discourse/app/assets/javascripts/pretty-text/engines/discourse-markdown/code.js.es6

import { escape } from 'pretty-text/sanitizer';
import { registerOption } from 'pretty-text/pretty-text';

// Support for various code blocks
const TEXT_CODE_CLASSES = ["text", "pre", "plain"];

function codeFlattenBlocks(blocks) {
  let result = "";
  blocks.forEach(function(b) {
    result += b;
    if (b.trailing) { result += b.trailing; }
  });
  return result;
}

registerOption((siteSettings, opts) => {
  opts.features.code = true;
  opts.defaultCodeLang = siteSettings.default_code_lang;
  opts.acceptableCodeClasses = (siteSettings.highlighted_languages || "").split("|").concat(['auto', 'nohighlight']);
});

export function setup(helper) {

  helper.whiteList({
    custom(tag, name, value) {
      if (tag === 'code' && name === 'class') {
        const m = /^lang\-(.+)$/.exec(value);
        if (m) {
          return helper.getOptions().acceptableCodeClasses.indexOf(m[1]) !== -1;
        }
      }
    }
  });

  helper.replaceBlock({
    start: /^`{3}([^\n\[\]]+)?\n?([\s\S]*)?/gm,
    stop: /^```$/gm,
    withoutLeading: /\[quote/gm, //if leading text contains a quote this should not match
    emitter(blockContents, matches) {
      const opts = helper.getOptions();

      let codeLang = opts.defaultCodeLang;
      const acceptableCodeClasses = opts.acceptableCodeClasses;
      if (acceptableCodeClasses && matches[1] && acceptableCodeClasses.indexOf(matches[1]) !== -1) {
        codeLang = matches[1];
      }

      if (TEXT_CODE_CLASSES.indexOf(matches[1]) !== -1) {
        return ['p', ['pre', ['code', {'class': 'lang-nohighlight'}, codeFlattenBlocks(blockContents) ]]];
      } else  {
        return ['p', ['pre', ['code', {'class': 'lang-' + codeLang}, codeFlattenBlocks(blockContents) ]]];
      }
    }
  });

  helper.replaceBlock({
    start: /(<pre[^\>]*\>)([\s\S]*)/igm,
    stop: /<\/pre>/igm,
    rawContents: true,
    skipIfTradtionalLinebreaks: true,

    emitter(blockContents) {
      return ['p', ['pre', codeFlattenBlocks(blockContents)]];
    }
  });

  // Ensure that content in a code block is fully escaped. This way it's not white listed
  // and we can use HTML and Javascript examples.
  helper.onParseNode(function(event) {
    const node = event.node,
    path = event.path;

    if (node[0] === 'code') {
      const regexp = (path && path[path.length-1] && path[path.length-1][0] && path[path.length-1][0] === "pre") ?
                     / +$/g : /^ +| +$/g;

      const contents = node[node.length-1];
      node[node.length-1] = escape(contents.replace(regexp,''));
    }
  });
}