Add context to "file must be sorted" error message in ios/PRESUBMIT.py

build/ios/PRESUBMIT.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import os
 
 """Chromium presubmit script for src/tools/ios.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details on the presubmit API built into gcl.
 """
 
 WHITELIST_FILE = 'build/ios/grit_whitelist.txt'
 
 def _CheckWhitelistSorted(input_api, output_api):
   for path in input_api.LocalPaths():
     if WHITELIST_FILE == path:
       lines = open(os.path.join('../..', WHITELIST_FILE)).readlines()
-      sorted = all(lines[i] <= lines[i + 1] for i in xrange(len(lines) - 1))
-      if not sorted:
+      i = 0
+      while i < len(lines) - 1 and lines[i] <= lines[i + 1]:
+        i += 1
+      if i < len(lines) - 1:
         return [output_api.PresubmitError(
-            'The file ' + WHITELIST_FILE + ' must be sorted.')]
+            'The file ' + WHITELIST_FILE + ' must be sorted.  ' +
+            'First offending line: #' + str(i + 2))]
   return []
 
 def _CommonChecks(input_api, output_api):
   """Checks common to both upload and commit."""
   results = []
   results.extend(_CheckWhitelistSorted(input_api, output_api))
   return results
 
 def CheckChangeOnUpload(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))
   return results
 
 def CheckChangeOnCommit(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))
   return results