From c5d43a4adaac31b2e9fe60d80b9993ccc43be106 Mon Sep 17 00:00:00 2001
From: Athanasius <github@miggy.org>
Date: Fri, 31 Jul 2020 12:34:12 +0100
Subject: [PATCH] Try a whole new method of referring to 'base', and checkout
 'head'

---
 .github/workflows/pr-checks.yml | 36 ++++++++++++++++++++-------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/.github/workflows/pr-checks.yml b/.github/workflows/pr-checks.yml
index c3de1a0d..3f75da38 100644
--- a/.github/workflows/pr-checks.yml
+++ b/.github/workflows/pr-checks.yml
@@ -15,28 +15,30 @@ jobs:
   flake8:
     runs-on: ubuntu-18.04
 
+    ####################################################################
+    # Show full github context to aid debugging.
+    ####################################################################
     steps:
     - name: Show github context
       run: cat $GITHUB_EVENT_PATH
+    ####################################################################
 
+    ####################################################################
+    # Checkout the necessary commits
+    ####################################################################
+    # We need the commits from the 'head' of the PR, not what it's
+    # based on.
     - name: Checkout commits
       # https://github.com/actions/checkout
       uses: actions/checkout@v2
       with:
+        repository: ${{github.head.repo.full_name}}
         fetch-depth: 0
+    ####################################################################
 
-    - name: Checkout base ref
-      uses: actions/checkout@v2
-      with:
-        ref: ${{github.base_ref}}
-        fetch-depth: 0
-
-    - name: Checkout head of PR
-      uses: actions/checkout@v2
-      with:
-        ref: ${{github.head_ref}}
-        fetch-depth: 0
-
+    ####################################################################
+    # Get Python set up
+    ####################################################################
     - name: Set up Python 3.7
       uses: actions/setup-python@v2
       with:
@@ -46,13 +48,19 @@ jobs:
         python -m pip install --upgrade pip
         pip install flake8
         if [ -f requirements-dev.txt ]; then pip install -r requirements-dev.txt; elif [ -f requirements.txt ]; then pip install -r requirements.txt ; fi
+    ####################################################################
 
+    ####################################################################
+    # Lint with flake8
+    ####################################################################
     - name: Lint with flake8
       env:
+        BASE_REPO: ${{github.base.full_name}}
         BASE_REF: ${{github.base_ref}}
 
       run: |
         # stop the build if there are Python syntax errors or undefined names, ignore existing 
-        git diff "refs/remotes/origin/${BASE_REF}" -- | flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics --diff
+        git diff "refs/remotes/${BASE_REPO}/${BASE_REF}" -- | flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics --diff
         # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
-        git diff "refs/remotes/origin/${BASE_REF}" -- | flake8 . --count --exit-zero --statistics --diff
+        git diff "refs/remotes/${BASE_REPO}/${BASE_REF}" -- | flake8 . --count --exit-zero --statistics --diff
+    ####################################################################