7 files changed, 63 insertions, 19 deletions
diff --git a/app/services/issues/base_service.rb b/app/services/issues/base_service.rb
index 34199eb5d13..4c198fc96ea 100644
--- a/app/services/issues/base_service.rb
+++ b/app/services/issues/base_service.rb
@@ -7,6 +7,14 @@ module Issues
       issue_data
     end
 
+    def reopen_service
+      Issues::ReopenService
+    end
+
+    def close_service
+      Issues::CloseService
+    end
+
     private
 
     def create_assignee_note(issue, old_assignees)
diff --git a/app/services/issues/close_service.rb b/app/services/issues/close_service.rb
index 85c616ca576..74459c3342c 100644
--- a/app/services/issues/close_service.rb
+++ b/app/services/issues/close_service.rb
@@ -16,19 +16,19 @@ module Issues
     # The code calling this method is responsible for ensuring that a user is
     # allowed to close the given issue.
     def close_issue(issue, commit: nil, notifications: true, system_note: true)
-      if project.jira_tracker? && project.jira_service.active
+      if project.jira_tracker? && project.jira_service.active && issue.is_a?(ExternalIssue)
         project.jira_service.close_issue(commit, issue)
         todo_service.close_issue(issue, current_user)
         return issue
       end
 
-      if project.default_issues_tracker? && issue.close
+      if project.issues_enabled? && issue.close
         event_service.close_issue(issue, current_user)
         create_note(issue, commit) if system_note
         notification_service.close_issue(issue, current_user) if notifications
         todo_service.close_issue(issue, current_user)
         execute_hooks(issue, 'close')
-        invalidate_cache_counts(issue.assignees, issue)
+        invalidate_cache_counts(issue, users: issue.assignees)
       end
 
       issue
diff --git a/app/services/issues/create_service.rb b/app/services/issues/create_service.rb
index 3cf4b82b9f2..718a7ac1f22 100644
--- a/app/services/issues/create_service.rb
+++ b/app/services/issues/create_service.rb
@@ -30,8 +30,8 @@ module Issues
 
       Discussions::ResolveService.new(project, current_user,
                                       merge_request: merge_request_to_resolve_discussions_of,
-                                      follow_up_issue: issue).
-        execute(discussions_to_resolve)
+                                      follow_up_issue: issue)
+        .execute(discussions_to_resolve)
     end
 
     private
diff --git a/app/services/issues/duplicate_service.rb b/app/services/issues/duplicate_service.rb
new file mode 100644
index 00000000000..5c0854e664d
--- /dev/null
+++ b/app/services/issues/duplicate_service.rb
@@ -0,0 +1,24 @@
+module Issues
+  class DuplicateService < Issues::BaseService
+    def execute(duplicate_issue, canonical_issue)
+      return if canonical_issue == duplicate_issue
+      return unless can?(current_user, :update_issue, duplicate_issue)
+      return unless can?(current_user, :create_note, canonical_issue)
+
+      create_issue_duplicate_note(duplicate_issue, canonical_issue)
+      create_issue_canonical_note(canonical_issue, duplicate_issue)
+
+      close_service.new(project, current_user, {}).execute(duplicate_issue)
+    end
+
+    private
+
+    def create_issue_duplicate_note(duplicate_issue, canonical_issue)
+      SystemNoteService.mark_duplicate_issue(duplicate_issue, duplicate_issue.project, current_user, canonical_issue)
+    end
+
+    def create_issue_canonical_note(canonical_issue, duplicate_issue)
+      SystemNoteService.mark_canonical_issue_of_duplicate(canonical_issue, canonical_issue.project, current_user, duplicate_issue)
+    end
+  end
+end
diff --git a/app/services/issues/move_service.rb b/app/services/issues/move_service.rb
index 711f4035c55..29def25719d 100644
--- a/app/services/issues/move_service.rb
+++ b/app/services/issues/move_service.rb
@@ -61,8 +61,18 @@ module Issues
     end
 
     def cloneable_milestone_id
-      @new_project.milestones
-        .find_by(title: @old_issue.milestone.try(:title)).try(:id)
+      title = @old_issue.milestone&.title
+      return unless title
+
+      if @new_project.group && can?(current_user, :read_group, @new_project.group)
+        group_id = @new_project.group.id
+      end
+
+      params =
+        { title: title, project_ids: @new_project.id, group_ids: group_id }
+
+      milestones = MilestonesFinder.new(params).execute
+      milestones.first&.id
     end
 
     def rewrite_notes
diff --git a/app/services/issues/reopen_service.rb b/app/services/issues/reopen_service.rb
index 80ea6312768..35de4337b15 100644
--- a/app/services/issues/reopen_service.rb
+++ b/app/services/issues/reopen_service.rb
@@ -5,10 +5,10 @@ module Issues
 
       if issue.reopen
         event_service.reopen_issue(issue, current_user)
-        create_note(issue)
+        create_note(issue, 'reopened')
         notification_service.reopen_issue(issue, current_user)
         execute_hooks(issue, 'reopen')
-        invalidate_cache_counts(issue.assignees, issue)
+        invalidate_cache_counts(issue, users: issue.assignees)
       end
 
       issue
@@ -16,8 +16,8 @@ module Issues
 
     private
 
-    def create_note(issue)
-      SystemNoteService.change_status(issue, issue.project, current_user, issue.state, nil)
+    def create_note(issue, state = issue.state)
+      SystemNoteService.change_status(issue, issue.project, current_user, state, nil)
     end
   end
 end
diff --git a/app/services/issues/update_service.rb b/app/services/issues/update_service.rb
index cd9f9a4a16e..8d918ccc635 100644
--- a/app/services/issues/update_service.rb
+++ b/app/services/issues/update_service.rb
@@ -5,6 +5,7 @@ module Issues
     def execute(issue)
       handle_move_between_iids(issue)
       filter_spam_check_params
+      change_issue_duplicate(issue)
       update(issue)
     end
 
@@ -53,14 +54,6 @@ module Issues
       end
     end
 
-    def reopen_service
-      Issues::ReopenService
-    end
-
-    def close_service
-      Issues::CloseService
-    end
-
     def handle_move_between_iids(issue)
       return unless params[:move_between_iids]
 
@@ -72,6 +65,15 @@ module Issues
       issue.move_between(issue_before, issue_after)
     end
 
+    def change_issue_duplicate(issue)
+      canonical_issue_id = params.delete(:canonical_issue_id)
+      canonical_issue = IssuesFinder.new(current_user).find_by(id: canonical_issue_id)
+
+      if canonical_issue
+        Issues::DuplicateService.new(project, current_user).execute(issue, canonical_issue)
+      end
+    end
+
     private
 
     def get_issue_if_allowed(project, iid)