dart2js cps: 'is'-check directly against type variables.

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 366 matching lines @@
           ? 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]);
+    } else if (type is TypeVariableType) {
+      glue.registerIsCheck(type, registry);
+      // The only type argument is the type held in the type variable.
+      js.Expression typeValue = typeArguments.single;
+
+      // We use the helper:

[karlklose, 2015/05/28 07:42:30]

I am not sure these comments have much value. Maybe we should add documentation
to glue, where the helpers are located?

[asgerf, 2015/05/28 08:52:55]

I added the doc comments to glue and removed this instance of the comment.

I decided to keep the one for checkSubtype since it gives meaning to some
variable names and explains why some things are nulled.

+      //
+      //     checkSubtypeOfRuntime(value, runtimeType)
+      //
+      return buildStaticHelperInvocation(
+          glue.getCheckSubtypeOfRuntime(),
+          [value, typeValue]);

[karlklose, 2015/05/28 07:42:30]

Add type arguments to list (also in line 386.)

[asgerf, 2015/05/28 08:52:55]

Done.

     }
     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";
   }
 }