Cleans up mirror capacity if project is a scheduled mirror

app/services/ee/projects/destroy_service.rb

@@ -6,9 +6,16 @@ module EE
 
         super
 
+        mirror_cleanup(project)
         log_geo_event(project)
       end
 
+      def mirror_cleanup(project)
+        return unless project.mirror?
+
+        ::Gitlab::Mirror.decrement_capacity(project.id)
+      end
+
       def log_geo_event(project)
         ::Geo::RepositoryDeletedEventStore.new(project,
           repo_path: repo_path,

changelogs/unreleased-ee/mirror-cleanup-in-project-destroy-service.yml

+---
+title: Cleans up mirror capacity in project destroy service if project is a scheduled
+  mirror
+merge_request: 2445
+author:

spec/services/ee/projects/destroy_service_spec.rb

@@ -18,6 +18,19 @@ describe Projects::DestroyService, services: true do
     stub_container_registry_tags(repository: :any, tags: [])
   end
 
+  context 'when project is a mirror' do
+    it 'decrements capacity if mirror was scheduled' do
+      max_capacity = current_application_settings.mirror_max_capacity
+      project_mirror = create(:project, :mirror, :repository, :import_scheduled)
+
+      Gitlab::Mirror.increment_capacity(project_mirror.id)
+
+      expect do
+        Projects::DestroyService.new(project_mirror, project_mirror.owner, {}).execute
+      end.to change { Gitlab::Mirror.available_capacity }.from(max_capacity - 1).to(max_capacity)
+    end
+  end
+
   context 'when running on a primary node' do
     let!(:geo_node) { create(:geo_node, :primary, :current) }