Exclude project namespaces from namespace searches

When searching namespces by path or name we are not expecting
to get ProjectNamespaces in results yet, so we need to filter
those out for now.

app/models/namespace.rb

@@ -125,7 +125,7 @@ class Namespace < ApplicationRecord
   scope :user_namespaces, -> { where(type: [nil, Namespaces::UserNamespace.sti_name]) }
   # TODO: this can be simplified with `type != 'Project'`  when working on issue
   #       https://gitlab.com/gitlab-org/gitlab/-/issues/341070
-  scope :without_project_namespaces, -> { where("type IS DISTINCT FROM ?", Namespaces::ProjectNamespace.sti_name) }
+  scope :without_project_namespaces, -> { where(Namespace.arel_table[:type].is_distinct_from(Namespaces::ProjectNamespace.sti_name)) }
   scope :sort_by_type, -> { order(Gitlab::Database.nulls_first_order(:type)) }
   scope :include_route, -> { includes(:route) }
   scope :by_parent, -> (parent) { where(parent_id: parent) }
@@ -192,9 +192,9 @@ class Namespace < ApplicationRecord
     # Returns an ActiveRecord::Relation.
     def search(query, include_parents: false)
       if include_parents
-        where(id: Route.for_routable_type(Namespace.name).fuzzy_search(query, [Route.arel_table[:path], Route.arel_table[:name]]).select(:source_id))
+        without_project_namespaces.where(id: Route.for_routable_type(Namespace.name).fuzzy_search(query, [Route.arel_table[:path], Route.arel_table[:name]]).select(:source_id))
       else
-        fuzzy_search(query, [:path, :name])
+        without_project_namespaces.fuzzy_search(query, [:path, :name])
       end
     end
 

spec/models/namespace_spec.rb

@@ -559,6 +559,25 @@ RSpec.describe Namespace do
     it 'returns namespaces with a matching route path regardless of the casing' do
       expect(described_class.search('PARENT-PATH/NEW-PATH', include_parents: true)).to eq([second_group])
     end
+
+    context 'with project namespaces' do
+      let_it_be(:project) { create(:project, namespace: parent_group, path: 'some-new-path') }
+      let_it_be(:project_namespace) { create(:project_namespace, project: project) }
+
+      it 'does not return project namespace' do
+        search_result = described_class.search('path')
+
+        expect(search_result).not_to include(project_namespace)
+        expect(search_result).to match_array([first_group, parent_group, second_group])
+      end
+
+      it 'does not return project namespace when including parents' do
+        search_result = described_class.search('path', include_parents: true)
+
+        expect(search_result).not_to include(project_namespace)
+        expect(search_result).to match_array([first_group, parent_group, second_group])
+      end
+    end
   end
 
   describe '.with_statistics' do