Fetch the merged branches at once

app/controllers/projects/branches_controller.rb

@@ -15,6 +15,8 @@ class Projects::BranchesController < Projects::ApplicationController
     respond_to do |format|
       format.html do
         @refs_pipelines = @project.pipelines.latest_successful_for_refs(@branches.map(&:name))
+        @merged_branch_names =
+          repository.merged_branch_names(@branches.map(&:name))
         # n+1: https://gitlab.com/gitlab-org/gitlab-ce/issues/37429
         Gitlab::GitalyClient.allow_n_plus_1_calls do
           @max_commits = @branches.reduce(0) do |memo, branch|

app/models/repository.rb

@@ -902,18 +902,27 @@ class Repository
     end
   end
 
-  def merged_to_root_ref?(branch_name)
-    branch_commit = commit(branch_name)
-    root_ref_commit = commit(root_ref)
+  def merged_to_root_ref?(branch_or_name, pre_loaded_merged_branches = nil)
+    branch = Gitlab::Git::Branch.find(self, branch_or_name)
+
+    if branch
+      root_ref_sha = commit(root_ref).sha
+      same_head = branch.target == root_ref_sha
+      merged =
+        if pre_loaded_merged_branches
+          pre_loaded_merged_branches.include?(branch.name)
+        else
+          ancestor?(branch.target, root_ref_sha)
+        end
 
-    if branch_commit
-      same_head = branch_commit.id == root_ref_commit.id
-      !same_head && ancestor?(branch_commit.id, root_ref_commit.id)
+      !same_head && merged
     else
       nil
     end
   end
 
+  delegate :merged_branch_names, to: :raw_repository
+
   def merge_base(first_commit_id, second_commit_id)
     first_commit_id = commit(first_commit_id).try(:id) || first_commit_id
     second_commit_id = commit(second_commit_id).try(:id) || second_commit_id

app/views/projects/branches/_branch.html.haml

+- merged = local_assigns.fetch(:merged, false)
 - commit = @repository.commit(branch.dereferenced_target)
 - bar_graph_width_factor = @max_commits > 0 ? 100.0/@max_commits : 0
 - diverging_commit_counts = @repository.diverging_commit_counts(branch)
@@ -12,7 +13,7 @@
      
     - if branch.name == @repository.root_ref
       %span.label.label-primary default
-    - elsif @repository.merged_to_root_ref? branch.name
+    - elsif merged
       %span.label.label-info.has-tooltip{ title: s_('Branches|Merged into %{default_branch}') % { default_branch: @repository.root_ref } }
         = s_('Branches|merged')
 
@@ -47,7 +48,7 @@
                 target: "#modal-delete-branch",
                 delete_path: project_branch_path(@project, branch.name),
                 branch_name: branch.name,
-                is_merged: ("true" if @repository.merged_to_root_ref?(branch.name)) } }
+                is_merged: ("true" if merged) } }
               = icon("trash-o")
           - else
             %button{ class: "btn btn-remove remove-row js-ajax-loading-spinner has-tooltip disabled",

app/views/projects/branches/index.html.haml

@@ -38,7 +38,7 @@
   - if @branches.any?
     %ul.content-list.all-branches
       - @branches.each do |branch|
-        = render "projects/branches/branch", branch: branch
+        = render "projects/branches/branch", branch: branch, merged: @repository.merged_to_root_ref?(branch, @merged_branch_names)
     = paginate @branches, theme: 'gitlab'
   - else
     .nothing-here-block

changelogs/unreleased/use-git-branch-merged.yml

+---
+title: Improve branch listing page performance
+merge_request: 14729
+author:
+type: performance

lib/gitlab/git/branch.rb

@@ -3,6 +3,14 @@
 module Gitlab
   module Git
     class Branch < Ref
+      def self.find(repo, branch_name)
+        if branch_name.is_a?(Gitlab::Git::Branch)
+          branch_name
+        else
+          repo.find_branch(branch_name)
+        end
+      end
+
       def initialize(repository, name, target, target_commit)
         super(repository, name, target, target_commit)
       end

lib/gitlab/git/repository.rb

@@ -511,6 +511,10 @@ module Gitlab
         gitaly_commit_client.ancestor?(from, to)
       end
 
