Implement type argument access and reification of runtime types.

pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
index 6cdec14b9abd7096ef4cddb4c1b865b65fdb8e32..ed1a2898d16f6a5d9394a51e357f5313cbba3e60 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
@@ -956,14 +956,15 @@ abstract class IrBuilderVisitor extends ResolvedVisitor<ir.Primitive>
 
     DartType type = elements.getTypeLiteralType(node);
     if (type is TypeVariableType) {
-      ir.Primitive prim = new ir.ReifyTypeVar(type.element);
-      irBuilder.add(new ir.LetPrim(prim));
-      return prim;
+      return buildReifyTypeVariable(new ir.This(), type);

[asgerf, 2015/03/02 13:52:36]

Use irBuilder.buildThis(), otherwise 'this' inside a nested function will be
translated to a JS 'this' instead of the captured receiver.

[karlklose, 2015/03/05 09:54:58]

Done.

     } else {
       return translateConstant(node);
     }
   }
 
+  ir.Primitive buildReifyTypeVariable(ir.Primitive target,
+                                      TypeVariableType variable);
+
   ir.Primitive visitSendSet(ast.SendSet node) {
     assert(irBuilder.isOpen);
     Element element = elements[node];
@@ -1377,6 +1378,15 @@ class DartIrBuilderVisitor extends IrBuilderVisitor {
       List<ir.Primitive> arguments) {
     return arguments;
   }
+
+  @override
+  ir.Primitive buildReifyTypeVariable(ir.Primitive target,
+                                      TypeVariableType variable) {
+    assert(target is ir.This);

[asgerf, 2015/03/02 13:52:36]

FYI I believe this assertion is still valid with the above change.

[karlklose, 2015/03/05 09:54:58]

Acknowledged.

+    ir.Primitive prim = new ir.ReifyTypeVar(variable.element);
+    irBuilder.add(new ir.LetPrim(prim));
+    return prim;
+  }
 }
 
 /// IR builder specific to the JavaScript backend, coupled to the [JsIrBuilder].
@@ -1903,5 +1913,18 @@ class JsIrBuilderVisitor extends IrBuilderVisitor {
     return result;
   }
 
+
+  @override
+  ir.Primitive buildReifyTypeVariable(ir.Primitive target,
+                                      TypeVariableType variable) {
+    ClassElement context = variable.element.enclosingClass;
+    irBuilder.add(new ir.LetPrim(target));
+    ir.Primitive typeArgument =
+        new ir.ReadTypeVariable(variable, context, target);

[asgerf, 2015/03/02 13:52:36]

This seems wrong. We are always passing variable.element.enclosingClass as the
context. Why do we have two fields when one can be derived from the other? (Also
see long comment in the ir_nodes file).

[karlklose, 2015/03/05 09:54:58]

I removed the context. We do not need it until we inline or specialize and we
should introduce it, when we need it for these features.

+    irBuilder.add(new ir.LetPrim(typeArgument));
+    var type = new ir.ReifyRuntimeType(typeArgument);
+    irBuilder.add(new ir.LetPrim(type));
+    return type;
+  }
 }