Add A Prepare Commit Message To Customize Git Commits

If you work with any agile software or Github issues it is sometimes useful to prepend your commit message with a reference to the ticket or issue so commits can be associated with a work item. Using a prepare-commit-msg allows you with the correct branch to automatically prepend a git commit with the ticket/issue reference.

If you create a branch that is in reference to a Github issue, Github will automatically link back to that Github issue. If you use some other software you can update the Github settings under “Integrations” -> “Autolink references”

autolink-image

So if you have a branch that is named gh-#143-update-all-the-things with a prepare-commit-msg in your .git/hooks directory any git commit could automatically have [gh-#143] prepended to it! Check this example prepare-commit-msg to see how this could work.

If you’re using something like pre-commit you could write a quick Python script to accomplish the same with this configuration

repos:
  - repo: local
    hooks:
      - id: add-github-issue
        name: Add Github issue to commits
        entry: ./git/hooks/prepare-commit-msg.py
        language: python
        stages: [prepare-commit-msg]
        verbose: true
        always_run: true

The following python logic could be used:

#!/usr/bin/python
import re
import subprocess
import sys

# inspiration taken from https://gist.github.com/lorin/2963131

def get_issue():
    """Return the Github issue from the branch"""
    branchname = subprocess.check_output(["/usr/bin/git", "symbolic-ref", "HEAD"])
    branch = branchname.split("/")[2]
    github_issue = re.match("([aA-zZ]+-#[0-9]+)[-].*", branch).group(1)
    return github_issue


def prepend_commit_msg(text):
    """Prepend the commit message with `text`"""
    msgfile = sys.argv[1]

    with open(msgfile) as f:
        contents = f.read()

    with open(msgfile, "w") as f:
        # Don't append if it's already there
        if not contents.startswith(text):
            f.write(text)
        f.write(contents)


def main():
    try:
        github_issue = get_issue()
        header = "[%s] " % github_issue
        prepend_commit_msg(header)
    except Exception as exc:
        print(exc)
        pass


if __name__ == "__main__":
    main()