Extracted ProtectableDropdown to clean up Project#open_branches

Makes it clear this is only used in dropdowns, instead of cluttering up Project class. Since we only care about branch names, it is also possible to refactor out a lot of the set/reject logic.

A benchmark on Array/Set subtraction favoured using Arrays. This was with 5000 ‘branches’ and 2000 ‘protections’ to ensure a similar comparison to the commit which introduced using Set for intersection.

Comparison:
   array subtraction:      485.8 i/s
     set subtraction:      128.7 i/s - 3.78x slower

1 files changed, 7 insertions, 18 deletions

diff --git a/app/controllers/projects/settings/repository_controller.rb b/app/controllers/projects/settings/repository_controller.rb
index 5160ee5e1e4..a87927fe1ec 100644
--- a/app/controllers/projects/settings/repository_controller.rb
+++ b/app/controllers/projects/settings/repository_controller.rb
@@ -4,8 +4,7 @@ module Projects
       before_action :authorize_admin_project!
 
       def show
-        @deploy_keys = DeployKeysPresenter
-          .new(@project, current_user: current_user)
+        @deploy_keys = DeployKeysPresenter.new(@project, current_user: current_user)
 
         define_protected_refs
       end
@@ -38,27 +37,17 @@ module Projects
         }
       end
 
-      #TODO: Move to Protections::TagMatcher.new(project).unprotected
-      def unprotected_tags
-        exact_protected_tag_names = @project.protected_tags.reject(&:wildcard?).map(&:name)
-        tag_names = @project.repository.tags.map(&:name)
-        non_open_tag_names = Set.new(exact_protected_tag_names).intersection(Set.new(tag_names))
-        @project.repository.tags.reject { |tag| non_open_tag_names.include? tag.name }
+      def protectable_tags_for_dropdown
+        { open_tags: ProtectableDropdown.new(@project, :tags).hash }
       end
 
-      def unprotected_tags_hash
-        tags = unprotected_tags.map { |tag| { text: tag.name, id: tag.name, title: tag.name } }
-        { open_tags: tags }
-      end
-
-      def open_branches
-        branches = @project.open_branches.map { |br| { text: br.name, id: br.name, title: br.name } }
-        { open_branches: branches }
+      def protectable_branches_for_dropdown
+        { open_branches: ProtectableDropdown.new(@project, :branches).hash }
       end
 
       def load_gon_index
-        gon.push(open_branches)
-        gon.push(unprotected_tags_hash)
+        gon.push(protectable_tags_for_dropdown)
+        gon.push(protectable_branches_for_dropdown)
         gon.push(access_levels_options)
       end
     end