differing before/after in update_build_env for opened/synchronized

Author: trevorcampbell

.github/workflows/update_build_environment.yml

@@ -15,18 +15,23 @@ jobs:
       with:
         fetch-depth: '0'
         ref: ${{ github.head_ref }}
-    - name: Print GitHub context for debugging
-      env:
-        GITHUB_CONTEXT: ${{ toJson(github) }}
-      run: echo "$GITHUB_CONTEXT"
     - name: Check if Dockerfile needs to be rebuilt
       id: check-stale
       run: |
+        echo "Checking if Dockerfile was modified since last commit on this PR"
         echo "GitHub PR action type: ${{ github.event.action }}"
-        echo "Checking if the PR modifies the Dockerfile"
-        echo "GitHub event before: ${{ github.event.before }}"
-        echo "GitHub event after: ${{ github.event.after }}"
-        if git diff --quiet ${{ github.event.before }} ${{ github.event.after }} Dockerfile; then
+        if [ "${{ github.event.action }}" == "opened" ]; then
+            echo "GitHub base ref: ${{ github.base_ref }}"
+            echo "GitHub head ref: ${{ github.head_ref }}"
+            BEFORE=${{ github.base_ref }}
+            AFTER=${{ github.head_ref }}
+        else
+            echo "GitHub event before: ${{ github.event.before }}"
+            echo "GitHub event after: ${{ github.event.after }}"
+            BEFORE=${{ github.event.before }}
+            AFTER=${{ github.event.after }}
+        fi
+        if git diff --quiet $BEFORE $AFTER Dockerfile; then
             echo "PR synchronized, but Dockerfile was not edited. Not rebuilding the image."
             echo "stale_dockerfile=false" >> "$GITHUB_OUTPUT"
         else