Fixes mermaid graphs not rendering when switching diff tabs

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/220889

app/assets/javascripts/behaviors/markdown/render_mermaid.js

@@ -174,7 +174,7 @@ export default function renderMermaid($els) {
   if (!$els.length) return;
 
   const visibleMermaids = $els.filter(function filter() {
-    return $(this).closest('details').length === 0;
+    return $(this).closest('details').length === 0 && $(this).is(':visible');
   });
 
   renderMermaids(visibleMermaids);

app/assets/javascripts/merge_request_tabs.js

@@ -226,6 +226,8 @@ export default class MergeRequestTabs {
         this.resetViewContainer();
         this.destroyPipelinesView();
       }
+
+      $('.detail-page-description').renderGFM();
     } else if (action === this.currentAction) {
       // ContentTop is used to handle anything at the top of the page before the main content
       const mainContentContainer = document.querySelector('.content-wrapper');

changelogs/unreleased/ph-220889-fixMermaidNotRendering.yml

+---
+title: Fixed mermaid not rendering when switching diff tabs
+merge_request:
+author:
+type: fixed