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

pkg/dev_compiler/lib/src/compiler/code_generator.dart

Index: pkg/dev_compiler/lib/src/compiler/code_generator.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/code_generator.dart b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
index c62aa11e635e922f45cb7278f7ae3701ea1a856d..54f4b6fd5741d5b8f1aecfdb910a2a55b657e225 100644
--- a/pkg/dev_compiler/lib/src/compiler/code_generator.dart
+++ b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
@@ -1,4 +1,5 @@
 // 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.
 
@@ -29,7 +30,7 @@ import 'package:analyzer/src/summary/summarize_elements.dart'
     show PackageBundleAssembler;
 import 'package:analyzer/src/summary/summary_sdk.dart';
 import 'package:analyzer/src/task/strong/ast_properties.dart'
-    show isDynamicInvoke, setIsDynamicInvoke;
+    show isDynamicInvoke, setIsDynamicInvoke, getImplicitAssignmentCast;
 import 'package:path/path.dart' show separator;
 
 import '../closure/closure_annotator.dart' show ClosureAnnotator;
@@ -559,19 +560,13 @@ class CodeGenerator extends GeneralizingAstVisitor
     var type = _emitType(to,
         nameType: options.nameTypeTests || options.hoistTypeTests,
         hoistType: options.hoistTypeTests);
-    if (isReifiedCoercion(node)) {
+    if (CoercionReifier.isImplicitCast(node)) {
       return js.call('#._check(#)', [type, jsFrom]);
     } else {
       return js.call('#.as(#)', [type, jsFrom]);
     }
   }
 
-  bool isReifiedCoercion(AstNode node) {
-    // TODO(sra): Find a better way to recognize reified coercion, since we
-    // can't set the isSynthetic attribute.
-    return (node is AsExpression) && (node.asOperator.offset == 0);
-  }
-
   @override
   visitIsExpression(IsExpression node) {
     // Generate `is` as `dart.is` or `typeof` depending on the RHS type.
@@ -1930,8 +1925,8 @@ class CodeGenerator extends GeneralizingAstVisitor
 
       var fun = new JS.Fun(
           params,
-          js.statement(
-              '{ return $newKeyword #(#); }', [_visit(redirect), params]),
+          js.statement('{ return $newKeyword #(#); }',
+              [_visit(redirect) as JS.Node, params]),
           returnType: returnType);
       return annotate(
           new JS.Method(name, fun, isStatic: true), node, node.element);
@@ -3014,9 +3009,12 @@ class CodeGenerator extends GeneralizingAstVisitor
     // (for example, x is IndexExpression) we evaluate those once.
     var vars = <JS.MetaLetVariable, JS.Expression>{};
     var lhs = _bindLeftHandSide(vars, left, context: context);
-    var inc = AstBuilder.binaryExpression(lhs, op, right);
-    inc.staticElement = element;
-    inc.staticType = getStaticType(left);
+    Expression inc = AstBuilder.binaryExpression(lhs, op, right)
+      ..staticElement = element
+      ..staticType = getStaticType(lhs);
+
+    var castTo = getImplicitAssignmentCast(left);
+    if (castTo != null) inc = CoercionReifier.castExpression(inc, castTo);
     return new JS.MetaLet(vars, [_emitSet(lhs, inc)]);
   }
 
@@ -4544,7 +4542,8 @@ class CodeGenerator extends GeneralizingAstVisitor
       }
     }
     if (tail.isEmpty) return _visit(node);
-    return js.call('dart.nullSafe(#, #)', [_visit(node), tail.reversed]);
+    return js.call(
+        'dart.nullSafe(#, #)', [_visit(node) as JS.Expression, tail.reversed]);
   }
 
   static Token _getOperator(Expression node) {
@@ -4697,8 +4696,8 @@ class CodeGenerator extends GeneralizingAstVisitor
       // dynamic dispatch
       var dynamicHelper = const {'[]': 'dindex', '[]=': 'dsetindex'}[name];
       if (dynamicHelper != null) {
-        return js.call(
-            'dart.$dynamicHelper(#, #)', [_visit(target), _visitList(args)]);
+        return js.call('dart.$dynamicHelper(#, #)',
+            [_visit(target) as JS.Expression, _visitList(args)]);
       } else {
         return js.call('dart.dsend(#, #, #)',
             [_visit(target), memberName, _visitList(args)]);
@@ -5052,7 +5051,7 @@ class CodeGenerator extends GeneralizingAstVisitor
     // TODO(jmesserly): we can likely make these faster.
     JS.Expression emitMap() {
       var entries = node.entries;
-      var mapArguments = null;
+      Object mapArguments = null;
       var type = node.staticType as InterfaceType;
       var typeArgs = type.typeArguments;
       var reifyTypeArgs = typeArgs.any((t) => !t.isDynamic);
@@ -5174,10 +5173,9 @@ class CodeGenerator extends GeneralizingAstVisitor
       if (op == '&&') return shortCircuit('# && #');
       if (op == '||') return shortCircuit('# || #');
     }
-    if (isReifiedCoercion(node)) {
-      AsExpression asNode = node;
-      assert(asNode.staticType == types.boolType);
-      return js.call('dart.test(#)', _visit(asNode.expression));
+    if (node is AsExpression && CoercionReifier.isImplicitCast(node)) {
+      assert(node.staticType == types.boolType);
+      return js.call('dart.test(#)', _visit(node.expression));
     }
     JS.Expression result = _visit(node);
     if (isNullable(node)) result = js.call('dart.test(#)', result);
@@ -5458,7 +5456,8 @@ String jsLibraryName(String libraryRoot, LibraryElement library) {
         uri.path.substring(libraryRoot.length).replaceAll('/', separator);
   } else {
     // We don't have a unique name.
-    throw 'Invalid library root. $libraryRoot does not contain ${uri.toFilePath()}';
+    throw 'Invalid library root. $libraryRoot does not contain ${uri
+        .toFilePath()}';
   }
   return pathToJSIdentifier(qualifiedPath);
 }
@@ -5479,10 +5478,12 @@ JS.LiteralString _propertyName(String name) => js.string(name, "'");
 /// everywhere in the tree where they are treated as the same variable.
 class TemporaryVariableElement extends LocalVariableElementImpl {
   final JS.Expression jsVariable;
+
   TemporaryVariableElement.forNode(Identifier name, this.jsVariable)
       : super.forNode(name);
 
   int get hashCode => identityHashCode(this);
+
   bool operator ==(Object other) => identical(this, other);
 }