Emit forwarding getter/setter when overriding just a getter or setter.

lib/src/compiler/code_generator.dart

Index: lib/src/compiler/code_generator.dart
diff --git a/lib/src/compiler/code_generator.dart b/lib/src/compiler/code_generator.dart
index 199a629e74a9a4fbdc601c56b03680ae25dd8ca9..ac52c9be15d358240986d78807deb9dcaec9a9ed 100644
--- a/lib/src/compiler/code_generator.dart
+++ b/lib/src/compiler/code_generator.dart
@@ -73,6 +73,11 @@ class CodeGenerator extends GeneralizingAstVisitor
   /// need storage slots.
   HashSet<FieldElement> _fieldsNeedingStorage;
 
+  /// Information that indicates which properties are partial overrides of
+  /// superclass properties (e.g., getter-only override of a setter or
+  /// vice-versa).
+  HashSet<FieldElement> _propertyOverrides;

[Jennifer Messerly, 2016/04/20 21:16:39]

if following my suggestion in the next file, this and _fieldsNeedingStorage
won't be needed :)

[Harry Terkelsen, 2016/04/20 23:33:27]

Acknowledged.

+
   /// The variable for the target of the current `..` cascade expression.
   ///
   /// Usually a [SimpleIdentifier], but it can also be other expressions
@@ -184,7 +189,10 @@ class CodeGenerator extends GeneralizingAstVisitor
       throw new StateError('Can only call emitModule once.');
     }
 
-    _fieldsNeedingStorage = findFieldsNeedingStorage(
+    _fieldsNeedingStorage = new HashSet<FieldElement>();
+    _propertyOverrides = new HashSet<FieldElement>();
+
+    findFieldsNeedingStorage(_fieldsNeedingStorage, _propertyOverrides,
         compilationUnits.map((u) => u.element), _extensionTypes);
 
     // Transform the AST to make coercions explicit.
@@ -782,6 +790,28 @@ class CodeGenerator extends GeneralizingAstVisitor
       } else if (m is MethodDeclaration) {
         jsMethods.add(_emitMethodDeclaration(type, m));
 
+        var methodElement = m.element;
+        if (methodElement is PropertyAccessorElement) {

[Jennifer Messerly, 2016/04/20 21:16:39]

it would be good to refactor this into a method

_emitSuperAccessorWrapper?

[Harry Terkelsen, 2016/04/20 23:33:27]

Done.

+          var fieldElement = methodElement.variable;
+          if (_propertyOverrides.contains(fieldElement)) {

[Jennifer Messerly, 2016/04/20 21:16:39]

here we can just call make a call to ask if our property needed an override. 

+            // Generate a corresponding virtual getter / setter.
+            var name = _elementMemberName(methodElement,
+                allowExtensions: _extensionTypes.contains(type.element));
+            if (m.isGetter) {
+              // Generate a setter
+              var value = new JS.TemporaryId('value');
+              var fn = new JS.Fun(

[Jennifer Messerly, 2016/04/20 21:16:39]

this could be done a bit simpler:

var fn = js.call('function(#) { super.# = #; }', [value, name, value]);

In this case, we know there's no user variable named "value" in scope, so you
could even skip the temp:

var fn = js.call('function(value) { super.# = value; }', [name]);

[Harry Terkelsen, 2016/04/20 23:33:28]

Done.

+                  [value], js.statement('{ super[#] = #; }', [name, value]));
+              jsMethods.add(new JS.Method(name, fn, isSetter: true));
+            } else {
+              // Generate a getter
+              var fn =

[Jennifer Messerly, 2016/04/20 21:16:39]

same here. if using js_ast, I find it's easier to just use it the maximum it
can.

BTW, the reason we need the `new JS.Method` explicitly is I didn't make a
`js.method` helper yet. But we can parse methods so it likely wouldn't be hard,
if we wanted to do that. That would simplify even further:

    jsMethods.add(js.method('#() { return super.#; }', name, name));

I think the "hard" part would be JS_AST parser allowing #-interpolation for the
method name.

[Harry Terkelsen, 2016/04/20 23:33:27]

Done.

+                  new JS.Fun([], js.statement('{ return super[#]; }', [name]));
+              jsMethods.add(new JS.Method(name, fn, isGetter: true));
+            }
+          }
+        }
+
         if (!hasJsPeer && m.isGetter && m.name.name == 'iterator') {
           hasIterator = true;
           jsMethods.add(_emitIterable(type));