Add a new check: ProvidesMethodOutsideOfModule. This detects when

@provides methods are defined outside of Module classes.

MOE_MIGRATED_REVID=131638455

core/pom.xml

@@ -154,6 +154,12 @@
       <version>4.0-beta5</version>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>com.google.gwt.inject</groupId>
+      <artifactId>gin</artifactId>
+      <version>2.1.2</version>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>org.mockito</groupId>
       <artifactId>mockito-core</artifactId>

core/src/main/java/com/google/errorprone/bugpatterns/inject/guice/ProvidesMethodOutsideOfModule.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2016 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.inject.guice;
+
+import static com.google.errorprone.BugPattern.Category.GUICE;
+import static com.google.errorprone.BugPattern.MaturityLevel.EXPERIMENTAL;
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.enclosingClass;
+import static com.google.errorprone.matchers.Matchers.isSubtypeOf;
+import static com.google.errorprone.matchers.Matchers.isType;
+import static com.google.errorprone.matchers.Matchers.not;
+
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.AnnotationTreeMatcher;
+import com.google.errorprone.fixes.SuggestedFix;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.matchers.Matchers;
+import com.sun.source.tree.AnnotationTree;
+import com.sun.source.tree.ClassTree;
+
+/** @author glorioso@google.com (Nick Glorioso) */
+@BugPattern(
+  name = "ProvidesMethodOutsideOfModule",
+  summary = "@Provides methods need to be declared in a Module to have any effect.",
+  explanation =
+      "Guice `@Provides` methods annotate methods that are used as a means of declaring"
+          + " bindings. However, this is only helpful inside of a module. Methods outside of these"
+          + " modules are not used for binding declaration.",
+  category = GUICE,
+  severity = ERROR,
+  maturity = EXPERIMENTAL
+)
+public class ProvidesMethodOutsideOfModule extends BugChecker implements AnnotationTreeMatcher {
+  private static final Matcher<AnnotationTree> PROVIDES_ANNOTATION_ON_METHOD_OUTSIDE_OF_MODULE =
+      allOf(
+          isType("com.google.inject.Provides"),
+          enclosingClass(
+              not(
+                  Matchers.<ClassTree>anyOf(
+                      isSubtypeOf("com.google.inject.Module"),
+                      isSubtypeOf("com.google.gwt.inject.client.GinModule")))));
+
+  @Override
+  public Description matchAnnotation(AnnotationTree annotation, VisitorState state) {
+    if (PROVIDES_ANNOTATION_ON_METHOD_OUTSIDE_OF_MODULE.matches(annotation, state)) {
+      return describeMatch(annotation, SuggestedFix.delete(annotation));
+    }
+    return Description.NO_MATCH;
+  }
+}

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

@@ -170,6 +170,7 @@
 import com.google.errorprone.bugpatterns.inject.guice.InjectOnFinalField;
 import com.google.errorprone.bugpatterns.inject.guice.OverridesGuiceInjectableMethod;
 import com.google.errorprone.bugpatterns.inject.guice.OverridesJavaxInjectableMethod;
+import com.google.errorprone.bugpatterns.inject.guice.ProvidesMethodOutsideOfModule;
 import com.google.errorprone.bugpatterns.threadsafety.DoubleCheckedLocking;
 import com.google.errorprone.bugpatterns.threadsafety.GuardedByChecker;
 import com.google.errorprone.bugpatterns.threadsafety.GuardedByValidator;
@@ -368,6 +369,7 @@ public static ScannerSupplier errorChecks() {
           PrimitiveArrayPassedToVarargsMethod.class,
           PrivateConstructorForUtilityClass.class,
           PrivateConstructorForNoninstantiableModule.class,
+          ProvidesMethodOutsideOfModule.class,
           ProtoStringFieldReferenceEquality.class,
           RedundantThrows.class,
           RemoveUnusedImports.class,

core/src/test/java/com/google/errorprone/bugpatterns/inject/guice/ProvidesMethodOutsideOfModuleTest.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2016 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.inject.guice;
+
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** @author glorioso@google.com (Nick Glorioso) */
+@RunWith(JUnit4.class)
+public class ProvidesMethodOutsideOfModuleTest {
+  private CompilationTestHelper compilationHelper;
+
+  @Before
+  public void setUp() {
+    compilationHelper =
+        CompilationTestHelper.newInstance(ProvidesMethodOutsideOfModule.class, getClass());
+  }
+
+  @Test
+  public void testPositiveCase() throws Exception {
+    compilationHelper.addSourceFile("ProvidesMethodOutsideOfModulePositiveCases.java").doTest();
+  }
+
+  @Test
+  public void testNegativeCase() throws Exception {
+    compilationHelper.addSourceFile("ProvidesMethodOutsideOfModuleNegativeCases.java").doTest();
+  }
+}

core/src/test/java/com/google/errorprone/bugpatterns/inject/guice/testdata/ProvidesMethodOutsideOfModuleNegativeCases.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2016 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.inject.guice.testdata;
+
+import com.google.gwt.inject.client.AbstractGinModule;
+import com.google.gwt.inject.client.GinModule;
+import com.google.gwt.inject.client.binder.GinBinder;
+import com.google.inject.AbstractModule;
+import com.google.inject.Binder;
+import com.google.inject.Module;
+import com.google.inject.Provides;
+
+/** Tests for {@code ProvidesMethodOutsideOfModule} */
+public class ProvidesMethodOutsideOfModuleNegativeCases {
+
+  /** Regular module */
+  class Module1 extends AbstractModule {
+    @Override
+    protected void configure() {}
+
+    @Provides
+    int providesFoo() {
+      return 42;
+    }
+  }
+
+  /** implements the Module interface directly */
+  class Module2 implements Module {
+    @Override
+    public void configure(Binder binder) {}
+
+    @Provides
+    int providesFoo() {
+      return 42;
+    }
+  }
+
+  /** Regular GinModule */
+  class GinModule1 extends AbstractGinModule {
+
+    @Override
+    protected void configure() {}
+
+    @Provides
+    int providesFoo() {
+      return 42;
+    }
+  }
+
+  /** Implements the GinModule interface directly */
+  class GinModule2 implements GinModule {
+    @Override
+    public void configure(GinBinder binder) {}
+
+    @Provides
+    int providesFoo() {
+      return 42;
+    }
+  }
+}

core/src/test/java/com/google/errorprone/bugpatterns/inject/guice/testdata/ProvidesMethodOutsideOfModulePositiveCases.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2016 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.inject.guice.testdata;
+
+import com.google.inject.AbstractModule;
+import com.google.inject.Provides;
+
+/** Tests for {@code ProvidesMethodOutsideOfModule} */
+public class ProvidesMethodOutsideOfModulePositiveCases {
+
+  /** Random class contains a provides method. */
+  public class TestClass1 {
+    // BUG: Diagnostic contains: remove
+    @Provides
+    void providesBlah() {}
+  }
+
+  /** Module contains an anonymous inner with a Provides method. */
+  public class TestModule extends AbstractModule {
+    @Override
+    protected void configure() {
+      Object x =
+          new Object() {
+            // BUG: Diagnostic contains: remove
+            @Provides
+            void providesBlah() {}
+          };
+    }
+  }
+
+  /** Class has inner module class */
+  public class TestClass2 {
+    class NestedModule extends AbstractModule {
+      @Override
+      protected void configure() {}
+
+      @Provides
+      int thisIsOk() {
+        return 42;
+      }
+    }
+
+    // BUG: Diagnostic contains: remove
+    @Provides
+    int thisIsNotOk() {
+      return 42;
+    }
+  }
+}