fixes #231, mixin application (aka ClassTypeAlias) implicit ctors

lib/src/codegen/js_codegen.dart

Index: lib/src/codegen/js_codegen.dart
diff --git a/lib/src/codegen/js_codegen.dart b/lib/src/codegen/js_codegen.dart
index 55731d2e74ff4fb5290e6dd956894c5a4d9ceea8..3b6d287ba550f7d6f27d18797d46e32dfa46cd2b 100644
--- a/lib/src/codegen/js_codegen.dart
+++ b/lib/src/codegen/js_codegen.dart
@@ -332,8 +332,23 @@ class JSCodegenVisitor extends GeneralizingAstVisitor {
     // If we've already emitted this class, skip it.

[vsm, 2015/06/19 23:20:40]

Is this comment still valid?

[Jennifer Messerly, 2015/06/22 15:55:44]

Good catch, removed (from 3 places!)

     var element = node.element;
 
+    // Forward all generative constructors from the base class.
+    var body = [];
+
+    var supertype = element.supertype;
+    if (!supertype.isObject) {
+      for (var ctor in element.constructors) {
+        var parentCtor = supertype.lookUpConstructor(ctor.name, ctor.library);
+        var fun = js.call('function() { super.#(...#); }', [

[vsm, 2015/06/19 23:20:40]

It'd be nice to have the args here to show the actual API.

[Jennifer Messerly, 2015/06/22 15:55:44]

Agreed. However, there are a few reasons for not doing that:
* we don't have a FormalParameterList here, just the element model, so can't
reuse existing visit* code.
* we don't have an ArgumentList, so we'd have to emit parameters in argument
position. Happens to be valid at the moment, probably won't be when we have
destructuring.
* it's less error prone to do forward all arguments this way. It avoids obscure
bugs that could happen, like "default value is incorrect in mixin application
constructor super calls" or "named arguments don't work in mixin application" :)

In the very long term I'm in favor of this kind of readability tweak, but I
think we have a lot of higher priority things to do first.

+          _constructorName(parentCtor),
+          new JS.Identifier('arguments', allowRename: false)
+        ]);
+        body.add(new JS.Method(_constructorName(ctor), fun));
+      }
+    }
+
     var classDecl = new JS.ClassDeclaration(new JS.ClassExpression(
-        new JS.Identifier(element.name), _classHeritage(element), []));
+        new JS.Identifier(element.name), _classHeritage(element), body));
 
     return _finishClassDef(element.type, classDecl);
   }