Use a generic markup class to display externally rendered files and diffs (#15735)

* creates and implements generic markup less class

* How to give custom CSS to externally rendered html

* Clarifies sources of CSS styling of markup

* further clarification of sources of markup styling

* rename _markdown to _markup

* remove defunct import

* fix orphaned reference

* Update docs/content/doc/advanced/external-renderers.en-us.md

* more renames markdown -> markup

* do not suggest less customization

* add back tokens

* fix class whitespace, remove useless if-clause

* remove unused csv-data rules

* use named exports and rename functions

* sort imports

Co-authored-by: HarvsG <11440490+HarvsG@users.noreply.github.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: silverwind <me@silverwind.io>

web_src/js/markup/anchors.js

@@ -0,0 +1,32 @@
+import {svg} from '../svg.js';
+
+const headingSelector = '.markup h1, .markup h2, .markup h3, .markup h4, .markup h5, .markup h6';
+
+function scrollToAnchor() {
+  if (document.querySelector(':target')) return;
+  if (!window.location.hash || window.location.hash.length <= 1) return;
+  const id = decodeURIComponent(window.location.hash.substring(1));
+  const el = document.getElementById(`user-content-${id}`);
+  if (el) {
+    el.scrollIntoView();
+  } else if (id.startsWith('user-content-')) { // compat for links with old 'user-content-' prefixed hashes
+    const el = document.getElementById(id);
+    if (el) el.scrollIntoView();
+  }
+}
+
+export function initMarkupAnchors() {
+  if (!document.querySelector('.markup')) return;
+
+  for (const heading of document.querySelectorAll(headingSelector)) {
+    const originalId = heading.id.replace(/^user-content-/, '');
+    const a = document.createElement('a');
+    a.classList.add('anchor');
+    a.setAttribute('href', `#${encodeURIComponent(originalId)}`);
+    a.innerHTML = svg('octicon-link');
+    heading.prepend(a);
+  }
+
+  scrollToAnchor();
+  window.addEventListener('hashchange', scrollToAnchor);
+}

web_src/js/markup/content.js

@@ -0,0 +1,5 @@
+import {renderMermaid} from './mermaid.js';
+
+export async function renderMarkupContent() {
+  await renderMermaid(document.querySelectorAll('code.language-mermaid'));
+}

web_src/js/markup/mermaid.js

@@ -0,0 +1,56 @@
+const MAX_SOURCE_CHARACTERS = 5000;
+
+function displayError(el, err) {
+  el.closest('pre').classList.remove('is-loading');
+  const errorNode = document.createElement('div');
+  errorNode.setAttribute('class', 'ui message error markup-block-error mono');
+  errorNode.textContent = err.str || err.message || String(err);
+  el.closest('pre').before(errorNode);
+}
+
+export async function renderMermaid(els) {
+  if (!els || !els.length) return;
+
+  const mermaid = await import(/* webpackChunkName: "mermaid" */'mermaid');
+
+  mermaid.initialize({
+    mermaid: {
+      startOnLoad: false,
+    },
+    flowchart: {
+      useMaxWidth: true,
+      htmlLabels: false,
+    },
+    theme: 'neutral',
+    securityLevel: 'strict',
+  });
+
+  for (const el of els) {
+    if (el.textContent.length > MAX_SOURCE_CHARACTERS) {
+      displayError(el, new Error(`Mermaid source of ${el.textContent.length} characters exceeds the maximum allowed length of ${MAX_SOURCE_CHARACTERS}.`));
+      continue;
+    }
+
+    let valid;
+    try {
+      valid = mermaid.parse(el.textContent);
+    } catch (err) {
+      displayError(el, err);
+    }
+
+    if (!valid) {
+      el.closest('pre').classList.remove('is-loading');
+      continue;
+    }
+
+    try {
+      mermaid.init(undefined, el, (id) => {
+        const svg = document.getElementById(id);
+        svg.classList.add('mermaid-chart');
+        svg.closest('pre').replaceWith(svg);
+      });
+    } catch (err) {
+      displayError(el, err);
+    }
+  }
+}