Utility script which insert branch creation commands in a git rebase-TODO

git-rebase-branches

#!/usr/bin/env python3
import os
import re
import subprocess as sp
import sys


def find_git_folder():
    parts = os.getcwd().split(os.path.sep)
    parts[0] = '/'  # instead of ''
    while len(parts) > 0:
        p = os.path.join(*parts, '.git')
        if os.path.exists(p):
            return p
        parts.pop()
    raise RuntimeError(f'Unable to find a git folder in {os.getcwd()!r} '
                       'or one of its parents')


def main(args):
    git_folder = find_git_folder()
    rebase_todo_path = f'{git_folder}/rebase-merge/git-rebase-todo'
    if not os.path.exists(rebase_todo_path):
        raise RuntimeError('Unable to find git rebase TODO '
                           f'at {rebase_todo_path!r}. No rebase in progress?')

    git_branches = sp.Popen(['git', '-C', git_folder, 'branch', '-v'],
                            stdout=sp.PIPE, stderr=sp.PIPE)
    out, err = git_branches.communicate()
    if git_branches.returncode != 0:
        raise RuntimeError(err.decode('utf-8'))

    branches = {}
    for m in re.finditer(r'^[* ] ([^ ]+) +([0-9a-f]*) ', out.decode('utf-8'),
                         re.MULTILINE):
        branches[m.group(2)] = m.group(1)

    with open(rebase_todo_path, 'r') as fp:
        rebase_todo = fp.readlines()

    new_todo = []
    line_expr = re.compile(r'^(?P<cmd>p|r|e|s|f|x|b|d|l|t|m|pick|reword|edit|'
                           r'squash|fixup|exec|break|drop|label|reset|merge) '
                           r'(?P<hash>[0-9a-f]{7})')
    append_cmd = None
    for line in rebase_todo:
        m = line_expr.match(line)
        if m:
            if append_cmd is not None:
                new_todo.append(append_cmd)
                append_cmd = None
            hash = m.group('hash')
            if hash in branches:
                append_cmd = f'exec git branch -f {branches[hash]} HEAD\n'
        new_todo.append(line)
    # Last append_cmd is not added because the branch will be moved by git-rebase
    # If we move it ourselves, git-rebase will be lost and will fail

    with open(rebase_todo_path, 'w') as fp:
        fp.write(''.join(new_todo))

if __name__ == '__main__':
    try:
        main(sys.argv[1:])
    except Exception as e:
        print(e, file=sys.stderr)
        sys.exit(1)