Allow people to remove source branch of fork project in MR

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/controllers/projects/merge_requests_controller.rb

@@ -216,7 +216,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   end
 
   def allowed_to_merge?
-    allowed_to_push_code?(project)
+    allowed_to_push_code?(project, @merge_request.target_branch)
   end
 
   def invalid_mr
@@ -225,17 +225,17 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   end
 
   def allowed_to_remove_source_branch?
-    allowed_to_push_code?(@merge_request.source_project) &&
+    allowed_to_push_code?(@merge_request.source_project, @merge_request.source_branch) &&
       !@merge_request.disallow_source_branch_removal?
   end
 
-  def allowed_to_push_code?(project)
-    action = if project.protected_branch?(@merge_request.target_branch)
+  def allowed_to_push_code?(project, branch)
+    action = if project.protected_branch?(branch)
                :push_code_to_protected_branches
              else
                :push_code
              end
 
-    can?(current_user, action, @project)
+    can?(current_user, action, project)
   end
 end

app/models/merge_request.rb

@@ -210,7 +210,7 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def disallow_source_branch_removal?
-    (source_project.root_ref? source_branch) || for_fork?
+    source_project.root_ref?(source_branch) || source_project.protected_branches.include?(source_branch)
   end
 
   def project