Introduce Mono#using{,When} Refaster rules

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

@@ -55,6 +55,7 @@
 import tech.picnic.errorprone.refaster.annotation.Description;
 import tech.picnic.errorprone.refaster.annotation.OnlineDocumentation;
 import tech.picnic.errorprone.refaster.matchers.IsEmpty;
+import tech.picnic.errorprone.refaster.matchers.IsFunctionReturningMono;
 import tech.picnic.errorprone.refaster.matchers.IsIdentityOperation;
 import tech.picnic.errorprone.refaster.matchers.ThrowsCheckedException;
 
@@ -541,6 +542,152 @@ Mono<T> after(Mono<T> mono) {
     }
   }
 
+  /**
+   * Don't unnecessarily transform a {@link Flux#using(Callable, Function)} to a mono, instead use
+   * the equivalent API provided by {@link Mono}.
+   */
+  static final class MonoUsing<
+      D extends AutoCloseable, T, P extends Publisher<? extends T>, M extends Mono<? extends T>> {
+    @BeforeTemplate
+    Mono<T> before(
+        Callable<D> resourceSupplier,
+        @Matches(IsFunctionReturningMono.class) Function<D, P> sourceSupplier) {
+      return Flux.using(resourceSupplier, sourceSupplier).single();
+    }
+
+    @AfterTemplate
+    Mono<T> after(Callable<D> resourceSupplier, Function<D, M> sourceSupplier) {
+      return Mono.using(resourceSupplier, sourceSupplier);
+    }
+  }
+
+  /**
+   * Don't unnecessarily transform a {@link Flux#using(Callable, Function, boolean)} to a mono,
+   * instead use the equivalent API provided by {@link Mono}.
+   */
+  static final class MonoUsingEager<
+      D extends AutoCloseable, T, P extends Publisher<? extends T>, M extends Mono<? extends T>> {
+    @BeforeTemplate
+    Mono<T> before(
+        Callable<D> resourceSupplier,
+        @Matches(IsFunctionReturningMono.class) Function<D, P> sourceSupplier,
+        boolean eager) {
+      return Flux.using(resourceSupplier, sourceSupplier, eager).single();
+    }
+
+    @AfterTemplate
+    Mono<T> after(Callable<D> resourceSupplier, Function<D, M> sourceSupplier, boolean eager) {
+      return Mono.using(resourceSupplier, sourceSupplier, eager);
+    }
+  }
+
+  /**
+   * Don't unnecessarily transform a {@link Flux#using(Callable, Function, Consumer)} to a mono,
+   * instead use the equivalent API provided by {@link Mono}.
+   */
+  static final class MonoUsing2<
+      D, T, P extends Publisher<? extends T>, M extends Mono<? extends T>> {
+    @BeforeTemplate
+    Mono<T> before(
+        Callable<D> resourceSupplier,
+        @Matches(IsFunctionReturningMono.class) Function<D, P> sourceSupplier,
+        Consumer<D> resourceCleanup) {
+      return Flux.using(resourceSupplier, sourceSupplier, resourceCleanup).single();
+    }
+
+    @AfterTemplate
+    Mono<T> after(
+        Callable<D> resourceSupplier, Function<D, M> sourceSupplier, Consumer<D> resourceCleanup) {
+      return Mono.using(resourceSupplier, sourceSupplier, resourceCleanup);
+    }
+  }
+
+  /**
+   * Don't unnecessarily transform a {@link Flux#using(Callable, Function, Consumer, boolean)} to a
+   * mono, instead use the equivalent API provided by {@link Mono}.
