Fix URLs with anchors in wiki

CHANGELOG

@@ -129,6 +129,7 @@ v 8.12.0 (unreleased)
   - Allow bulk update merge requests from merge requests index page
   - Add notification_settings API calls !5632 (mahcsig)
   - Remove duplication between project builds and admin builds view !5680 (Katarzyna Kobierska Ula Budziszewska)
+  - Fix URLs with anchors in wiki !6300 (houqp)
   - Deleting source project with existing fork link will close all related merge requests !6177 (Katarzyna Kobierska Ula Budziszeska)
 
 v 8.11.6 (unreleased)

lib/banzai/filter/wiki_link_filter/rewriter.rb

@@ -31,6 +31,7 @@ module Banzai
         def apply_relative_link_rules!
           if @uri.relative? && @uri.path.present?
             link = ::File.join(@wiki_base_path, @uri.path)
+            link = "#{link}##{@uri.fragment}" if @uri.fragment
             @uri = Addressable::URI.parse(link)
           end
         end

spec/lib/banzai/pipeline/wiki_pipeline_spec.rb

@@ -127,6 +127,13 @@ describe Banzai::Pipeline::WikiPipeline do
 
               expect(output).to include("href=\"#{relative_url_root}/wiki_link_ns/wiki_link_project/wikis/nested/twice/page.md\"")
             end
+
+            it 'rewrites links with anchor' do
+              markdown = '[Link to Header](start-page#title)'
+              output = described_class.to_html(markdown, project: project, project_wiki: project_wiki, page_slug: page.slug)
+
+              expect(output).to include("href=\"#{relative_url_root}/wiki_link_ns/wiki_link_project/wikis/start-page#title\"")
+            end
           end
 
           describe "when creating root links" do