loader.js

import NativeModule from 'module';

import loaderUtils from 'loader-utils';
import NodeTemplatePlugin from 'webpack/lib/node/NodeTemplatePlugin';
import NodeTargetPlugin from 'webpack/lib/node/NodeTargetPlugin';
import LibraryTemplatePlugin from 'webpack/lib/LibraryTemplatePlugin';
import SingleEntryPlugin from 'webpack/lib/SingleEntryPlugin';
import LimitChunkCountPlugin from 'webpack/lib/optimize/LimitChunkCountPlugin';

const MODULE_TYPE = 'css/mini-extract';
const pluginName = 'mini-css-extract-plugin';

const exec = (loaderContext, code, filename) => {
  const module = new NativeModule(filename, loaderContext);
  module.paths = NativeModule._nodeModulePaths(loaderContext.context); // eslint-disable-line no-underscore-dangle
  module.filename = filename;
  module._compile(code, filename); // eslint-disable-line no-underscore-dangle
  return module.exports;
};

const findModuleById = (modules, id) => {
  for (const module of modules) {
    if (module.id === id) {
      return module;
    }
  }
  return null;
};

export function pitch(request) {
  const query = loaderUtils.getOptions(this) || {};
  const loaders = this.loaders.slice(this.loaderIndex + 1);
  this.addDependency(this.resourcePath);
  const childFilename = '*'; // eslint-disable-line no-path-concat
  const publicPath =
    typeof query.publicPath === 'string'
      ? query.publicPath
      : this._compilation.outputOptions.publicPath;
  const outputOptions = {
    filename: childFilename,
    publicPath,
  };
  const childCompiler = this._compilation.createChildCompiler(
    `${pluginName} ${request}`,
    outputOptions
  );
  new NodeTemplatePlugin(outputOptions).apply(childCompiler);
  new LibraryTemplatePlugin(null, 'commonjs2').apply(childCompiler);
  new NodeTargetPlugin().apply(childCompiler);
  new SingleEntryPlugin(this.context, `!!${request}`, pluginName).apply(
    childCompiler
  );
  new LimitChunkCountPlugin({ maxChunks: 1 }).apply(childCompiler);
  // We set loaderContext[MODULE_TYPE] = false to indicate we already in
  // a child compiler so we don't spawn another child compilers from there.
  childCompiler.hooks.thisCompilation.tap(
    `${pluginName} loader`,
    (compilation) => {
      compilation.hooks.normalModuleLoader.tap(
        `${pluginName} loader`,
        (loaderContext, module) => {
          loaderContext[MODULE_TYPE] = false; // eslint-disable-line no-param-reassign
          if (module.request === request) {
            // eslint-disable-next-line no-param-reassign
            module.loaders = loaders.map((loader) => {
              return {
                loader: loader.path,
                options: loader.options,
                ident: loader.ident,
              };
            });
          }
        }
      );
    }
  );

  let source;
  childCompiler.hooks.afterCompile.tap(pluginName, (compilation) => {
    source =
      compilation.assets[childFilename] &&
      compilation.assets[childFilename].source();

    // Remove all chunk assets
    compilation.chunks.forEach((chunk) => {
      chunk.files.forEach((file) => {
        delete compilation.assets[file]; // eslint-disable-line no-param-reassign
      });
    });
  });

  const callback = this.async();
  childCompiler.runAsChild((err, entries, compilation) => {
    if (err) return callback(err);

    if (compilation.errors.length > 0) {
      return callback(compilation.errors[0]);
    }
    compilation.fileDependencies.forEach((dep) => {
      this.addDependency(dep);
    }, this);
    compilation.contextDependencies.forEach((dep) => {
      this.addContextDependency(dep);
    }, this);
    if (!source) {
      return callback(new Error("Didn't get a result from child compiler"));
    }
    let text;
    let locals;
    try {
      text = exec(this, source, request);
      locals = text && text.locals;
      if (!Array.isArray(text)) {
        text = [[null, text]];
      } else {
        text = text.map((line) => {
          const module = findModuleById(compilation.modules, line[0]);
          return {
            identifier: module.identifier(),
            content: line[1],
            media: line[2],
            sourceMap: line[3],
          };
        });
      }
      this[MODULE_TYPE](text);
    } catch (e) {
      return callback(e);
    }
    let resultSource = `// extracted by ${pluginName}`;
    if (locals && typeof resultSource !== 'undefined') {
      resultSource += `\nmodule.exports = ${JSON.stringify(locals)};`;
    }

    return callback(null, resultSource);
  });
}
export default function() {}