Fix infinite loop on empty variable name.

pylib/gyp/input.py

 # Copyright (c) 2012 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from compiler.ast import Const
 from compiler.ast import Dict
 from compiler.ast import Discard
 from compiler.ast import List
 from compiler.ast import Module
 from compiler.ast import Node
@@ skipping 39 matching lines @@
 
 # These per-process dictionaries are used to cache build file data when loading
 # in parallel mode.
 per_process_data = {}
 per_process_aux_data = {}
 
 def IsPathSection(section):
   # If section ends in one of the '=+?!' characters, it's applied to a section
   # without the trailing characters.  '/' is notably absent from this list,
   # because there's no way for a regular expression to be treated as a path.
-  while section[-1:] in '=+?!':
+  while section and section[-1:] in '=+?!':
     section = section[:-1]
 
   if section in path_sections:
     return True
 
   # Sections mathing the regexp '_(dir|file|path)s?$' are also
   # considered PathSections. Using manual string matching since that
   # is much faster than the regexp and this can be called hundreds of
   # thousands of times so micro performance matters.
   if "_" in section:
@@ skipping 2808 matching lines @@
     ValidateRunAsInTarget(target, target_dict, build_file)
     ValidateActionsInTarget(target, target_dict, build_file)
 
   # Generators might not expect ints.  Turn them into strs.
   TurnIntIntoStrInDict(data)
 
   # TODO(mark): Return |data| for now because the generator needs a list of
   # build files that came in.  In the future, maybe it should just accept
   # a list, and not the whole data dict.
   return [flat_list, targets, data]