webpack code to string loader with child compiler

compile-loader.js

import loaderUtils from 'loader-utils';
import SingleEntryPlugin from 'webpack/lib/SingleEntryPlugin';

/** StringLoader */
export default function loader() {}

export function pitch(request) {
  const options = loaderUtils.getOptions(this) || {};

  if (!this.webpack) {
    throw new Error('This loader is only usable with webpack');
  }

  const cb = this.async();

  const filename = loaderUtils.interpolateName(this, options.name || '[hash].inline.js', {
    context: options.context || this.rootContext || this.options.context,
    regExp: options.regExp,
  });

  const worker = {};

  worker.options = {
    filename,
    chunkFilename: `[id].${filename}`,
    namedChunkFilename: null,
  };

  worker.compiler = this._compilation
    .createChildCompiler('inline', worker.options);

  worker.compiler.apply(new SingleEntryPlugin(this.context, `!!${request}`, 'main'));

  const subCache = `subcache ${__dirname} ${request}`;

  worker.compilation = (compilation) => {
    if (compilation.cache) {
      if (!compilation.cache[subCache]) {
        compilation.cache[subCache] = {};
      }

      compilation.cache = compilation.cache[subCache];
    }
  };

  if (worker.compiler.hooks) {
    const plugin = { name: 'StringLoader' };

    worker.compiler.hooks.compilation.tap(plugin, worker.compilation);
  } else {
    worker.compiler.plugin('compilation', worker.compilation);
  }

  worker.compiler.runAsChild((err, entries, compilation) => {
    if (err) return cb(err);

    if (entries[0]) {
      worker.file = entries[0].files[0];
      const source = compilation.assets[worker.file].source()
      delete this._compilation.assets[worker.file];

      // see raw-loader
      const json = JSON.stringify(source)
        .replace(/\u2028/g, '\\u2028')
        .replace(/\u2029/g, '\\u2029');

      return cb(null, `module.exports = ${json}`);
    }

    return cb(null, null);
  });
}