Move syntax highlighting to web worker (go-gitea#11017)

This should eliminate page freezes when loading big files/diff.
`highlightBlock` is needed to preserve existing nodes when highlighting
and for that, highlight.js needs access to the DOM API so I added a DOM
implementation to make it work, which adds around 300kB to the output
file size of the lazy-loaded `highlight.js`.

Co-authored-by: Lauris BH <[email protected]>

.eslintrc

@@ -24,6 +24,13 @@ globals:
  SimpleMDE: false
  u2fApi: false
 
+overrides:
+ - files: ["web_src/**/*.worker.js"]
+ env:
+ worker: true
+ rules:
+ no-restricted-globals: [0]
+
 rules:
  arrow-body-style: [0]
  arrow-parens: [2, always]

package.json

@@ -17,6 +17,7 @@
  "core-js": "3.6.4",
  "css-loader": "3.4.2",
  "cssnano": "4.1.10",
+ "domino": "2.1.4",
  "dropzone": "5.7.0",
  "fast-glob": "3.2.2",
  "fomantic-ui": "2.8.4",
@@ -44,7 +45,8 @@
  "vue-template-compiler": "2.6.11",
  "webpack": "4.42.0",
  "webpack-cli": "3.3.11",
- "webpack-fix-style-only-entries": "0.4.0"
+ "webpack-fix-style-only-entries": "0.4.0",
+ "worker-loader": "2.0.0"
  },
  "devDependencies": {
  "eslint": "6.8.0",

web_src/js/features/highlight.js

@@ -1,12 +1,19 @@
-export default async function initHighlight() {
- if (!window.config || !window.config.HighlightJS) return;
+export default async function highlight(elementOrNodeList) {
+ if (!window.config || !window.config.HighlightJS || !elementOrNodeList) return;
+ const nodes = 'length' in elementOrNodeList ? elementOrNodeList : [elementOrNodeList];
+ if (!nodes.length) return;
 
- const hljs = await import(/* webpackChunkName: "highlight" */'highlight.js');
+ const {default: Worker} = await import(/* webpackChunkName: "highlight" */'./highlight.worker.js');
+ const worker = new Worker();
 
- const nodes = [].slice.call(document.querySelectorAll('pre code') || []);
- for (let i = 0; i < nodes.length; i++) {
- hljs.highlightBlock(nodes[i]);
- }
+ worker.addEventListener('message', ({data}) => {
+  const {index, html} = data;
+ nodes[index].outerHTML = html;
+ });
 
- return hljs;
+ for (let index = 0; index < nodes.length; index++) {
+ const node = nodes[index];
+ if (!node) continue;
+ worker.postMessage({index, html: node.outerHTML});
+ }
 }

web_src/js/features/highlight.worker.js

@@ -0,0 +1,12 @@
+import {highlightBlock} from 'highlight.js';
+import {createWindow} from 'domino';
+
+self.onmessage = function ({data}) {
+ const window = createWindow();
+ self.document = window.document;
+
+ const {index, html} = data;
+ document.body.innerHTML = html;
+ highlightBlock(document.body.firstChild);
+ self.postMessage({index, html: document.body.innerHTML});
+};

web_src/js/index.js

@@ -11,12 +11,12 @@ import './vendor/semanticdropdown.js';
 import {svg} from './utils.js';
 
 import initContextPopups from './features/contextpopup.js';
-import initHighlight from './features/highlight.js';
 import initGitGraph from './features/gitgraph.js';
 import initClipboard from './features/clipboard.js';
 import initUserHeatmap from './features/userheatmap.js';
 import initDateTimePicker from './features/datetimepicker.js';
 import createDropzone from './features/dropzone.js';
+import highlight from './features/highlight.js';
 import ActivityTopAuthors from './components/ActivityTopAuthors.vue';
 
 const {AppSubUrl, StaticUrlPrefix, csrf} = window.config;
@@ -29,7 +29,6 @@ let previewFileModes;
 let simpleMDEditor;
 const commentMDEditors = {};
 let codeMirrorEditor;
-let hljs;
 
 // Silence fomantic's error logging when tabs are used without a target content element
 $.fn.tab.settings.silent = true;
@@ -49,7 +48,7 @@ function initCommentPreviewTab($form) {
  $previewPanel.html(data);
  emojify.run($previewPanel[0]);
  $('pre code', $previewPanel[0]).each(function () {
- hljs.highlightBlock(this);
+ highlight(this);
  });
  });
  });
@@ -75,7 +74,7 @@ function initEditPreviewTab($form) {
  $previewPanel.html(data);
  emojify.run($previewPanel[0]);
  $('pre code', $previewPanel[0]).each(function () {
- hljs.highlightBlock(this);
+ highlight(this);
  });
  });
  });
@@ -1011,7 +1010,7 @@ async function initRepository() {
  $renderContent.html(data.content);
  emojify.run($renderContent[0]);
  $('pre code', $renderContent[0]).each(function () {
- hljs.highlightBlock(this);
+ highlight(this);
  });
  }
  const $content = $segment.parent();
@@ -1337,7 +1336,7 @@ function initWikiForm() {
  preview.innerHTML = `<div class="markdown ui segment">${data}</div>`;
  emojify.run($('.editor-preview')[0]);
  $(preview).find('pre code').each((_, e) => {
- hljs.highlightBlock(e);
+ highlight(e);
  });
  });
  };
@@ -2633,8 +2632,8 @@ $(document).ready(async () => {
  });
 
  // parallel init of lazy-loaded features
- [hljs] = await Promise.all([
- initHighlight(),
+ await Promise.all([
+ highlight(document.querySelectorAll('pre code')),
  initGitGraph(),
  initClipboard(),
  initUserHeatmap(),

webpack.config.js

@@ -51,6 +51,7 @@ module.exports = {
  sourceMap: true,
  extractComments: false,
  terserOptions: {
+ keep_fnames: /^(HTML|SVG)/, // https://github.com/fgnass/domino/issues/144
  output: {
  comments: false,
  },
@@ -89,6 +90,19 @@ module.exports = {
  test: require.resolve('jquery-datetimepicker'),
  use: 'imports-loader?define=>false,exports=>false',
  },
+ {
+ test: /\.worker\.js$/,
+ use: [
+ {
+ loader: 'worker-loader',
+ options: {
+ name: '[name].js',
+ inline: true,
+ fallback: false,
+ },
+ },
+ ],
+ },
  {
  test: /\.js$/,
  exclude: /node_modules/,