Do not export library prefix names used in a library

Do not export library prefix names used in a library

The spec is unclear whether library prefix names are part of
the export namespace of a library or whether they are private
to that library. The latter makes more sense and is what dart2js
implements, so here's a VM change that implements the same
behavior. Spec will be clarified.

Fixes issue 12713.

R=iposva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=27079

[Ivan Posva, 2013-09-03 21:56:05]

LGTM with a simple question about conflicts and re-exports.

-Ivan

https://codereview.chromium.org/23613006/diff/7001/runtime/vm/object.cc
File runtime/vm/object.cc (right):

https://codereview.chromium.org/23613006/diff/7001/runtime/vm/object.cc#newco...
runtime/vm/object.cc:7699: obj = lib.LookupExport(name);
Wouldn't it be a conflict if the library is re-exporting something which
conflicts with a library prefix?

As far as I understand this will just cause us to overwrite the found library
prefix with a null from LookupExport, but it feels a bit weird.

[hausner, 2013-09-03 22:19:09]

https://codereview.chromium.org/23613006/diff/7001/runtime/vm/object.cc
File runtime/vm/object.cc (right):

https://codereview.chromium.org/23613006/diff/7001/runtime/vm/object.cc#newco...
runtime/vm/object.cc:7699: obj = lib.LookupExport(name);
On 2013/09/03 21:56:06, Ivan Posva wrote:
> Wouldn't it be a conflict if the library is re-exporting something which
> conflicts with a library prefix?
> 
> As far as I understand this will just cause us to overwrite the found library
> prefix with a null from LookupExport, but it feels a bit weird.

That is part of what Gilad has to clarify for us. If a library prefix does not
belong to the exported namespace, then there can be no conflict with a
re-exported name. In other words, library L can contain a prefix P and may
re-export a class P from another library L2.

The IsLibraryPrefix() check in line 7701 below is actually redundant. We should
never get a library prefix back from lib.LookupExport().

[hausner, 2013-09-03 22:19:34]

Committed patchset #3 manually as r27079 (presubmit successful).