Add a system note and update relevant merge requests when a branch is deleted or re-added

If a branch is deleted with an open merge request, amended offline, and then pushed again,
GitLab doesn't bother to update the merge request even though the last commit ID and/or
code may have changed. This MR ensures that each push will update any relevant merge
requests and adds a system note if this happens as well.

Closes #2926

1 files changed, 19 insertions, 0 deletions

diff --git a/app/services/system_note_service.rb b/app/services/system_note_service.rb
index 8253c1f780d..24e06504078 100644
--- a/app/services/system_note_service.rb
+++ b/app/services/system_note_service.rb
@@ -168,6 +168,25 @@ class SystemNoteService
     create_note(noteable: noteable, project: project, author: author, note: body)
   end
 
+  # Called when a branch in Noteable is added or deleted
+  #
+  # noteable    - Noteable object
+  # project     - Project owning noteable
+  # author      - User performing the change
+  # branch_type - 'source' or 'target'
+  # branch      - branch name
+  # presence    - 'deleted' or 'created'
+  #
+  # Example Note text:
+  #
+  #   "Target branch `feature` deleted"
+  #
+  # Returns the created Note object
+  def self.change_branch_presence(noteable, project, author, branch_type, branch, presence)
+    body = "#{branch_type} branch `#{branch}` #{presence}".capitalize
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
   # Called when a Mentionable references a Noteable
   #
   # noteable  - Noteable object being referenced