git-patch-to-hg-patch

#!/usr/bin/env python3

r"""Git format-patch to hg importable patch.

(Who knew this was so complicated?)

>>> process(StringIO('From 3ce1ccc06 Mon Sep 17 00:00:00 2001\nFrom: fromuser <fromemail>\nSubject: subject\n\nRest of patch.\nMore patch.\n'))
'# HG changeset patch\n# User fromuser <fromemail>\n\nsubject\n\nRest of patch.\nMore patch.\n'

>>> process(StringIO('From 3ce1ccc06 Mon Sep 17 00:00:00 2001\nFrom: "A. J. Quoted" <fromemail>\nSubject: subject\n\nRest of patch.\nMore patch.\n'))
'# HG changeset patch\n# User A. J. Quoted <fromemail>\n\nsubject\n\nRest of patch.\nMore patch.\n'

>>> process(StringIO('From: fromuser <fromemail>\nSubject: A very long subject line.  Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi faucibus, arcu sit amet\n\nRest of patch.\nMore patch.\n'))
'# HG changeset patch\n# User fromuser <fromemail>\n\nA very long subject line.  Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi faucibus, arcu sit amet\n\nRest of patch.\nMore patch.\n'

>>> process(StringIO('From: f <f>\nSubject: =?UTF-8?q?Bug=20655877=20-=20Dont=20treat=20SVG=20text=20frames=20?= =?UTF-8?q?as=20being=20positioned.=20r=3D=3F?=\n\nPatch.'))
'# HG changeset patch\n# User f <f>\n\nBug 655877 - Dont treat SVG text frames as being positioned. r=?\n\nPatch.'
"""

# Original author: bholley

import sys
import re
import fileinput
import email, email.parser, email.header, email.utils
import math
from io import StringIO
from itertools import takewhile

def decode_header(hdr_string):
  r"""Clean up weird encoding crap.

  >>> clean_header('[PATCH] =?UTF-8?q?Bug=20655877=20r=3D=3F?=')
  '[PATCH] Bug 655877 r=?'
  """
  rv = []
  hdr = email.header.Header(hdr_string, maxlinelen=float('inf'))
  for (part, encoding) in email.header.decode_header(hdr):
    if encoding is None:
      rv.append(part)
    else:
      rv.append(part.decode(encoding))
  return ' '.join(rv)

def clean_header(hdr_string):
  r"""Transform a header split over many lines into a header split only where
  linebreaks are intended.  This is important because hg cares about the first
  line of the commit message.

  Also clean up weird encoding crap.

  >>> clean_header('Foo\n bar\n baz')
  'Foo bar baz'
  >>> clean_header('Foo\n bar\nSpam\nEggs')
  'Foo bar\nSpam\nEggs'
  """

  lines = []
  curline = ''
  for line in decode_header(hdr_string).split('\n'):
    if not line.startswith(' '):
      lines.append(curline)
      curline = ''
    curline += line
  lines.append(curline)
  return '\n'.join(lines[1:])

def process(git_patch_file):
  parser = email.parser.Parser()
  msg = parser.parse(git_patch_file)
  from_hdr = clean_header(msg['From'])
  commit_title = clean_header(msg['subject'])
  if not len(commit_title) or not len(from_hdr):
    sys.stderr.write("%s does not look like a valid git patch file, skipping\n"
                     % git_patch_file.name)
    return

  parsed_from = email.utils.parseaddr(from_hdr)
  nuke_prefix = r"\[PATCH( \d+/\d+)?\] "
  match = re.match(nuke_prefix, commit_title)
  if match:
    commit_title = commit_title[match.end():]

  patch_body = msg.get_payload()

  # git format-patch wraps the diff (including trailing whitespace):
  #   ---
  #   <diff>
  #   -- 
  #   2.0.3
  # This doesn't hurt parsing the diff at all, but the version number is
  # nonsense once the git specific items have been stripped
  patch_body = re.sub(r'--\s?\n[0-9\.]+\n$', '', patch_body)

  return '\n'.join(['# HG changeset patch',
                    '# User %s <%s>' % parsed_from,
                    '',
                    commit_title,
                    '',
                    patch_body])

if __name__ == "__main__":
  if len(sys.argv) > 1 and sys.argv[1] == '--test':
    import doctest
    doctest.testmod()
    sys.exit(0)

  # If there were no arguments, do stdin->stdout.
  filelist = sys.argv[1:]
  if not filelist:
    lines = process(sys.stdin)
    sys.stdout.writelines(lines)
    sys.exit(0)

  # Otherwise, we take a list of files.
  for filename in filelist:

    # Read the lines.
    f = open(filename, 'r')
    lines = process(f)
    f.close()

    # Process.

    if lines:
      # Write them back to the same file.
      f = open(filename, 'w')
      f.writelines(lines)
      f.close()