a GitHub action to run pre-commit

To use this action, make a file .github/workflows/pre-commit.yml. Here's a template to get started:

name: pre-commit

on:
  pull_request:
  push:
    branches: [master]

jobs:
  pre-commit:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v2
    - uses: actions/setup-python@v2
    - uses: pre-commit/action@v2.0.2

This does a few things:

• clones the code
• installs python
• sets up the pre-commit cache

By default, this action runs all the hooks against all the files. extra_args lets users specify a single hook id and/or options to pass to pre-commit run.

Here's a sample step configuration that only runs the flake8 hook against all the files (use the template above except for the pre-commit action):

    - uses: pre-commit/action@v2.0.2
      with:
        extra_args: flake8 --all-files

this action also provides an additional behaviour when used in private repositories. when configured with a github token, the action will push back fixes to the pull request branch.

using the template above, you'll make two replacements for individual actions:

first is the checkout step, which needs to use unlimited fetch depth for pushing

    - uses: actions/checkout@v2
      with:
        fetch-depth: 0

next is passing the token to the pre-commit action

    - uses: pre-commit/action@v2.0.2
      with:
        token: ${{ secrets.GITHUB_TOKEN }}

note that secrets.GITHUB_TOKEN is automatically provisioned and will not require any special configuration.

while you could technically configure this for a public repository (using a personal access token), I can't think of a way to do this safely without exposing a privileged token to pull requests -- if you have any ideas, please leave an issue!