tree a1b393fa030c8abf12ed63c056f21513a804028f
parent 0894cbc1a9f0564e77dfbe74ed09d03bc7eaf30d
author Colin Cross <ccross@android.com> 1436575915 -0700
committer Colin Cross <ccross@android.com> 1438643296 -0700

Fix bugs related to local vs. inherited variables

The Go race detector found a race condition in the parser, which
 highlighted a few related bugs. A variable could be defined but
not referenced in a Blueprints file, then appended to in multiple
subdirs= Blueprints files.  The race detector caught the multiple
writes to assignment.Referenced from the parsers for the subdirs
Blueprints files, but multiple appends would be much more serious.

To fix this, keep local and inherited variables separate in the
Scope object and export that info to the parser.  Disallow
appending to non-local variables, which was already the intended
behavior.  Only update the referenced boolean for local variables.
Together, this should prevent all writes to Assignment objects
from parsers other than the one that created them.

Also improves the error handling code and some error messages.

Change-Id: Idb4f7d2e61bbe28d90b93074764e64e60d1eba8f