Fix project deletion when feature visibility is set to private

Projects that are destroyed are put in the pending_delete state.
The ProjectDestroyWorker checks whether the current user has
access, but since the ProjectFeature class uses the default scope
of the Project, it will not be able to find the right project.

This was a regression in 8.12 that caused the following stack trace:

```
NoMethodError: undefined method `team' for nil:NilClass
  from app/models/project_feature.rb:62:in `get_permission'
  from app/models/project_feature.rb:34:in `feature_available?'
  from app/models/project.rb:21:in `feature_available?'
  from app/policies/project_policy.rb:170:in `disabled_features!'
  from app/policies/project_policy.rb:29:in `rules'
  from app/policies/base_policy.rb:82:in `block in abilities'
  from app/policies/base_policy.rb:113:in `collect_rules'
  from app/policies/base_policy.rb:82:in `abilities'
  from app/policies/base_policy.rb:50:in `abilities'
  from app/models/ability.rb:64:in `uncached_allowed'
  from app/models/ability.rb:58:in `allowed'
  from app/models/ability.rb:49:in `allowed?'
  from app/services/base_service.rb:11:in `can?'
  from lib/gitlab/metrics/instrumentation.rb:155:in `block in can?'
  from lib/gitlab/metrics/method_call.rb:23:in `measure'
  from lib/gitlab/metrics/instrumentation.rb:155:in `can?'
  from app/services/projects/destroy_service.rb:18:in `execute'
```

Closes #22948

CHANGELOG

@@ -53,6 +53,7 @@ v 8.13.0 (unreleased)
 v 8.12.4 (unreleased)
   - Fix type mismatch bug when closing Jira issue
   - Skip wiki creation when GitHub project has wiki enabled
+  - Fix failed project deletion when feature visibility set to private
   - Fix issues importing services via Import/Export
   - Restrict failed login attempts for users with 2FA enabled
   - Fix "Copy to clipboard" tooltip to say "Copied!" when clipboard button is clicked. (lukehowell)

app/models/project_feature.rb

@@ -20,7 +20,10 @@ class ProjectFeature < ActiveRecord::Base
 
   FEATURES = %i(issues merge_requests wiki snippets builds)
 
-  belongs_to :project
+  # Default scopes force us to unscope here since a service may need to check
+  # permissions for a project in pending_delete
+  # http://stackoverflow.com/questions/1540645/how-to-disable-default-scope-for-a-belongs-to
+  belongs_to :project, -> { unscope(where: :pending_delete) }
 
   default_value_for :builds_access_level,         value: ENABLED, allows_nil: false
   default_value_for :issues_access_level,         value: ENABLED, allows_nil: false

spec/services/projects/destroy_service_spec.rb

@@ -5,6 +5,7 @@ describe Projects::DestroyService, services: true do
   let!(:project) { create(:project, namespace: user.namespace) }
   let!(:path) { project.repository.path_to_repo }
   let!(:remove_path) { path.sub(/\.git\Z/, "+#{project.id}+deleted.git") }
+  let!(:async) { false } # execute or async_execute
 
   context 'Sidekiq inline' do
     before do
@@ -28,6 +29,22 @@ describe Projects::DestroyService, services: true do
     it { expect(Dir.exist?(remove_path)).to be_truthy }
   end
 
+  context 'async delete of project with private issue visibility' do
+    let!(:async) { true }
+
+    before do
+      project.project_feature.update_attribute("issues_access_level", ProjectFeature::PRIVATE)
+      # Run sidekiq immediately to check that renamed repository will be removed
+      Sidekiq::Testing.inline! { destroy_project(project, user, {}) }
+    end
+
+    it 'deletes the project' do
+      expect(Project.all).not_to include(project)
+      expect(Dir.exist?(path)).to be_falsey
+      expect(Dir.exist?(remove_path)).to be_falsey
+    end
+  end
+
   context 'container registry' do
     before do
       stub_container_registry_config(enabled: true)
@@ -52,6 +69,10 @@ describe Projects::DestroyService, services: true do
   end
 
   def destroy_project(project, user, params)
-    Projects::DestroyService.new(project, user, params).execute
+    if async
+      Projects::DestroyService.new(project, user, params).async_execute
+    else
+      Projects::DestroyService.new(project, user, params).execute
+    end
   end
 end