Fix N+1 problem for fork controller

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/329751

Temporary removes code responsible for N+1 query.

The new frontend code does not use the result from
`can_create_project` field

Changelog: performance

app/serializers/fork_namespace_entity.rb

@@ -31,8 +31,12 @@ class ForkNamespaceEntity < Grape::Entity
   end
 
   expose :can_create_project do |namespace, options|
+    if Feature.enabled?(:fork_project_form, options[:project], default_enabled: :yaml)
+      true
+    else
       options[:current_user].can?(:create_projects, namespace)
     end
+  end
 
   private
 

spec/controllers/projects/forks_controller_spec.rb

@@ -211,11 +211,7 @@ RSpec.describe Projects::ForksController do
 
             create(:group, :public).add_owner(user)
 
-            # TODO: There is another N+1 caused by user.can?(:create_projects, namespace)
-            # Defined in ForkNamespaceEntity
-            extra_count = 1
-
-            expect { do_request.call }.not_to exceed_query_limit(control.count + extra_count)
+            expect { do_request.call }.not_to exceed_query_limit(control)
           end
         end
       end

spec/serializers/fork_namespace_entity_spec.rb

@@ -60,6 +60,15 @@ RSpec.describe ForkNamespaceEntity do
     expect(json[:permission]).to eql 'Developer'
   end
 
+  it 'exposes can_create_project' do
+    expect(json[:can_create_project]).to be true
+  end
+
+  context 'when fork_project_form feature flag is disabled' do
+    before do
+      stub_feature_flags(fork_project_form: false)
+    end
+
     it 'sets can_create_project to true when user can create projects in namespace' do
       allow(user).to receive(:can?).with(:create_projects, namespace).and_return(true)
 
@@ -71,4 +80,5 @@ RSpec.describe ForkNamespaceEntity do
 
       expect(json[:can_create_project]).to be false
     end
+  end
 end