Show authors of changed lines in commit message template

prepare-commit-msg

#!/usr/bin/env python

"""
Makes it easy to pick a reviewer by showing who authored lines you changed
in a commit. You better have `git findreviewers` installed.

This is a Python script because every single time I try to write a shell
script, I regret it and have to rewrite.
"""

import re
import subprocess
import sys


debug = False


def log(s):
    if debug:
        print s


log('prepare-commit-msg debug')

if subprocess.call(['git', 'symbolic-ref', '-q', 'HEAD']):
    # exit code 1 (error) means no HEAD
    print "detached head, probably a rebase"
    sys.exit(0)

if len(sys.argv) > 3:
    log("looks like an amend: '{}'".format(sys.argv[3]))
    sys.exit(0)


log('$3 is empty, so this is probably a regular commit!')

with open(sys.argv[1], 'r') as f:
    message = f.read()

if "Differential Revision:" in message:
    log('looks like phabricator')
    sys.exit(0)

if re.search(r'(Auditor|Reviewer)s?:\s*\w', message, re.IGNORECASE):
    log('reviewer already specified')
    sys.exit(0)

with open(sys.argv[1], 'a') as f:
    f.write("# Reviewers:\n")
    authors = subprocess.check_output(['git', 'findreviewers'])
    for a in (a for a in authors.split('\n') if a):
        f.write("# ")
        f.write(a)
        f.write("\n")