Set correct timestamps when creating past issues

Sets `system_note_timestamp` from `created_at`

app/models/concerns/noteable.rb

@@ -13,7 +13,7 @@ module Noteable
     end
   end
 
-  # The timestamp of the note (e.g. the :updated_at attribute if provided via
+  # The timestamp of the note (e.g. the :created_at or :updated_at attribute if provided via
   # API call)
   def system_note_timestamp
     @system_note_timestamp || Time.now # rubocop:disable Gitlab/ModuleWithInstanceVariables

changelogs/unreleased/58361-issue-create-system-note-timestamp.yml

@@ -0,0 +1,5 @@
+---
+title: Fix system notes timestamp when creating issue in the past
+merge_request: 27406
+author:
+type: fixed

lib/api/issues.rb

@@ -192,6 +192,7 @@ module API
         params.delete(:iid) unless current_user.can?(:set_issue_iid, user_project)
 
         issue_params = declared_params(include_missing: false)
+        issue_params[:system_note_timestamp] = params[:created_at]
 
         issue_params = convert_parameters_from_legacy_format(issue_params)
 

spec/requests/api/issues_spec.rb

@@ -1480,12 +1480,20 @@ describe API::Issues do
       let(:params) { { title: 'new issue', labels: 'label, label2', created_at: creation_time } }
 
       context 'by an admin' do
-        it 'sets the creation time on the new issue' do
+        before do
           post api("/projects/#{project.id}/issues", admin), params: params
+        end
 
+        it 'sets the creation time on the new issue' do
           expect(response).to have_gitlab_http_status(201)
           expect(Time.parse(json_response['created_at'])).to be_like_time(creation_time)
         end
+
+        it 'sets the system notes timestamp based on creation time' do
+          issue = Issue.find(json_response['id'])
+
+          expect(issue.resource_label_events.last.created_at).to be_like_time(creation_time)
+        end
       end
 
       context 'by a project owner' do