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Date: Mon, 5 Aug 2024 18:50:20 +0200
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Subject: Re: [PHP-DEV] [RFC] [VOTE] Transform exit() from a language construct
 into a standard function
To: Derick Rethans <derick@php.net>, "Christoph M. Becker" <cmbecker69@gmx.de>
Cc: "Gina P. Banyard" <internals@gpb.moe>,
 PHP internals <internals@lists.php.net>
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 <1a8650d2-7eb5-d645-8132-e5522ad24637@php.net>
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From: tim@bastelstu.be (=?UTF-8?Q?Tim_D=C3=BCsterhus?=)

Hi

On 8/5/24 13:04, Derick Rethans wrote:
>> As userland PHP developer, I always regarded `exit` as a control flow
>> instruction (quite similar to `break`), and as such I'm not really in
>> favor of converting it to a proper function (especially since it is
>> not, because the parantheses could be omitted).
> 
> Xdebug uses exit for exactly that too. For control flow analysis. And I
> also always have considered it to be a control flow instruction.
> 
> I see no benefit in changing it to a function, especially because
> there will never be a function "exit" from it, just only an "entry".
> This breaks function execution symmetry (and causes issues with Xdebug
> when I last tried to make it work with a development branch for this
> RFC).

This is false. The observers are perfectly capable of detecting that the 
`exit()` function returns / throws when observing 
`zend_observer_fcall_end_handler` as demonstrated by the following script:

     <?php
     class MyClass {
     	public function __destruct() {
     		echo __METHOD__, PHP_EOL;
     	}
     }

     function a() {
     	$dummy = new MyClass();

     	exit();
     }

     a();

Running this script as:

     sapi/cli/php -d zend_test.observer.enabled=1 -d 
zend_test.observer.observe_all=1 test.php

will return the following output:

     <!-- init 'php-src/test.php' -->
     <file 'php-src/test.php'>
       <!-- init a() -->
       <a>
         <!-- init exit() -->
         <exit>
           <!-- Exception: UnwindExit -->
         </exit>
         <!-- Exception: UnwindExit -->
       </a>
       <!-- init MyClass::__destruct() -->
       <MyClass::__destruct>
     MyClass::__destruct
       </MyClass::__destruct>
       <!-- Exception: UnwindExit -->
     </file 'php-src/test.php'>

Leaving the exit() function will be observed as indicated by `</exit>`. 
It also shows that any destructors will be called and it also shows the 
internal UnwindExit exception.

Thus you are able to detect if `exit()` has successfully been called by 
observing an fcall_end and checking for 
`zend_is_unwind_exit(EG(exception))` to determine if the exception 
you're dealing with is the unwind exception.

That way you will also correctly handle that `exit()` is not successful, 
e.g. when a non-stringable class is passed to it and a TypeError is 
thrown, because then the output will look something like this:

     <!-- init 'php-src/test.php' -->
     <file 'php-src/test.php'>
       <!-- init a() -->
       <a>
         <!-- init exit() -->
         <exit>
           <!-- Exception: TypeError -->
         </exit>
         <!-- Exception: TypeError -->
       </a>
       <!-- Exception: TypeError -->
     </file 'php-src/test.php'>
     <!-- init Error::__toString() -->
     <Error::__toString>
       <!-- init Error::getTraceAsString() -->
       <Error::getTraceAsString>
       </Error::getTraceAsString>
     </Error::__toString>

     Fatal error: Uncaught TypeError: exit(): Argument #1 ($code) must 
be of type string|int, MyClass given in php-src/test.php:11
     Stack trace:
     #0 php-src/test.php(11): exit(Object(MyClass))
     #1 php-src/test.php(14): a()
     #2 {main}
       thrown in php-src/test.php on line 11
     <!-- init MyClass::__destruct() -->
     <MyClass::__destruct>
     MyClass::__destruct
     </MyClass::__destruct>

Best regards
Tim Düsterhus