A `post-rewrite` Git hook for moving tags from the old to new commit

post-rewrite

#!/usr/bin/env python
"""Move tags from old commit to new commit on every re-written commit.

WARNING: This is generally not a good idea.

Why would you want to do this? I hope you have a _very_ good reason! For example,
applying metadata changes to every release on a pre-commit mirror.
"""
import subprocess
import sys


def git(*args: list[str]) -> str:
    """Run a git command with `args`."""
    args = ['git', *args]
    subp = subprocess.run(args, check=True, capture_output=True)
    return subp.stdout.decode('utf-8').strip()


def retag(old_commit: str, new_commit: str) -> None:
    """For each old/new commit pair, move tags from old commit to new."""
    tags = git('tag', '--points-at', old_commit).split('\n')
    if tags == ['']:
        tags = []

    for tag in tags:
        git('tag', '--force', tag, new_commit)


def main(lines) -> None:
    rewrites: list[tuple[str, str]] = []
    for line in lines:
        old, new = line.strip().split(' ')
        rewrites.append((old, new))

    for old, new in rewrites:
        retag(old, new)


if __name__ == "__main__":
    main(sys.stdin)