Merge pull request tock#4298 from tock/dev/treadmill-ghactions-pull-r…

…equest-check

treadmill-ci: add dummy pull_request trigger to allow using as required check

.github/workflows/treadmill-ci.yml

@@ -32,16 +32,26 @@ on:
       - master
       # Add any additional branches you want to include
       # - dev/test_ci_branch
+
   # Pull requests from forks will not have access to the required GitHub API
   # secrets below, even if they are using an appropriate deployment environment
   # and the workflow runs have been approved according to this environment's
   # rules. We don't know whether this is a bug on GitHub's end or deliberate.
+  #
   # Either way, for now we disable this workflow to run on PRs until we have
   # an API proxy that securely performs these GitHub API calls (adding runners
   # and starting Treadmill jobs with those runner registration tokens), which
   # allows this workflow to run without access to repository secrets.
-  #pull_request:
+  #
+  # However, because GitHub's merge queues don't allow to differentiate required
+  # checks for *entering* the merge queue from those that are required to *pass*
+  # it, we also can't disable this trigger entirely. Instead, we use a selector
+  # to avoid running any actual checks on this trigger, while still technically
+  # succeeding for PRs.
+  pull_request:
+
   merge_group: # Run CI for the GitHub merge queue
+
   # Manually dispatch for a specific branch (will require approval
   # through the treadmill-ci-merged environment:
   workflow_dispatch:
@@ -55,16 +65,19 @@ on:
         required: true
         default: 'master'
       tests-json:
-        description: 'tests-json value passed to HWCI workflow (if empty, output from determine-tests step is used)'
+        description: 'tests-json value passed to HWCI workflow (if empty, output from hwci-determine-tests step is used)'
         required: false
 
 permissions:
   contents: read
 
 jobs:
-  determine-tests:
+  hwci-determine-tests:
     runs-on: ubuntu-latest
 
+    # Don't run on a pull request, as explained above.
+    if: github.event_name != 'pull_request'
+
     outputs:
       hwci-tests-json: ${{ steps.determine-tests.outputs.hwci-tests-json }}
 
@@ -105,12 +118,14 @@ jobs:
           hwci_tests_json=$(cat selected_tests.json | jq -c '.')
           echo "hwci-tests-json=${hwci_tests_json}" >> "$GITHUB_OUTPUT"
 
-  treadmill-ci:
-    needs: [determine-tests]
+  hwci-treadmill-dispatch:
+    needs: [hwci-determine-tests]
 
     # This checks whether there is at least one test to run, see
     # https://github.com/orgs/community/discussions/27125#discussioncomment-3254720
-    if: fromJSON(needs.determine-tests.outputs.hwci-tests-json)[0] != null || github.event_name == 'workflow_dispatch'
+    #
+    # Don't run on a pull request, as explained above.
+    if: github.event_name != 'pull_request' && (fromJSON(needs.hwci-determine-tests.outputs.hwci-tests-json)[0] != null || github.event_name == 'workflow_dispatch')
 
     # The main tock-hardware-ci workflow is imported from another repository. It
     # can be reused across multiple Tock repositories such as the kernel,
@@ -139,6 +154,25 @@ jobs:
       libtock-c-ref: ${{ github.event_name == 'workflow_dispatch' && inputs.libtock-c-ref || 'master' }}
 
       # Pass the selected tests:
-      tests-json: ${{ (github.event_name == 'workflow_dispatch' && inputs.tests-json != '') && inputs.tests-json || needs.determine-tests.outputs.hwci-tests-json }}
+      tests-json: ${{ (github.event_name == 'workflow_dispatch' && inputs.tests-json != '') && inputs.tests-json || needs.hwci-determine-tests.outputs.hwci-tests-json }}
 
     secrets: inherit
+
+  # We cannot depend on *all* test-execute jobs of hwci-treadmill-dispatch as
+  # required checks for pull requests and merge queues. Thus, we run another
+  # single dummy step here that waits for all the hwci-treadmill-dispatch jobs
+  # to complete and report success.
+  #
+  # We also use this to report a "dummy" success value for the "pull_request"
+  # trigger, as explained in the comment of the "on:" parameters above.
+  hwci-report-success:
+    needs: [hwci-determine-tests, hwci-treadmill-dispatch]
+
+    if: always()
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Fail if any of the 'hwci-treadmill-dispatch' jobs failed
+        if: github.event_name != 'pull_request' && contains(needs.*.result, 'failure')
+        run: exit 1