Fix milestone references in group context

Fixes a bug where Markdown in Epics that contain both project and group
milestone references fails to render.

Changelog: fixed

ee/lib/ee/banzai/filter/references/iteration_reference_filter.rb

@@ -65,16 +65,12 @@ module EE
           end
 
           def group_context?(parent)
-            strong_memoize(:group_context) do
             parent.is_a?(Group)
           end
-          end
 
           def project_context?(parent)
-            strong_memoize(:project_context) do
             parent.is_a?(Project)
           end
-          end
 
           def references_in(text, pattern = ::Iteration.reference_pattern)
             # We'll handle here the references that follow the `reference_pattern`.

lib/banzai/filter/references/milestone_reference_filter.rb

@@ -5,8 +5,6 @@ module Banzai
     module References
       # HTML filter that replaces milestone references with links.
       class MilestoneReferenceFilter < AbstractReferenceFilter
-        include Gitlab::Utils::StrongMemoize
-
         self.reference_type = :milestone
         self.object_class   = Milestone
 
@@ -63,22 +61,16 @@ module Banzai
         end
 
         def valid_context?(parent)
-          strong_memoize(:valid_context) do
           group_context?(parent) || project_context?(parent)
         end
-        end
 
         def group_context?(parent)
-          strong_memoize(:group_context) do
           parent.is_a?(Group)
         end
-        end
 
         def project_context?(parent)
-          strong_memoize(:project_context) do
           parent.is_a?(Project)
         end
-        end
 
         def references_in(text, pattern = Milestone.reference_pattern)
           # We'll handle here the references that follow the `reference_pattern`.

spec/lib/banzai/filter/references/milestone_reference_filter_spec.rb

@@ -437,6 +437,19 @@ RSpec.describe Banzai::Filter::References::MilestoneReferenceFilter do
         expect(reference_filter(act, context).to_html).to eq exp
       end
     end
+
+    context 'when referencing both project and group milestones' do
+      let(:milestone) { create(:milestone, project: project) }
+      let(:group_milestone) { create(:milestone, title: 'group_milestone', group: group) }
+
+      it 'links to valid references' do
+        links = reference_filter("See #{milestone.to_reference(full: true)} and #{group_milestone.to_reference}", context).css('a')
+
+        expect(links.length).to eq(2)
+        expect(links[0].attr('href')).to eq(urls.milestone_url(milestone))
+        expect(links[1].attr('href')).to eq(urls.milestone_url(group_milestone))
+      end
+    end
   end
 
   context 'when milestone is open' do