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:

on:
  pull_request:
  push:
    branches: [master]

jobs:
  pre-commit:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v1
    - uses: actions/setup-python@v1
    - name: set PY
      run: echo "::set-env name=PY::$(python --version --version | sha256sum | cut -d' ' -f1)"
    - uses: actions/cache@v1
      with:
        path: ~/.cache/pre-commit
        key: pre-commit|${{ env.PY }}|${{ hashFiles('.pre-commit-config.yaml') }}
    - uses: pre-commit/[email protected]

This does a few things:

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

Hopefully in the future when actions matures the yaml can be simplified.

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.

here's an example configuration for that (use the template above except for the pre-commit action):

    - uses: pre-commit/[email protected]
      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!