Reduce Namespace queries in UserReferenceFilterbanzai-user-filter-queries

This changes UserReferenceFilter so it operates using the following
steps:

1. Grab all username references from the input document.
2. Query the corresponding Namespace objects using a single query.
3. Iterate over all nodes to build links while re-using the objects
   queried in step 2.

The impact of these changes is that a comment mentioning 5 different
usernames no longer runs 5 different queries (1 for every username),
instead it only runs a single query.

1 files changed, 19 insertions, 0 deletions

diff --git a/spec/lib/banzai/filter/user_reference_filter_spec.rb b/spec/lib/banzai/filter/user_reference_filter_spec.rb
index d7dfd6699ef..108b36a97cc 100644
--- a/spec/lib/banzai/filter/user_reference_filter_spec.rb
+++ b/spec/lib/banzai/filter/user_reference_filter_spec.rb
@@ -136,4 +136,23 @@ describe Banzai::Filter::UserReferenceFilter, lib: true do
       expect(link.attr('data-user')).to eq user.namespace.owner_id.to_s
     end
   end
+
+  describe '#namespaces' do
+    it 'returns a Hash containing all Namespaces' do
+      document = Nokogiri::HTML.fragment("<p>#{user.to_reference}</p>")
+      filter = described_class.new(document, project: project)
+      ns = user.namespace
+
+      expect(filter.namespaces).to eq({ ns.path => ns })
+    end
+  end
+
+  describe '#usernames' do
+    it 'returns the usernames mentioned in a document' do
+      document = Nokogiri::HTML.fragment("<p>#{user.to_reference}</p>")
+      filter = described_class.new(document, project: project)
+
+      expect(filter.usernames).to eq([user.username])
+    end
+  end
 end