preinstall_check.js

const isUsingNpm = process.env.npm_config_git !== undefined;

if (isUsingNpm) {
  throw "Use Yarn instead of npm, see Kibana's contributing guidelines";
}

// The value of the `npm_config_argv` env for each command:
//
// - `npm install`: '{"remain":[],"cooked":["install"],"original":[]}'
// - `yarn`: '{"remain":[],"cooked":["install"],"original":[]}'
// - `yarn kbn bootstrap`: '{"remain":[],"cooked":["run","kbn"],"original":["kbn","bootstrap"]}'
const rawArgv = process.env.npm_config_argv;

if (rawArgv === undefined) {
  return;
}

try {
  const argv = JSON.parse(rawArgv);

  if (argv.cooked.includes('kbn')) {
    // all good, trying to install deps using `kbn`
    return;
  }

  if (argv.cooked.includes('install')) {
    console.log('\nWARNING: When installing dependencies, prefer `yarn kbn bootstrap`\n');
  }
} catch (e) {
  // if it fails we do nothing, as this is just intended to be a helpful message
}