Fix bug with merge request branch select

Merge request target branch select is broken if you submit form and have
some errors on page
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/controllers/projects/merge_requests_controller.rb

@@ -60,7 +60,6 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     @merge_request = MergeRequest.new(params[:merge_request])
     @merge_request.source_project = @project unless @merge_request.source_project
     @merge_request.target_project = @project unless @merge_request.target_project
-    @target_branches = @merge_request.target_project.nil? ? [] : @merge_request.target_project.repository.branch_names
     @source_project = @merge_request.source_project
     @merge_request
   end
@@ -167,7 +166,11 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   protected
 
   def selected_target_project
-    ((@project.id.to_s == params[:target_project_id]) || @project.forked_project_link.nil?) ? @project : @project.forked_project_link.forked_from_project
+    if @project.id.to_s == params[:target_project_id] || @project.forked_project_link.nil?
+      @project
+    else
+      @project.forked_project_link.forked_from_project
+    end
   end
 
   def merge_request

app/models/merge_request.rb

@@ -253,4 +253,24 @@ class MergeRequest < ActiveRecord::Base
     message << description.to_s
     message
   end
+
+  # Return array of possible target branches
+  # dependes on target project of MR
+  def target_branches
+    if target_project.nil?
+      []
+    else
+      target_project.repository.branch_names
+    end
+  end
+
+  # Return array of possible source branches
+  # dependes on source project of MR
+  def source_branches
+    if source_project.nil?
+      []
+    else
+      source_project.repository.branch_names
+    end
+  end
 end

app/views/projects/merge_requests/_form.html.haml

@@ -13,7 +13,7 @@
             = f.select(:source_project_id, [[@merge_request.source_project_path,@merge_request.source_project.id]] , {}, { class: 'source_project select2 span3', disabled: @merge_request.persisted? })
           .pull-left
              
-            = f.select(:source_branch, @merge_request.source_project.repository.branch_names, { include_blank: "Select branch" }, {class: 'source_branch select2 span2'})
+            = f.select(:source_branch, @merge_request.source_branches, { include_blank: "Select branch" }, {class: 'source_branch select2 span2'})
         .mr_source_commit.prepend-top-10
       .col-md-2
         .merge-request-angle
@@ -25,7 +25,7 @@
             = f.select(:target_project_id, options_from_collection_for_select(projects, 'id', 'path_with_namespace'), {}, { class: 'target_project select2 span3', disabled: @merge_request.persisted? })
           .pull-left
              
-            = f.select(:target_branch, @target_branches, { include_blank: "Select branch" }, {class: 'target_branch select2 span2'})
+            = f.select(:target_branch, @merge_request.target_branches, { include_blank: "Select branch" }, {class: 'target_branch select2 span2'})
         .mr_target_commit.prepend-top-10
 
   %hr