chore(ci): Add required checks job for Check Package.swift Diff (#6040)

Author: philprime

.github/file-filters.yml

@@ -311,6 +311,18 @@ run_build_for_prs: &run_build_for_prs # Build-related code
   - "Makefile" # Make commands used for CI build setup
   - "Brewfile*" # Dependency installation affects build environment
 
+run_check_package_diff_for_prs: &run_check_package_diff_for_prs # Package.swift diff checking
+  # GH Actions
+  - ".github/workflows/check-package-diff.yml"
+  - ".github/file-filters.yml"
+
+  # Package files
+  - "Package*.swift"
+
+  # Other
+  - "Makefile" # Make commands used for package diff checking
+  - "Utils/expected_package_diff.patch"
+
 run_codeql_analysis_for_prs: &run_codeql_analysis_for_prs # CodeQL security analysis
   - "Sources/**"
 

.github/workflows/check-package-diff.yml

@@ -8,17 +8,49 @@ on:
       - main
 
   pull_request:
-    paths:
-      - ".github/workflows/check-package-diff.yml"
-      - "Package*.swift"
-      - "Makefile"
-      - "Utils/expected_package_diff.patch"
 
 jobs:
+  files-changed:
+    name: Detect File Changes
+    runs-on: ubuntu-latest
+    outputs:
+      run_check_package_diff_for_prs: ${{ steps.changes.outputs.run_check_package_diff_for_prs }}
+    steps:
+      - uses: actions/checkout@v5
+      - name: Get changed files
+        id: changes
+        uses: dorny/paths-filter@de90cc6fb38fc0963ad72b210f1f284cd68cea36 # v3.0.2
+        with:
+          token: ${{ github.token }}
+          filters: .github/file-filters.yml
+
   check:
+    if: github.event_name != 'pull_request' || needs.files-changed.outputs.run_check_package_diff_for_prs == 'true'
+    needs: files-changed
     name: Check Package.swift Diff
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v5
       - name: Check Package.swift Diff
         run: make check-package-diff
+
+  # This check validates that either check-package-diff passed or was skipped, which allows us
+  # to make check-package-diff a required check with only running the check-package-diff when required.
+  # So, we don't have to run check-package-diff, for example, for unrelated changes.
+  check_package_diff-required-check:
+    needs:
+      [
+        files-changed,
+        check,
+      ]
+    name: Check Package.swift Diff
+    # This is necessary since a failed/skipped dependent job would cause this job to be skipped
+    if: always()
+    runs-on: ubuntu-latest
+    steps:
+      # If any jobs we depend on fails gets cancelled or times out, this job will fail.
+      # Skipped jobs are not considered failures.
+      - name: Check for failures
+        if: contains(needs.*.result, 'failure') || contains(needs.*.result, 'cancelled')
+        run: |
+          echo "One of the check-package-diff jobs has failed." && exit 1