Undercommit

Jam custom, unversioned hooks into a Git repo with existing hooks managed by Overcommit.

Note

There's a less hacky way to do this! See sds/overcommit#527 (comment).

Overview

Overcommit is a nice tool for managing Git hooks that assumes complete control of a repo. It treats hooks as first-class citizens of an application, with versioned configuration, etc. This is great for hooks that you want to apply for all contributors to a repo. However, it's tricky to configure hooks that apply only in an individual developer's environment.

For example, I want to add a post-checkout hook that calls ctags with some environment-specific parameters. Overcommit doesn't provide a convenient place to put a hook like this. Such a hook doesn't belong in version control, because other developers might not use ctags, etc.

Undercommit hacks support for unversioned hooks into an Overcommit-managed repo, so you can continue to use Overcommit for global, versioned hooks, and also write any custom hooks you might need.

Disclaimer

This is a hack. It might trash your git-hooks. However, you can always rm .git/hooks/*; overcommit --install if you get into a bad place ;o)

Approach

This script replaces Overcommit-managed hooks (.git/hooks/pre-commit, etc.) with a new master hook that first runs Overcommit's master hook, then any unversioned hook.

i.e. after running this script:

• Overcommit hooks are renamed to .git/hooks/{hook}-overcommit.

• Custom hooks can be installed as .git/hooks/{hook}-custom.

• Hooks in .git/hooks first call Overcommit hooks, then custom hooks, if they exist. (Note: Overcommit expects the hook executable to be named like e.g. pre-commit, not pre-commit-overcommit. See master-hook if you want to know how this is handled.)

To set this up, run undercommit-install from the root of the target repo.

Alternative approach

There is a way to accomplish unversioned hooks using the built-in features of Overcommit. (Note: untested example code follows.)

You could add something like this to your Overcommit configuration:

PostCheckout:
  CustomScript:
    enabled: true
    required_executable: './bin/maybe-run-custom-post-checkout-hook

Then, in bin/maybe-run-custom-post-checkout-hook:

if [[ -x ./bin/unversioned-hooks/post-checkout ]]; then
  ./bin/unversioned-hooks/post-checkout "$@"
fi

Then, add bin/unversioned-hooks to .gitignore.

This still requires changes to the repo. If the maintainer doesn't like it, you could use Undercommit instead.