Use default branch in wiki repositories

In this commit, we're making wiki repositories use the instance
default branch.

For that we're changing the branch inside HEAD, that later Gitaly
will use to write to.

app/models/wiki.rb

@@ -87,7 +87,7 @@ class Wiki
   end
 
   def create_wiki_repository
-    repository.create_if_not_exists
+    change_head_to_default_branch if repository.create_if_not_exists
 
     raise CouldNotCreateWikiError unless repository_exists?
   rescue StandardError => err
@@ -174,6 +174,7 @@ class Wiki
     commit = commit_details(:created, message, title)
 
     wiki.write_page(title, format.to_sym, content, commit)
+    repository.expire_status_cache if repository.empty?
     after_wiki_activity
 
     true
@@ -248,7 +249,9 @@ class Wiki
 
   override :default_branch
   def default_branch
-    wiki.class.default_ref
+    return 'master' if Feature.disabled?(:wiki_uses_default_branch, user, default_enabled: :yaml)
+
+    super || wiki.class.default_ref(container)
   end
 
   def wiki_base_path
@@ -320,6 +323,10 @@ class Wiki
 
     false
   end
+
+  def change_head_to_default_branch
+    repository.raw_repository.write_ref('HEAD', "refs/heads/#{default_branch}")
+  end
 end
 
 Wiki.prepend_mod_with('Wiki')

config/feature_flags/development/wiki_uses_default_branch.yml

+---
+name: wiki_uses_default_branch
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64891
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/334754
+milestone: '14.1'
+type: development
+group: group::editor
+default_enabled: false

ee/spec/lib/ee/gitlab/import_export/wiki_repo_saver_spec.rb

@@ -4,11 +4,7 @@ require 'spec_helper'
 
 RSpec.describe Gitlab::ImportExport::WikiRepoSaver do
   let_it_be(:user) { create(:user) }
-  let_it_be(:group) do
-    create(:group, :wiki_repo).tap do |g|
-      g.add_owner(user)
-    end
-  end
+  let_it_be(:group) { create(:group) }
 
   let(:exportable) { group }
   let(:shared) { Gitlab::ImportExport::Shared.new(group) }
@@ -16,15 +12,19 @@ RSpec.describe Gitlab::ImportExport::WikiRepoSaver do
   subject { described_class.new(exportable: exportable, shared: shared) }
 
   describe 'bundles a group wiki Git repo' do
-    let!(:group_wiki) { GroupWiki.new(group, user) }
+    let_it_be(:group_wiki) do
+      create(:group_wiki, user: user).tap do |wiki|
+        wiki.create_page('index', 'test content')
+      end
+    end
+
+    let(:group) { group_wiki.group }
     let(:export_path) { "#{Dir.tmpdir}/group_tree_saver_spec" }
 
     before do
       allow_next_instance_of(Gitlab::ImportExport) do |instance|
         allow(instance).to receive(:storage_path).and_return(export_path)
       end
-
-      group_wiki.create_page('index', 'test content')
     end
 
     after do
@@ -37,8 +37,6 @@ RSpec.describe Gitlab::ImportExport::WikiRepoSaver do
     end
 
     context 'when the repo is empty' do
-      let!(:group) { create(:group) }
-
       it 'bundles the repo successfully' do
         expect(subject.save).to be true
       end

ee/spec/lib/elastic/latest/project_wiki_class_proxy_spec.rb

@@ -3,12 +3,12 @@
 require 'spec_helper'
 
