github: Add pr-checks workflow

* flake8 checks

.github/workflows/pr-checks.yml

@@ -0,0 +1,93 @@
+# This workflow will:
+#
+#   * install Python dependencies
+#   * lint with a single version of Python
+#
+# For more information see: https://help.github.com/actions/language-and-framework-guides/using-python-with-github-actions
+
+name: PR-Checks
+
+on:
+  pull_request:
+    branches: [ develop ]
+
+jobs:
+  flake8:
+    runs-on: ubuntu-18.04
+
+    steps:
+
+    # Debug show the info we have to work with
+    - name: Show github context
+      run: cat $GITHUB_EVENT_PATH
+
+    ####################################################################
+    # Checkout the necessary commits
+    ####################################################################
+    # We need the repo from the 'head' of the PR, not what it's
+    # based on.
+    - name: Checkout head commits
+      # https://github.com/actions/checkout
+      uses: actions/checkout@v2.4.0
+      #with:
+        #ref: ${{github.head.sha}}
+        #repository: ${{github.event.pull_request.head.repo.full_name}}
+        #fetch-depth: 0
+
+    # But we do need the base references
+    - name: Fetch base commits
+      env:
+        BASE_REPO_URL: ${{github.event.pull_request.base.repo.svn_url}}
+        BASE_REPO_OWNER: ${{github.event.pull_request.base.repo.owner.login}}
+
+      run: |
+        echo "BASE_REPO_URL: ${BASE_REPO_URL}"
+        echo "BASE_REPO_OWNER: ${BASE_REPO_OWNER}"
+        # Add the 'base' repo as a new remote
+        git remote add ${BASE_REPO_OWNER} ${BASE_REPO_URL}
+        # And then fetch its references
+        git fetch ${BASE_REPO_OWNER}
+    ####################################################################
+
+    ####################################################################
+    # Get Python set up
+    ####################################################################
+    - name: Set up Python 3.9
+      uses: actions/setup-python@v2.2.2
+      with:
+        python-version: 3.9
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install wheel flake8
+        if [ -f requirements-dev.txt ]; then pip install -r requirements-dev.txt; elif [ -f requirements.txt ]; then pip install -r requirements.txt ; fi
+    ####################################################################
+
+    # Have issues be annotated on run
+    - name: Setup flake8 annotations
+      uses: rbialon/flake8-annotations@v1
+
+    ####################################################################
+    # Lint with flake8
+    ####################################################################
+    - name: Lint with flake8
+      env:
+        BASE_REPO_URL: ${{github.event.pull_request.base.repo.svn_url}}
+        BASE_REPO_OWNER: ${{github.event.pull_request.base.repo.owner.login}}
+        BASE_REF: ${{github.base_ref}}
+
+      run: |
+        echo "BASE_REPO_URL: ${BASE_REPO_URL}"
+        echo "BASE_REPO_OWNER: ${BASE_REPO_OWNER}"
+        echo "BASE_REF: ${BASE_REF}"
+        # Explicitly check for some errors
+        # E9 - Runtime (syntax and the like)
+        # F63 - 'tests' checking
+        # F7 - syntax errors
+        # F82 - undefined checking
+        git diff "refs/remotes/${BASE_REPO_OWNER}/${BASE_REF}" -- | flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics --diff
+        # Can optionally add `--exit-zero` to the flake8 arguments so that
+        # this doesn't fail the build.
+        # explicitly ignore docstring errors (start with D)
+        git diff "refs/remotes/${BASE_REPO_OWNER}/${BASE_REF}" -- | flake8 . --count --statistics --diff --extend-ignore D
+    ####################################################################