Skip unnecessary rebuilds when no dependencies changed (#100)

Add a check step to the rebuild workflow that compares the last commit
touching dependency files against the last dist build commit. If no
dependency files changed since the last rebuild, all subsequent steps
are skipped, avoiding unnecessary install and build cycles.

Author: mraible

.github/workflows/rebuild.yml

@@ -21,17 +21,39 @@ jobs:
         uses: actions/setup-node@395ad3262231945c25e8478fd5baf05154b1d79f  # v6.1.0
         with:
           node-version: 22
+      - name: Check if rebuild needed
+        id: check
+        run: |
+          LAST_BUILD=$(git log -1 --format=%H -- ui/extensions/hello/src/dist/)
+          if [ -z "$LAST_BUILD" ]; then
+            echo "skip=false" >> "$GITHUB_OUTPUT"
+            echo "No previous build found, rebuilding"
+            exit 0
+          fi
+          CHANGES=$(git diff --name-only "$LAST_BUILD" HEAD -- ui/extensions/hello/package.json ui/extensions/hello/package-lock.json)
+          if [ -z "$CHANGES" ]; then
+            echo "skip=true" >> "$GITHUB_OUTPUT"
+            echo "No dependency changes since last build, skipping"
+          else
+            echo "skip=false" >> "$GITHUB_OUTPUT"
+            echo "Dependency changes detected:"
+            echo "$CHANGES"
+          fi
       - name: Install dependencies
+        if: steps.check.outputs.skip != 'true'
         run: npm ci
         working-directory: ui/extensions/hello
       - name: Build React app
+        if: steps.check.outputs.skip != 'true'
         run: npm run build
         working-directory: ui/extensions/hello
       - name: Create commit
+        if: steps.check.outputs.skip != 'true'
         run: |
           git add .
           git commit -a -m "Rebuild UI with latest dependencies" || true
       - name: Create Pull Request
+        if: steps.check.outputs.skip != 'true'
         uses: peter-evans/create-pull-request@22a9089034f40e5a961c8808d113e2c98fb63676  # v7.0.11
         with:
           token: ${{ secrets.GITHUB_TOKEN }}