Format in pre-commit hook

[nojaf]

As mentioned in https://twitter.com/rastreus/status/1321296796124143617?s=20, how can Fantomas be used as a precommit hook?

On top of my head I think the local dotnet tool can be used for this. However, as I find this a good question we should write something out in the documentation to explain this.

Also mention in the docs that .fantomasignore file exist in case Fantomas is not able to format the file for some reason.

[nojaf]

@rastreus this seems to work for me (on Windows):

#!/bin/sh
FILES=$(git diff --cached --name-only --diff-filter=ACMR "*.fs" "*.fsx" | sed 's| |\\ |g')
[ -z "$FILES" ] && exit 0

# Format all selected files
echo "$FILES" | xargs dotnet fantomas

# Add back the modified/prettified files to staging
echo "$FILES" | xargs git add

exit 0

I stole some code from other places so I can't really explain each line 😅, but the dotnet fantomas part is doing the formatting.

[danalexilewis]

@nojaf i wrote something very similar to this once to take the diff and pass only those files with changes to the shopify cli for deployment.

Basically:

Line 1 gets the changed files filtering the git diff to what your after
Line 2 passes the files as args to Fantomas executed with dotnet
Line 3 stage them with git

I thinK the way to to this in a more automated way will be to create a git hook that runs the lines 1 and 2 of your script as a ‘pre-commit hook’.

That should do it.

[nojaf]

Hey @agentlewis, this is the content of the pre-commit file, so it is already a hook ;)