Allow creation of public symbols using MirrorSystem.getSymbol when passing a null library.

runtime/lib/mirrors_patch.dart

Index: runtime/lib/mirrors_patch.dart
diff --git a/runtime/lib/mirrors_patch.dart b/runtime/lib/mirrors_patch.dart
index 06eb5585a1462aec1945e47311b4d8dd5e72bca1..6f3c43609cc6847af7e59ba45b87cb7d66ac5202 100644
--- a/runtime/lib/mirrors_patch.dart
+++ b/runtime/lib/mirrors_patch.dart
@@ -2,7 +2,6 @@
 // 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.
 
-import "dart:nativewrappers";

[rmacnak, 2013/11/20 00:27:46]

We haven't needed this since the introduction of MirrorReference...

 // TODO(ahe): Move _symbol_dev.Symbol to its own "private" library?
 import "dart:_collection-dev" as _symbol_dev;
 
@@ -78,7 +77,7 @@ patch class MirrorSystem {
   }
 
   /* patch */ static Symbol getSymbol(String name, [LibraryMirror library]) {
-    if (library is! LibraryMirror ||
+    if ((library != null && library is! _LocalLibraryMirror) ||

[ahe, 2013/11/21 09:07:02]

Why are you checking for is! _LocalLibraryMirror?

My understanding is that it is too protect _mangleName from being called with
anything that isn't a _MirrorReference.

Using reflection, I can instantiate _LocalLibraryMirror and ensure it has a
bogus value for the field _reflectee. I believe I can provoke a crash that way
if Mirrors_mangleName makes too many assumptions. I'd argue that you should
remove the type test here and replace line 84 with:

if (library != null) {
  name = _mangleName(name, library._reflectee as _MirrorReference);
}

However, if _mangleName is so brittle, then you probably also need to write:

if (library != null) {
  name = _mangleName(name as String, library._reflectee as _MirrorReference);
}

If _mangleName is an instance method on _MirrorReference, you can reduce this
to:

if (library != null) {
  name = library._reflectee._mangleName(name as String);
}

Regardless, _mangleName can be invoked reflectively, so it should probably be
checking for String in C++, so really the first lines of this method should just
be:

if (library != null) {
  name = library._reflectee._mangleName(name);
} else if (name.startsWith('_')) {
  throw new ArgumentError("'$name' is private so this method needs a library");
}

         ((name.length > 0) && (name[0] == '_') && (library == null))) {
       throw new ArgumentError(library);
     }