[CE] - Add milestones autocomplete for epics

CE backport of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8632

lib/banzai/filter/milestone_reference_filter.rb

@@ -4,6 +4,8 @@ module Banzai
   module Filter
     # HTML filter that replaces milestone references with links.
     class MilestoneReferenceFilter < AbstractReferenceFilter
+      include Gitlab::Utils::StrongMemoize
+
       self.reference_type = :milestone
 
       def self.object_class
@@ -13,16 +15,34 @@ module Banzai
       # Links to project milestones contain the IID, but when we're handling
       # 'regular' references, we need to use the global ID to disambiguate
       # between group and project milestones.
-      def find_object(project, id)
-        return unless project.is_a?(Project)
+      def find_object(parent, id)
+        return unless valid_context?(parent)
 
-        find_milestone_with_finder(project, id: id)
+        find_milestone_with_finder(parent, id: id)
       end
 
-      def find_object_from_link(project, iid)
-        return unless project.is_a?(Project)
+      def find_object_from_link(parent, iid)
+        return unless valid_context?(parent)
+
+        find_milestone_with_finder(parent, iid: iid)
+      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
 
-        find_milestone_with_finder(project, iid: iid)
+      def project_context?(parent)
+        strong_memoize(:project_context) do
+          parent.is_a?(Project)
+        end
       end
 
       def references_in(text, pattern = Milestone.reference_pattern)
@@ -44,13 +64,15 @@ module Banzai
 
       def find_milestone(project_ref, namespace_ref, milestone_id, milestone_name)
         project_path = full_project_path(namespace_ref, project_ref)
-        project = parent_from_ref(project_path)
 
-        return unless project && project.is_a?(Project)
+        # Returns group if project is not found by path
+        parent = parent_from_ref(project_path)
+
+        return unless parent
 
         milestone_params = milestone_params(milestone_id, milestone_name)
 
-        find_milestone_with_finder(project, milestone_params)
+        find_milestone_with_finder(parent, milestone_params)
       end
 
       def milestone_params(iid, name)
@@ -61,16 +83,28 @@ module Banzai
         end
       end
 
-      def find_milestone_with_finder(project, params)
-        finder_params = { project_ids: [project.id], order: nil, state: 'all' }
+      def find_milestone_with_finder(parent, params)
+        finder_params = milestone_finder_params(parent, params[:iid].present?)
+
+        MilestonesFinder.new(finder_params).find_by(params)
+      end
 
-        # We don't support IID lookups for group milestones, because IIDs can
-        # clash between group and project milestones.
-        if project.group && !params[:iid]
-          finder_params[:group_ids] = project.group.self_and_ancestors_ids
+      def milestone_finder_params(parent, find_by_iid)
+        { order: nil, state: 'all' }.tap do |params|
+          params[:project_ids] = parent.id if project_context?(parent)
+
+          # We don't support IID lookups because IIDs can clash between
+          # group/project milestones and group/subgroup milestones.
+          params[:group_ids] = self_and_ancestors_ids(parent) unless find_by_iid
         end
+      end
 
-        MilestonesFinder.new(finder_params).find_by(params)
+      def self_and_ancestors_ids(parent)
+        if group_context?(parent)
+          parent.self_and_ancestors_ids
+        elsif project_context?(parent)
+          parent.group&.self_and_ancestors_ids
+        end
       end
 
       def url_for_object(milestone, project)

spec/lib/banzai/filter/milestone_reference_filter_spec.rb

@@ -351,21 +351,50 @@ describe Banzai::Filter::MilestoneReferenceFilter do
   end
 
   context 'group context' do
-    let(:context) { { project: nil, group: create(:group) } }
-    let(:milestone) { create(:milestone, project: project) }
+    let(:group) { create(:group) }
+    let(:context) { { project: nil, group: group } }
 
-    it 'links to a valid reference' do
-      reference = "#{project.full_path}%#{milestone.iid}"
+    context 'when project milestone' do
+      let(:milestone) { create(:milestone, project: project) }
 
-      result = reference_filter("See #{reference}", context)
+      it 'links to a valid reference' do
+        reference = "#{project.full_path}%#{milestone.iid}"
 
-      expect(result.css('a').first.attr('href')).to eq(urls.milestone_url(milestone))
+        result = reference_filter("See #{reference}", context)
+
+        expect(result.css('a').first.attr('href')).to eq(urls.milestone_url(milestone))
+      end
+
+      it 'ignores internal references' do
+        exp = act = "See %#{milestone.iid}"
+
+        expect(reference_filter(act, context).to_html).to eq exp
+      end
     end
 
-    it 'ignores internal references' do
-      exp = act = "See %#{milestone.iid}"
+    context 'when group milestone' do
+      let(:group_milestone) { create(:milestone, title: 'group_milestone', group: group) }
 
-      expect(reference_filter(act, context).to_html).to eq exp
+      context 'for subgroups', :nested_groups do
+        let(:sub_group) { create(:group, parent: group) }
+        let(:sub_group_milestone) { create(:milestone, title: 'sub_group_milestone', group: sub_group) }
+
+        it 'links to a valid reference of subgroup and group milestones' do
+          [group_milestone, sub_group_milestone].each do |milestone|
+            reference = "%#{milestone.title}"
+
+            result = reference_filter("See #{reference}", { project: nil, group: sub_group })
+
+            expect(result.css('a').first.attr('href')).to eq(urls.milestone_url(milestone))
+          end
+        end
+      end
+
+      it 'ignores internal references' do
+        exp = act = "See %#{group_milestone.iid}"
+
+        expect(reference_filter(act, context).to_html).to eq exp
+      end
     end
   end