index.js

import path from 'path';

import async from 'neo-async';
import pify from 'pify';
import semver from 'semver';

import formatSassError from './formatSassError';
import webpackImporter from './webpackImporter';
import normalizeOptions from './normalizeOptions';

let nodeSassJobQueue = null;

// Very hacky check
function hasGetResolve(loaderContext) {
  return (
    loaderContext.getResolve &&
    // eslint-disable-next-line no-underscore-dangle
    loaderContext._compiler &&
    // eslint-disable-next-line no-underscore-dangle
    loaderContext._compiler.resolverFactory &&
    // eslint-disable-next-line no-underscore-dangle
    loaderContext._compiler.resolverFactory._create &&
    /cachedCleverMerge/.test(
      // eslint-disable-next-line no-underscore-dangle
      loaderContext._compiler.resolverFactory._create.toString()
    )
  );
}

/**
 * The sass-loader makes node-sass and dart-sass available to webpack modules.
 *
 * @this {LoaderContext}
 * @param {string} content
 */
function loader(content) {
  const callback = this.async();
  const isSync = typeof callback !== 'function';
  const self = this;
  const { resourcePath } = this;

  function addNormalizedDependency(file) {
    // node-sass returns POSIX paths
    self.dependency(path.normalize(file));
  }

  if (isSync) {
    throw new Error(
      'Synchronous compilation is not supported anymore. See https://github.com/webpack-contrib/sass-loader/issues/333'
    );
  }

  let resolve = pify(this.resolve);

  // Supported since v4.36.0
  if (hasGetResolve(self)) {
    resolve = this.getResolve({
      mainFields: ['sass', 'style', 'main', '...'],
      mainFiles: ['_index', 'index', '...'],
      extensions: ['.scss', '.sass', '.css', '...'],
    });
  }

  const options = normalizeOptions(
    this,
    content,
    webpackImporter(resourcePath, resolve, addNormalizedDependency)
  );

  // Skip empty files, otherwise it will stop webpack, see issue #21
  if (options.data.trim() === '') {
    callback(null, '');
    return;
  }

  const render = getRenderFuncFromSassImpl(
    // eslint-disable-next-line import/no-extraneous-dependencies, global-require
    options.implementation || getDefaultSassImpl()
  );

  render(options, (error, result) => {
    if (error) {
      formatSassError(error, this.resourcePath);

      if (error.file) {
        this.dependency(error.file);
      }

      callback(error);
      return;
    }

    if (result.map && result.map !== '{}') {
      // eslint-disable-next-line no-param-reassign
      result.map = JSON.parse(result.map);

      // result.map.file is an optional property that provides the output filename.
      // Since we don't know the final filename in the webpack build chain yet, it makes no sense to have it.
      // eslint-disable-next-line no-param-reassign
      delete result.map.file;

      // One of the sources is 'stdin' according to dart-sass/node-sass because we've used the data input.
      // Now let's override that value with the correct relative path.
      // Since we specified options.sourceMap = path.join(process.cwd(), "/sass.map"); in normalizeOptions,
      // we know that this path is relative to process.cwd(). This is how node-sass works.
      // eslint-disable-next-line no-param-reassign
      const stdinIndex = result.map.sources.findIndex(
        (source) => source.indexOf('stdin') !== -1
      );

      if (stdinIndex !== -1) {
        // eslint-disable-next-line no-param-reassign
        result.map.sources[stdinIndex] = path.relative(
          process.cwd(),
          resourcePath
        );
      }
      // node-sass returns POSIX paths, that's why we need to transform them back to native paths.
      // This fixes an error on windows where the source-map module cannot resolve the source maps.
      // @see https://github.com/webpack-contrib/sass-loader/issues/366#issuecomment-279460722
      // eslint-disable-next-line no-param-reassign
      result.map.sourceRoot = path.normalize(result.map.sourceRoot);
      // eslint-disable-next-line no-param-reassign
      result.map.sources = result.map.sources.map(path.normalize);
    } else {
      // eslint-disable-next-line no-param-reassign
      result.map = null;
    }

    result.stats.includedFiles.forEach(addNormalizedDependency);

    callback(null, result.css.toString(), result.map);
  });
}

/**
 * Verifies that the implementation and version of Sass is supported by this loader.
 *
 * @param {Object} module
 * @returns {Function}
 */
function getRenderFuncFromSassImpl(module) {
  const { info } = module;

  if (!info) {
    throw new Error('Unknown Sass implementation.');
  }

  const components = info.split('\t');

  if (components.length < 2) {
    throw new Error(`Unknown Sass implementation "${info}".`);
  }

  const [implementation, version] = components;

  if (!semver.valid(version)) {
    throw new Error(`Invalid Sass version "${version}".`);
  }

  if (implementation === 'dart-sass') {
    if (!semver.satisfies(version, '^1.3.0')) {
      throw new Error(
        `Dart Sass version ${version} is incompatible with ^1.3.0.`
      );
    }

    return module.render.bind(module);
  } else if (implementation === 'node-sass') {
    if (!semver.satisfies(version, '^4.0.0')) {
      throw new Error(
        `Node Sass version ${version} is incompatible with ^4.0.0.`
      );
    }

    // There is an issue with node-sass when async custom importers are used
    // See https://github.com/sass/node-sass/issues/857#issuecomment-93594360
    // We need to use a job queue to make sure that one thread is always available to the UV lib
    if (nodeSassJobQueue === null) {
      const threadPoolSize = Number(process.env.UV_THREADPOOL_SIZE || 4);

      nodeSassJobQueue = async.queue(
        module.render.bind(module),
        threadPoolSize - 1
      );
    }

    return nodeSassJobQueue.push.bind(nodeSassJobQueue);
  }

  throw new Error(`Unknown Sass implementation "${implementation}".`);
}

function getDefaultSassImpl() {
  let sassImplPkg = 'node-sass';

  try {
    require.resolve('node-sass');
  } catch (error) {
    try {
      require.resolve('sass');
      sassImplPkg = 'sass';
    } catch (ignoreError) {
      sassImplPkg = 'node-sass';
    }
  }

  // eslint-disable-next-line import/no-dynamic-require, global-require
  return require(sassImplPkg);
}

export default loader;