ci: Add a job to populate the matrix with default values

Author: lqiu96

.github/workflows/downstream_protobuf_source_compatibility_check_nightly.yaml renamed to .github/workflows/downstream_protobuf_compatibility_check_nightly.yaml

@@ -2,17 +2,26 @@ on:
   workflow_dispatch:
     inputs:
       protobuf_versions:
-        description: 'Comma separated list of Protobuf-Java versions (i.e. "3.25.5","4.28.3")'
-        # Default value for workflow_dispatch flow. If updating default value, update below as well.
-        default: '"3.25.5","4.28.3"'
+        description: 'Comma separated list of Protobuf-Java versions (i.e. "3.25.x","4.x.y")'
         required: true
   schedule:
     - cron: '0 1 * * *' # Nightly at 1am
 
-name: Downstream Source Compatibility Nightly
+name: Downstream Compatibility Nightly
 jobs:
-  downstream-protobuf-source-test:
+  #
+  define-matrix:
     runs-on: ubuntu-22.04
+    outputs:
+      protobuf-version: ${{ steps.protobuf-versions.outputs.protobuf-versions }}
+    steps:
+      - name: Default Protobuf Versions
+        id: protobuf-versions
+        run: |
+          echo 'protobuf-versions=["3.25.4","4.28.3"]' >> "${GITHUB_OUTPUT}"
+  downstream-protobuf-test:
+    runs-on: ubuntu-22.04
+    needs: define-matrix
     strategy:
       fail-fast: false
       matrix:
@@ -31,16 +40,15 @@ jobs:
           - java-spanner
           - java-storage
           - java-storage-nio
-        # Specify the Protobuf versions here as well because the default values above are only supplied from
-        # the workflow_dispatch flow. Without this, the nightly workflow doesn't have a default input otherwise
-        # and would resolve to ''. When updating, update both places to keep default values consistent.
-        protobuf-version: ${{ fromJSON(format('[{0}]', inputs.protobuf_versions || '"3.25.5","4.28.3"')) }}
+        # Default values are specified from the `protobuf-versions` step in the `define-matrix` job. Without this,
+        # the nightly workflow doesn't have a default input and would resolve to ''.
+        protobuf-version: ${{ fromJSON(format('[{0}]', inputs.protobuf_versions || needs.define-matrix.outputs.protobuf-versions)) }}
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-java@v3
         with:
           java-version: 17
           distribution: temurin
-      - run: mvn -version
-      - name: Perform downstream compatibility testing
+      - run: echo "Testing with Protobuf-Java v${{ matrix.protobuf-version }}"
+      - name: Perform downstream source compatibility testing
         run: REPOS_UNDER_TEST="${{ matrix.repo }}" PROTOBUF_RUNTIME_VERSION="${{ matrix.protobuf-version}}" ./.kokoro/presubmit/downstream-protobuf-source-compatibility.sh

.kokoro/presubmit/downstream-protobuf-source-compatibility.sh

@@ -34,8 +34,6 @@ source "$scriptDir/common.sh"
 
 setup_maven_mirror
 
-echo "Testing with Protobuf-Java v${PROTOBUF_RUNTIME_VERSION}"
-
 for repo in ${REPOS_UNDER_TEST//,/ }; do # Split on comma
   # Perform source-compatibility testing on main (latest changes)
   git clone "https://github.com/googleapis/$repo.git" --depth=1