Fix project deletion when there is a export available

Project deletions were failing with "Can't modify frozen hash" because:

1. Project#remove_exports was called in the after_destroy hook
2. This would remove the file and update ImportExportUpload
3. ImportExportUpload#save would attempt to write to a destroyed model

To avoid this, we just check if ImportExportUpload has been destroyed
before attempting to save it.

This would have a side effect of not running after_commit hooks to delete the
repository on disk, making it impossible to delete the project entirely.

Closes #52362

app/models/project.rb

@@ -1789,7 +1789,7 @@ class Project < ActiveRecord::Base
     return unless export_file_exists?
     import_export_upload.remove_export_file!
-    import_export_upload.save
+    import_export_upload.save unless import_export_upload.destroyed?
   end
   def export_file_exists?

changelogs/unreleased/sh-fix-project-deletion-with-export.yml

+---
+title: Fix project deletion when there is a export available
+merge_request: 22276
+author:
+type: fixed

spec/services/projects/destroy_service_spec.rb

@@ -65,10 +65,12 @@ describe Projects::DestroyService do
   context 'Sidekiq inline' do
     before do
-      # Run sidekiq immediatly to check that renamed repository will be removed
+      # Run sidekiq immediately to check that renamed repository will be removed
       perform_enqueued_jobs { destroy_project(project, user, {}) }
     end
+    it_behaves_like 'deleting the project'
+
     context 'when has remote mirrors' do
       let!(:project) do
         create(:project, :repository, namespace: user.namespace).tap do |project|
@@ -82,13 +84,28 @@ describe Projects::DestroyService do
       end
     end
-    it_behaves_like 'deleting the project'
-
     it 'invalidates personal_project_count cache' do
       expect(user).to receive(:invalidate_personal_projects_count)
       destroy_project(project, user)
     end
+
+    context 'when project has exports' do
+      let!(:project_with_export) do
+        create(:project, :repository, namespace: user.namespace).tap do |project|
+          create(:import_export_upload,
+                 project: project,
+                 export_file: fixture_file_upload('spec/fixtures/project_export.tar.gz'))
+        end
+      end
+      let!(:async) { true }
+
+      it 'destroys project and export' do
+        expect { destroy_project(project_with_export, user) }.to change(ImportExportUpload, :count).by(-1)
+
+        expect(Project.all).not_to include(project_with_export)
+      end
+    end
   end
   context 'Sidekiq fake' do