Allowing e of any type in void f(...) => e in the analyzer.

Re-land, now including adjustment of two tests in pkg/analyzer/test.

[email protected]

Review-Url: https://codereview.chromium.org/2870363003 .

Author: eernstg

pkg/analyzer/lib/src/generated/error_verifier.dart

@@ -660,7 +660,8 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
           function is PropertyAccessorElement &&
           function.isSetter;
       if (!isSetterWithImplicitReturn) {
-        _checkForReturnOfInvalidType(node.expression, expectedReturnType);
+        _checkForReturnOfInvalidType(node.expression, expectedReturnType,
+            isArrowFunction: true);
       }
       return super.visitExpressionFunctionBody(node);
     } finally {
@@ -5598,7 +5599,8 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
    * See [StaticTypeWarningCode.RETURN_OF_INVALID_TYPE].
    */
   void _checkForReturnOfInvalidType(
-      Expression returnExpression, DartType expectedReturnType) {
+      Expression returnExpression, DartType expectedReturnType,
+      {bool isArrowFunction = false}) {
     if (_enclosingFunction == null) {
       return;
     }
@@ -5610,6 +5612,10 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
     }
     DartType staticReturnType = _computeReturnTypeForMethod(returnExpression);
     if (expectedReturnType.isVoid) {
+      if (isArrowFunction) {
+        // "void f(..) => e" admits all types for "e".
+        return;
+      }
       if (staticReturnType.isVoid ||
           staticReturnType.isDynamic ||
           staticReturnType.isBottom ||

pkg/analyzer/test/generated/static_type_warning_code_test.dart

@@ -1121,9 +1121,8 @@ class A {
         [StaticTypeWarningCode.RETURN_OF_INVALID_TYPE]);
   }
 
-  test_returnOfInvalidType_expressionFunctionBody_void() async {
-    await assertErrorsInCode(
-        "void f() => 42;", [StaticTypeWarningCode.RETURN_OF_INVALID_TYPE]);
+  test_returnOfInvalidType_not_issued_for_expressionFunctionBody_void() async {
+    await assertNoErrorsInCode("void f() => 42;");
   }
 
   test_returnOfInvalidType_function() async {

pkg/analyzer/test/src/task/strong/checker_test.dart

@@ -3536,7 +3536,7 @@ void voidFn() => null;
 class A {
   set a(y) => 4;
   set b(y) => voidFn();
-  void set c(y) => /*error:RETURN_OF_INVALID_TYPE*/4;
+  void set c(y) => 4;
   void set d(y) => voidFn();
   /*warning:NON_VOID_RETURN_FOR_SETTER*/int set e(y) => 4;
   /*warning:NON_VOID_RETURN_FOR_SETTER*/int set f(y) =>

tests/language/void_arrow_return_test.dart

@@ -0,0 +1,11 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Testing that a void arrow function is allowed to return any type of value.
+
+void foo() => 42;
+
+main() {
+  foo();
+}

tests/language/void_block_return_test.dart

@@ -0,0 +1,14 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Testing that a void block function is not allowed to `return e`
+// where `e` is non-void.
+
+void foo() {
+  return 42; //# 00: static type warning
+}
+
+main() {
+  foo();
+}