test('monitors only root paths for hg', async () => {
  if (process.env.CI) {
    // Circle and Travis have very old version of hg (v2, and current
    // version is v4.2) and its API changed since then and not compatible
    // any more. Changing the SCM version on CIs is not trivial, so we'll just
    // skip this test and run it only locally.
    return;
  }
  writeFiles(DIR, {
    'file1.txt': 'file1',
    'nested-dir/file2.txt': 'file2',
    'nested-dir/second-nested-dir/file3.txt': 'file3',
  });

  run(`${HG} init`, DIR);

  const roots = [path.resolve(DIR, 'nested-dir')];

  const {changedFiles: files} = await getChangedFilesForRoots(roots, {});
  expect(
    Array.from(files)
      .map(filePath => path.basename(filePath))
      .sort(),
  ).toEqual(['file2.txt', 'file3.txt']);
});

export default (
  globalConfig: Config.GlobalConfig,
  configs: Array<Config.ProjectConfig>,
): ChangedFilesPromise | undefined => {
  if (globalConfig.onlyChanged) {
    const allRootsForAllProjects = configs.reduce<Array<Config.Path>>(
      (roots, config) => [...roots, ...(config.roots || [])],
      [],
    );
    return getChangedFilesForRoots(allRootsForAllProjects, {
      changedSince: globalConfig.changedSince,
      lastCommit: globalConfig.lastCommit,
      withAncestor: globalConfig.changedFilesWithAncestor,
    }).catch(e => {
      const message = formatExecError(e, configs[0], {noStackTrace: true})
        .split('\n')
        .filter(line => !line.includes('Command failed:'))
        .join('\n');

      console.error(chalk.red(`\n\n${message}`));

      process.exit(1);

      // We do process.exit, so this is dead code
      return Promise.reject(e);
    });
  }

  return undefined;
};