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

// we need a custom renderer for code blocks cause we have a slightly non compliant
// format with special handling for text and so on

const TEXT_CODE_CLASSES = ["text", "pre", "plain"];


function render(tokens, idx, options, env, slf, md) {
  let token = tokens[idx],
      info = token.info ? md.utils.unescapeAll(token.info) : '',
      langName = md.options.discourse.defaultCodeLang,
      className,
      escapedContent = md.utils.escapeHtml(token.content);

  if (info) {
    // strip off any additional languages
    info = info.split(/\s+/g)[0];
  }

  const acceptableCodeClasses = md.options.discourse.acceptableCodeClasses;
  if (acceptableCodeClasses && info && acceptableCodeClasses.indexOf(info) !== -1) {
    langName = info;
  }

  className = TEXT_CODE_CLASSES.indexOf(info) !== -1 ? 'lang-nohighlight' : 'lang-' + langName;

  return `<pre><code class='${className}'>${escapedContent}</code></pre>\n`;
}

export function setup(helper) {
  if (!helper.markdownIt) { return; }

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

  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.registerPlugin(md=>{
    md.renderer.rules.fence = (tokens,idx,options,env,slf)=>render(tokens,idx,options,env,slf,md);
  });
}