Fix DDC errors on DDC

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 fc9137af6d91e2596ddc4aa528ccb6c9f9bc514e..a318daaf80da8f0083d347a302730afa60898250 100644
--- a/lib/src/codegen/js_codegen.dart
+++ b/lib/src/codegen/js_codegen.dart
@@ -523,8 +523,8 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
     // simple code size optimization.
     var parent = t.lookUpGetterInSuperclass('iterator', t.element.library);
     if (parent != null) return null;
-    parent = findSupertype(t, _implementsIterable);
-    if (parent != null) return null;
+    var parentType = findSupertype(t, _implementsIterable);
+    if (parentType != null) return null;
 
     // Otherwise, emit the adapter method, which wraps the Dart iterator in
     // an ES6 iterator.
@@ -1139,7 +1139,7 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
     // Get the original declaring element. If we had a property accessor, this
     // indirects back to a (possibly synthetic) field.
     var element = accessor;
-    if (element is PropertyAccessorElement) element = accessor.variable;
+    if (accessor is PropertyAccessorElement) element = accessor.variable;
 
     _loader.declareBeforeUse(element);
 
@@ -1149,7 +1149,8 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
     if (element is ClassElement ||
         element is DynamicElementImpl ||
         element is FunctionTypeAliasElement) {
-      return _emitTypeName(fillDynamicTypeArgs(element.type, types));
+      return _emitTypeName(
+          fillDynamicTypeArgs((element as dynamic).type, types));

[Paul Berry, 2015/06/01 22:00:45]

I'm curious why this change was necessary.  It seems counter-intuitive.

[Jennifer Messerly, 2015/06/01 22:17:38]

I don't think there's a common supertype of ClassElement and
FunctionTypeAliasElement that has the type getter. (Element does not have it).
This one trips me up occasionally.

And probably inference is causing `var element` to infer as Element, as that's
what SimpleIdentifier's staticElement is typed as.

[vsm, 2015/06/01 22:44:19]

Right, I don't think we have a common interface type with the "type" getter.

[Paul Berry, 2015/06/02 00:55:34]

Ah, ok.  I will look into whether it's possible to create a common interface
implemented by ClassElement, DynamicElementImpl, and FunctionTypeAliasElement
(maybe something like "TypeDefiningElement").  That way you could change this
code to a single "is" check and take advantage of type promotion, e.g.:

if (element is TypeDefiningElement) {
  return _emitTypeName(fillDynamicTypeArgs(element.type, types));
}

[Jennifer Messerly, 2015/06/02 16:28:58]

+1 that would be awesome!

     }
 
     // library member
@@ -1753,8 +1754,9 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
         // TODO(jmesserly): we'll likely need something that can handle a wider
         // variety of types, especially when we get to JS interop.
         var args = expr.argumentList.arguments;
-        if (args.isNotEmpty && args.first is SimpleStringLiteral) {
-          var types = args.first.stringValue;
+        var first = args.isNotEmpty ? args.first : null;
+        if (first is SimpleStringLiteral) {
+          var types = first.stringValue;
           if (!types.split('|').contains('Null')) {
             return true;
           }
@@ -2059,7 +2061,8 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
   /// Shared code for [PrefixedIdentifier] and [PropertyAccess].
   JS.Expression _emitGet(Expression target, SimpleIdentifier memberId) {
     var member = memberId.staticElement;
-    if (member is PropertyAccessorElement) member = member.variable;
+    if (member is PropertyAccessorElement) member =
+        (member as PropertyAccessorElement).variable;

[Jennifer Messerly, 2015/06/01 21:52:10]

This is going to be an analyzer hint because this cast is unnecessary, right?
That will be kind of annoying to see in the editor all the time (actually, won't
it break our presubmit too?)

Makes me think we need to fix DDC to understand promotion rules.

[vsm, 2015/06/01 21:59:36]

Actually, this one is an AnalyzerError.  Because member is modified in the body
of the if, no promotion.  This appears to be the letter of the law in the
spec....

[Jennifer Messerly, 2015/06/01 22:17:38]

oh, wow. crazy stuff.

small style nit: when "if" wraps to mutliline, usually use { ... } at that point

[vsm, 2015/06/01 22:44:19]

Done.

     bool isStatic = member is ClassMemberElement && member.isStatic;
     if (isStatic) {
       _loader.declareBeforeUse(member);
@@ -2246,7 +2249,7 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
   }
 
   JS.Statement _statement(Iterable stmts) {
-    var s = stmts is List ? stmts : new List<JS.Statement>.from(stmts);
+    List s = stmts is List ? stmts : new List<JS.Statement>.from(stmts);
     // TODO(jmesserly): empty block singleton?
     if (s.length == 0) return new JS.Block([]);
     if (s.length == 1) return s[0];