Force extension for given file type in a hook

Question

How can I configure a pre-commit hook which will force yaml/yml files to have yaml extension. Pass:

lol.yaml

Fail:

lol.yml

Answer 1

List all the cached files excluding the deleted ones. Check the extension of each file. Fail the hook if any of them ends with .yml .

A demo in Bash,

#!/bin/bash

git diff --cached --name-status --diff-filter=d | awk '
    /\.yml$/ {
        print "ERROR: pre-commit failed"
        print $NF
        print "The extension \".yml\" is not allowed. Use \".yaml\" instead"
        exit 1
    }
'

The demo checks only the extension. You could also check if a file is really a YAML file before checking its extension when necessary. A YAML file starts with three dashes, so it's not complicated to find out the real YAML files.

Answer 2

Actually it turned out to be fairly easy. It's enough to add the following hook to the config:

  - repo: local
    hooks:
      - id: yaml-file-extension
        name: Check if YAML files has *.yaml extension.
        entry: YAML filenames must have .yaml extension.
        language: fail
        files: .yml$

It will not verify the content however, just the extension.