For ReferenceEquality-based checkers, understand that all proto gette…

…rs never

return null when making suggestions.

RELNOTES: ReferenceEquality and similar checks understand that proto getters
never return null

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=159963821

check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/AbstractNullnessPropagationTransfer.java

@@ -307,7 +307,7 @@ public final TransferResult<Nullness, LocalStore<Nullness>> visitMethodInvocatio
      * if I'm careful to give it its correct Nullness instead of hardcoding it to NONNULL as the
      * current code does. To avoid problems, we return a RegularTransferResult when possible.
      */
-    if (tryGetMethodSymbol(node.getTree()).isBoolean) {
+    if (tryGetMethodSymbol(node.getTree(), null).isBoolean) {
       ResultingStore thenStore = updateStore(input.getThenStore(), thenUpdates, bothUpdates);
       ResultingStore elseStore = updateStore(input.getElseStore(), elseUpdates, bothUpdates);
       return conditionalResult(

check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/MethodInfo.java

@@ -29,4 +29,6 @@ public interface MethodInfo {
   boolean isStatic();
 
   boolean isPrimitive();
+
+  boolean isKnownNonNullReturning();
 }

check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/NullnessPropagationTransfer.java

@@ -47,8 +47,12 @@
 import com.sun.source.util.Trees;
 import com.sun.tools.javac.code.Flags;
 import com.sun.tools.javac.code.Symbol;
+import com.sun.tools.javac.code.Symbol.ClassSymbol;
 import com.sun.tools.javac.code.Symbol.MethodSymbol;
+import com.sun.tools.javac.code.Symbol.TypeSymbol;
 import com.sun.tools.javac.code.Symbol.VarSymbol;
+import com.sun.tools.javac.code.Type;
+import com.sun.tools.javac.code.Types;
 import com.sun.tools.javac.processing.JavacProcessingEnvironment;
 import com.sun.tools.javac.tree.JCTree.JCFieldAccess;
 import com.sun.tools.javac.tree.JCTree.JCIdent;
@@ -193,6 +197,9 @@ public boolean apply(MethodInfo methodInfo) {
       if (methodInfo.isPrimitive()) {
         return true;
       }
+      if (methodInfo.isKnownNonNullReturning()) {
+        return true;
+      }
       if (CLASSES_WITH_NON_NULLABLE_RETURNS.contains(methodInfo.clazz())) {
         return true;
       }
@@ -473,7 +480,7 @@ Nullness visitMethodInvocation(
       LocalVariableUpdates thenUpdates,
       LocalVariableUpdates elseUpdates,
       LocalVariableUpdates bothUpdates) {
-    ClassAndMethod callee = tryGetMethodSymbol(node.getTree());
+    ClassAndMethod callee = tryGetMethodSymbol(node.getTree(), Types.instance(context));
     setReceiverNonnull(bothUpdates, node.getTarget().getReceiver(), callee);
     setUnconditionalArgumentNullness(bothUpdates, node.getArguments(), callee);
     setConditionalArgumentNullness(elseUpdates, node.getArguments(), callee);
@@ -575,10 +582,10 @@ private static ClassAndField tryGetFieldSymbol(Tree tree) {
     return null;
   }
 
-  static ClassAndMethod tryGetMethodSymbol(MethodInvocationTree tree) {
+  static ClassAndMethod tryGetMethodSymbol(MethodInvocationTree tree, Types types) {
     Symbol symbol = tryGetSymbol(tree.getMethodSelect());
     if (symbol instanceof MethodSymbol) {
-      return ClassAndMethod.make((MethodSymbol) symbol);
+      return ClassAndMethod.make((MethodSymbol) symbol, types);
     }
     return null;
   }
@@ -791,35 +798,69 @@ static final class ClassAndMethod implements Member, MethodInfo {
     final boolean isStatic;
     final boolean isPrimitive;
     final boolean isBoolean;
+    final boolean isNonNullReturning;
 
     private ClassAndMethod(
         String clazz,
         String method,
         List<String> annotations,
         boolean isStatic,
         boolean isPrimitive,
-        boolean isBoolean) {
+        boolean isBoolean,
+        boolean isNonNullReturning) {
       this.clazz = clazz;
       this.method = method;
       this.annotations = ImmutableList.copyOf(annotations);
       this.isStatic = isStatic;
       this.isPrimitive = isPrimitive;
       this.isBoolean = isBoolean;
+      this.isNonNullReturning = isNonNullReturning;
     }
 
