FIX Set fetch-depth for parent-branch

.github/workflows/ci.yml

@@ -140,8 +140,42 @@ jobs:
 
     steps:
 
+      - name: Set fetch depth
+        id: set-fetch-depth
+        env:
+          GITHUB_REPOSITORY: ${{ github.repository }}
+        shell: bash
+        run: |
+          # Default fetch-depth of 1 will only fetch the latest commit
+          # This is fine for non-pull-request events where standard major.minor naming conventions
+          # are used so we do not need to attempt to get the name of the parent branch
+          FETCH_DEPTH=1
+          # For pull-requests, set fetch-depth to one more than the number of commits
+          # so we can later make a best attempt at getting the name of the parent branch
+          if [[ "${{ github.event_name }}" == "pull_request" ]]; then
+            PR_NUMBER=${{ github.event.pull_request.number }}
+            # https://docs.github.com/en/rest/pulls/pulls#list-commits-on-a-pull-request
+            RESP_CODE=$(curl -w %{http_code} -s -o __pr_commits.json \
+            -X GET https://api.github.com/repos/$GITHUB_REPOSITORY/pulls/$PR_NUMBER/commits \
+            -H "Accept: application/vnd.github.v3+json" \
+            -H "Authorization: token ${{ github.token }}" \
+            )
+            if [[ $RESP_CODE == "200" ]]; then
+              NUM_COMMITS=$(cat __pr_commits.json | jq '. | length')
+              FETCH_DEPTH=$(( NUM_COMMITS + 1 ))
+              rm __pr_commits.json
+            else
+              echo "Failed to fetch commits for pull-request - HTTP response code was $RESP_CODE"
+              exit 1
+            fi
+          fi
+          echo "FETCH_DEPTH is $FETCH_DEPTH"
+          echo "::set-output name=fetch-depth::$FETCH_DEPTH"
+
       - name: Checkout code
         uses: actions/checkout@7884fcad6b5d53d10323aee724dc68d8b9096a2e # v2.4.2
+        with:
+          fetch-depth: ${{ steps.set-fetch-depth.outputs.fetch-depth }}
 
       - name: Install PHP
         # SHA will need to be updated to support new php version when they are released