emit 'this.x' when 'super.x' accesses a field

lib/src/compiler/code_generator.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.
 
 import 'dart:collection' show HashMap, HashSet;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/dart/ast/token.dart' show Token, TokenType;
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 3024 matching lines @@
     }
 
     // If the target could be `null`, we need static dispatch.
     // If the target may be an extension type, we also use static dispatch
     // as we don't symbolize object properties like hashCode.
     return isNullable(target) ||
         (_extensionTypes.contains(type.element) && target is! SuperExpression);
   }
 
   /// Shared code for [PrefixedIdentifier] and [PropertyAccess].
   JS.Expression _emitGet(Expression target, SimpleIdentifier memberId) {

[Jennifer Messerly, 2016/04/18 21:10:12]

Suggestion: if you want to rename this "_emitProperty" or "_emitAccess" I think
that would be good too.

it is called as part of generating gets or sets, so the name is misleading :)

[Harry Terkelsen, 2016/04/18 21:28:58]

Done.

     var member = memberId.staticElement;
     if (member is PropertyAccessorElement) {
       member = (member as PropertyAccessorElement).variable;
     }
     bool isStatic = member is ClassMemberElement && member.isStatic;
     var name = _emitMemberName(memberId.name,
         type: getStaticType(target), isStatic: isStatic);
     if (DynamicInvoke.get(target)) {
       return js.call('dart.dload(#, #)', [_visit(target), name]);
     }
 
+    if (target is SuperExpression &&
+        member is FieldElement &&
+        member.getter.isSynthetic &&
+        member.setter.isSynthetic) {

[Jennifer Messerly, 2016/04/18 21:10:12]

Oops I didn't reply fast enough to the original thread :)
Here's what I was going to say in reply to Vijay:

I think the idea is that a field will always has an implied getter. We have
read-only fields (final int x = ...) but not write-only fields :). So checking
the getter is safe.

So the old code LGTM but not the new code :). I don't think a setter is
guaranteed to be there if you have a final field? Either way would be good to
add a test for it.

if it helps I can poke around in Analyzer and see if they have a better way of
seeing what is an "actual field". I'm a little worried if the `isSynthetic` bit
is reliable or if the check is necessary. But maybe it is.

[Jennifer Messerly, 2016/04/18 21:20:13]

Ah, so you should be able to just check `!member.isSynthetic` -- in other words,
check that the field itself is not synthetic. My grepping through Analyzer
(specifically pkg/analyzer/lib/src/dart/element/builder.dart) leads me to
believe that should work :)

[Harry Terkelsen, 2016/04/18 21:28:58]

On final fields, setter is null. I'll just check if member is synthetic per your
suggestion. I also added a test.

+      // If super.x is actually a field, then x is an instance property since
+      // subclasses cannot override x.
+      return js.call('this.#', [name]);
+    }
+
     String code;
     if (member != null && member is MethodElement && !isStatic) {
       // Tear-off methods: explicitly bind it.
       if (target is SuperExpression) {
         return js.call('dart.bind(this, #, #.#)', [name, _visit(target), name]);
       } else if (_requiresStaticDispatch(target, memberId.name)) {
         var type = member.type;
         var clos = js.call('dart.#.bind(#)', [name, _visit(target)]);
         return js.call('dart.fn(#, #)', [clos, _emitFunctionTypeParts(type)]);
       }
@@ skipping 682 matching lines @@
 }
 
 bool isLibraryPrefix(Expression node) =>
     node is SimpleIdentifier && node.staticElement is PrefixElement;
 
 LibraryElement _getLibrary(AnalysisContext c, String uri) =>
     c.computeLibraryElement(c.sourceFactory.forUri(uri));
 
 bool _isDartRuntime(LibraryElement l) =>
     l.isInSdk && l.source.uri.toString() == 'dart:_runtime';