re-land fix #27110 with proper DDC side of changes

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

 // Copyright (c) 2015, 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.
 
 library analyzer.test.src.task.strong.checker_test;
 
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'strong_test_helper.dart';
 
@@ skipping 252 matching lines @@
 
 class D {
   D operator +(D d) => null;
 }
 
 foo() => new A();
 
 test() {
   int x = 0;
   x += 5;
-  /*error:STATIC_TYPE_ERROR*/x += /*error:INVALID_ASSIGNMENT*/3.14;
+  x += /*error:INVALID_ASSIGNMENT*/3.14;
 
   double y = 0.0;
   y += 5;
   y += 3.14;
 
   num z = 0;
   z += 5;
   z += 3.14;
 
   x = /*info:DOWN_CAST_IMPLICIT*/x + z;
-  x += /*info:DOWN_CAST_IMPLICIT*/z;
+  /*info:DOWN_CAST_IMPLICIT_ASSIGN*/x += z;
   y = y + z;
   y += z;
 
   dynamic w = 42;
-  x += /*info:DYNAMIC_CAST*/w;
+  /*info:DOWN_CAST_IMPLICIT_ASSIGN*/x += /*info:DYNAMIC_CAST*/w;
   y += /*info:DYNAMIC_CAST*/w;
   z += /*info:DYNAMIC_CAST*/w;
 
   A a = new A();
   B b = new B();
   var c = foo();
   a = a * b;
   a *= b;
   a *= /*info:DYNAMIC_CAST*/c;
   a /= b;
   a ~/= b;
   a %= b;
   a += b;
   a += /*error:ARGUMENT_TYPE_NOT_ASSIGNABLE*/a;
   a -= b;
-  /*error:STATIC_TYPE_ERROR*/b -= /*error:INVALID_ASSIGNMENT*/b;
+  b -= /*error:INVALID_ASSIGNMENT*/b;
   a <<= b;
   a >>= b;
   a &= b;
   a ^= b;
   a |= b;
   /*info:DYNAMIC_INVOKE*/c += b;
 
   var d = new D();
   a[b] += d;
   a[/*info:DYNAMIC_CAST*/c] += d;
@@ skipping 50 matching lines @@
   final List<Q> list = /*info:INFERRED_TYPE_LITERAL*/const [];
   final Map<Q, Iterable<Q>> m =  /*info:INFERRED_TYPE_LITERAL*/const {};
   const C();
 }
 main() {
   const SetEquality<String>();
 }
     ''');
   }
 
+  void test_compoundAssignment_returnsDynamic() {
+    checkFile(r'''
+class Foo {
+  operator +(other) => null;
+}
+
+main() {
+  var foo = new Foo();
+  foo = /*info:DYNAMIC_CAST*/foo + 1;
+  /*info:DYNAMIC_CAST*/foo += 1;
+}
+    ''');
+  }
+
   void test_constructorInvalid() {
     // Regression test for https://github.com/dart-lang/sdk/issues/26695
     checkFile('''
 class A {
   B({ /*error:FIELD_INITIALIZER_OUTSIDE_CONSTRUCTOR*/this.test: 1.0 }) {}
   final double test = 0.0;
 }
 ''');
   }
 
@@ skipping 3452 matching lines @@
   }
 
   void test_unaryOperators() {
     checkFile('''
 class A {
   A operator ~() => null;
   A operator +(int x) => null;
   A operator -(int x) => null;
   A operator -() => null;
 }
+class B extends A {}
 
 foo() => new A();
 
 test() {
   A a = new A();
+  B b = new B();
   var c = foo();
   dynamic d;
 
   ~a;
   (/*info:DYNAMIC_INVOKE*/~d);
 
   !/*error:NON_BOOL_NEGATION_EXPRESSION*/a;
   !/*info:DYNAMIC_CAST*/d;
 
   -a;
   (/*info:DYNAMIC_INVOKE*/-d);
 
   ++a;
   --a;
   (/*info:DYNAMIC_INVOKE*/++d);
   (/*info:DYNAMIC_INVOKE*/--d);
 
   a++;
   a--;
   (/*info:DYNAMIC_INVOKE*/d++);
   (/*info:DYNAMIC_INVOKE*/d--);
+
+  ++/*info:DOWN_CAST_IMPLICIT_ASSIGN*/b;
+  --/*info:DOWN_CAST_IMPLICIT_ASSIGN*/b;
+  /*info:DOWN_CAST_IMPLICIT_ASSIGN*/b++;
+  /*info:DOWN_CAST_IMPLICIT_ASSIGN*/b--;

[Leaf, 2016/09/22 22:30:17]

Maybe test the case where we are assigning the result to something requiring a
downcast?

[Jennifer Messerly, 2016/09/22 22:32:19]

great idea! Adding.

 }''');
   }
 
   void test_unboundRedirectingConstructor() {
     // This is a regression test for https://github.com/dart-lang/sdk/issues/25071
     checkFile('''
 class Foo {
   Foo() : /*error:REDIRECT_GENERATIVE_TO_MISSING_CONSTRUCTOR*/this.init();
 }
  ''');
@@ skipping 30 matching lines @@
 void _addMetaLibrary() {
   addFile(r'''
 library meta;
 class _Checked { const _Checked(); }
 const Object checked = const _Checked();
 
 class _Virtual { const _Virtual(); }
 const Object virtual = const _Virtual();
     ''', name: '/meta.dart');
 }