dart2js cps: 'is' checks on types with type arguments.

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library code_generator;
 
 import 'glue.dart';
 
 import '../../tree_ir/tree_ir_nodes.dart' as tree_ir;
 import '../../js/js.dart' as js;
@@ skipping 332 matching lines @@
     return new js.Prefix("!", visitExpression(node.operand));
   }
 
   @override
   js.Expression visitThis(tree_ir.This node) {
     return new js.This();
   }
 
   @override
   js.Expression visitTypeOperator(tree_ir.TypeOperator node) {
+    js.Expression value = visitExpression(node.value);
+    List<js.Expression> typeArguments =
+        node.typeArguments.map(visitExpression).toList();
     if (!node.isTypeTest) {
       giveup(node, 'type casts not implemented.');
     }
     DartType type = node.type;
-    if (type is InterfaceType && type.isRaw) {
+    // Note that the trivial (but special) cases of Object, dynamic, and Null
+    // are handled at build-time and must not occur in a TypeOperator.
+    assert(!type.isObject && !type.isDynamic);
+    if (type is InterfaceType) {
       glue.registerIsCheck(type, registry);
-      js.Expression value = visitExpression(node.receiver);
-      return js.js('!!#.#', [value, glue.getTypeTestTag(type)]);
+      ClassElement clazz = type.element;
+
+      // We use the helper:
+      //
+      //     checkSubtype(value, $isT, typeArgs, $asT)
+      //
+      // Any of the last two arguments may be null if there are no type
+      // arguments, and/or if no substitution is required.
+
+      js.Expression isT = js.string(glue.getTypeTestTag(type));
+
+      js.Expression typeArgumentArray = typeArguments.isNotEmpty
+          ? new js.ArrayInitializer(typeArguments)
+          : new js.LiteralNull();
+
+      js.Expression asT = glue.hasStrictSubtype(clazz)
+          ? js.string(glue.getTypeSubstitutionTag(clazz))
+          : new js.LiteralNull();
+
+      return buildStaticHelperInvocation(
+          glue.getCheckSubtype(),
+          [value, isT, typeArgumentArray, asT]);
     }
     return giveup(node, 'type check unimplemented for $type.');
   }
 
   @override
   js.Expression visitVariableUse(tree_ir.VariableUse node) {
     return buildVariableAccess(node.variable);
   }
 
   js.Expression buildVariableAccess(tree_ir.Variable variable) {
@@ skipping 298 matching lines @@
 
   @override
   visitVariableDeclaration(tree_ir.VariableDeclaration node) {
     return errorUnsupportedNode(node);
   }
 
   errorUnsupportedNode(tree_ir.DartSpecificNode node) {
     throw "Unsupported node in JS backend: $node";
   }
 }