Include user namespace in list of fork targets

With the fork_project_form feature flag enabled, we don't pay any
attention to the `@own_namespace` instance variable, instead expecting
to get the full list of namespaces we can fork to in the JSON payload
given by Projects::ForksController#new

Adding `@own_namespace` to that json payload allows us to render it
without any special handling. It does mean that we now have a mixed
array of Namespace and Group, so a few Group-specific things need to
be supported by Namespace.

app/controllers/projects/forks_controller.rb

@@ -44,13 +44,17 @@ class Projects::ForksController < Projects::ApplicationController
   def new
     respond_to do |format|
       format.html do
-        @own_namespace = current_user.namespace if fork_service.valid_fork_targets.include?(current_user.namespace)
+        @own_namespace = current_user.namespace if can_fork_to?(current_user.namespace)
         @project = project
       end
 
       format.json do
         namespaces = load_namespaces_with_associations - [project.namespace]
 
+        namespaces = [current_user.namespace] + namespaces if
+          Feature.enabled?(:fork_project_form, project, default_enabled: :yaml) &&
+          can_fork_to?(current_user.namespace)
+
         render json: {
           namespaces: ForkNamespaceSerializer.new.represent(namespaces, project: project, current_user: current_user, memberships: memberships_hash)
         }
@@ -78,6 +82,10 @@ class Projects::ForksController < Projects::ApplicationController
 
   private
 
+  def can_fork_to?(namespace)
+    ForkTargetsFinder.new(@project, current_user).execute.id_in(current_user.namespace).any?
+  end
+
   def load_forks
     forks = ForkProjectsFinder.new(
       project,

app/serializers/fork_namespace_entity.rb

@@ -23,7 +23,7 @@ class ForkNamespaceEntity < Grape::Entity
   end
 
   expose :relative_path do |namespace|
-    polymorphic_path(namespace)
+    group_path(namespace)
   end
 
   expose :markdown_description do |namespace|

ee/app/models/ee/namespace.rb

@@ -103,6 +103,11 @@ module EE
       before_save :clear_feature_available_cache
     end
 
+    # Only groups can be marked for deletion
+    def marked_for_deletion?
+      false
+    end
+
     def namespace_limit
       limit = has_parent? ? root_ancestor.namespace_limit : super
 

spec/controllers/projects/forks_controller_spec.rb

@@ -153,8 +153,11 @@ RSpec.describe Projects::ForksController do
   end
 
   describe 'GET new' do
-    subject do
+    let(:format) { :html }
+
+    subject(:do_request) do
       get :new,
+          format: format,
           params: {
             namespace_id: project.namespace,
             project_id: project
@@ -166,24 +169,32 @@ RSpec.describe Projects::ForksController do
         sign_in(user)
       end
 
-      context 'when JSON requested' do
-        it 'responds with available groups' do
-          get :new,
-              format: :json,
-              params: {
-                namespace_id: project.namespace,
-                project_id: project
-              }
+      it 'responds with status 200' do
+        request
 
-          expect(json_response['namespaces'].length).to eq(1)
-          expect(json_response['namespaces'].first['id']).to eq(group.id)
-        end
+        expect(response).to have_gitlab_http_status(:ok)
       end
 
-      it 'responds with status 200' do
-        subject
+      context 'when JSON is requested' do
+        let(:format) { :json }
 
-        expect(response).to have_gitlab_http_status(:ok)
+        it 'responds with user namespace + groups' do
+          do_request
+
+          expect(response).to have_gitlab_http_status(:ok)
+          expect(json_response['namespaces'].length).to eq(2)
+          expect(json_response['namespaces'][0]['id']).to eq(user.namespace.id)
+          expect(json_response['namespaces'][1]['id']).to eq(group.id)
+        end
+
+        it 'responds with group only when fork_project_form feature flag is disabled' do
+          stub_feature_flags(fork_project_form: false)
+          do_request
+
+          expect(response).to have_gitlab_http_status(:ok)
+          expect(json_response['namespaces'].length).to eq(1)
+          expect(json_response['namespaces'][0]['id']).to eq(group.id)
+        end
       end
     end