node_modules_paths.js

/**
 * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * Adapted from: https://github.com/substack/node-resolve
 *
 * @flow
 */

import type {Path} from 'types/Config';
import path from 'path';
import {sync as realpath} from 'realpath-native';

type NodeModulesPathsOptions = {|
  moduleDirectory?: Array<string>,
  paths?: ?Array<Path>,
|};

export default function nodeModulesPaths(
  basedir: Path,
  options: NodeModulesPathsOptions,
): Path[] {
  const modules =
    options && options.moduleDirectory
      ? [].concat(options.moduleDirectory)
      : ['node_modules'];

  // ensure that `basedir` is an absolute path at this point,
  // resolving against the process' current working directory
  const basedirAbs = path.resolve(basedir);

  let prefix = '/';
  if (/^([A-Za-z]:)/.test(basedirAbs)) {
    prefix = '';
  } else if (/^\\\\/.test(basedirAbs)) {
    prefix = '\\\\';
  }

  // The node resolution algorithm (as implemented by NodeJS
  // and TypeScript) traverses parents of the physical path,
  // not the symlinked path
  const physicalBasedir = realpath(basedirAbs);

  const paths = [physicalBasedir];
  let parsed = path.parse(physicalBasedir);
  while (parsed.dir !== paths[paths.length - 1]) {
    const realParsedDir = realpath(parsed.dir);
    paths.push(realParsedDir);
    parsed = path.parse(realParsedDir);
  }

  const dirs = paths
    .reduce(
      (dirs, aPath) =>
        dirs.concat(
          modules.map(
            moduleDir =>
              path.isAbsolute(moduleDir)
                ? aPath === basedirAbs
                  ? moduleDir
                  : ''
                : path.join(prefix, aPath, moduleDir),
          ),
        ),
      [],
    )
    .filter(dir => dir !== '');

  return options.paths ? dirs.concat(options.paths) : dirs;
}