Add system notes when moving issues between epics

app/models/system_note_metadata.rb

@@ -17,6 +17,7 @@ class SystemNoteMetadata < ActiveRecord::Base
     outdated
     approved unapproved relate unrelate
     epic_issue_added issue_added_to_epic epic_issue_removed issue_removed_from_epic
+    epic_issue_moved issue_changed_epic
   ].freeze
 
   validates :note, presence: true

app/services/system_note_service.rb

@@ -576,6 +576,20 @@ module SystemNoteService
     create_note(NoteSummary.new(epic, nil, user, body, action: action))
   end
 
+  def epic_issue_moved(from_epic, issue, to_epic, user)
+    epic_issue_moved_act(from_epic, issue, to_epic, user, verb: 'added', direction: 'from')
+    epic_issue_moved_act(to_epic, issue, from_epic, user, verb: 'moved', direction: 'to')
+  end
+
+  def epic_issue_moved_act(subject_epic, issue, object_epic, user, verb:, direction:)
+    action = 'epic_issue_moved'
+
+    body = "#{verb} issue #{issue.to_reference(subject_epic.group)} #{direction}" \
+      " epic #{subject_epic.to_reference(object_epic.group)}"
+
+    create_note(NoteSummary.new(object_epic, nil, user, body, action: action))
+  end
+
   def issue_on_epic(issue, epic, user, type)
     return unless validate_epic_issue_action_type(type)
 
@@ -592,6 +606,13 @@ module SystemNoteService
     create_note(NoteSummary.new(issue, issue.project, user, body, action: action))
   end
 
+  def issue_epic_change(issue, epic, user)
+    body = "changed epic to #{epic.to_reference(issue.project)}"
+    action = 'issue_changed_epic'
+
+    create_note(NoteSummary.new(issue, issue.project, user, body, action: action))
+  end
+
   def validate_epic_issue_action_type(type)
     [:added, :removed].include?(type)
   end

changelogs/unreleased-ee/4261-moving-issue-note.yml

+---
+title: Add system notes when moving issues between epics
+merge_request:
+author:
+type: added

ee/app/services/epic_issues/create_service.rb

@@ -4,17 +4,31 @@ module EpicIssues
 
     def relate_issues(referenced_issue)
       link = EpicIssue.find_or_initialize_by(issue: referenced_issue)
+
+      params = if link.persisted?
+                 { issue_moved: true, original_epic: link.epic }
+               else
+                 {}
+               end
+
       link.epic = issuable
       link.move_to_start
       link.save!
 
-      link
+      yield params
     end
 
-    def create_notes(referenced_issue)
+    def create_notes(referenced_issue, params)
+      if params[:issue_moved]
+        SystemNoteService.epic_issue_moved(
+          params[:original_epic], referenced_issue, issuable, current_user
+        )
+        SystemNoteService.issue_epic_change(referenced_issue, issuable, current_user)
+      else
         SystemNoteService.epic_issue(issuable, referenced_issue, current_user, :added)
         SystemNoteService.issue_on_epic(referenced_issue, issuable, current_user, :added)
       end
+    end
 
     def extractor_context
       { group: issuable.group }

ee/app/services/issuable_links/create_service.rb

@@ -19,11 +19,9 @@ module IssuableLinks
 
     def create_issue_links
       referenced_issues.each do |referenced_issue|
-        link = relate_issues(referenced_issue)
-
-        next unless link.persisted?
-
-        create_notes(referenced_issue)
+        relate_issues(referenced_issue) do |params|
+          create_notes(referenced_issue, params)
+        end
       end
     end
 

ee/app/services/issue_links/create_service.rb

 module IssueLinks
   class CreateService < IssuableLinks::CreateService
     def relate_issues(referenced_issue)
-      IssueLink.create(source: issuable, target: referenced_issue)
+      link = IssueLink.create(source: issuable, target: referenced_issue)
+
+      yield if link.persisted?
     end
 
     def linkable_issues(issues)
       issues.select { |issue| can?(current_user, :admin_issue_link, issue) }
     end
 
-    def create_notes(referenced_issue)
+    def create_notes(referenced_issue, params)
       SystemNoteService.relate_issue(issuable, referenced_issue, current_user)
       SystemNoteService.relate_issue(referenced_issue, issuable, current_user)
     end

spec/ee/spec/services/epic_issues/create_service_spec.rb

@@ -223,6 +223,37 @@ describe EpicIssues::CreateService do
         it 'returns success status' do
           is_expected.to eq(status: :success)
         end
+
+        it 'creates 3 system notes' do
+          expect { subject }.to change { Note.count }.from(0).to(3)
+        end
+
+        it 'creates a note correctly for the original epic' do
+          subject
+
+          note = Note.find_by(system: true, noteable_type: 'Epic', noteable_id: epic.id)
+
+          expect(note.note).to eq("moved issue #{issue.to_reference(epic.group)} to epic #{another_epic.to_reference(epic.group)}")
+          expect(note.system_note_metadata.action).to eq('epic_issue_moved')
+        end
+
+        it 'creates a note correctly for the new epic' do
+          subject
+
+          note = Note.find_by(system: true, noteable_type: 'Epic', noteable_id: another_epic.id)
+
+          expect(note.note).to eq("added issue #{issue.to_reference(epic.group)} from epic #{epic.to_reference(epic.group)}")
+          expect(note.system_note_metadata.action).to eq('epic_issue_moved')
+        end
+
+        it 'creates a note correctly for the issue' do
+          subject
+
+          note = Note.find_by(system: true, noteable_type: 'Issue', noteable_id: issue.id)
+
+          expect(note.note).to eq("changed epic to #{another_epic.to_reference(issue.project)}")
+          expect(note.system_note_metadata.action).to eq('issue_changed_epic')
+        end
       end
 
       context 'when issue from non group project is given' do