      return Mono.fromSupplier(RxJava2ReactorMigrationUtil.callableAsSupplier(callable))
+          .as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  // XXX: Also handle `Future`s that don't extend `CompletableFuture`.
+  static final class CompletableFromFuture<T> {
+    @BeforeTemplate
+    Completable before(CompletableFuture<T> future) {
+      return Completable.fromFuture(future);
+    }
+
+    @AfterTemplate
+    Completable after(CompletableFuture<T> future) {
+      return Mono.fromFuture(future).as(RxJava2Adapter::monoToCompletable);
+    }
+  }
+
+  // XXX: Next up: migrate `Completable#fromMaybe(Maybe)`
+
+  // XXX: Move to a separate Maven module.
+  static final class RxJava2ReactorMigrationUtil {
+    private RxJava2ReactorMigrationUtil() {}
+
+    // XXX: Rename.
+    // XXX: Introduce Refaster rules to drop this wrapper when possible.
+    static <T> T getUnchecked(Callable<T> callable) {
+      try {
+        return callable.call();
+      } catch (Exception e) {
+        throw new RuntimeException("Callable threw checked exception", e);
+      }
+    }
+
+    // XXX: Rename.
+    // XXX: Introduce Refaster rules to drop this wrapper when possible.
+    static <T> Supplier<T> callableAsSupplier(Callable<T> callable) {
+      return () -> {
+        try {
+          return callable.call();
+        } catch (Exception e) {
+          throw new RuntimeException("Callable threw checked exception", e);
+        }
+      };
+    }
+
+    static <T, U, R> BiFunction<? super T, ? super U, ? extends R> toJdkBiFunction(
+        io.reactivex.functions.BiFunction<? super T, ? super U, ? extends R> biFunction) {
+      return (t, u) -> {
+        try {
+          return biFunction.apply(t, u);
+        } catch (Exception e) {
+          throw new RuntimeException("BiFunction threw checked exception", e);
+        }
+      };
+    }
+  }
+
+  ///////////////////////////////// FLOWABLE - MOVE!
+
+  static final class FlowableCombineLatest<T1, T2, R> {
+    @BeforeTemplate
+    Flowable<R> before(
+        Publisher<? extends T1> publisher1,
+        Publisher<? extends T2> publisher2,
+        io.reactivex.functions.BiFunction<? super T1, ? super T2, ? extends R> combiner) {
+      return Flowable.combineLatest(publisher1, publisher2, combiner);
+    }
+
+    @AfterTemplate
+    Flowable<R> after(
+        Publisher<? extends T1> publisher1,
+        Publisher<? extends T2> publisher2,
+        io.reactivex.functions.BiFunction<? super T1, ? super T2, ? extends R> combiner) {
+      // XXX: Generic type parameters are specified to appease IDEA; review.
+      return RxJava2Adapter.fluxToFlowable(
+          Flux.<T1, T2, R>combineLatest(
+              publisher1, publisher2, RxJava2ReactorMigrationUtil.toJdkBiFunction(combiner)));
+    }
+  }
+}

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

@@ -0,0 +1,155 @@
+package tech.picnic.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode.TEXT_MATCH;
+
+import com.google.errorprone.BugCheckerRefactoringTestHelper;
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.jupiter.api.Test;
+
+final class NonEmptyMonoTest {
+  private final CompilationTestHelper compilationTestHelper =
+      CompilationTestHelper.newInstance(NonEmptyMono.class, getClass());
+  private final BugCheckerRefactoringTestHelper refactoringTestHelper =
+      BugCheckerRefactoringTestHelper.newInstance(NonEmptyMono.class, getClass());
+
+  @Test
+  void identification() {
+    compilationTestHelper
+        .addSourceLines(
+            "A.java",
+            "import static com.google.common.collect.ImmutableList.toImmutableList;",
+            "import static java.util.function.Function.identity;",
+            "",
+            "import com.google.common.collect.ImmutableList;",
+            "import com.google.common.collect.ImmutableMap;",
+            "import java.util.ArrayList;",
+            "import java.util.HashMap;",
+            "import java.util.List;",
+            "import reactor.core.publisher.Flux;",
+            "import reactor.core.publisher.Mono;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Mono.just(1).defaultIfEmpty(2);",
+            "    Mono.just(1).single();",
