Fix regression in FOSS for search issue description highlight

This fixes https://gitlab.com/gitlab-org/gitlab/-/issues/254840

The `#use_elasticsearch?` method is not defined in FOSS so we cannot
refer to it. As such the easiest way to handle this is to move the logic
into a helper and override in EE.

app/helpers/search_helper.rb

@@ -294,6 +294,11 @@ module SearchHelper
     sanitize(html, tags: %w(a p ol ul li pre code))
   end
 
+  # _search_highlight is used in EE override
+  def highlight_and_truncate_issue(issue, search_term, _search_highlight)
+    simple_search_highlight_and_truncate(issue.description, search_term, highlighter: '<span class="gl-text-black-normal gl-font-weight-bold">\1</span>')
+  end
+
   def simple_search_highlight_and_truncate(text, phrase, options = {})
     truncate_length = options.delete(:length) { 200 }
     text = truncate(text, length: truncate_length)

app/views/search/results/_issue.html.haml

@@ -10,7 +10,4 @@
   .gl-text-gray-500.gl-my-3
     = sprintf(s_(' %{project_name}#%{issue_iid} · opened %{issue_created} by %{author}'), { project_name: issue.project.full_name, issue_iid: issue.iid, issue_created: time_ago_with_tooltip(issue.created_at, placement: 'bottom'), author: link_to_member(@project, issue.author, avatar: false) }).html_safe
   .description.term.col-sm-10.gl-px-0
-  - if search_service.use_elasticsearch? && @search_highlight[issue.id]&.description.present?
-    = Truncato.truncate(@search_highlight[issue.id].description.first, count_tags: false, count_tail: false, max_length: 200).html_safe
-  - elsif issue.description.present?
-    = simple_search_highlight_and_truncate(issue.description, @search_term, highlighter: '<span class="gl-text-black-normal gl-font-weight-bold">\1</span>')
+    = highlight_and_truncate_issue(issue, @search_term, @search_highlight)

ee/app/helpers/ee/search_helper.rb

@@ -52,6 +52,14 @@ module EE
       end
     end
 
+    override :highlight_and_truncate_issue
+    def highlight_and_truncate_issue(issue, search_term, search_highlight)
+      return super unless search_service.use_elasticsearch? && search_highlight[issue.id]&.description.present?
+
+      # We use Elasticsearch highlighting for results from Elasticsearch
+      Truncato.truncate(search_highlight[issue.id].description.first, count_tags: false, count_tail: false, max_length: 200).html_safe
+    end
+
     def revert_to_basic_search_filter_url
       search_params = params
         .permit(::SearchHelper::SEARCH_PERMITTED_PARAMS)