in src/Codegen.hack [92:100]
public static function forTree(
string $source_root,
self::TCodegenConfig $config,
): Codegen {
// leaving for now as it's a public API
/* HHAST_IGNORE_ERROR[DontUseAsioJoin] fix before final release */
return
new self(\HH\Asio\join(TreeParser::fromPathAsync($source_root)), $config);
}