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Bug #80535 Backward compatibility issue - FATAL error
Submitted: 2020-12-20 16:01 UTC Modified: 2021-01-03 01:34 UTC
From: legrand101 at gmail dot com Assigned: cmb (profile)
Status: Not a bug Package: Scripting Engine problem
PHP Version: 8.0.0 OS:
Private report: No CVE-ID: None
View Developer Edit
 [2020-12-20 16:01 UTC] legrand101 at gmail dot com 
Description:
------------
After upgrading to PHP 8, I start getting FATAL error for simple statement that use to work on PHP 7. This statement is now producing a FATAL error (PHP Fatal error:  Uncaught Error: Attempt to modify property  on null) on PHP 8:
$T = &$r->country->state->city;

Before PHP8 both $r and properties (r->country, r->country->state, r->country->state->city) are implicitly instantiated as standard classs and $T is pointer.




Test script:
---------------
$T = &$r->country->state->city;
$T = 'home';

Expected result:
----------------
no fatal error. $r object implicitly created. $T and $r->country->state->city value are 'home'.

var_dump($r);
object(stdClass)#34 (1) {
  ["country"]=>
  object(stdClass)#36 (1) {
    ["state"]=>
    object(stdClass)#37 (1) {
      ["city"]=>
      &string(4) "home"
    }
  }
}


var_dump($T);
string(4) "home"


Actual result:
--------------
PHP Fatal error:  Uncaught Error: Attempt to modify property  on null

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 [2020-12-20 16:11 UTC] cmb@php.net
-Status: Open +Status: Not a bug -Package: Reproducible crash +Package: Scripting Engine problem -Assigned To: +Assigned To: cmb
 [2020-12-20 16:11 UTC] cmb@php.net 
That code already issued E_WARNING as of PHP 7.4.0[1], and the
warning was promoted to an Error exception according to the
respective RFC[2].  It is also documented as backward incompatible
change in the migration guide[3].

Note that an Error exception is not a fatal error per se, and that
even a fatal error is not a crash.

[1] <https://3v4l.org/h3NJj>
[2] <https://wiki.php.net/rfc/engine_warnings>
[3] <https://www.php.net/manual/en/migration80.incompatible.php>
 [2020-12-20 20:39 UTC] legrand101 at gmail dot com 
Thanks for the quick response. I was upgrading from PHP7.0 so didn't get any warnings. By crash, I meant the my script was crashing.

So, is there any work around other than explicitly instantiating each variable. This seems like a big inconvenience, special if one relied this behavior for API development.
 [2020-12-20 23:14 UTC] cmb@php.net 
> So, is there any work around other than explicitly instantiating
> each variable.

I don't think so.  If you strongly feel that this "feature" should
not have been disallowed, please raise that on the internals
mailing list, although I consider it unlikely that the change will
be reverted.

> there is a reason to introduce warnings years before

In this case it has been only *one* year.
 [2020-12-21 00:35 UTC] legrand101 at gmail dot com 
This is project personal I started more three years ago, so it's no big deal for me. I just revert back to PHP7. I only wanted to checkout the performance improvements.

Even though, it's unlike to be reverted, I would like to add this issue to the internals mailing list. I don't see why making more things more restrictive is an improvement. How do I bring it up to the internals mailing list?
 [2020-12-21 09:27 UTC] nikic@php.net 
Worth noting that this warning is actually very old (dating back all the way to PHP 5.0: https://3v4l.org/nkocf). PHP 7.4 fixed a special case where the warning was missing (references as opposed to direct writes) and PHP 8.0 removed this functionality completely.

Note that auto-vivification is still supported for arrays (and I don't believe there are plans to remove it there).
 [2021-01-03 01:19 UTC] legrand101 at gmail dot com 
Hi nikic,

https://3v4l.org/nkocf is different example than what is have. Using a pointer will work(there's no warning for that until 7.4.0). See https://3v4l.org/H5SPf.
 [2021-01-03 01:34 UTC] legrand101 at gmail dot com 
https://3v4l.org/H5SPf
 
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