+            "    Mono.just(1).switchIfEmpty(Mono.just(2));",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).all(x -> true).defaultIfEmpty(true);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).any(x -> true).single();",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collect(toImmutableList()).switchIfEmpty(Mono.just(ImmutableList.of()));",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collect(ArrayList::new, List::add).defaultIfEmpty(new ArrayList<>());",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collectList().single();",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collectMap(identity()).switchIfEmpty(Mono.just(ImmutableMap.of()));",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collectMap(identity(), identity()).defaultIfEmpty(ImmutableMap.of());",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collectMap(identity(), identity(), HashMap::new).single();",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collectMultimap(identity()).switchIfEmpty(Mono.just(ImmutableMap.of()));",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collectMultimap(identity(), identity()).defaultIfEmpty(ImmutableMap.of());",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collectMultimap(identity(), identity(), HashMap::new).single();",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collectSortedList().defaultIfEmpty(ImmutableList.of());",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).collectSortedList((o1, o2) -> 0).single();",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).count().switchIfEmpty(Mono.just(2L));",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).elementAt(0).defaultIfEmpty(1);",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).elementAt(0, 2).single();",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).hasElement(2).switchIfEmpty(Mono.just(true));",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).hasElements().defaultIfEmpty(true);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).last().single();",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).last(2).switchIfEmpty(Mono.just(3));",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).reduceWith(() -> 0, Integer::sum).defaultIfEmpty(2);",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).single().single();",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).single(2).switchIfEmpty(Mono.just(3));",
+            "",
+            "    Flux.just(1).reduce(Integer::sum).defaultIfEmpty(2);",
+            "    // BUG: Diagnostic contains:",
+            "    Flux.just(1).reduce(2, Integer::sum).single();",
+            "",
+            "    // BUG: Diagnostic contains:",
+            "    Mono.just(1).defaultIfEmpty(1).switchIfEmpty(Mono.just(2));",
+            "    // BUG: Diagnostic contains:",
+            "    Mono.just(1).hasElement().defaultIfEmpty(true);",
+            "    // BUG: Diagnostic contains:",
+            "    Mono.just(1).single().single();",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  void replacement() {
+    refactoringTestHelper
+        .addInputLines(
+            "A.java",
+            "import static com.google.common.collect.ImmutableList.toImmutableList;",
+            "",
+            "import com.google.common.collect.ImmutableList;",
+            "import reactor.core.publisher.Flux;",
+            "import reactor.core.publisher.Mono;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Flux.just(1).collect(toImmutableList()).single();",
+            "    Flux.just(1).collect(toImmutableList()).defaultIfEmpty(ImmutableList.of());",
+            "    Flux.just(1).collect(toImmutableList()).switchIfEmpty(Mono.just(ImmutableList.of()));",
+            "",
+            "    Mono.just(2).hasElement().single();",
+            "    Mono.just(2).hasElement().defaultIfEmpty(true);",
+            "    Mono.just(2).hasElement().switchIfEmpty(Mono.just(true));",
+            "  }",
+            "}")
+        .addOutputLines(
+            "A.java",
+            "import static com.google.common.collect.ImmutableList.toImmutableList;",
+            "",
+            "import com.google.common.collect.ImmutableList;",
+            "import reactor.core.publisher.Flux;",
+            "import reactor.core.publisher.Mono;",
+            "",
+            "class A {",
+            "  void m() {",
+            "    Flux.just(1).collect(toImmutableList());",
+            "    Flux.just(1).collect(toImmutableList());",
+            "    Flux.just(1).collect(toImmutableList());",
+            "",
+            "    Mono.just(2).hasElement();",
+            "    Mono.just(2).hasElement();",
+            "    Mono.just(2).hasElement();",
+            "  }",
+            "}")
+        .doTest(TEXT_MATCH);
+  }
+}