 RSpec.describe Elastic::Latest::ProjectWikiClassProxy, :elastic do
-  let_it_be(:project) { create(:project, :wiki_repo) }
+  let(:project) { create(:project, :wiki_repo) }
 
   subject { described_class.new(project.wiki.repository) }
 
   describe '#elastic_search_as_wiki_page' do
-    let_it_be(:page) { create(:wiki_page, wiki: project.wiki) }
+    let!(:page) { create(:wiki_page, wiki: project.wiki) }
 
     before do
       stub_ee_application_setting(elasticsearch_search: true, elasticsearch_indexing: true)

ee/spec/lib/gitlab/elastic/project_search_results_spec.rb

@@ -33,8 +33,8 @@ RSpec.describe Gitlab::Elastic::ProjectSearchResults, :elastic, :clean_gitlab_re
   end
 
   describe "search", :sidekiq_inline do
-    let_it_be(:project) { create(:project, :public, :repository, :wiki_repo) }
-    let_it_be(:private_project) { create(:project, :repository, :wiki_repo) }
+    let(:project) { create(:project, :public, :repository, :wiki_repo) }
+    let(:private_project) { create(:project, :repository, :wiki_repo) }
 
     before do
       [project, private_project].each do |p|

ee/spec/models/concerns/elastic/project_wiki_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe ProjectWiki, :elastic do
-  let_it_be(:project) { create(:project, :wiki_repo) }
+  let(:project) { create(:project, :wiki_repo) }
 
   before do
     stub_ee_application_setting(elasticsearch_search: true, elasticsearch_indexing: true)

lib/gitlab/git/wiki.rb

@@ -54,8 +54,11 @@ module Gitlab
 
       attr_reader :repository
 
-      def self.default_ref
-        'master'
+      # TODO remove argument when issue
+      # https://gitlab.com/gitlab-org/gitlab/-/issues/329190
+      # is closed.
+      def self.default_ref(container = nil)
+        Gitlab::DefaultBranch.value(object: container)
       end
 
       # Initialize with a Gitlab::Git::Repository instance

spec/lib/gitlab/project_search_results_spec.rb

@@ -209,11 +209,10 @@ RSpec.describe Gitlab::ProjectSearchResults do
 
   describe 'wiki search' do
     let(:project) { create(:project, :public, :wiki_repo) }
-    let(:wiki) { build(:project_wiki, project: project) }
 
     before do
-      wiki.create_page('Files/Title', 'Content')
-      wiki.create_page('CHANGELOG', 'Files example')
+      project.wiki.create_page('Files/Title', 'Content')
+      project.wiki.create_page('CHANGELOG', 'Files example')
     end
 
     it_behaves_like 'general blob search', 'wiki', 'wiki_blobs' do

spec/lib/gitlab/wiki_file_finder_spec.rb

@@ -4,12 +4,11 @@ require 'spec_helper'
 
 RSpec.describe Gitlab::WikiFileFinder do
   describe '#find' do
-    let(:project) { create(:project, :public, :wiki_repo) }
-    let(:wiki) { build(:project_wiki, project: project) }
-
-    before do
-      wiki.create_page('Files/Title', 'Content')
-      wiki.create_page('CHANGELOG', 'Files example')
+    let_it_be(:project) do
+      create(:project, :public, :wiki_repo).tap do |project|
+        project.wiki.create_page('Files/Title', 'Content')
+        project.wiki.create_page('CHANGELOG', 'Files example')
+      end
     end
 
     it_behaves_like 'file finder' do

spec/services/git/wiki_push_service_spec.rb

@@ -5,11 +5,12 @@ require 'spec_helper'
 RSpec.describe Git::WikiPushService, services: true do
   include RepoHelpers
 
+  let_it_be(:current_user) { create(:user) }
   let_it_be(:key_id) { create(:key, user: current_user).shell_id }
-  let_it_be(:wiki) { create(:project_wiki) }
-  let_it_be(:current_user) { wiki.container.default_owner }
-  let_it_be(:git_wiki) { wiki.wiki }
-  let_it_be(:repository) { wiki.repository }
+
+  let(:wiki) { create(:project_wiki, user: current_user) }
+  let(:git_wiki) { wiki.wiki }
+  let(:repository) { wiki.repository }
 