+   */
+  static final class MonoUsing2Eager<
+      D, T, P extends Publisher<? extends T>, M extends Mono<? extends T>> {
+    @BeforeTemplate
+    Mono<T> before(
+        Callable<D> resourceSupplier,
+        @Matches(IsFunctionReturningMono.class) Function<D, P> sourceSupplier,
+        Consumer<D> resourceCleanup,
+        boolean eager) {
+      return Flux.using(resourceSupplier, sourceSupplier, resourceCleanup, eager).single();
+    }
+
+    @AfterTemplate
+    Mono<T> after(
+        Callable<D> resourceSupplier,
+        Function<D, M> sourceSupplier,
+        Consumer<D> resourceCleanup,
+        boolean eager) {
+      return Mono.using(resourceSupplier, sourceSupplier, resourceCleanup, eager);
+    }
+  }
+
+  /**
+   * Don't unnecessarily transform a {@link Flux#usingWhen(Publisher, Function, Function)} to a
+   * mono, instead use the equivalent API provided by {@link Mono}.
+   */
+  static final class MonoUsingWhen<
+      D,
+      T,
+      P extends Publisher<? extends T>,
+      P2 extends Publisher<?>,
+      M extends Mono<? extends T>> {
+    @BeforeTemplate
+    Mono<T> before(
+        Publisher<D> resourceSupplier,
+        @Matches(IsFunctionReturningMono.class) Function<D, P> resourceClosure,
+        Function<D, P2> asyncCleanup) {
+      return Flux.usingWhen(resourceSupplier, resourceClosure, asyncCleanup).single();
+    }
+
+    @AfterTemplate
+    Mono<T> after(
+        Publisher<D> resourceSupplier,
+        Function<D, M> resourceClosure,
+        Function<D, P2> asyncCleanup) {
+      return Mono.usingWhen(resourceSupplier, resourceClosure, asyncCleanup);
+    }
+  }
+
+  /**
+   * Don't unnecessarily transform a {@link Flux#usingWhen(Publisher, Function, Function,
+   * BiFunction, Function)} to a mono, instead use the equivalent API provided by {@link Mono}.
+   */
+  static final class MonoUsingWhen2<
+      D,
+      T,
+      P extends Publisher<? extends T>,
+      P2 extends Publisher<?>,
+      M extends Mono<? extends T>> {
+    @BeforeTemplate
+    Mono<T> before(
+        Publisher<D> resourceSupplier,
+        @Matches(IsFunctionReturningMono.class) Function<D, P> resourceClosure,
+        Function<D, P2> asyncComplete,
+        BiFunction<D, ? super Throwable, P2> asyncError,
+        Function<D, P2> asyncCancel) {
+      return Flux.usingWhen(
+              resourceSupplier, resourceClosure, asyncComplete, asyncError, asyncCancel)
+          .single();
+    }
+
+    @AfterTemplate
+    Mono<T> after(
+        Publisher<D> resourceSupplier,
+        Function<D, M> resourceClosure,
+        Function<D, P2> asyncComplete,
+        BiFunction<D, ? super Throwable, ? extends Publisher<?>> asyncError,
+        Function<D, P2> asyncCancel) {
+      return Mono.usingWhen(
+          resourceSupplier, resourceClosure, asyncComplete, asyncError, asyncCancel);
+    }
+  }
+
   /** Don't unnecessarily pass an empty publisher to {@link Flux#switchIfEmpty(Publisher)}. */
   static final class FluxSwitchIfEmptyOfEmptyPublisher<T> {
     @BeforeTemplate

