UserNamespace should be created for new users

as opposed to a generic Namespace

app/models/namespace.rb

@@ -44,6 +44,8 @@ class Namespace < ApplicationRecord
 
   # This should _not_ be `inverse_of: :namespace`, because that would also set
   # `user.namespace` when this user creates a group with themselves as `owner`.
+  # TODO: can this be moved into the UserNamespace class?
+  #       evaluate in issue https://gitlab.com/gitlab-org/gitlab/-/issues/341070
   belongs_to :owner, class_name: "User"
 
   belongs_to :parent, class_name: "Namespace"

app/models/user.rb

@@ -112,9 +112,14 @@ class User < ApplicationRecord
   #
 
   # Namespace for personal projects
-  # TODO: change to `type: Namespaces::UserNamespace.sti_name` when
-  #       working on issue https://gitlab.com/gitlab-org/gitlab/-/issues/341070
-  has_one :namespace, -> { where(type: [nil, Namespaces::UserNamespace.sti_name]) }, dependent: :destroy, foreign_key: :owner_id, inverse_of: :owner, autosave: true # rubocop:disable Cop/ActiveRecordDependent
+  # TODO: change to `:namespace, -> { where(type: Namespaces::UserNamespace.sti_name}, class_name: 'Namespaces::UserNamespace'...`
+  #       when working on issue https://gitlab.com/gitlab-org/gitlab/-/issues/341070
+  has_one :namespace,
+          -> { where(type: [nil, Namespaces::UserNamespace.sti_name]) },
+          dependent: :destroy, # rubocop:disable Cop/ActiveRecordDependent
+          foreign_key: :owner_id,
+          inverse_of: :owner,
+          autosave: true # rubocop:disable Cop/ActiveRecordDependent
 
   # Profile
   has_many :keys, -> { regular_keys }, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
@@ -1437,7 +1442,10 @@ class User < ApplicationRecord
       namespace.path = username if username_changed?
       namespace.name = name if name_changed?
     else
-      namespace = build_namespace(path: username, name: name)
+      # TODO: we should no longer need the `type` parameter once we can make the
+      #       the `has_one :namespace` association use the correct class.
+      #       issue https://gitlab.com/gitlab-org/gitlab/-/issues/341070
+      namespace = build_namespace(path: username, name: name, type: ::Namespaces::UserNamespace.sti_name)
       namespace.build_namespace_settings
     end
   end

spec/factories/namespaces.rb

@@ -5,6 +5,8 @@ FactoryBot.define do
     sequence(:name) { |n| "namespace#{n}" }
     path { name.downcase.gsub(/\s/, '_') }
 
+    # TODO: can this be moved into the :user_namespace factory?
+    #       evaluate in issue https://gitlab.com/gitlab-org/gitlab/-/issues/341070
     owner { association(:user, strategy: :build, namespace: instance, username: path) }
 
     trait :with_aggregation_schedule do

spec/models/user_spec.rb

@@ -378,7 +378,7 @@ RSpec.describe User do
       end
 
       context 'when username is changed' do
-        let(:user) { build_stubbed(:user, username: 'old_path', namespace: build_stubbed(:namespace)) }
+        let(:user) { build_stubbed(:user, username: 'old_path', namespace: build_stubbed(:user_namespace)) }
 
         it 'validates move_dir is allowed for the namespace' do
           expect(user.namespace).to receive(:any_project_has_container_registry_tags?).and_return(true)
@@ -3853,7 +3853,7 @@ RSpec.describe User do
     end
 
     context 'with runner in a personal project' do
-      let!(:namespace) { create(:namespace, owner: user) }
+      let!(:namespace) { create(:user_namespace, owner: user) }
       let!(:project) { create(:project, namespace: namespace) }
       let!(:runner) { create(:ci_runner, :project, projects: [project]) }
 
@@ -3921,7 +3921,7 @@ RSpec.describe User do
     end
 
     context 'with personal project runner in an owned group in an owned namespace and a group runner in that group' do
-      let!(:namespace) { create(:namespace, owner: user) }
+      let!(:namespace) { create(:user_namespace, owner: user) }
       let!(:group) { create(:group) }
       let!(:group_runner) { create(:ci_runner, :group, groups: [group]) }
       let!(:project) { create(:project, namespace: namespace, group: group) }
@@ -3935,7 +3935,7 @@ RSpec.describe User do
     end
 
     context 'with personal project runner in an owned namespace, an owned group, a subgroup and a group runner in that subgroup' do
-      let!(:namespace) { create(:namespace, owner: user) }
+      let!(:namespace) { create(:user_namespace, owner: user) }
       let!(:group) { create(:group) }
       let!(:subgroup) { create(:group, parent: group) }
       let!(:group_runner) { create(:ci_runner, :group, groups: [subgroup]) }
@@ -4617,6 +4617,7 @@ RSpec.describe User do
         user.save!
 
         expect(user.namespace).not_to be_nil
+        expect(user.namespace).to be_kind_of(Namespaces::UserNamespace)
       end
 
       it 'creates the namespace setting' do