git-blame-tags

#!/usr/bin/env python3
"""
Usage: git-blame-tags <path>

Annotate lines of <path> with the oldest tag each line is contained in.
"""

from functools import cache
import os.path
import subprocess
import sys


def parse(lines):
    try:
        while True:
            line = next(lines)
            sha = line[:40]
            for line in lines:
                if line.startswith(b"\t"):
                    line = line[1:].decode()
                    break
            yield sha, line
    except StopIteration:
        pass


@cache
def tag_for_sha(sha):
    o = subprocess.check_output(
        [
            "git",
            "tag",
            "--list",
            "--contains",
            sha,
            "--format",
            "%(objecttype) %(refname:strip=2)",
            "--sort",
            "v:refname",
        ]
    )
    for line in o.splitlines():
        match (line.split(b" ", 1)):
            case [b"tag", refname]:
                return refname.decode()


if __name__ == "__main__":
    path = sys.argv[1]
    o = subprocess.check_output(["git", "blame", "-p", path])
    for sha, line in parse(l for l in o.splitlines()):
        tag = tag_for_sha(sha)
        print(f"{tag:10s} {line}")