array_walk_recursive( $descriptor, function ( $path ) use ( &$extensions ) {
$extensions[] = pathinfo( $path, PATHINFO_EXTENSION );
} );
$extensions = array_unique( $extensions );
if ( count( $extensions ) !== 1 ) {
throw new InvalidArgumentException(
array_walk_recursive( $descriptor, function ( $path ) use ( &$extensions ) {
$extensions[] = pathinfo( $path, PATHINFO_EXTENSION );
} );
$extensions = array_unique( $extensions );
if ( count( $extensions ) !== 1 ) {
throw new InvalidArgumentException(