¬ just serendipity 🍀 (not just serendipity)

Is it possible to transparently invoke pre-commit in the background upon saving in vim (:w)?

Initially I found this Stack Overflow question, but it had no answer.

Digging a bit deeper I realized that I could do it with an autocmd:

autocmd BufWritePost * execute '! if [ -e $(git root)/.pre-commit-config.yaml >/dev/null 2>&1 ]; then pre-commit run; fi'

That trashes the screen upon completion. This can be resolved by invoking :redraw! afterwards:

autocmd BufWritePost * execute '! if [ -e $(git root)/.pre-commit-config.yaml >/dev/null 2>&1 ]; then pre-commit run; fi' | redraw!

We can be less intrusive by prepending silent! so that, even if the command fails, it doesn’t get in the way:

autocmd BufWritePost * silent! execute '! if [ -e $(git root)/.pre-commit-config.yaml >/dev/null 2>&1 ]; then pre-commit run; fi' | redraw!

And last but not least, ideally pre-commit should run only on the file associated with the current buffer. Pass --files to pre-commit with the % argument:

autocmd BufWritePost * silent! execute '! if [ -e $(git root)/.pre-commit-config.yaml >/dev/null 2>&1 ]; then pre-commit run --files %; fi' | redraw!

This approach works as intended. There’s a brief period in which you can see pre-commit running in the background. It’s arguable whether that’s a feature or a bug.

Ah, and git root is simply an alias in my ~/.gitconfig:

root = rev-parse --show-toplevel

Whenever there are pre-commit violations (e.g. end-of-file-fixer) they are applied inplace. There’s no need to run :e!.

This is bare, but I am happy.

Perhaps the only missing piece is to extend it in such a way it’s only executed in the repositories I opt into.

If this turns out to be too intrusive, I am thinking to switch to using a vim keymap e.g. <leader>p instead of an autocmd.