Discourage public Foo stream() where Foo does _not_ end with "Stream"

PiperOrigin-RevId: 390684609

core/src/main/java/com/google/errorprone/bugpatterns/PublicApiNamedStreamShouldReturnStream.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2021 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.errorprone.bugpatterns;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.methodHasVisibility;
+import static com.google.errorprone.matchers.Matchers.methodIsNamed;
+
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.matchers.MethodVisibility;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.MethodTree;
+import com.sun.tools.javac.code.Type;
+
+/**
+ * Checks if public APIs named "stream" returns a type whose name ends with Stream.
+ *
+ * @author sauravtiwary@google.com (Saurav Tiwary)
+ */
+@BugPattern(
+    name = "PublicApiNamedStreamShouldReturnStream",
+    summary =
+        "Public methods named stream() are generally expected to return a type whose name ends with"
+            + " Stream. Consider choosing a different method name instead.",
+    severity = SUGGESTION)
+public class PublicApiNamedStreamShouldReturnStream extends BugChecker
+    implements MethodTreeMatcher {
+  private static final String STREAM = "stream";
+
+  private static final Matcher<MethodTree> CONFUSING_PUBLIC_API_STREAM_MATCHER =
+      allOf(
+          methodIsNamed(STREAM),
+          methodHasVisibility(MethodVisibility.Visibility.PUBLIC),
+          PublicApiNamedStreamShouldReturnStream::returnTypeDoesNotEndsWithStream);
+
+  private static boolean returnTypeDoesNotEndsWithStream(
+      MethodTree methodTree, VisitorState state) {
+    Type returnType = ASTHelpers.getSymbol(methodTree).getReturnType();
+
+    // Constructors have no return type.
+    return returnType != null && !returnType.tsym.getSimpleName().toString().endsWith("Stream");
+  }
+
+  @Override
+  public Description matchMethod(MethodTree tree, VisitorState state) {
+    if (!CONFUSING_PUBLIC_API_STREAM_MATCHER.matches(tree, state)) {
+      return Description.NO_MATCH;
+    }
+
+    return describeMatch(tree);
+  }
+}

core/src/main/java/com/google/errorprone/scanner/BuiltInCheckerSuppliers.java

@@ -278,6 +278,7 @@
 import com.google.errorprone.bugpatterns.ProtoTruthMixedDescriptors;
 import com.google.errorprone.bugpatterns.ProtocolBufferOrdinal;
 import com.google.errorprone.bugpatterns.ProtosAsKeyOfSetOrMap;
+import com.google.errorprone.bugpatterns.PublicApiNamedStreamShouldReturnStream;
 import com.google.errorprone.bugpatterns.PublicConstructorForAbstractClass;
 import com.google.errorprone.bugpatterns.RandomCast;
 import com.google.errorprone.bugpatterns.RandomModInteger;
@@ -1036,6 +1037,7 @@ public static ScannerSupplier errorChecks() {
           PrivateConstructorForNoninstantiableModule.class,
           PrivateConstructorForUtilityClass.class,
           ProtosAsKeyOfSetOrMap.class,
+          PublicApiNamedStreamShouldReturnStream.class,
           PublicConstructorForAbstractClass.class,
           QualifierWithTypeUse.class,
           RedundantCondition.class,

core/src/test/java/com/google/errorprone/bugpatterns/PublicApiNamedStreamShouldReturnStreamTest.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright 2021 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.errorprone.bugpatterns;
+
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Unit tests for {@link PublicApiNamedStreamShouldReturnStream}. */
+@RunWith(JUnit4.class)
+public class PublicApiNamedStreamShouldReturnStreamTest {
+
+  private CompilationTestHelper compilationHelper;
+
+  @Before
+  public void setup() {
+    compilationHelper =
+        CompilationTestHelper.newInstance(PublicApiNamedStreamShouldReturnStream.class, getClass());
+  }
+
+  @Test
+  public void abstractMethodPositiveCase() {
+    compilationHelper
+        .addSourceLines(
+            "in/Test.java",
+            "public abstract class Test {",
+            "  // BUG: Diagnostic contains: PublicApiNamedStreamShouldReturnStream",
+            "  public abstract int stream();",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  public void regularMethodPositiveCase() {
+    compilationHelper
+        .addSourceLines(
+            "in/Test.java",
+            "public class Test {",
+            "  // BUG: Diagnostic contains: PublicApiNamedStreamShouldReturnStream",
+            "  public String stream() { return \"hello\";}",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  public void compliantNegativeCase() {
+    compilationHelper
+        .addSourceLines(
+            "in/Test.java",
+            "import java.util.stream.Stream;",
+            "public abstract class Test {",
+            "  public abstract Stream<Integer> stream();",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  public void differentNameNegativeCase() {
+    compilationHelper
+        .addSourceLines(
+            "in/Test.java",
+            "public class Test {",
+            "  public int differentMethodName() { return 0; }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  public void privateMethodNegativeCase() {
+    compilationHelper
+        .addSourceLines(
+            "in/Test.java",
+            "public class Test {",
+            "  private String stream() { return \"hello\"; }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  public void returnTypeEndingWithStreamNegativeCase() {
+    compilationHelper
+        .addSourceLines(
+            "in/Test.java",
+            "public class Test {",
+            "  private static class TestStream {}",
+            "  public TestStream stream() { return new TestStream(); }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  public void returnTypeNotEndingWithStreamPositiveCase() {
+    compilationHelper
+        .addSourceLines(
+            "in/Test.java",
+            "public class Test {",
+            "  private static class TestStreamRandomSuffix {}",
+            "  // BUG: Diagnostic contains: PublicApiNamedStreamShouldReturnStream",
+            "  public TestStreamRandomSuffix stream() { return new TestStreamRandomSuffix(); }",
+            "}")
+        .doTest();
+  }
+}