You can't use anonymous functions for inline flow control; just use a regular if
statement and don't shun writing things on multiple lines:
if ($data->input_size) {
if ($begun_files) {
$str .= $data->input_logic ? ' OR ' : ' AND ';
$begun_files = true;
}
$str .= sprintf('size %s "%f"',
$data->input_size_op ? '<=' : '>=',
$data->input_size * pow(1024,$data->input_size_unit)
);
}