Per-hook flake output `check` derivations

[gekoke]

It would be nice if each hook could be built as a separate derivation. Currently, only one flake check output with the name pre-commit is produced.

If the hooks could be split into separate derivations, one could:

• run each check separately
• run checks in parallel in CI with tools like https://github.com/nix-community/nix-github-actions
• get more granular feedback for CI checks from GitHub's web UI

Is this something that is possible to implement? I understand there is the upstream dependency on pre-commit-hooks that might come into play here.

[sandydoo]

I suppose so. One thing to keep in mind is that there'll be a setup cost to pay for each check, not to mention the cost of launching a whole new job for each check.

git-hooks.nix/modules/pre-commit.nix

Lines 54 to 82 in 6fb82e4

	run =
	runCommand "pre-commit-run" { buildInputs = [ git ]; } ''
	set +e
	HOME=$PWD
	# Use `chmod +w` instead of `cp --no-preserve=mode` to be able to write and to
	# preserve the executable bit at the same time
	cp -R ${cfg.rootSrc} src
	chmod -R +w src
	ln -fs ${configFile} src/.pre-commit-config.yaml
	cd src
	rm -rf .git
	git init -q
	git add .
	git config --global user.email "you@example.com"
	git config --global user.name "Your Name"
	git commit -m "init" -q
	if [[ ${toString (compare install_stages [ "manual" ])} -eq 0 ]]
	then
	echo "Running: $ pre-commit run --hook-stage manual --all-files"
	${cfg.package}/bin/pre-commit run --hook-stage manual --all-files
	else
	echo "Running: $ pre-commit run --all-files"
	${cfg.package}/bin/pre-commit run --all-files
	fi
	exitcode=$?
	git --no-pager diff --color
	touch $out
	[ $? -eq 0 ] && exit $exitcode
	'';