Python script to help find which Git revision a diff file will successfully apply onto

git-find-diff-parent.py

#!/usr/bin/env python

import os
import subprocess
import sys

devnull = open(os.devnull, "w")

def patch_applies(diff_file):
  return not subprocess.call(["git", "apply", "--check", "--inaccurate-eof"] +
                             [diff_file], stderr=devnull)

def current_rev():
  return subprocess.check_output(["git", "rev-parse", "HEAD"]).strip()

if __name__ == "__main__":
  if len(sys.argv) != 2:
    sys.exit("Usage: %s path/to/your.diff" % sys.argv[0])

  diff_file = sys.argv[1]
  initial_rev = current_rev()

  if patch_applies(diff_file):
    print("HEAD")
  else:
    while subprocess.call(["git", "checkout", "HEAD~"], stderr=devnull) == 0:
      if patch_applies(diff_file):
        print(current_rev())
        break
    else:
      print("Failed to apply diff on any ancestor of rev %s" % initial_rev)

  subprocess.call(["git", "checkout", initial_rev])