constant() behaves inconsistent when class is undefined

[AMRoche]

Description

The following code:

<?php

try {
    \constant("\ExistantClass::non_existant_constant");
} catch (\Throwable|\Error|\Exception $e) {
    echo($e->getMessage());
}

Resulted in this output:

⇒  php test.php
PHP Fatal error:  Class "ExistantClass" not found in /Users/alexroche/Desktop/test.php on line 4

Fatal error: Class "ExistantClass" not found in /Users/alexroche/Desktop/test.php on line 4

But I expected this output instead:

"Error : Class "ExistantClass" not found"

(i.e. the error to be caught and the message to be echo'd - what that message is is purely semantics)

PHP Version

8.0.25, 8.1.12

Operating System

No response

[cmb69]

If you are referring to a non-existant class, that results in a fatal error (E_ERROR). It is not possible to catch these, since they are no Errors. What you can do, however, is to check whether the class is available, and not even try to use it otherwise: https://3v4l.org/LQfZp

Anyhow, as is, this is not a bug. We could treat this as feature request to change the fatal error to an Error, but I'm not sure if that could be reasonably done.

[AMRoche]

Hi @cmb69 - Honestly, whatever y'all think is best is fine by me, but then at the very least the documentation for constant() is misleading (https://www.php.net/manual/en/function.constant) as it states an Error will be thrown if the constant doesn't exist (which logically if the class doesn't it won't), and that it also works with class constants.

In addition there's the following;

<?php

try {
    // does not work as i'd expected
    // constant("\NonExistantClass::constant");

    //does work as i'd expect
    //$temp = \NonExistantClass::constant;
    
    // new NonExistantClass();

    //$temp = "\NonExistantClass::constant";
    //eval($temp.";");

    //does what the old behavior of constant was
    //$temp = "\NonExistantClass::constant";
    //$$temp;
} catch (\Throwable|\Error|\Exception $e) {
    echo($e->getMessage());
}

[cmb69]

Hmm, given that other cases of undefined classes throw an Error, the constant() case might just have been missed.