Trigger subscription when assignees are updated

This triggers the GraphQL subscription when assignees on an issue are
updated

app/graphql/graphql_triggers.rb

+# frozen_string_literal: true
+
+module GraphqlTriggers
+  def self.issuable_assignees_updated(issuable)
+    GitlabSchema.subscriptions.trigger('issuableAssigneesUpdated', { issuable_id: issuable.to_gid }, issuable)
+  end
+end

app/services/issues/update_service.rb

@@ -61,12 +61,7 @@ module Issues
         todo_service.update_issue(issue, current_user, old_mentioned_users)
       end
 
-      if issue.assignees != old_assignees
-        create_assignee_note(issue, old_assignees)
-        notification_service.async.reassigned_issue(issue, current_user, old_assignees)
-        todo_service.reassigned_assignable(issue, current_user, old_assignees)
-        track_incident_action(current_user, issue, :incident_assigned)
-      end
+      handle_assignee_changes(issue, old_assignees)
 
       if issue.previous_changes.include?('confidential')
         # don't enqueue immediately to prevent todos removal in case of a mistake
@@ -90,6 +85,19 @@ module Issues
       end
     end
 
+    def handle_assignee_changes(issue, old_assignees)
+      return if issue.assignees == old_assignees
+
+      create_assignee_note(issue, old_assignees)
+      notification_service.async.reassigned_issue(issue, current_user, old_assignees)
+      todo_service.reassigned_assignable(issue, current_user, old_assignees)
+      track_incident_action(current_user, issue, :incident_assigned)
+
+      if Gitlab::ActionCable::Config.in_app? || Feature.enabled?(:broadcast_issue_updates, issue.project)
+        GraphqlTriggers.issuable_assignees_updated(issue)
+      end
+    end
+
     def handle_task_changes(issuable)
       todo_service.resolve_todos_for_target(issuable, current_user)
       todo_service.update_issue(issuable, current_user)

spec/graphql/graphql_triggers_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe GraphqlTriggers do
+  describe '.issuable_assignees_updated' do
+    it 'triggers the issuableAssigneesUpdated subscription' do
+      assignees = create_list(:user, 2)
+      issue = create(:issue, assignees: assignees)
+
+      expect(GitlabSchema.subscriptions).to receive(:trigger).with(
+        'issuableAssigneesUpdated',
+        { issuable_id: issue.to_gid },
+        issue
+      )
+
+      GraphqlTriggers.issuable_assignees_updated(issue)
+    end
+  end
+end

spec/services/issues/update_service_spec.rb

@@ -1014,13 +1014,15 @@ RSpec.describe Issues::UpdateService, :mailer do
 
       with_them do
         it 'broadcasts to the issues channel based on ActionCable and feature flag values' do
-          expect(Gitlab::ActionCable::Config).to receive(:in_app?).and_return(action_cable_in_app_enabled)
+          allow(Gitlab::ActionCable::Config).to receive(:in_app?).and_return(action_cable_in_app_enabled)
           stub_feature_flags(broadcast_issue_updates: feature_flag_enabled)
 
           if should_broadcast
             expect(IssuesChannel).to receive(:broadcast_to).with(issue, event: 'updated')
+            expect(GraphqlTriggers).to receive(:issuable_assignees_updated).with(issue)
           else
             expect(IssuesChannel).not_to receive(:broadcast_to)
+            expect(GraphqlTriggers).not_to receive(:issuable_assignees_updated).with(issue)
           end
 
           update_issue(update_params)