+      def merged_branch_names(branch_names = [])
+        Set.new(git_merged_branch_names(branch_names))
+      end
+
       # Return an array of Diff objects that represent the diff
       # between +from+ and +to+.  See Diff::filter_diff_options for the allowed
       # diff options.  The +options+ hash can also include :break_rewrites to
@@ -1190,6 +1194,13 @@ module Gitlab
         sort_branches(branches, sort_by)
       end
 
+      def git_merged_branch_names(branch_names = [])
+        lines = run_git(['branch', '--merged', root_ref] + branch_names)
+          .first.lines
+
+        lines.map(&:strip)
+      end
+
       def log_using_shell?(options)
         options[:path].present? ||
           options[:disable_walk] ||

spec/lib/gitlab/git/branch_spec.rb

@@ -7,6 +7,38 @@ describe Gitlab::Git::Branch, seed_helper: true do
 
   it { is_expected.to be_kind_of Array }
 
+  describe '.find' do
+    subject { described_class.find(repository, branch) }
+
+    before do
+      allow(repository).to receive(:find_branch).with(branch)
+        .and_call_original
+    end
+
+    context 'when finding branch via branch name' do
+      let(:branch) { 'master' }
+
+      it 'returns a branch object' do
+        expect(subject).to be_a(described_class)
+        expect(subject.name).to eq(branch)
+
+        expect(repository).to have_received(:find_branch).with(branch)
+      end
+    end
+
+    context 'when the branch is already a branch' do
+      let(:commit) { repository.commit('master') }
+      let(:branch) { described_class.new(repository, 'master', commit.sha, commit) }
+
+      it 'returns a branch object' do
+        expect(subject).to be_a(described_class)
+        expect(subject).to eq(branch)
+
+        expect(repository).not_to have_received(:find_branch).with(branch)
+      end
+    end
+  end
+
   describe '#size' do
     subject { super().size }
     it { is_expected.to eq(SeedRepo::Repo::BRANCHES.size) }

spec/lib/gitlab/git/repository_spec.rb

@@ -1135,6 +1135,32 @@ describe Gitlab::Git::Repository, seed_helper: true do
     end
   end
 
+  describe '#merged_branch_names' do
+    context 'when branch names are passed' do
+      it 'only returns the names we are asking' do
+        names = repository.merged_branch_names(%w[merge-test])
+
+        expect(names).to contain_exactly('merge-test')
+      end
+
+      it 'does not return unmerged branch names' do
+        names = repository.merged_branch_names(%w[feature])
+
+        expect(names).to be_empty
+      end
+    end
+
+    context 'when no branch names are specified' do
+      it 'returns all merged branch names' do
+        names = repository.merged_branch_names
+
+        expect(names).to include('merge-test')
+        expect(names).to include('fix-mode')
+        expect(names).not_to include('feature')
+      end
+    end
+  end
+
   describe "#ls_files" do
     let(:master_file_paths) { repository.ls_files("master") }
     let(:not_existed_branch) { repository.ls_files("not_existed_branch") }

spec/models/repository_spec.rb

@@ -299,6 +299,24 @@ describe Repository do
 
       it { is_expected.to be_falsey }
     end
+
+    context 'when pre-loaded merged branches are provided' do
+      using RSpec::Parameterized::TableSyntax
+
+      where(:branch, :pre_loaded, :expected) do
+        'not-merged-branch' | ['branch-merged']     | false
+        'branch-merged'     | ['not-merged-branch'] | false
+        'branch-merged'     | ['branch-merged']     | true
+        'not-merged-branch' | ['not-merged-branch'] | false
+        'master'            | ['master']            | false
+      end
+
+      with_them do
+        subject { repository.merged_to_root_ref?(branch, pre_loaded) }
+
+        it { is_expected.to eq(expected) }
+      end
+    end
   end
 
   describe '#can_be_merged?' do