Fix typo in native_helper and add dartc test.

tests/language/src/GettersSettersTypeTest.dart

+// Copyright (c) 2012, 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.
+// Getters and setters can have different types, but it is a warning if the
+// two types are not assignable.
+
+int bar = 499;
+
+int  /// 01: static type warning
+get foo() => bar;

[zundel, 2012/03/30 00:25:01]

First of all, I agree something is going wrong in dartc, but I think there is an
issue with the test:

I don't understand why this is a warning?  top level field bar is an int so the
return type should be OK.

If you are just running case 1 you don't have a conflict
with String type used in the setter because it is commented out.  Its type would
be considered dynamic and dynamic is assignable to int, so the 2 types are valid
for getter/setter on the same field.

If you run case 2 I think it should also run without warnings.  But the fact
that it is passing does expose something.  If the setter has a type, but the
getter is Dynamic, BUT, it assumes the type of the setter for the getter, which
is wrong.

I think the cases you want to test are:

int  /// 01: static type warning 
int  /// 02: ... should run without warning
get foo() {   ... }

void set foo (
  String  /// 01:continued
  String /// 03: should run without warning
  str) { ... }

but I'm not sure how to express cases 2 & 3 with the test framework we've got.

There are still bugs in dartc, though. If you fix up test case 1 to look like
the above, it reports static type warnings on the assignments below, not the
getter and setter definitions where they belong.  I fixed a similar issue in
dartc recently, but it apparently does not work with top level fields.

[zundel, 2012/03/30 02:53:51]

Actually, if you want to write 2 extra (non multi-test) cases, you can use
@static-clean to make sure that cases 2 and 3 outlined above run without errors.

[floitsch, 2012/03/30 05:36:10]

Done.

+
+void set foo(
+             String   /// 02: static type warning
+             str) { bar = str.length; }
+

[zundel, 2012/03/30 00:25:01]

FYI, A second test case where getters and setters are in classes works as
expected in dartc:

class A {
  int  
    get foo() => bar;

  void set foo( String
             str) { bar = str.length; }
}

+main() {
+  int x = foo;
+  Expect.equals(499, x);
+  foo = "1234";
+  int y = foo;
+  Expect.equals(4, y);
+}