Fix removing milestones when moving on boards

Don't remove milestones when
moving issues to backlog from non-milestone list

ee/app/services/ee/boards/issues/move_service.rb

@@ -41,7 +41,7 @@ module EE
 
         def milestone_id(issue)
           # We want to nullify the issue milestone.
-          return if moving_to_list.backlog?
+          return if moving_to_list.backlog? && moving_from_list.milestone?
 
           # Moving to a list which is not a 'milestone list' will keep
           # the already existent milestone.

ee/changelogs/unreleased/8333-add-related-epics-support.yml

+---
+title: Don't remove milestones when moving issues to board backlog from non-milestone list
+merge_request:
+author:
+type: fixed

ee/spec/services/ee/boards/issues/move_service_spec.rb

@@ -102,7 +102,7 @@ describe Boards::Issues::MoveService, services: true do
   end
 
   shared_examples 'moving an issue to/from assignee lists' do
-    let(:issue)  { create(:labeled_issue, project: project, labels: [bug, development]) }
+    let(:issue)  { create(:labeled_issue, project: project, labels: [bug, development], milestone: milestone1) }
     let(:params) { { board_id: board1.id, from_list_id: label_list1.id, to_list_id: label_list2.id } }
 
     context 'from assignee to label list' do
@@ -116,11 +116,12 @@ describe Boards::Issues::MoveService, services: true do
         issue.reload
         expect(issue.labels).to contain_exactly(bug, development, testing)
         expect(issue.assignees).to contain_exactly(user_list1.user)
+        expect(issue.milestone).to eq(milestone1)
       end
     end
 
     context 'from assignee to backlog' do
-      it 'removes assignment' do
+      it 'removes assignment and keeps milestone' do
         params = { board_id: board1.id, from_list_id: user_list1.id, to_list_id: backlog.id }
         issue.assignees.push(user_list1.user)
         expect(issue.assignees).to contain_exactly(user_list1.user)
@@ -130,6 +131,7 @@ describe Boards::Issues::MoveService, services: true do
         issue.reload
         expect(issue.assignees).to eq([])
         expect(issue).not_to be_closed
+        expect(issue.milestone).to eq(milestone1)
       end
     end
 
@@ -144,6 +146,7 @@ describe Boards::Issues::MoveService, services: true do
         issue.reload
         expect(issue.assignees).to contain_exactly(user_list1.user)
         expect(issue).to be_closed
+        expect(issue.milestone).to eq(milestone1)
       end
     end
 
@@ -156,6 +159,7 @@ describe Boards::Issues::MoveService, services: true do
         issue.reload
         expect(issue.labels).to contain_exactly(bug, development)
         expect(issue.assignees).to contain_exactly(user_list1.user)
+        expect(issue.milestone).to eq(milestone1)
       end
     end
 
@@ -170,6 +174,7 @@ describe Boards::Issues::MoveService, services: true do
         issue.reload
         expect(issue.labels).to contain_exactly(bug, development)
         expect(issue.assignees).to contain_exactly(user)
+        expect(issue.milestone).to eq(milestone1)
       end
     end
   end

spec/support/shared_examples/services/boards/issues_move_service.rb

@@ -39,6 +39,22 @@ shared_examples 'issues move service' do |group|
     end
   end
 
+  context 'when moving to backlog' do
+    let(:milestone) { create(:milestone, project: project) }
+    let!(:backlog)  { create(:backlog_list, board: board1) }
+
+    let(:issue)  { create(:labeled_issue, project: project, labels: [bug, development, testing, regression], milestone: milestone) }
+    let(:params) { { board_id: board1.id, from_list_id: list2.id, to_list_id: backlog.id } }
+
+    it 'keeps labels and milestone' do
+      described_class.new(parent, user, params).execute(issue)
+      issue.reload
+
+      expect(issue.labels).to contain_exactly(bug, regression)
+      expect(issue.milestone).to eq(milestone)
+    end
+  end
+
   context 'when moving from closed' do
     let(:issue)  { create(:labeled_issue, :closed, project: project, labels: [bug]) }
     let(:params) { { board_id: board1.id, from_list_id: closed.id, to_list_id: list2.id } }