Put Pages moves from namespace renames in Sidekiq

When we rename a namespace, any projects in that namespace with Pages
enabled have to have their directories moved on the filesystem to match.
We want all operations that touch Pages disk paths to happen in Sidekiq,
not Puma; this puts that in Sidekiq behind the
`async_pages_move_namespace_rename` feature flag.

app/models/concerns/storage/legacy_namespace.rb

@@ -26,7 +26,16 @@ module Storage
         Gitlab::PagesTransfer.new.move_namespace(path, former_parent_full_path, parent_full_path)
       else
         Gitlab::UploadsTransfer.new.rename_namespace(full_path_before_last_save, full_path)
-        Gitlab::PagesTransfer.new.rename_namespace(full_path_before_last_save, full_path)
+
+        if ::Feature.enabled?(:async_pages_move_namespace_rename, self)
+          full_path_was = full_path_before_last_save
+
+          run_after_commit do
+            Gitlab::PagesTransfer.new.async.rename_namespace(full_path_was, full_path)
+          end
+        else
+          Gitlab::PagesTransfer.new.rename_namespace(full_path_before_last_save, full_path)
+        end
       end
 
       # If repositories moved successfully we need to

config/feature_flags/development/async_pages_move_namespace_rename.yml

+---
+name: async_pages_move_namespace_rename
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/40259
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/235808
+group: team::Scalability
+type: development
+default_enabled: false

spec/models/namespace_spec.rb

@@ -407,8 +407,24 @@ RSpec.describe Namespace do
           FileUtils.mkdir_p(File.join(pages_dir, project.full_path))
         end
 
+        after do
+          FileUtils.remove_entry(File.join(TestEnv.repos_path, parent.full_path), true)
+          FileUtils.remove_entry(File.join(uploads_dir, project.full_path), true)
+          FileUtils.remove_entry(File.join(pages_dir, project.full_path), true)
+        end
+
         context 'renaming child' do
-          it 'correctly moves the repository, uploads and pages' do
+          context 'when async_pages_move_namespace_rename is disabled' do
+            it 'correctly moves the repository, uploads and pages' do
+              stub_feature_flags(async_pages_move_namespace_rename: false)
+
+              child.update!(path: 'renamed')
+
+              expect_project_directories_at('parent/renamed')
+            end
+          end
+
+          it 'correctly moves the repository, uploads and pages', :sidekiq_inline do
             child.update!(path: 'renamed')
 
             expect_project_directories_at('parent/renamed')
@@ -416,7 +432,17 @@ RSpec.describe Namespace do
         end
 
         context 'renaming parent' do
-          it 'correctly moves the repository, uploads and pages' do
+          context 'when async_pages_move_namespace_rename is disabled' do
+            it 'correctly moves the repository, uploads and pages' do
+              stub_feature_flags(async_pages_move_namespace_rename: false)
+
+              parent.update!(path: 'renamed')
+
+              expect_project_directories_at('renamed/child')
+            end
+          end
+
+          it 'correctly moves the repository, uploads and pages', :sidekiq_inline do
             parent.update!(path: 'renamed')
 
             expect_project_directories_at('renamed/child')