Merge branch 'support-edit-target-branch-in-mr' into 'master'

Support editing target branch of merge request

### What does this MR do?

This MR makes it possible to edit the target branch of a merge request and adds a system note when this happens.

### Why was this MR needed?

Because lots of people requested this feature. :)

### Screenshots

**Edit MR page**

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/9b3d405bf7b5f945e35bae3534c2b67b/image.png)

**New MR page**

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/3657a2a9efad6d10e8470637d1166bdb/image.png)

**System note**

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/cc8066f3d3bdf09c0cce27193210567d/image.png)

### What are the relevant issue numbers?

* Closes https://github.com/gitlabhq/gitlabhq/issues/7105
* See: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/130!

See merge request !738

3 files changed, 37 insertions, 1 deletions

diff --git a/app/services/issuable_base_service.rb b/app/services/issuable_base_service.rb
index c5769a5ad27..1d99223cfe6 100644
--- a/app/services/issuable_base_service.rb
+++ b/app/services/issuable_base_service.rb
@@ -20,4 +20,10 @@ class IssuableBaseService < BaseService
     SystemNoteService.change_title(
       issuable, issuable.project, current_user, old_title)
   end
+
+  def create_branch_change_note(issuable, branch_type, old_branch, new_branch)
+    SystemNoteService.change_branch(
+      issuable, issuable.project, current_user, branch_type,
+      old_branch, new_branch)
+  end
 end
diff --git a/app/services/merge_requests/update_service.rb b/app/services/merge_requests/update_service.rb
index 34fd59d6927..34c190bf621 100644
--- a/app/services/merge_requests/update_service.rb
+++ b/app/services/merge_requests/update_service.rb
@@ -5,7 +5,7 @@ require_relative 'close_service'
 module MergeRequests
   class UpdateService < MergeRequests::BaseService
     def execute(merge_request)
-      # We dont allow change of source/target projects
+      # We don't allow change of source/target projects
       # after merge request was created
       params.except!(:source_project_id)
       params.except!(:target_project_id)
@@ -41,6 +41,12 @@ module MergeRequests
           )
         end
 
+        if merge_request.previous_changes.include?('target_branch')
+          create_branch_change_note(merge_request, 'target',
+                                    merge_request.previous_changes['target_branch'].first,
+                                    merge_request.target_branch)
+        end
+
         if merge_request.previous_changes.include?('milestone_id')
           create_milestone_note(merge_request)
         end
@@ -54,6 +60,11 @@ module MergeRequests
           create_title_change_note(merge_request, merge_request.previous_changes['title'].first)
         end
 
+        if merge_request.previous_changes.include?('target_branch') ||
+            merge_request.previous_changes.include?('source_branch')
+          merge_request.mark_as_unchecked
+        end
+
         merge_request.notice_added_references(merge_request.project, current_user)
         execute_hooks(merge_request, 'update')
       end
diff --git a/app/services/system_note_service.rb b/app/services/system_note_service.rb
index 1527ae0486d..b6801a92330 100644
--- a/app/services/system_note_service.rb
+++ b/app/services/system_note_service.rb
@@ -149,6 +149,25 @@ class SystemNoteService
     create_note(noteable: noteable, project: project, author: author, note: body)
   end
 
+  # Called when a branch in Noteable is changed
+  #
+  # noteable    - Noteable object
+  # project     - Project owning noteable
+  # author      - User performing the change
+  # branch_type - 'source' or 'target'
+  # old_branch  - old branch name
+  # new_branch  - new branch nmae
+  #
+  # Example Note text:
+  #
+  #   "Target branch changed from `Old` to `New`"
+  #
+  # Returns the created Note object
+  def self.change_branch(noteable, project, author, branch_type, old_branch, new_branch)
+    body = "#{branch_type} branch changed from `#{old_branch}` to `#{new_branch}`".capitalize
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
   # Called when a Mentionable references a Noteable
   #
   # noteable  - Noteable object being referenced