Merge pull request #81 from per1234/compare-tag

Use previous tag as base when "Compare Performance" workflow triggered by tag

.github/workflows/compare-performance.yml

@@ -34,17 +34,42 @@ jobs:
       base-ref: ${{ steps.base-ref.outputs.ref }}
 
     steps:
+      # Repo is required to get the previous tag ref that is the base of the comparison on tag push triggered run.
+      - name: Checkout repository
+        if: ${{ startsWith(github.ref, 'refs/tags/') }}
+        uses: actions/checkout@v2
+
       - name: Determine comparison ref
         id: base-ref
         run: |
           if [[ "${{ github.event_name }}" == "workflow_dispatch" ]]; then
-            echo "::set-output name=ref::${{ github.event.inputs.comparison-ref }}"
+            COMPARISON_REF="${{ github.event.inputs.comparison-ref }}"
           elif [[ "${{ github.event_name }}" == "pull_request" ]]; then
-            echo "::set-output name=ref::${{ github.base_ref }}"
+            COMPARISON_REF="${{ github.base_ref }}"
+          elif [[ "${{ startsWith(github.ref, 'refs/tags/') }}" == "true" ]]; then
+            COMPARISON_REF="$( \
+              git ls-remote \
+              --quiet \
+              --tags \
+              --refs \
+              --sort=version:refname | \
+                cut \
+                  --delimiter='/' \
+                  --fields=3 | \
+                    tail -2 | \
+                      head -1
+            )"
           else
-            echo "::set-output name=ref::${{ github.event.before }}"
+            COMPARISON_REF="${{ github.event.before }}"
           fi
 
+          if [[ "$COMPARISON_REF" == "" ]]; then
+            echo "::error::Unable to determine comparison ref"
+            exit 1
+          fi
+
+          echo "::set-output name=ref::$COMPARISON_REF"
+
   run:
     name: Run at ${{ matrix.data.ref }} (${{ matrix.data.description }})
     needs: init