Fixes #2960 - Ticket removal of merged / linked tickets doesn't remove references

app/assets/javascripts/app/controllers/_application_controller_generic.coffee

@@ -645,11 +645,17 @@ class App.GenericHistory extends App.ControllerModal
         content = "#{ @T( item.type ) } #{ @T( 'sent to' ) } '#{ item.value_to }'"
       else if item.type is 'received_merge'
         ticket = App.Ticket.find( item.id_from )
-        ticket_link = "<a href=\"#ticket/zoom/#{ item.id_from }\">##{ ticket.number }</a>"
+        ticket_link = if ticket
+                        "<a href=\"#ticket/zoom/#{ item.id_from }\">##{ ticket.number }</a>"
+                      else
+                        item.value_from
         content = "#{ @T( 'Ticket' ) } #{ ticket_link } #{ @T( 'was merged into this ticket' ) }"
       else if item.type is 'merged_into'
         ticket = App.Ticket.find( item.id_to )
-        ticket_link = "<a href=\"#ticket/zoom/#{ item.id_to }\">##{ ticket.number }</a>"
+        ticket_link = if ticket
+                        "<a href=\"#ticket/zoom/#{ item.id_to }\">##{ ticket.number }</a>"
+                      else
+                        item.value_to
         content = "#{ @T( 'This ticket was merged into' ) } #{ @T( 'ticket' ) } #{ ticket_link }"
       else
         content = "#{ @T( item.type ) } #{ @T(item.object) } "

app/models/ticket.rb

@@ -20,6 +20,7 @@ class Ticket < ApplicationModel
   include Ticket::Assets
   include Ticket::SearchIndex
   include Ticket::Search
+  include Ticket::MergeHistory
 
   store          :preferences
   before_create  :check_generate, :check_defaults, :check_title, :set_default_state, :set_default_priority

app/models/ticket/merge_history.rb

@@ -0,0 +1,28 @@
+module Ticket::MergeHistory
+  extend ActiveSupport::Concern
+
+  included do
+    after_destroy :merge_history_cleanup
+  end
+
+  private
+
+  def merge_history_cleanup
+    cleanup_type :received_merge, :id_from, :value_from
+    cleanup_type :merged_into,    :id_to,   :value_to
+  end
+
+  def cleanup_type(history_type_name, lookup_attribute_name, target_attribute_name)
+    type   = History.type_lookup   history_type_name
+    object = History.object_lookup self.class.name
+
+    History
+      .where(history_object_id: object, history_type_id: type)
+      .find_by(lookup_attribute_name =>  id)
+      &.update!(target_attribute_name => replacement_title)
+  end
+
+  def replacement_title
+    "##{number} #{title}"
+  end
+end

spec/models/ticket_spec.rb

@@ -81,7 +81,6 @@ RSpec.describe Ticket, type: :model do
         end
       end
 
-      # Issue #2469 - Add information "Ticket merged" to History
       context 'when merging' do
         let(:merge_user) { create(:user) }
 
@@ -91,11 +90,12 @@ RSpec.describe Ticket, type: :model do
           # when creating the history entries
           target_ticket
           travel 5.minutes
+
+          ticket.merge_to(ticket_id: target_ticket.id, user_id: merge_user.id)
         end
 
+        # Issue #2469 - Add information "Ticket merged" to History
         it 'creates history entries in both the origin ticket and the target ticket' do
-          ticket.merge_to(ticket_id: target_ticket.id, user_id: merge_user.id)
-
           expect(target_ticket.history_get.size).to eq 2
 
           target_history = target_ticket.history_get.last
@@ -124,6 +124,24 @@ RSpec.describe Ticket, type: :model do
 
           expect(ExternalSync).to have_received(:migrate).with('Ticket', ticket.id, target_ticket.id)
         end
+
+        # Issue #2960 - Ticket removal of merged / linked tickets doesn't remove references
+        context 'and deleting the origin ticket' do
+          it 'adds reference number and title to the target ticket' do
+            expect { ticket.destroy }
+              .to change { target_ticket.history_get.find { |elem| elem.fetch('type') == 'received_merge' }.dig('value_from') }
+              .to("##{ticket.number} #{ticket.title}")
+          end
+        end
+
+        # Issue #2960 - Ticket removal of merged / linked tickets doesn't remove references
+        context 'and deleting the target ticket' do
+          it 'adds reference number and title to the origin ticket' do
+            expect { target_ticket.destroy }
+              .to change { ticket.history_get.find { |elem| elem.fetch('type') == 'merged_into' }.dig('value_to') }
+              .to("##{target_ticket.number} #{target_ticket.title}")
+          end
+        end
       end
     end
 

spec/system/ticket/update_spec.rb

@@ -170,14 +170,17 @@ RSpec.describe 'Ticket Update', type: :system do
     end
   end
 
-  # Issue #2469 - Add information "Ticket merged" to History
   context 'when merging tickets' do
-    it 'tickets history of both tickets should show the merge event' do
-      user = create :user
-      origin_ticket = create :ticket, group: group
-      target_ticket = create :ticket, group: group
-      origin_ticket.merge_to(ticket_id: target_ticket.id, user_id: user.id)
+    let!(:user) { create(:user) }
+    let!(:origin_ticket) { create :ticket, group: group }
+    let!(:target_ticket) { create :ticket, group: group }
 
+    before do
+      origin_ticket.merge_to(ticket_id: target_ticket.id, user_id: user.id)
+    end
+
+    # Issue #2469 - Add information "Ticket merged" to History
+    it 'tickets history of both tickets should show the merge event' do
       visit "#ticket/zoom/#{origin_ticket.id}"
       within(:active_content) do
         expect(page).to have_css('.js-actions .dropdown-toggle', wait: 3)
@@ -200,6 +203,50 @@ RSpec.describe 'Ticket Update', type: :system do
         expect(modal).to have_link "##{origin_ticket.number}", href: "#ticket/zoom/#{origin_ticket.id}"
       end
     end
+
+    # Issue #2960 - Ticket removal of merged / linked tickets doesn't remove references
+    context 'when the merged origin ticket is deleted' do
+      before do
+        origin_ticket.destroy
+      end
+
+      it 'shows the target ticket history' do
+        visit "#ticket/zoom/#{target_ticket.id}"
+        within(:active_content) do
+          expect(page).to have_css('.js-actions .dropdown-toggle', wait: 3)
+          click '.js-actions .dropdown-toggle'
+          click '.js-actions .dropdown-menu [data-type="ticket-history"]'
+        end
+
+        modal_ready
+
+        within('.modal-body') do
+          expect(page).to have_text "##{origin_ticket.number} #{origin_ticket.title}"
+        end
+      end
+    end
+
+    # Issue #2960 - Ticket removal of merged / linked tickets doesn't remove references
+    context 'when the merged target ticket is deleted' do
+      before do
+        target_ticket.destroy
+      end
+
+      it 'shows the origin history' do
+        visit "#ticket/zoom/#{origin_ticket.id}"
+        within(:active_content) do
+          expect(page).to have_css('.js-actions .dropdown-toggle', wait: 3)
+          click '.js-actions .dropdown-toggle'
+          click '.js-actions .dropdown-menu [data-type="ticket-history"]'
+        end
+
+        modal_ready
+
+        within('.modal-body') do
+          expect(page).to have_text "##{target_ticket.number} #{target_ticket.title}"
+        end
+      end
+    end
   end
 
   context 'when using text modules' do