This always works for me:

ini_set('display_errors', '1');
ini_set('display_startup_errors', '1');

However, this doesn't make PHP to show parse errors - the only way to show those errors is to modify your php.ini with this line:

display_errors = on

(if you don't have access to php.ini, then putting this line in .htaccess might work too):

php_flag display_errors 1