Running CI only on comment trigger

Author: michalChrobot

.github/workflows/pr-keyword-check.yml

@@ -0,0 +1,10 @@
+name: PR keyword check
+on:
+  workflow_dispatch:
+
+# This workflow deliberately does nothing of value. The branch rules require the associated "Check PR issue comments for trigger keywords" job to have run before the PR being merged
+jobs:
+  pr-keyword-check:
+    runs-on: unity-linux-runner
+    steps:
+      - run: ls

.yamato/_triggers.yml

@@ -15,6 +15,8 @@
     # Focuses on critical validation paths that we should validate before merging PRs
     # Cancels previous runs on new commits
     # Excludes draft PRs
+    # Excludes running when changes ONLY touching documentation files
+    # Requires `/ci ngo` or `/ci ignore` comment to trigger the job. This was implemented and explained in https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/pull/3577
 
   # Nightly:
     # This test validates same subset as pull_request_trigger with addition of mobile/console tests and webgl builds
@@ -38,6 +40,20 @@
 
 #-----------------------------------------------------------------------------------
 
+# Gates the merger of PRs as a pre-requisite. Runs when `/ci ngo` or `/ci ignore` is present as an issue comment
+# Notice that I needed this job to do "something" and that's why there is a placeholder GitHub action used
+# TODO: In the future we could have comment like "docs" or "project" to run a specific subset of tests
+check_pr_issue_comments_for_trigger_keywords:
+  name: Check PR for trigger comments of ngo or ignore. For example /ci ngo
+  agent:
+    type: Unity::github::action
+    action_source: pr-keyword-check.yml
+  triggers:
+    expression: |-
+      pull_request.comment eq "ngo" OR
+      pull_request.comment eq "ignore"
+
+
 # Run all relevant tasks when a pull request targeting the develop or release branch is created or updated.
 # In order to have better coverage we run desktop standalone tests with different configurations which allows to mostly cover for different platforms, scripting backends and editor versions.
 # Since standards job is a part of initial checks it's not present as direct dependency here
@@ -61,15 +77,10 @@ pull_request_trigger:
     # Coverage on other standalone machines is present in Nightly job so it's enough to not run all of them for PRs
     - .yamato/desktop-standalone-tests.yml#desktop_standalone_test_testproject_ubuntu_il2cpp_2022.3
   triggers:
+    expression: |-
+      pull_request.comment eq "ngo" AND
+      NOT pull_request.changes.all match "**/Documentation~/**"
     cancel_old_ci: true
-    pull_requests:
-      - targets:
-          only:
-            - "develop"
-            - "develop-2.0.0"
-            - "/release\/.*/"
-      - drafts: false
-
 
 # Run all tests on trunk on nightly basis.
 # Same subset as pull_request_trigger with addition of mobile/desktop/console tests and webgl builds