parcel-bundler/src/assets/LESSAsset.js

<p align="center"> <a href="https://parceljs.org/" target="_blank"> <img alt="Parcel" src="https://user-images.githubusercontent.com/19409/31321658-f6aed0f2-ac3d-11e7-8100-1587e676e0ec.png" width="749"> </a> </p>

const CSSAsset = require('./CSSAsset');
const config = require('../utils/config');
const localRequire = require('../utils/localRequire');
const promisify = require('../utils/promisify');

class LESSAsset extends CSSAsset {
  async parse(code) {
    // less should be installed locally in the module that's being required
    let less = await localRequire('less', this.name);
    let render = promisify(less.render.bind(less));

    let opts =
      this.package.less ||
      (await config.load(this.name, ['.lessrc', '.lessrc.js'])) ||
      {};
    opts.filename = this.name;
    opts.plugins = (opts.plugins || []).concat(urlPlugin(this));

    let res = await render(code, opts);
    res.render = () => res.css;
    return res;
  }

  collectDependencies() {
    for (let dep of this.ast.imports) {
      this.addDependency(dep, {includedInParent: true});
    }
  }
}

function urlPlugin(asset) {
  return {
    install: (less, pluginManager) => {
      let visitor = new less.visitors.Visitor({
        visitUrl: (node) => {
          node.value.value = asset.addURLDependency(
            node.value.value,
            node.currentFileInfo.filename
          );
          return node;
        }
      });

      visitor.run = visitor.visit;
      pluginManager.addVisitor(visitor);
    }
  };
}

module.exports = LESSAsset;