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

@@ -15,6 +15,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
+import java.io.ByteArrayInputStream;
 import java.time.Duration;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -204,6 +205,57 @@ Mono<Integer> testMonoSingle() {
     return Mono.just(1).flux().single();
   }
 
+  ImmutableSet<Mono<String>> testMonoUsing() {
+    return ImmutableSet.of(
+        Flux.using(() -> new ByteArrayInputStream(new byte[] {}), s -> Mono.just("foo")).single(),
+        Flux.using(() -> new ByteArrayInputStream(new byte[] {}), s -> Flux.just("bar")).single());
+  }
+
+  ImmutableSet<Mono<String>> testMonoUsingEager() {
+    return ImmutableSet.of(
+        Flux.using(() -> new ByteArrayInputStream(new byte[] {}), s -> Mono.just("foo"), false)
+            .single(),
+        Flux.using(() -> new ByteArrayInputStream(new byte[] {}), s -> Flux.just("bar"), false)
+            .single());
+  }
+
+  ImmutableSet<Mono<String>> testMonoUsing2() {
+    return ImmutableSet.of(
+        Flux.using(() -> "foo", foo -> Mono.just("bar"), foo -> {}).single(),
+        Flux.using(() -> "foo", foo -> Flux.just("bar"), foo -> {}).single());
+  }
+
+  ImmutableSet<Mono<String>> testMonoUsing2Eager() {
+    return ImmutableSet.of(
+        Flux.using(() -> "foo", foo -> Mono.just("bar"), foo -> {}, false).single(),
+        Flux.using(() -> "foo", foo -> Flux.just("bar"), foo -> {}, false).single());
+  }
+
+  ImmutableSet<Mono<String>> testMonoUsingWhen() {
+    return ImmutableSet.of(
+        Flux.usingWhen(Mono.just("foo"), foo -> Mono.just("bar"), foo -> Mono.just("baz")).single(),
+        Flux.usingWhen(Mono.just("foo"), foo -> Flux.just("bar"), foo -> Mono.just("baz"))
+            .single());
+  }
+
+  ImmutableSet<Mono<String>> testMonoUsingWhen2() {
+    return ImmutableSet.of(
+        Flux.usingWhen(
+                Mono.just("foo"),
+                foo -> Mono.just("bar"),
+                foo -> Mono.just("baz"),
+                (foo, e) -> Mono.just("qux"),
+                foo -> Mono.just("thud"))
+            .single(),
+        Flux.usingWhen(
+                Mono.just("foo"),
+                foo -> Flux.just("bar"),
+                foo -> Mono.just("baz"),
+                (foo, e) -> Mono.just("qux"),
+                foo -> Mono.just("thud"))
+            .single());
+  }
+
   ImmutableSet<Flux<Integer>> testFluxSwitchIfEmptyOfEmptyPublisher() {
     return ImmutableSet.of(
         Flux.just(1).switchIfEmpty(Mono.empty()), Flux.just(2).switchIfEmpty(Flux.empty()));

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

@@ -17,6 +17,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
+import java.io.ByteArrayInputStream;
 import java.time.Duration;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -208,6 +209,55 @@ Mono<Integer> testMonoSingle() {
     return Mono.just(1).single();
   }
 
+  ImmutableSet<Mono<String>> testMonoUsing() {
+    return ImmutableSet.of(
+        Mono.using(() -> new ByteArrayInputStream(new byte[] {}), s -> Mono.just("foo")),
+        Flux.using(() -> new ByteArrayInputStream(new byte[] {}), s -> Flux.just("bar")).single());
+  }
+
+  ImmutableSet<Mono<String>> testMonoUsingEager() {
+    return ImmutableSet.of(
+        Mono.using(() -> new ByteArrayInputStream(new byte[] {}), s -> Mono.just("foo"), false),
+        Flux.using(() -> new ByteArrayInputStream(new byte[] {}), s -> Flux.just("bar"), false)
+            .single());
+  }
+
+  ImmutableSet<Mono<String>> testMonoUsing2() {
+    return ImmutableSet.of(
+        Mono.using(() -> "foo", foo -> Mono.just("bar"), foo -> {}),
+        Flux.using(() -> "foo", foo -> Flux.just("bar"), foo -> {}).single());
+  }
+
+  ImmutableSet<Mono<String>> testMonoUsing2Eager() {
+    return ImmutableSet.of(
+        Mono.using(() -> "foo", foo -> Mono.just("bar"), foo -> {}, false),
+        Flux.using(() -> "foo", foo -> Flux.just("bar"), foo -> {}, false).single());
+  }
+
+  ImmutableSet<Mono<String>> testMonoUsingWhen() {
+    return ImmutableSet.of(
+        Mono.usingWhen(Mono.just("foo"), foo -> Mono.just("bar"), foo -> Mono.just("baz")),
+        Flux.usingWhen(Mono.just("foo"), foo -> Flux.just("bar"), foo -> Mono.just("baz"))
+            .single());
+  }
+
+  ImmutableSet<Mono<String>> testMonoUsingWhen2() {
+    return ImmutableSet.of(
+        Mono.usingWhen(
+            Mono.just("foo"),
+            foo -> Mono.just("bar"),
+            foo -> Mono.just("baz"),
+            (foo, e) -> Mono.just("qux"),
+            foo -> Mono.just("thud")),
+        Flux.usingWhen(
+                Mono.just("foo"),
+                foo -> Flux.just("bar"),
+                foo -> Mono.just("baz"),
+                (foo, e) -> Mono.just("qux"),
+                foo -> Mono.just("thud"))
+            .single());
+  }
+
   ImmutableSet<Flux<Integer>> testFluxSwitchIfEmptyOfEmptyPublisher() {
     return ImmutableSet.of(Flux.just(1), Flux.just(2));
   }

