#888 prevent to remove source_branch

app/models/project/repository_trait.rb

@@ -114,5 +114,9 @@ module Project::RepositoryTrait
     def root_ref 
       default_branch || "master"
     end
+
+    def root_ref? branch
+      root_ref == branch
+    end
   end
 end

app/views/merge_requests/show.html.haml

@@ -65,6 +65,7 @@
         = form_for [:automerge, @project, @merge_request], :remote => true, :method => :get do |f|
           You can accept this request automatically. If you still want to do it manually - #{link_to "click here", "#", :class => "how_to_merge_link vlink", :title => "How To Merge"} for instructions
           %br
+          -unless @project.root_ref? @merge_request.source_branch 
             = check_box_tag :should_remove_source_branch
             = label_tag :should_remove_source_branch, "Remove source-branch"
              

lib/gitlab/merge.rb

@@ -50,7 +50,7 @@ module Gitlab
             output = merge_repo.git.pull({}, "--no-ff", "origin", merge_request.source_branch)
 
             #remove source-branch
-            if merge_request.should_remove_source_branch
+            if merge_request.should_remove_source_branch && !project.root_ref?(merge_request.source_branch)
               merge_repo.git.sh "git push origin :#{merge_request.source_branch}"
             end