add support for pull request events

.github/workflows/engine-build.yml

@@ -8,6 +8,7 @@ on:
  default: false
  schedule:
  - cron: "36 00 * * *"
+ pull_request:
 jobs:
  build-engine:
  strategy:
@@ -33,12 +34,26 @@ jobs:
  uses: namespacelabs/nscloud-cache-action@v1
  with:
  path: bazel-remote-data
+ - name: Restore pull request's bazel remote cache overlay
+ id: pr-cache-restore
+ if: github.event_name == 'pull_request'
+ uses: actions/cache/restore@v4
+ with:
+ path: bazel-remote-data-overlay
+ key: pr-bazel-remote-data
+ - name: Mount bazel remote overlay
+ id: mount-overlay
+ if: github.event_name == 'pull_request'
+ run: |
+ sudo apt-get install --yes fuse-overlayfs
+ mkdir overlay-workdir
+ sudo fuse-overlayfs -o lowerdir=bazel-remote-data,upperdir=bazel-remote-data-overlay,workdir=overlay-workdir bazel-remote-data
  - name: Start remote ccache fetcher
  env:
  BAZEL_REMOTE_S3_ENDPOINT: ${{ vars.R2_ACCOUNT_ID }}.r2.cloudflarestorage.com
  BAZEL_REMOTE_S3_BUCKET: ${{ vars.R2_BUCKET_BUILD_CACHE }}
- BAZEL_REMOTE_S3_ACCESS_KEY_ID: ${{ vars.R2_ACCESS_KEY_ID }}
- BAZEL_REMOTE_S3_SECRET_ACCESS_KEY: ${{ secrets.R2_ACCESS_KEY_SECRET }}
+ BAZEL_REMOTE_S3_ACCESS_KEY_ID: ${{ github.event_name == 'pull_request' && vars.R2_RO_ACCESS_KEY_ID || vars.R2_ACCESS_KEY_ID }}
+ BAZEL_REMOTE_S3_SECRET_ACCESS_KEY: ${{ github.event_name == 'pull_request' && vars.R2_RO_ACCESS_KEY_SECRET || secrets.R2_ACCESS_KEY_SECRET }}
  run: |
  docker network create --driver bridge engine-build
  docker run -d --rm \
@@ -57,6 +72,7 @@ jobs:
  --s3.auth_method access_key \
  --s3.region auto \
  --max_size 5 \
+ --num_uploaders ${{ github.event_name == 'pull_request' && '0' || '100' }} \
  --disable_http_ac_validation
 
  cat > remote_ccache.conf <<EOF
@@ -101,3 +117,13 @@ jobs:
  run: |
  docker stop builder || true
  docker stop remote-cache
+ - name: Unmount bazel remote overlay
+ if: always() && steps.mount-overlay.outcome == 'success'
+ run: sudo fusermount -u bazel-remote-data
+ - name: Save pull request's bazel remote cache overlay
+ id: pr-cache-save
+ if: always() && steps.pr-cache-restore.outcome == 'success'
+ uses: actions/cache/save@v4
+ with:
+ path: bazel-remote-data-overlay
+ key: ${{ steps.pr-cache-restore.outputs.cache-primary-key }}