presubmit: Call 'git diff' once per change instead of once per file

presubmit_canned_checks.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.
 
 """Generic presubmit checks that can be reused by other presubmit checks."""
 
 import os as _os
 _HERE = _os.path.dirname(_os.path.abspath(__file__))
 
 
@@ skipping 310 matching lines @@
       'mk': 200,
       '': maxlen,
   }
   # Note: these are C++ specific but processed on all languages. :(
   MACROS = ('#define', '#include', '#import', '#pragma', '#if', '#endif')
 
   # Special java statements.
   SPECIAL_JAVA_STARTS = ('package ', 'import ')
 
   def no_long_lines(file_extension, line):
-    # Allow special java statements to be as long as neccessary.
+    # Allow special java statements to be as long as necessary.
     if file_extension == 'java' and line.startswith(SPECIAL_JAVA_STARTS):
       return True
 
     file_maxlen = maxlens.get(file_extension, maxlens[''])
     # Stupidly long symbols that needs to be worked around if takes 66% of line.
     long_symbol = file_maxlen * 2 / 3
     # Hard line length limit at 50% more.
     extra_maxlen = file_maxlen * 3 / 2
 
     line_len = len(line)
@@ skipping 138 matching lines @@
                                           long_text=long_text)]
   except IOError as e:
     return [output_api.PresubmitError('Error fetching tree status.',
                                       long_text=str(e))]
   return []
 
 def GetUnitTestsInDirectory(
     input_api, output_api, directory, whitelist=None, blacklist=None):
   """Lists all files in a directory and runs them. Doesn't recurse.
 
-  It's mainly a wrapper for RunUnitTests. USe whitelist and blacklist to filter
+  It's mainly a wrapper for RunUnitTests. Use whitelist and blacklist to filter
   tests accordingly.
   """
   unit_tests = []
   test_path = input_api.os_path.abspath(
       input_api.os_path.join(input_api.PresubmitLocalPath(), directory))
 
   def check(filename, filters):
     return any(True for i in filters if input_api.re.match(i, filename))
 
   to_run = found = 0
@@ skipping 39 matching lines @@
     if input_api.verbose:
       print('Running %s' % unit_test)
       cmd.append('--verbose')
     results.append(input_api.Command(
         name=unit_test,
         cmd=cmd,
         kwargs={'cwd': input_api.PresubmitLocalPath()},
         message=message_type))
   return results
 
+
 def GetPythonUnitTests(input_api, output_api, unit_tests):
   """Run the unit tests out of process, capture the output and use the result
   code to determine success.
 
   DEPRECATED.
   """
   # We don't want to hinder users from uploading incomplete patches.
   if input_api.is_committing:
     message_type = output_api.PresubmitError
   else:
@@ skipping 461 matching lines @@
     snapshot("checking description")
     results.extend(input_api.canned_checks.CheckChangeHasDescription(
         input_api, output_api))
     results.extend(input_api.canned_checks.CheckDoNotSubmitInDescription(
         input_api, output_api))
     snapshot("checking do not submit in files")
     results.extend(input_api.canned_checks.CheckDoNotSubmitInFiles(
         input_api, output_api))
   snapshot("done")
   return results