Ignore eager loading in Project.search UNION

The queries that are UNION'd together don't need any eager loading
(since we really only use the resulting SQL instead of having
ActiveRecord actually run the queries). By dropping any eager loaded
associations queries such as the following work instead of producing a
SQL error:

    Project.all.includes(:namespace).search('foo')

app/models/project.rb

@@ -286,7 +286,14 @@ class Project < ActiveRecord::Base
           or(ptable[:description].matches(pattern))
       )
 
+      # We explicitly remove any eager loading clauses as they're:
+      #
+      # 1. Not needed by this query
+      # 2. Combined with .joins(:namespace) lead to all columns from the
+      #    projects & namespaces tables being selected, leading to a SQL error
+      #    due to the columns of all UNION'd queries no longer being the same.
       namespaces = select(:id).
+        except(:includes).
         joins(:namespace).
         where(ntable[:name].matches(pattern))
 

spec/models/project_spec.rb

@@ -634,6 +634,12 @@ describe Project, models: true do
     it 'returns projects with a matching namespace name regardless of the casing' do
       expect(described_class.search(project.namespace.name.upcase)).to eq([project])
     end
+
+    it 'returns projects when eager loading namespaces' do
+      relation = described_class.all.includes(:namespace)
+
+      expect(relation.search(project.namespace.name)).to eq([project])
+    end
   end
 
   describe '#rename_repo' do