Create main branch by default for snippets

Extract the main over master logic into a separate module
This module can be removed when the migration is over

app/models/project.rb

@@ -2535,7 +2535,7 @@ class Project < ApplicationRecord
   def default_branch_or_main
     return default_branch if default_branch
 
-    Feature.enabled?(:main_branch_over_master, self, default_enabled: :yaml) ? 'main' : 'master'
+    Gitlab::DefaultBranch.value(project: self)
   end
 
   def ci_config_path_or_default

app/models/snippet.rb

@@ -20,7 +20,6 @@ class Snippet < ApplicationRecord
   extend ::Gitlab::Utils::Override
 
   MAX_FILE_COUNT = 10
-  MASTER_BRANCH = 'master'
 
   cache_markdown_field :title, pipeline: :single_line
   cache_markdown_field :description
@@ -316,19 +315,19 @@ class Snippet < ApplicationRecord
 
   override :default_branch
   def default_branch
-    super || MASTER_BRANCH
+    super || Gitlab::DefaultBranch.value(project: project)
   end
 
   def repository_storage
     snippet_repository&.shard_name || Repository.pick_storage_shard
   end
 
-  # Repositories are created by default with the `master` branch.
+  # Repositories are created with a default branch. This branch
+  # can be different from the default branch set in the platform.
   # This method changes the `HEAD` file to point to the existing
-  # default branch in case it's not master.
+  # default branch in case it's different.
   def change_head_to_default_branch
     return unless repository.exists?
-    return if default_branch == MASTER_BRANCH
     # All snippets must have at least 1 file. Therefore, if
     # `HEAD` is empty is because it's pointing to the wrong
     # default branch

lib/gitlab/default_branch.rb

+# frozen_string_literal: true
+
+# Class is used while we're migrating from master to main
+module Gitlab
+  module DefaultBranch
+    def self.value(project: nil)
+      Feature.enabled?(:main_branch_over_master, project, default_enabled: :yaml) ? 'main' : 'master'
+    end
+  end
+end

spec/lib/gitlab/default_branch_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+# We disabled main_branch_over_master feature for tests
+# In order to have consistent branch usages
+# When we migrate the branch name to main, we can enable it
+RSpec.describe Gitlab::DefaultBranch do
+  context 'main_branch_over_master is enabled' do
+    before do
+      stub_feature_flags(main_branch_over_master: true)
+    end
+
+    it 'returns main' do
+      expect(described_class.value).to eq('main')
+    end
+  end
+
+  context 'main_branch_over_master is disabled' do
+    it 'returns master' do
+      expect(described_class.value).to eq('master')
+    end
+  end
+end

spec/models/project_spec.rb

@@ -6903,11 +6903,6 @@ RSpec.describe Project, factory_default: :keep do
   describe '#default_branch_or_main' do
     let(:project) { create(:project, :repository) }
 
-    before do
-      # Stubbing it as true since the FF disabled for tests globally
-      stub_feature_flags(main_branch_over_master: true)
-    end
-
     it 'returns default branch' do
       expect(project.default_branch_or_main).to eq(project.default_branch)
     end
@@ -6915,18 +6910,8 @@ RSpec.describe Project, factory_default: :keep do
     context 'when default branch is nil' do
       let(:project) { create(:project, :empty_repo) }
 
-      it 'returns main' do
-        expect(project.default_branch_or_main).to eq('main')
-      end
-
-      context 'main_branch_over_master is disabled' do
-        before do
-          stub_feature_flags(main_branch_over_master: false)
-        end
-
-        it 'returns master' do
-          expect(project.default_branch_or_main).to eq('master')
-        end
+      it 'returns Gitlab::DefaultBranch.value' do
+        expect(project.default_branch_or_main).to eq(Gitlab::DefaultBranch.value)
       end
     end
   end

spec/models/snippet_spec.rb

@@ -826,18 +826,6 @@ RSpec.describe Snippet do
         allow(Gitlab::CurrentSettings).to receive(:default_branch_name).and_return(default_branch)
       end
 
-      context 'when default branch in settings is "master"' do
-        let(:default_branch) { 'master' }
-
-        it 'does nothing' do
-          expect(File.read(head_path).squish).to eq 'ref: refs/heads/master'
-
-          expect(snippet.repository.raw_repository).not_to receive(:write_ref)
-
-          subject
-        end
-      end
-
       context 'when default branch in settings is different from "master"' do
         let(:default_branch) { 'main' }