Stop using branch_names.include? and use branch_exists?

app/helpers/compare_helper.rb

@@ -4,8 +4,8 @@ module CompareHelper
       to.present? &&
       from != to &&
       can?(current_user, :create_merge_request, project) &&
-      project.repository.branch_names.include?(from) &&
-      project.repository.branch_names.include?(to)
+      project.repository.branch_exists?(from) &&
+      project.repository.branch_exists?(to)
   end
 
   def create_mr_path(from = params[:from], to = params[:to], project = @project)

app/models/merge_request.rb

@@ -675,13 +675,13 @@ class MergeRequest < ActiveRecord::Base
   def source_branch_exists?
     return false unless self.source_project
 
-    self.source_project.repository.branch_names.include?(self.source_branch)
+    self.source_project.repository.branch_exists?(self.source_branch)
   end
 
   def target_branch_exists?
     return false unless self.target_project
 
-    self.target_project.repository.branch_names.include?(self.target_branch)
+    self.target_project.repository.branch_exists?(self.target_branch)
   end
 
   def merge_commit_message(include_description: false)

app/services/quick_actions/interpret_service.rb

@@ -458,7 +458,7 @@ module QuickActions
       target_branch_param.strip
     end
     command :target_branch do |branch_name|
-      @updates[:target_branch] = branch_name if project.repository.branch_names.include?(branch_name)
+      @updates[:target_branch] = branch_name if project.repository.branch_exists?(branch_name)
     end
 
     desc 'Move issue from one column of the board to another'

changelogs/unreleased/an-use-branch-exists-over-branch-names-include.yml

@@ -0,0 +1,5 @@
+---
+title: Avoid fetching all branches for branch existence checks
+merge_request: 14778
+author:
+type: changed

spec/controllers/projects/branches_controller_spec.rb

@@ -62,7 +62,7 @@ describe Projects::BranchesController do
         let(:branch) { "feature%2Ftest" }
         let(:ref) { "<script>alert('ref');</script>" }
         it { is_expected.to render_template('new') }
-        it { project.repository.branch_names.include?('feature/test') }
+        it { project.repository.branch_exists?('feature/test') }
       end
     end
 

spec/features/projects/issuable_templates_spec.rb

@@ -118,7 +118,7 @@ feature 'issuable templates', :js do
   context 'user creates a merge request from a forked project using templates' do
     let(:template_content) { 'this is a test "feature-proposal" template' }
     let(:fork_user) { create(:user) }
-    let(:forked_project) { fork_project(project, fork_user) }
+    let(:forked_project) { fork_project(project, fork_user, repository: true) }
     let(:merge_request) { create(:merge_request, :with_diffs, source_project: forked_project, target_project: project) }
 
     background do

spec/features/projects/merge_requests/user_views_open_merge_request_spec.rb

@@ -6,7 +6,7 @@ describe 'User views an open merge request' do
   end
 
   context 'when a merge request does not have repository' do
-    let(:project) { create(:project, :public) }
+    let(:project) { create(:project, :public, :repository) }
 
     before do
       visit(merge_request_path(merge_request))

spec/features/task_lists_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 feature 'Task Lists' do
   include Warden::Test::Helpers
 
-  let(:project) { create(:project) }
+  let(:project) { create(:project, :repository) }
   let(:user)    { create(:user) }
   let(:user2)   { create(:user) }
 

spec/serializers/merge_request_entity_spec.rb

@@ -1,7 +1,7 @@
 require 'spec_helper'
 
 describe MergeRequestEntity do
-  let(:project)  { create :project }
+  let(:project)  { create :project, :repository }
   let(:resource) { create(:merge_request, source_project: project, target_project: project) }
   let(:user)     { create(:user) }