Move label-triggered PR builds to a separate workflow file

GitHub's PR Checks UI summarizes one row per workflow file using the latest check_suite. When the main build-pull-request.yml workflow handled both 'opened' and 'labeled' events, adding any label after the build started would create a newer (skipped) check_suite that hid the in-progress real build from the PR Checks tab. A simpler conditional concurrency-group fix prevented the cancellation but couldn't fix this UI shadowing — the latest check_suite per workflow file still won.

Move 'labeled' events to a new build-pull-request-on-label.yml so they live in a separate workflow file (and thus a separate check_suite). The main workflow's row in the PR Checks UI is now always populated by the real build. Build-affecting labels ('test native', 'test openj9', 'test windows') share the main per-PR concurrency group, so they still cancel and supersede an in-progress build (equivalent UX to pushing a new commit). Non-build-affecting labels go to a unique throwaway concurrency group; the build job's 'if:' skips them instantly without affecting the main workflow.

Author: trask

.github/workflows/build-pull-request-on-label.yml

@@ -0,0 +1,51 @@
+name: Build pull request (on label)
+
+# This workflow handles `labeled` pull_request events as a separate workflow
+# (and thus a separate check_suite) so that label-triggered runs don't shadow
+# the main `Build pull request` workflow's check_suite in the PR Checks UI.
+# GitHub's PR Checks tab summarizes per workflow file using the latest
+# check_suite, so when a `labeled` event ran in the same workflow file as
+# the main build, the (skipped) labeled check_suite hid the in-progress
+# real build from the PR UI.
+#
+# Adding a non-build-affecting label (e.g. `automated code review`,
+# anything from `.github/labeler.yml`) routes here, hits the job's `if:`
+# filter, and is skipped instantly. Adding a build-affecting label
+# (`test native`, `test openj9`, `test windows`) cancels any in-progress
+# main build (via the shared per-PR concurrency group) and re-runs the
+# full build with the corresponding skip flag flipped — equivalent UX to
+# pushing a new commit.
+on:
+  pull_request:
+    types:
+      - labeled
+
+concurrency:
+  # Build-affecting labels share the main `build-pull-request.yml`
+  # concurrency group, so they cancel and supersede any in-progress
+  # build. Other labels go to a unique throwaway group so they neither
+  # cancel nor are cancelled by anything.
+  group: >-
+    ${{
+      (github.event.label.name == 'test native' ||
+       github.event.label.name == 'test openj9' ||
+       github.event.label.name == 'test windows')
+      && format('build-pull-request-{0}', github.event.pull_request.number)
+      || format('build-pull-request-on-label-noop-{0}', github.run_id)
+    }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    if: |
+      github.event.label.name == 'test native' ||
+      github.event.label.name == 'test openj9' ||
+      github.event.label.name == 'test windows'
+    uses: ./.github/workflows/reusable-pr-build.yml
+    with:
+      skip-native-tests: ${{ !contains(github.event.pull_request.labels.*.name, 'test native') }}
+      skip-openj9-tests: ${{ !contains(github.event.pull_request.labels.*.name, 'test openj9') }}
+      skip-windows-smoke-tests: ${{ !contains(github.event.pull_request.labels.*.name, 'test windows') }}

.github/workflows/build-pull-request.yml

@@ -6,7 +6,6 @@ on:
       - opened
       - synchronize
       - reopened
-      - labeled
 
 concurrency:
   group: build-pull-request-${{ github.event.pull_request.number }}
@@ -17,21 +16,16 @@ permissions:
 
 jobs:
   build:
-    # On `labeled` events, only proceed when the added label affects what we
-    # build. All other event types (opened, synchronize, reopened) always
-    # proceed.
-    if: |
-      github.event.action != 'labeled' ||
-      github.event.label.name == 'test native' ||
-      github.event.label.name == 'test openj9' ||
-      github.event.label.name == 'test windows'
     uses: ./.github/workflows/reusable-pr-build.yml
     with:
       # it's rare for only the openj9 tests, openj9 smoke variants, the windows
       # smoke tests, or the native tests to break, so they are gated by labels.
       # `test native` is applied automatically by .github/labeler.yml when the
       # PR diff touches native-relevant paths; `test openj9` and `test windows`
-      # are applied manually.
+      # are applied manually. Adding any of these labels to a PR is handled
+      # by the separate `build-pull-request-on-label.yml` workflow, which
+      # cancels this run and re-runs the build with the corresponding skip
+      # flag flipped.
       skip-native-tests: ${{ !contains(github.event.pull_request.labels.*.name, 'test native') }}
       skip-openj9-tests: ${{ !contains(github.event.pull_request.labels.*.name, 'test openj9') }}
       skip-windows-smoke-tests: ${{ !contains(github.event.pull_request.labels.*.name, 'test windows') }}