-    static ClassAndMethod make(MethodSymbol symbol) {
-      List<? extends AnnotationMirror> annotationMirrors = symbol.getAnnotationMirrors();
+    static ClassAndMethod make(MethodSymbol methodSymbol, @Nullable Types types) {
+      List<? extends AnnotationMirror> annotationMirrors = methodSymbol.getAnnotationMirrors();
       List<String> annotations = new ArrayList<>(annotationMirrors.size());
       for (AnnotationMirror annotationMirror : annotationMirrors) {
         annotations.add(annotationMirror.getAnnotationType().toString());
       }
+
+      ClassSymbol clazzSymbol = (ClassSymbol) methodSymbol.owner;
+
       return new ClassAndMethod(
-          symbol.owner.getQualifiedName().toString(),
-          symbol.getSimpleName().toString(),
+          clazzSymbol.getQualifiedName().toString(),
+          methodSymbol.getSimpleName().toString(),
           annotations,
-          symbol.isStatic(),
-          symbol.getReturnType().isPrimitive(),
-          symbol.getReturnType().getTag() == BOOLEAN);
+          methodSymbol.isStatic(),
+          methodSymbol.getReturnType().isPrimitive(),
+          methodSymbol.getReturnType().getTag() == BOOLEAN,
+          knownNonNullMethod(methodSymbol, clazzSymbol, types));
+    }
+
+    private static boolean knownNonNullMethod(
+        MethodSymbol methodSymbol, ClassSymbol clazzSymbol, @Nullable Types types) {
+      if (types == null) {
+        return false;
+      }
+
+      // Proto getters are not null
+      if (methodSymbol.name.toString().startsWith("get")
+          && methodSymbol.params().isEmpty()
+          && !methodSymbol.isStatic()) {
+        Type type = clazzSymbol.type;
+        while (type != null) {
+          TypeSymbol typeSymbol = type.asElement();
+          if (typeSymbol == null) {
+            break;
+          }
+          if (typeSymbol
+              .getQualifiedName()
+              .contentEquals("com.google.protobuf.AbstractMessageLite")) {
+            return true;
+          }
+          type = types.supertype(type);
+        }
+      }
+      return false;
     }
 
     @Override
@@ -850,6 +891,11 @@ public List<String> annotations() {
     public boolean isPrimitive() {
       return isPrimitive;
     }
+
+    @Override
+    public boolean isKnownNonNullReturning() {
+      return isNonNullReturning;
+    }
   }
 
   static final class ClassAndField implements Member {

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

@@ -43,6 +43,33 @@ public class ReferenceEqualityTest {
   private final BugCheckerRefactoringTestHelper refactoringTestHelper =
       BugCheckerRefactoringTestHelper.newInstance(new ReferenceEquality(), getClass());
 
+  @Test
+  public void protoGetter_nonnull() throws Exception {
+    refactoringTestHelper
+        .addInput("proto/ProtoTest.java")
+        .expectUnchanged()
+        .addInputLines(
+            "in/Foo.java",
+            "import com.google.errorprone.bugpatterns.proto.ProtoTest.TestProtoMessage;",
+            "class Foo {",
+            "  void something(TestProtoMessage f1, TestProtoMessage f2) {",
+            "     boolean b = f1 == f2;",
+            "     b = f1.getMessage() == f2.getMessage();",
+            "  }",
+            "}")
+        .addOutputLines(
+            "out/Foo.java",
+            "import com.google.errorprone.bugpatterns.proto.ProtoTest.TestProtoMessage;",
+            "import java.util.Objects;",
+            "class Foo {",
+            "  void something(TestProtoMessage f1, TestProtoMessage f2) {",
+            "     boolean b = Objects.equals(f1, f2);",
+            "     b = f1.getMessage().equals(f2.getMessage());",
+            "  }",
+            "}")
+        .doTest();
+  }
+
   @Test
   public void negative_const() throws Exception {
     compilationHelper

core/src/test/java/com/google/errorprone/bugpatterns/testdata/proto/ProtoTest.java

@@ -19,6 +19,7 @@
 
 package com.google.errorprone.bugpatterns.proto;
 
+@SuppressWarnings("ReferenceEquality")
 public final class ProtoTest {
   private ProtoTest() {}