Add a simple script to simulate BUILD file glob() expansion.

tools/BUILD_simulator.py

+#!/usr/bin/env python
+#
+# Copyright 2015 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# This script does a very rough simulation of BUILD file expansion,
+# mostly to see the effects of glob().
+
+# We start by adding some symbols to our namespace that BUILD.public calls.
+
+# We don't really care about this, so just no-op it.
+def exports_files(files):
+  pass
+
+# Simulates BUILD file glob().
+def glob(include, exclude=()):
+  from glob import glob as python_glob
+
+  files = set()
+  for pattern in include:
+    files.update(python_glob(pattern))
+  for pattern in exclude:
+    files.difference_update(python_glob(pattern))
+  return list(sorted(files))
+
+# We've put enough into our environment now to treat BUILD.public as if it were
+# Python code.  This pulls its variable definitions (SRCS, HDRS, DEFINES, etc.)
+# into our local namespace.
+execfile('BUILD.public')
+
+# Pretty-print every variable whose name is COMPLETELY_UPPERCASE,
+# i.e. every variable from BUILD.public.  This is obviously quite heuristic.
+from pprint import pprint
+with open('tools/BUILD.public.expected', 'w') as out:
+  print >>out, "This file is auto-generated by tools/BUILD_simulator.py."
+  print >>out, "It expands BUILD.public to make it easy to see changes."
+  for name, value in sorted(locals().items()):
+    if name.isupper():
+      print >>out, name, '= ',
+      pprint(value, out)