Use the runtime for generic subsitution of variable types, return types, parameter types.

tests/lib/mirrors/generic_local_function_test.dart

+// Copyright (c) 2013, 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 test.generic_function_typedef;
+
+import 'dart:mirrors';
+
+import 'package:expect/expect.dart';
+
+import 'generics_helper.dart';
+
+class C<T> {
+  makeClosure1() {
+    T closure1(T t) {}
+    return closure1;
+  }
+
+  makeClosure2() {
+    enclosing() {
+      T closure2(T t) {}
+      return closure2;
+    };
+    return enclosing();
+  }
+}
+
+main() {
+  ClosureMirror closure1 = reflect(new C<String>().makeClosure1());
+  Expect.equals(reflectClass(String), closure1.function.returnType);
+  Expect.equals(reflectClass(String), closure1.function.parameters[0].type);
+
+  ClosureMirror closure2 = reflect(new C<String>().makeClosure2());
+  Expect.equals(reflectClass(String), closure2.function.returnType);
+  Expect.equals(reflectClass(String), closure2.function.parameters[0].type);
+}