freifunk-app/node_modules/react-native/local-cli/util/yarn.js

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */
'use strict';

const execSync = require('child_process').execSync;
const fs = require('fs');
const path = require('path');
const semver = require('semver');

/**
 * Use Yarn if available, it's much faster than the npm client.
 * Return the version of yarn installed on the system, null if yarn is not available.
 */
function getYarnVersionIfAvailable() {
  let yarnVersion;
  try {
    // execSync returns a Buffer -> convert to string
    yarnVersion = (execSync('yarn --version', {
      stdio: [ 0, 'pipe', 'ignore', ]
    }).toString() || '').trim();
  } catch (error) {
    return null;
  }
  // yarn < 0.16 has a 'missing manifest' bug
  try {
    if (semver.gte(yarnVersion, '0.16.0')) {
      return yarnVersion;
    } else {
      return null;
    }
  } catch (error) {
    console.error('Cannot parse yarn version: ' + yarnVersion);
    return null;
  }
}

/**
 * Check that 'react-native init' itself used yarn to install React Native.
 * When using an old global react-native-cli@1.0.0 (or older), we don't want
 * to install React Native with npm, and React + Jest with yarn.
 * Let's be safe and not mix yarn and npm in a single project.
 * @param projectDir e.g. /Users/martin/AwesomeApp
 */
function isGlobalCliUsingYarn(projectDir) {
  return fs.existsSync(path.join(projectDir, 'yarn.lock'));
}

module.exports = {
  getYarnVersionIfAvailable: getYarnVersionIfAvailable,
  isGlobalCliUsingYarn: isGlobalCliUsingYarn,
};