linhist.py

#!/usr/bin/env python3

import sys
import argparse
import logging
from git import Repo, InvalidGitRepositoryError, GitCommandError


def main():
    logging.basicConfig(
        level=logging.INFO, format="%(name)s - %(levelname)s - %(message)s"
    )
    logger = logging.getLogger("linhist")

    parser = argparse.ArgumentParser(
        prog="linhist",
        description="A tool to check and maintain a linear Git history",
        epilog="For more help on Linhist check https://github.com/wiltonloch/linhist",
    )
    subparsers = parser.add_subparsers()

    check_merge_parser = subparsers.add_parser(
        "check-merge", help="Checks if a merge operation would result in linear history"
    )
    check_merge_parser.add_argument(
        "--repository",
        type=str,
        help="Path to the repository where to perform the check",
        default=".",
        required=False,
    )
    check_merge_parser.add_argument(
        "--source", type=str, help="Source branch for the merge check", required=True
    )
    check_merge_parser.add_argument(
        "--target", type=str, help="Target branch for the merge check", required=True
    )

    args = parser.parse_args()

    # Checks if no arguments where passed and if so prints help information
    if len(sys.argv) == 1:
        parser.print_help()
        sys.exit(1)

    repository_path = args.repository
    source = args.source
    target = args.target

    try:
        repository = Repo(repository_path)
    except InvalidGitRepositoryError:
        logger.error(
            'The argument passed to "--repository" is not a valid Git repository'
        )
        sys.exit(1)

    if source not in repository.branches:
        try:
            repository.git.switch(source)
        except GitCommandError:
            logger.error(
                'The argument passed to "--source" is not an existing branch in the Git repository'
            )
            sys.exit(1)

    if target not in repository.branches:
        try:
            repository.git.switch(target)
        except GitCommandError:
            logger.error(
                'The argument passed to "--target" is not an existing branch in the Git repository'
            )
            sys.exit(1)

    common_ancestor = repository.merge_base(source, target)[0]
    target_tip = repository.rev_parse(target)

    if target_tip == common_ancestor:
        logger.info("CHECK PASSED: Merging will result in linear Git history")
        sys.exit(0)
    else:
        logger.info("CHECK FAILED: Merging will result in non-linear Git history.")
        logger.info(
            "If both branches have some common ancestor, try rebasing the source on the target."
        )
        logger.info(
            "Remember that child branches should be rebased on their parents, not the opposite."
        )
        sys.exit(1)


if __name__ == "__main__":
    main()