Merge branch 'sh-fix-branches-api-timeout' into 'master'

Fix timeout issues retrieving branches via API

Closes #55724

See merge request gitlab-org/gitlab-ce!24034

changelogs/unreleased/sh-fix-branches-api-timeout.yml

+---
+title: Fix timeout issues retrieving branches via API
+merge_request: 24034
+author:
+type: performance

lib/api/branches.rb

@@ -34,11 +34,11 @@ module API
         repository = user_project.repository
 
         branches = BranchesFinder.new(repository, declared_params(include_missing: false)).execute
-
+        branches = ::Kaminari.paginate_array(branches)
         merged_branch_names = repository.merged_branch_names(branches.map(&:name))
 
         present(
-          paginate(::Kaminari.paginate_array(branches)),
+          paginate(branches),
           with: Entities::Branch,
           current_user: current_user,
           project: user_project,

spec/requests/api/branches_spec.rb

@@ -20,6 +20,12 @@ describe API::Branches do
     let(:route) { "/projects/#{project_id}/repository/branches" }
 
     shared_examples_for 'repository branches' do
+      RSpec::Matchers.define :has_merged_branch_names_count do |expected|
+        match do |actual|
+          actual[:merged_branch_names].count == expected
+        end
+      end
+
       it 'returns the repository branches' do
         get api(route, current_user), params: { per_page: 100 }
 
@@ -30,6 +36,12 @@ describe API::Branches do
         expect(branch_names).to match_array(project.repository.branch_names)
       end
 
+      it 'determines only a limited number of merged branch names' do
+        expect(API::Entities::Branch).to receive(:represent).with(anything, has_merged_branch_names_count(2))
+
+        get api(route, current_user), params: { per_page: 2 }
+      end
+
       context 'when repository is disabled' do
         include_context 'disabled repository'