git-log-divergence

#!/usr/bin/env python3
# Author: Jan Larres <jan@majutsushi.net>
# License: MIT/X11

import argparse
import logging
import sys
from subprocess import CalledProcessError, check_output, run

logging.basicConfig(format="%(message)s", level=logging.INFO)
log = logging.getLogger(__name__)


def main(args: argparse.Namespace) -> None:
    if args.verbose:
        log.setLevel(logging.DEBUG)

    revs = args.rev
    match len(revs):
        case 0:
            revs = ["@{upstream}", "HEAD"]
        case 1:
            revs += ["HEAD"]

    cmd = ["git", "merge-base", "--octopus", "--all", *revs]
    log.debug("merge-base command: '%s'", " ".join(cmd))
    try:
        merge_bases = check_output(cmd).decode(sys.stdout.encoding).splitlines()
    except CalledProcessError as e:
        die("Failed to find merge bases", args.verbose, e)

    exclusions = [f"{base}^" for base in merge_bases]
    log.debug("Exclusions: '%s'", " ".join(exclusions))

    rev_args = [*revs, "--not", *exclusions]

    extra_args = ["--topo-order", "--boundary"]

    if args.simplify:
        extra_args.append("--simplify-by-decoration")

    if args.long:
        extra_args.append(
            '--pretty=tformat:"'
            "%C(auto,yellow)%h"
            " %C(auto,blue)%ad"
            " %C(auto,green)%<(15,trunc)%an"
            " %C(auto)%d"
            ' %Creset%s"'
        )

    if args.print_args:
        print(" ".join(extra_args + rev_args))
        sys.exit(0)

    log_cmd = ["git", "log", "--oneline", "--decorate", "--graph"]
    log_cmd += extra_args + rev_args
    log.debug("Full command: '%s'", " ".join(log_cmd))
    run(log_cmd, check=True)


def parse_args() -> argparse.Namespace:
    parser = argparse.ArgumentParser(description="Log graph of branch diverge")
    parser.add_argument("rev", nargs="*", help="Revisions to log")
    parser.add_argument(
        "-v",
        "--verbose",
        action="store_true",
        default=False,
        help="increase output verbosity",
    )
    parser.add_argument(
        "-s",
        "--simplify",
        action="store_true",
        default=False,
        help="only show commits with symbolic refs",
    )
    parser.add_argument(
        "-p",
        "--print-args",
        action="store_true",
        default=False,
        help="print revision args instead of running git log",
    )
    parser.add_argument(
        "-l",
        "--long",
        action="store_true",
        default=False,
        help="print revisions with a longer format",
    )
    return parser.parse_args()


def die(msg: str, verbose: bool, e=None) -> None:
    log.error(msg, exc_info=e if verbose else None)
    sys.exit(1)


if __name__ == "__main__":
    main(parse_args())