Type inference should always infer the return type of operator []= as…

… void. R=brianwilkerson@google.com, paulberry@google.com Bug: #31779 Change-Id: I1c396cce3f148585218e02ff4e41bc2f85cc924a #31638 Reviewed-on: https://dart-review.googlesource.com/32687 Reviewed-by: Paul Berry <paulberry@google.com> Reviewed-by: Brian Wilkerson <brianwilkerson@google.com> Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
dart-lang · Jan 9, 2018 · bb52d1a · bb52d1a
1 parent b264dc6
commit bb52d1a
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Showing 3 changed files with 53 additions and 4 deletions.
diff --git a/pkg/analyzer/lib/src/summary/link.dart b/pkg/analyzer/lib/src/summary/link.dart
@@ -1982,10 +1982,13 @@ abstract class ExecutableElementForLink extends Object
    * better return type).
    */
   DartType _computeDefaultReturnType() {
-    if (_unlinkedExecutable.kind == UnlinkedExecutableKind.setter &&
+    var kind = _unlinkedExecutable.kind;
+    var isMethod = kind == UnlinkedExecutableKind.functionOrMethod;
+    var isSetter = kind == UnlinkedExecutableKind.setter;
+    if ((isSetter || isMethod && _unlinkedExecutable.name == '[]=') &&
         (library as LibraryElementForLink)._linker.strongMode) {
-      // In strong mode, setters without an explicit return type are
-      // considered to return `void`.
+      // In strong mode, setters and `[]=` operators without an explicit
+      // return type are considered to return `void`.
       return VoidTypeImpl.instance;
     } else {
       return DynamicTypeImpl.instance;

diff --git a/pkg/analyzer/lib/src/task/strong_mode.dart b/pkg/analyzer/lib/src/task/strong_mode.dart
@@ -363,7 +363,7 @@ class InstanceMemberInferrer {
     //
     // Infer the return type.
     //
-    if (element.hasImplicitReturnType) {
+    if (element.hasImplicitReturnType && element.displayName != '[]=') {
       (element as ExecutableElementImpl).returnType =
           _computeReturnType(overriddenTypes.map((t) => t.returnType));
       if (element is PropertyAccessorElement) {

diff --git a/pkg/analyzer/test/src/task/strong/dart2_inference_test.dart b/pkg/analyzer/test/src/task/strong/dart2_inference_test.dart
@@ -6,6 +6,7 @@ import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
@@ -654,6 +655,51 @@ class C {
     assertType('f()) {} // top setter');
   }
 
+  test_implicitVoidReturnType_default() async {
+    var code = r'''
+class C {
+  set x(_) {}
+  operator []=(int index, double value) => null;
+}
+''';
+    var source = addSource(code);
+    var analysisResult = await computeAnalysisResult(source);
+    var unit = analysisResult.unit;
+
+    ClassElement c = unit.element.getType('C');
+
+    PropertyAccessorElement x = c.accessors[0];
+    expect(x.returnType, VoidTypeImpl.instance);
+
+    MethodElement operator = c.methods[0];
+    expect(operator.displayName, '[]=');
+    expect(operator.returnType, VoidTypeImpl.instance);
+  }
+
+  test_implicitVoidReturnType_derived() async {
+    var code = r'''
+class Base {
+  dynamic set x(_) {}
+  dynamic operator[]=(int x, int y) => null;
+}
+class Derived extends Base {
+  set x(_) {}
+  operator[]=(int x, int y) {}
+}''';
+    var source = addSource(code);
+    var analysisResult = await computeAnalysisResult(source);
+    var unit = analysisResult.unit;
+
+    ClassElement c = unit.element.getType('Derived');
+
+    PropertyAccessorElement x = c.accessors[0];
+    expect(x.returnType, VoidTypeImpl.instance);
+
+    MethodElement operator = c.methods[0];
+    expect(operator.displayName, '[]=');
+    expect(operator.returnType, VoidTypeImpl.instance);
+  }
+
   test_inferObject_whenDownwardNull() async {
     var code = r'''
 int f(void Function(Null) f2) {}