Validate project namespace's parent

app/models/namespace.rb

@@ -530,17 +530,27 @@ class Namespace < ApplicationRecord
 
   def nesting_level_allowed
     if ancestors.count > Group::NUMBER_OF_ANCESTORS_ALLOWED
-      errors.add(:parent_id, 'has too deep level of nesting')
+      errors.add(:parent_id, _('has too deep level of nesting'))
     end
   end
 
   def validate_parent_type
-    return unless has_parent?
+    unless has_parent?
+      if project?
+        errors.add(:parent_id, _('must be set for a project namespace'))
+      end
+
+      return
+    end
+
+    if parent.project?
+      errors.add(:parent_id, _('project namespace cannot be the parent of another namespace'))
+    end
 
     if user?
-      errors.add(:parent_id, 'a user namespace cannot have a parent')
+      errors.add(:parent_id, _('cannot not be used for user namespace'))
     elsif group?
-      errors.add(:parent_id, 'a group cannot have a user namespace as its parent') if parent.user?
+      errors.add(:parent_id, _('user namespace cannot be the parent of another namespace')) if parent.user?
     end
   end
 

locale/gitlab.pot

@@ -39445,6 +39445,9 @@ msgstr ""
 msgid "cannot merge"
 msgstr ""
 
+msgid "cannot not be used for user namespace"
+msgstr ""
+
 msgid "ciReport|%{degradedNum} degraded"
 msgstr ""
 
@@ -39955,6 +39958,9 @@ msgstr ""
 msgid "has been completed."
 msgstr ""
 
+msgid "has too deep level of nesting"
+msgstr ""
+
 msgid "help"
 msgstr ""
 
@@ -40503,6 +40509,9 @@ msgstr ""
 msgid "must be less than the limit of %{tag_limit} tags"
 msgstr ""
 
+msgid "must be set for a project namespace"
+msgstr ""
+
 msgid "must be unique by status and elapsed time within a policy"
 msgstr ""
 
@@ -40664,6 +40673,9 @@ msgstr ""
 msgid "project name"
 msgstr ""
 
+msgid "project namespace cannot be the parent of another namespace"
+msgstr ""
+
 msgid "projects"
 msgstr ""
 
@@ -40900,6 +40912,9 @@ msgstr ""
 msgid "user avatar"
 msgstr ""
 
+msgid "user namespace cannot be the parent of another namespace"
+msgstr ""
+
 msgid "user preferences"
 msgstr ""
 

spec/factories/namespaces/project_namespaces.rb

@@ -7,5 +7,6 @@ FactoryBot.define do
     path { project.path }
     type { Namespaces::ProjectNamespace.sti_name }
     owner { nil }
+    parent factory: :group
   end
 end

spec/models/group_spec.rb

@@ -82,7 +82,7 @@ RSpec.describe Group do
           group = build(:group, parent: build(:namespace))
 
           expect(group).not_to be_valid
-          expect(group.errors[:parent_id].first).to eq('a group cannot have a user namespace as its parent')
+          expect(group.errors[:parent_id].first).to eq('user namespace cannot be the parent of another namespace')
         end
 
         it 'allows a group to have another group as its parent' do

spec/models/namespace_spec.rb

@@ -36,27 +36,34 @@ RSpec.describe Namespace do
     it { is_expected.to validate_numericality_of(:max_artifacts_size).only_integer.is_greater_than(0) }
 
     context 'validating the parent of a namespace' do
-      context 'when the namespace has no parent' do
-        it 'allows a namespace to have no parent associated with it' do
-          namespace = build(:namespace)
+      using RSpec::Parameterized::TableSyntax
 
-          expect(namespace).to be_valid
-        end
+      where(:parent_type, :child_type, :error) do
+        nil         | 'User'      | nil
+        nil         | 'Group'     | nil
+        nil         | 'Project'   | 'must be set for a project namespace'
+        'Project'   | 'User'      | 'project namespace cannot be the parent of another namespace'
+        'Project'   | 'Group'     | 'project namespace cannot be the parent of another namespace'
+        'Project'   | 'Project'   | 'project namespace cannot be the parent of another namespace'
+        'Group'     | 'User'      | 'cannot not be used for user namespace'
+        'Group'     | 'Group'     | nil
+        'Group'     | 'Project'   | nil
+        'User'      | 'User'      | 'cannot not be used for user namespace'
+        'User'      | 'Group'     | 'user namespace cannot be the parent of another namespace'
+        'User'      | 'Project'   | nil
       end
 
-      context 'when the namespace has a parent' do
-        it 'does not allow a namespace to have a group as its parent' do
-          namespace = build(:namespace, parent: build(:group))
+      with_them do
+        it 'validates namespace parent' do
+          parent = build(:namespace, type: parent_type) if parent_type
+          namespace = build(:namespace, type: child_type, parent: parent)
 
+          if error
             expect(namespace).not_to be_valid
-          expect(namespace.errors[:parent_id].first).to eq('a user namespace cannot have a parent')
+            expect(namespace.errors[:parent_id].first).to eq(error)
+          else
+            expect(namespace).to be_valid
           end
-
-        it 'does not allow a namespace to have another namespace as its parent' do
-          namespace = build(:namespace, parent: build(:namespace))
-
-          expect(namespace).not_to be_valid
-          expect(namespace.errors[:parent_id].first).to eq('a user namespace cannot have a parent')
         end
       end
 
@@ -159,7 +166,8 @@ RSpec.describe Namespace do
 
   describe 'handling STI', :aggregate_failures do
     let(:namespace_type) { nil }
-    let(:namespace) { Namespace.find(create(:namespace, type: namespace_type).id) }
+    let(:parent) { nil }
+    let(:namespace) { Namespace.find(create(:namespace, type: namespace_type, parent: parent).id) }
 
     context 'creating a Group' do
       let(:namespace_type) { 'Group' }
@@ -173,6 +181,7 @@ RSpec.describe Namespace do
 
     context 'creating a ProjectNamespace' do
       let(:namespace_type) { 'Project' }
+      let(:parent) { create(:group) }
 
       it 'is valid' do
         expect(Namespace.find(namespace.id)).to be_a(Namespaces::ProjectNamespace)