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

Closure compiler chokes on super classes that aren't qualified paths.

(example: http://goo.gl/5mHC7S)

BUG=
[email protected]

Review URL: https://codereview.chromium.org/1638533004 .

Author: Olivier Chafik

lib/runtime/dart/_runtime.js

@@ -732,7 +732,8 @@ dart_library.library('dart/_runtime', null, /* Imports */[
   const _mixins = Symbol("mixins");
   const implements_ = Symbol("implements");
   const metadata = Symbol("metadata");
-  const TypeRep = class TypeRep extends LazyTagged(() => core.Type) {
+  const _TypeRepBase = LazyTagged(() => core.Type);
+  const TypeRep = class TypeRep extends _TypeRepBase {
     get name() {
       return this.toString();
     }

lib/src/codegen/js_codegen.dart

@@ -379,10 +379,11 @@ 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, _emitClassHeritageWorkaround(classExpr));
   }
 
   JS.Statement _emitJsType(String dartClassName, DartObject jsName) {
@@ -674,6 +675,27 @@ 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;
+
+  /// Workaround for Closure: super classes must be qualified paths.
+  JS.Statement _emitClassHeritageWorkaround(JS.ClassExpression cls) {
+    if (options.closure &&
+        cls.heritage != null &&
+        !_isQualifiedPath(cls.heritage)) {
+      var superVar = new JS.TemporaryId(cls.name.name + r'$super');
+      return _statement([
+        js.statement('const # = #;', [superVar, cls.heritage]),
+        new JS.ClassDeclaration(
+            new JS.ClassExpression(cls.name, superVar, cls.methods))
+      ]);
+    }
+    return new JS.ClassDeclaration(cls);
+  }
+
   /// 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.
@@ -702,7 +724,7 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ClosureAnnotator {
       }
     }
 
-    body.add(new JS.ClassDeclaration(cls));
+    body.add(_emitClassHeritageWorkaround(cls));
 
     // TODO(jmesserly): we should really just extend native Array.
     if (jsPeerName != null && classElem.typeParameters.isNotEmpty) {

test/codegen/expect/closure.js

@@ -117,7 +117,8 @@ dart_library.library('closure', null, /* Imports */[
   });
   let Foo = Foo$();
   class Bar extends core.Object {}
-  class Baz extends dart.mixin(Foo$(core.int), Bar) {
+  const Baz$super = dart.mixin(Foo$(core.int), Bar);
+  class Baz extends Baz$super {
     /** @param {?number} i */
     Baz(i) {
       super.Foo(i, 123);

tool/input_sdk/private/types.dart

@@ -38,8 +38,9 @@ final metadata = JS('', 'Symbol("metadata")');
 ///  String toString();
 ///
 ///
+final _TypeRepBase = JS('', '$LazyTagged(() => $Type)');
 final TypeRep = JS('', '''
-  class TypeRep extends $LazyTagged(() => $Type) {
+  class TypeRep extends $_TypeRepBase {
     get name() {return this.toString();}
   }
 ''');