name: Linting

on: [push, pull_request]

jobs:
  lint:

    runs-on: ubuntu-latest

    env:
      PIP_CACHE_DIR: /tmp/pip-cache-dir

    steps:
      - name: Checks out repository
        uses: actions/checkout@v2

      - name: Set up Python 3.9
        id: python
        uses: actions/setup-python@v2
        with:
          python-version: 3.9

      # This step caches our Python dependencies. To make sure we
      # only restore a cache when the dependencies, the python version and
      # the runner operating system we create a cache key
      # that is a composite of those states.
      # Only when the context is exactly the same, we will restore the cache.
      - name: Restore pip cache
        uses: actions/cache@v2
        with:
          path: ${{ env.PIP_CACHE_DIR }}
          key: "python-0-${{ runner.os }}-\
          ${{ steps.python.outputs.python-version }}-\
          ${{ hashFiles('./requirements.txt', './requirements-dev.txt') }}"

      - name: Install dependencies
        run: |
          pip install -r requirements.txt
          pip install -r requirements-dev.txt

      # Run flake8 and have it format the linting errors in the format of
      # the GitHub Workflow command to register error annotations. This
      # means that our flake8 output is automatically added as an error
      # annotation to both the run result and in the "Files" tab of a
      # pull request.
      #
      # Format used:
      # ::error file={filename},line={line},col={col}::{message}
      - name: Run flake8
        run: "flake8 \
        --format='::error file=%(path)s,line=%(row)d,col=%(col)d::[flake8] %(code)s: %(text)s'"