Add FeatureFlag to disable hashed storage migration when renaming

We usually want a feature flag to be disabled by default and
hide the feature until it's enabled.

This is an unconventional use: when the flag is enabled, it will
"DISABLE" the behavior.

app/models/project.rb

@@ -2072,13 +2072,19 @@ class Project < ActiveRecord::Base
   private
 
   def rename_or_migrate_repository!
-    if Gitlab::CurrentSettings.hashed_storage_enabled? && storage_version != LATEST_STORAGE_VERSION
+    if Gitlab::CurrentSettings.hashed_storage_enabled? &&
+        storage_upgradable? &&
+        Feature.disabled?(:disable_hashed_storage_upgrade) # kill switch in case we need to disable upgrade behavior
       ::Projects::HashedStorageMigrationService.new(self, full_path_was).execute
     else
       storage.rename_repo
     end
   end
 
+  def storage_upgradable?
+    storage_version != LATEST_STORAGE_VERSION
+  end
+
   def after_rename_repository(full_path_before, path_before)
     execute_rename_repository_hooks!(full_path_before)
 

spec/services/projects/update_service_spec.rb

@@ -249,7 +249,17 @@ describe Projects::UpdateService do
           expect(project.errors.messages[:base]).to include('There is already a repository with that name on disk')
         end
 
-        context 'when hashed storage enabled' do
+        it 'renames the project without upgrading it' do
+          result = update_project(project, admin, path: 'new-path')
+
+          expect(result).not_to include(status: :error)
+          expect(project).to be_valid
+          expect(project.errors).to be_empty
+          expect(project.disk_path).to include('new-path')
+          expect(project.reload.hashed_storage?(:repository)).to be_falsey
+        end
+
+        context 'when hashed storage is enabled' do
           before do
             stub_application_setting(hashed_storage_enabled: true)
           end
@@ -262,6 +272,22 @@ describe Projects::UpdateService do
             expect(project.errors).to be_empty
             expect(project.reload.hashed_storage?(:repository)).to be_truthy
           end
+
+          context 'when disable_hashed_storage_upgrade feature flag is enabled' do
+            before do
+              expect(Feature).to receive(:enabled?).with(:disable_hashed_storage_upgrade) { true }
+            end
+
+            it 'renames the project without upgrading it' do
+              result = update_project(project, admin, path: 'new-path')
+
+              expect(result).not_to include(status: :error)
+              expect(project).to be_valid
+              expect(project.errors).to be_empty
+              expect(project.disk_path).to include('new-path')
+              expect(project.reload.hashed_storage?(:repository)).to be_falsey
+            end
+          end
         end
       end