Fix bug where destroying a namespace would not always destroy projects

There is a race condition in DestroyGroupService now that projects are deleted asynchronously:

1. User attempts to delete group
2. DestroyGroupService iterates through all projects and schedules a Sidekiq job to delete each Project
3. DestroyGroupService destroys the Group, leaving all its projects without a namespace
4. Projects::DestroyService runs later but the can?(current_user,
   :remove_project) is `false` because the user no longer has permission to
   destroy projects with no namespace.
5. This leaves the project in pending_delete state with no namespace/group.

Projects without a namespace or group also adds another problem: it's not possible to destroy the container
registry tags, since container_registry_path_with_namespace is the wrong value.

The fix is to destroy the group asynchronously and to run execute directly on Projects::DestroyService.

Closes #17893

1 files changed, 12 insertions, 0 deletions

diff --git a/db/migrate/20160805041956_add_deleted_at_to_namespaces.rb b/db/migrate/20160805041956_add_deleted_at_to_namespaces.rb
new file mode 100644
index 00000000000..a853de3abfb
--- /dev/null
+++ b/db/migrate/20160805041956_add_deleted_at_to_namespaces.rb
@@ -0,0 +1,12 @@
+class AddDeletedAtToNamespaces < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def change
+    add_column :namespaces, :deleted_at, :datetime
+    add_concurrent_index :namespaces, :deleted_at
+  end
+end