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

@@ -0,0 +1,38 @@
+package tech.picnic.errorprone.refaster.matchers;
+
+import static com.google.errorprone.matchers.Matchers.isSameType;
+
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.suppliers.Suppliers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.LambdaExpressionTree;
+import com.sun.source.tree.Tree;
+import com.sun.source.tree.Tree.Kind;
+import java.util.function.Function;
+
+/**
+ * A matcher of lambda expressions that are of type {@code java.util.function.Function} that returns
+ * a {@code reactor.core.publisher.Mono}.
+ */
+public final class IsFunctionReturningMono implements Matcher<ExpressionTree> {
+  private static final long serialVersionUID = 1L;
+  private static final Matcher<Tree> MONO_TYPE =
+      isSameType(Suppliers.typeFromString("reactor.core.publisher.Mono"));
+  private static final Matcher<Tree> FUNCTION_TYPE =
+      isSameType(Suppliers.typeFromString(Function.class.getCanonicalName()));
+
+  /** Instantiates a new {@link IsFunctionReturningMono} instance. */
+  public IsFunctionReturningMono() {}
+
+  @Override
+  public boolean matches(ExpressionTree tree, VisitorState state) {
+    if (tree.getKind() != Kind.LAMBDA_EXPRESSION) {
+      return false;
+    }
+
+    LambdaExpressionTree lambdaExpressionTree = (LambdaExpressionTree) tree;
+    return MONO_TYPE.matches(lambdaExpressionTree.getBody(), state)
+        && FUNCTION_TYPE.matches(lambdaExpressionTree, state);
+  }
+}

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

@@ -0,0 +1,44 @@
+package tech.picnic.errorprone.refaster.matchers;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.CompilationTestHelper;
+import com.google.errorprone.bugpatterns.BugChecker;
+import org.junit.jupiter.api.Test;
+
+final class IsFunctionReturningMonoTest {
+  @Test
+  void matches() {
+    CompilationTestHelper.newInstance(MatcherTestChecker.class, getClass())
+        .addSourceLines(
+            "A.java",
+            "import java.util.function.Function;",
+            "import java.util.function.Supplier;",
+            "import reactor.core.publisher.Flux;",
+            "import reactor.core.publisher.Mono;",
+            "",
+            "class A {",
+            "  // BUG: Diagnostic contains:",
+            "  Function<String, Mono<String>> positive = s -> Mono.just(s);",
+            "",
+            "  Function<String, Flux<String>> negative = s -> Flux.just(s);",
+            "",
+            "  Supplier<Mono<String>> negative2 = () -> Mono.just(\"s\");",
+            "}")
+        .doTest();
+  }
+
+  /** A {@link BugChecker} that simply delegates to {@link IsFunctionReturningMono}. */
+  @BugPattern(summary = "Flags expressions matched by `IsFunctionReturningMono`", severity = ERROR)
+  public static final class MatcherTestChecker extends AbstractMatcherTestChecker {
+    private static final long serialVersionUID = 1L;
+
+    // XXX: This is a false positive reported by Checkstyle. See
+    // https://github.com/checkstyle/checkstyle/issues/10161#issuecomment-1242732120.
+    @SuppressWarnings("RedundantModifier")
+    public MatcherTestChecker() {
+      super(new IsFunctionReturningMono());
+    }
+  }
+}