Change PHP behavior for undefined constants?

Question

Is there a php.ini setting or some other trick to force PHP to produce a fatal error or similar when an undefined constant is used, rather than the (ridiculous) default behavior of assuming a string of the same name?

The default behavior can be a gaping security risk, but more often than not it just leads to application errors. I realize that I can use defined() to check the existence of the constant prior to asking for the value, but this leads to redundant/ugly code, and is still prone to developer error. We're very careful about ensuring that used constants are defined, but this problem still sneaks into production once in a while, and I'd like to prevent it if possible. A fatal error would be more "in your face" and much less likely to squeeze by QA.

Answer 1

set_error_handler(function($type, $error) {
    if(stripos($error, 'Use of undefined constant') !== FALSE)
    {
        // god forbid - someone's used an undefined constant. Act appropriately.
        trigger_error($error, E_USER_ERROR); // Triggers a fatal error.
        return TRUE;
    }
}, E_NOTICE);

This is maybe what you're looking for, as far as I'm aware there's no way to modify PHP's error 'ranking'.

Answer 2

Undefined constants generate a PHP notice.

You can just throw an exception for any PHP warning, at least in development mode:

set_error_handler(function ($errno, $errstr, $errfile, $errline) {

    throw new ErrorException($errstr, $errno, 1, $errfile, $errline);

    // or turn it in a fatal error

    trigger_error($errstr, E_USER_ERROR);
});

If you want to handle only undefined constant warnings, test if the $errstr matches against Use of undefined constant FOO - assumed 'FOO'.

---

Note: only unqualified, global constants behave like this. PHP throws a fatal error for undefined class constants and undefined namespaced constants (e.g. Foo::BAR or Foo\BAR).

So if you want PHP to throw fatal errors when using undefined constants, an other solution is to use class constants or namespaced constants.