   describe '#execute' do
     it 'executes model-specific callbacks' do

spec/support/shared_examples/models/wiki_shared_examples.rb

@@ -2,6 +2,7 @@
 
 RSpec.shared_examples 'wiki model' do
   let_it_be(:user) { create(:user, :commit_email) }
+
   let(:wiki_container) { raise NotImplementedError }
   let(:wiki_container_without_repo) { raise NotImplementedError }
   let(:wiki_lfs_enabled) { false }
@@ -536,4 +537,94 @@ RSpec.shared_examples 'wiki model' do
       expect(subject.hook_attrs.keys).to contain_exactly(:web_url, :git_ssh_url, :git_http_url, :path_with_namespace, :default_branch)
     end
   end
+
+  describe '#default_branch' do
+    subject { wiki.default_branch }
+
+    before do
+      allow(Gitlab::DefaultBranch).to receive(:value).and_return('main')
+    end
+
+    shared_examples 'feature flag wiki_uses_default_branch is disabled' do
+      it 'returns "master"' do
+        stub_feature_flags(wiki_uses_default_branch: false)
+
+        expect(subject).to eq 'master'
+      end
+    end
+
+    context 'when repository is not created' do
+      let(:wiki_container) { wiki_container_without_repo }
+
+      it 'returns the instance default branch' do
+        expect(subject).to eq 'main'
+      end
+
+      it_behaves_like 'feature flag wiki_uses_default_branch is disabled'
+    end
+
+    context 'when repository is empty' do
+      let(:wiki_container) { wiki_container_without_repo }
+
+      before do
+        wiki.repository.create_if_not_exists
+      end
+
+      it 'returns the instance default branch' do
+        expect(subject).to eq 'main'
+      end
+
+      it_behaves_like 'feature flag wiki_uses_default_branch is disabled'
+    end
+
+    context 'when repository is not empty' do
+      it 'returns the repository default branch' do
+        wiki.create_page('index', 'test content')
+
+        expect(subject).to eq wiki.repository.root_ref
+      end
+    end
+  end
+
+  describe '#create_wiki_repository' do
+    subject { wiki.create_wiki_repository }
+
+    context 'when repository is not created' do
+      let(:wiki_container) { wiki_container_without_repo }
+      let(:head_path) { Rails.root.join(TestEnv.repos_path, "#{wiki.disk_path}.git", 'HEAD') }
+      let(:default_branch) { 'foo' }
+
+      it 'changes the HEAD reference to the default branch' do
+        expect(wiki.empty?).to eq true
+
+        allow(Gitlab::CurrentSettings).to receive(:default_branch_name).and_return(default_branch)
+
+        subject
+
+        expect(File.read(head_path).squish).to eq "ref: refs/heads/#{default_branch}"
+      end
+    end
+
+    context 'when repository is empty' do
+      let(:wiki_container) { wiki_container_without_repo }
+
+      it 'does nothing' do
+        wiki.repository.create_if_not_exists
+
+        expect(wiki).not_to receive(:change_head_to_default_branch)
+
+        subject
+      end
+    end
+
+    context 'when repository is not empty' do
+      it 'does nothing' do
+        wiki.create_page('index', 'test content')
+
+        expect(wiki).not_to receive(:change_head_to_default_branch)
+
+        subject
+      end
+    end
+  end
 end

spec/views/search/_results.html.haml_spec.rb

@@ -62,7 +62,7 @@ RSpec.describe 'search/_results' do
     let_it_be(:merge_request) { create(:merge_request, title: '*', source_project: project, target_project: project) }
     let_it_be(:milestone) { create(:milestone, title: '*', project: project) }
     let_it_be(:note) { create(:discussion_note_on_issue, project: project, note: '*') }
-    let_it_be(:wiki_blob) { create(:wiki_page, project: project, content: '*') }
+    let_it_be(:wiki_blob) { create(:wiki_page, wiki: project.wiki, content: '*') }
     let_it_be(:user) { create(:admin) }
 
     %w[issues merge_requests].each do |search_scope|