Create local alias for super class in --closure mode (issue #312)

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 8104a628f51c1dbc5fe6dfcd8ab8ebd0563e8fa0..bcd0eb579cd1309f234a6eda93ed9210064d511d 100644
--- a/lib/src/codegen/js_codegen.dart
+++ b/lib/src/codegen/js_codegen.dart
@@ -375,10 +375,10 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ClosureAnnotator {
       }
     }
 
-    var classDecl = new JS.ClassDeclaration(new JS.ClassExpression(
-        new JS.Identifier(element.name), _classHeritage(element), body));
+    var classExpr = new JS.ClassExpression(
+        new JS.Identifier(element.name), _classHeritage(element), body);
 
-    return _finishClassDef(element.type, classDecl);
+    return _finishClassDef(element.type, _emitClassDeclaration(classExpr));

[Jennifer Messerly, 2016/02/01 23:59:55]

The same fix is likely needed for ClassTypeAlias

[ochafik, 2016/02/03 19:41:33]

Done.

   }
 
   JS.Statement _emitJsType(String dartClassName, DartObject jsName) {
@@ -669,6 +669,25 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ClosureAnnotator {
     }
   }
 
+  _isQualifiedPath(JS.Expression node) =>
+      node is JS.Identifier ||
+      node is JS.PropertyAccess &&
+          _isQualifiedPath(node.receiver) &&
+          node.selector is JS.LiteralString;
+
+  JS.Statement _emitClassDeclaration(JS.ClassExpression cls) {

[Jennifer Messerly, 2016/02/01 23:59:55]

from the naming convention, I would probably expect that this emits a Dart
ClassDeclaration.

Maybe _emitClassHeritageWorkaround

[ochafik, 2016/02/03 19:41:33]

Done.

+    var body = <JS.Statement>[];

[Jennifer Messerly, 2016/02/01 23:59:55]

this can go inside the if:

if (...) {
  return new JS.Block(<JS.Statement>[
    js.statement('const # = #;', [superVar, cls.heritage]),
    new JS.ClassExpression(cls.name, superVar, cls.methods)
  ]);
}
return new JS.ClassDeclaration(cls);

that way we aren't building up a List just to immediately throw it away for the
normal code path.

[ochafik, 2016/02/03 19:41:33]

Done.

+    if (options.closure &&
+        cls.heritage != null && !_isQualifiedPath(cls.heritage)) {
+      // Workaround for Closure: super classes must be qualified paths.

[Jennifer Messerly, 2016/02/01 23:59:55]

After the method rename, this would be good as a doc comment.

[ochafik, 2016/02/03 19:41:33]

Done.

+      var superVar = new JS.Identifier(cls.name.name + r'$super');

[Jennifer Messerly, 2016/02/01 23:59:55]

This should be a temp. Use `new JS.TemporaryId`. That will let the compiler know
that it is safe to rename, in case it conflicts with any user-controlled names
in the Dart scope. JS.TemporaryId's use pointer identity to know whether it is a
use of the same variable.

[ochafik, 2016/02/03 19:41:33]

Done.

+      body.add(js.statement('const # = #;', [superVar, cls.heritage]));
+      cls = new JS.ClassExpression(cls.name, superVar, cls.methods);
+    }
+    body.add(new JS.ClassDeclaration(cls));
+    return _statement(body);
+  }
+
   /// Emit class members that need to come after the class declaration, such
   /// as static fields. See [_emitClassMethods] for things that are emitted
   /// inside the ES6 `class { ... }` node.
@@ -696,7 +715,7 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ClosureAnnotator {
       }
     }
 
-    body.add(new JS.ClassDeclaration(cls));
+    body.add(_emitClassDeclaration(cls));
 
     // TODO(jmesserly): we should really just extend native Array.
     if (jsPeerName != null && classElem.typeParameters.isNotEmpty) {