Git pre-commit hook to prevent JS trailing commas being checked in to projects.

pre-commit

#!/usr/bin/env python
"""
Git pre-commit hook to prevent JS trailing commas being checked in.
They have a tendency to sneak into the project and they crash MSIE7.
"""
import sys
import re
import subprocess


def has_trailing_commas( files ):

  single_str = ur"'(?:\\'|\\?[^'])*'"
  double_str = ur'"(?:\\"|\\?[^"])*"'
  regexp_lit = ur'\/(?:\\\/|[^\/\n])*\/'
  ml_comment = ur'\/\*[\S\s]*?\*\/'
  sl_comment = ur'//[^\n]*'

  re_trailing_comma = re.compile( ur'(,\s*(\n\s*)*\})' )
  re_ignore = re.compile( ur"(%s|%s|%s|%s|%s)" % (
          ml_comment, sl_comment, regexp_lit, single_str, double_str) )

  def str_collapse( m ):
    # remove all commas from match ...
    return ''.join(c if c != ',' else ' '
        for c in m.group(0))

  found = False
  for f in files:
    if f.endswith('.js'):
      js = open(f, "r").read()
      # neutralize comments & strings
      nostr_js = re_ignore.sub( str_collapse, js )
      # test remainder for problems
      if re_trailing_comma.search( nostr_js ):
        found = True
        problems = re_trailing_comma.finditer( nostr_js )
        lines = js.split('\n')
        print "Identified trailing comma problems in '%s'" % f
        for problem in problems:
            line_nr = len( nostr_js[0:problem.start()].split('\n') )
            line = lines[line_nr-1].strip()
            if problem.start() > 50:
              line = "... %s ..." % js[ problem.start()-15: problem.start()+15 ].replace('\n','\\n').strip()
            print ' -- line %s @%s: %s' % (line_nr, problem.start(), line)
  return found



if __name__ == '__main__':
    # get the files about to be changed
    stdout_text, stderr_text = subprocess.Popen(
                          ['git', 'diff', '--name-only', '--staged', '--diff-filter=AM'],
                          stdout=subprocess.PIPE).communicate(None)
    files = stdout_text.split()

    # scan files for problems
    if has_trailing_commas( files ): 
        sys.exit(1)