Run snapshot comparison on GitHub (#55922)

.github/workflows/validate-cxx-stable-api.yml

@@ -0,0 +1,62 @@
+name: Validate C++ Stable API
+
+on:
+  pull_request:
+  # pull_request_target:
+  #   types: [opened, edited, reopened, synchronize]
+
+env:
+  DOXYGEN_VERSION: '1.16.1'
+
+jobs:
+  validate_cxx_stable_api:
+    runs-on: ubuntu-latest
+    if: github.repository == 'facebook/react-native'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Install Doxygen
+        run: |
+          for i in 1 2 3; do
+            wget -q https://www.doxygen.nl/files/doxygen-${{ env.DOXYGEN_VERSION }}.linux.bin.tar.gz && break
+            echo "Download attempt $i failed, retrying in 10s..."
+            sleep 10
+          done
+          tar -xzf doxygen-${{ env.DOXYGEN_VERSION }}.linux.bin.tar.gz
+          echo "${{ github.workspace }}/doxygen-${{ env.DOXYGEN_VERSION }}/bin" >> $GITHUB_PATH
+
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+
+      - name: Install Python dependencies
+        run: pip install doxmlparser natsort pyyaml
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22.14.0
+
+      - name: Install Node dependencies
+        run: yarn install
+
+      - name: Verify C++ Stable API snapshots
+        id: verify
+        continue-on-error: true
+        env:
+          DOXYGEN_BIN: ${{ github.workspace }}/doxygen-${{ env.DOXYGEN_VERSION }}/bin/doxygen
+        working-directory: scripts/cxx-api
+        run: python -m parser --check --output-dir ${{ runner.temp }}/generated-api-snapshots
+
+      - name: Upload generated snapshots
+        if: always() && steps.verify.outcome != 'skipped'
+        uses: actions/upload-artifact@v4
+        with:
+          name: generated-cxx-api-snapshots
+          path: ${{ runner.temp }}/generated-api-snapshots/
+
+      - name: Fail if snapshots are out of date
+        if: steps.verify.outcome == 'failure'
+        run: exit 1

scripts/cxx-api/parser/__main__.py

@@ -234,8 +234,8 @@ def main():
     )
 
     with tempfile.TemporaryDirectory() as tmpdir:
-        snapshot_output_dir = (
-            tmpdir if args.check else args.output_dir or get_default_snapshot_dir()
+        snapshot_output_dir = args.output_dir or (
+            tmpdir if args.check else get_default_snapshot_dir()
         )
 
         build_snapshots(