PHP: rfc:warnings-php-8-5

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====== PHP RFC: Warnings for PHP 8.5 ======

  * Version: 0.1
  * Date: 2025-07-14
  * Author: Gina Peter Banyard <girgias@php.net>
  * Status: Under Discussion
  * Target Version: PHP 8.5
  * Implementation: TBD
  * First Published at: https://wiki.php.net/rfc/warnings-php-8-5

===== Introduction =====

The RFC proposes to add a few warnings when encountering certain edge cases in PHP 8.5,
and promote those to error in PHP 9.

The following list provides a short overview of the warnings being introduced,
while more detailed explanation is provided in the Proposal section:

  * Coercing <php>NAN</php> to other types
  * Destructuring non-<php>array</php> values
  * Using offsets on non-container values in <php>isset()</php>/<php>empty()</php>
  * Using invalid offset types when checking string offsets with <php>isset()</php>/<php>empty()</php>

===== Proposal =====

Each proposed warning is voted separately and requires a 2/3 majority.

==== Coercing NAN to other types ====

  * Author: Gina Peter Banyard <girgias@php.net>

The floating point value <php>NAN</php> is returned by functions to indicate some sort of error.

However, <php>NAN</php> can be coerced to other types without error and hide bugs (except for functions requiring an <php>int</php>).
More concerning is that the value <php>NAN</php> is considered truthy and will be coerced to the value <php>true</php>,
except when using an explicit <php>(int)</php> cast, in which case it is coerced to <php>0</php> which is falsy.

As having a <php>NAN</php> value is unlikely and points to some sort of bug in the code,
we propose to emit the following warning when <php>NAN</php> is coerced (be that implicitly or explicitly) to another type:

<blockquote>
Warning: unexpected NAN value was coerced to TYPE
</blockquote>

This affects passing <php>NAN</php> as an argument to parameters which do not declare <php>float</php> as a type, all casting operators,
logical operators, if statements, and ternary operator.

<doodle title="Warn when coercing NAN to other types?" auth="girgias" voteType="single" closed="true">
   * Yes
   * No
</doodle>

==== Destructuring non-array values ====

  * Author: Gina Peter Banyard <girgias@php.net>

The <php>list($v1, $v2) = $array</php> or <php>[$v1, $v2] = $array</php> language construction
allows destructing array values into their own variables.

When attempting to destructure an object, the following <php>Error</php> is thrown:

<blockquote>
Error: Cannot use object of type stdClass as array
</blockquote>

However, when using scalar values (<php>bool</php>, <php>int</php>, <php>float</php>, <php>string</php>), <php>null</php>, or <php>resource</php>
no <php>Error</php> is thrown, and each variable is assigned <php>null</php>.

We propose to emit the following warning when destructuring non-array values:

<blockquote>
Warning: Cannot use TYPE as array
</blockquote>

<doodle title="Warn when destructuring non-array values?" auth="girgias" voteType="single" closed="true">
   * Yes
   * No
</doodle>

==== Using offsets on non-container values in isset()/empty() ====

  * Author: Gina Peter Banyard <girgias@php.net>

This is lifted from the [[rfc:container-offset-behaviour|Improve language coherence for the behaviour of offsets and containers]] RFC as it is time-sensitive.

When attempting to check if an offset exists or is empty on objects that do not implement <php>ArrayOffset</php>
(or the relevant C object handlers) then the following error is thrown:

<blockquote>
Error: Cannot use object of type TYPE as array
</blockquote>

However, when using scalar values (<php>bool</php>, <php>int</php>, <php>float</php>, <php>string</php>), <php>null</php>, or <php>resource</php>
no <php>Error</php> is thrown and <php>false</php> is returned for <php>isset()</php> and <php>true</php> is returned for <php>empty()</php>.

As this points to some code expectation being violated,
we propose to emit the following warning when using a scalar value or a <php>resource</php> as a container:  

<blockquote>
Warning: Cannot use TYPE as array
</blockquote>

We do not propose to warn when using <php>null</php> as a container, as <php>null</php> supports auto-vivification to array,
and can be used as a sentinel value.

<doodle title="Warn when using offsets on non-container values in isset()/empty()?" auth="girgias" voteType="single" closed="true">
   * Yes
   * No
</doodle>


==== Using invalid offset types when checking string offsets with isset()/empty() ====

  * Author: Gina Peter Banyard <girgias@php.net>

This is lifted from the [[rfc:container-offset-behaviour|Improve language coherence for the behaviour of offsets and containers]] RFC as it is time-sensitive.

When attempting to check an array offset with <php>isset()</php> or <php>empty()</php>,
with an object or array as the offset, the following <php>TypeError</php> is thrown:

<blockquote>
TypeError: Illegal offset type in isset or empty
</blockquote>

This is similar to a <php>TypeError</php> being thrown by the <php>ArrayAccess::offsetExists()</php> (/the equivalent C object handler)
for some internal classes like <php>SplFixedArray</php>.

However, when using a string as a container (e.g. <php>$string[$offset]</php>) invalid offsets are ignored
and <php>false</php> is returned for <php>isset()</php> and <php>true</php> is returned for <php>empty()</php>.
This behaviour is even stranger, as the null-coalescing operator //does// throw the following <php>TypeError</php>,
using the following code snippet as an example:
<PHP>
$s = 'abcdefg';
$o = new stdClass();
var_dump(isset($s[$o]));
var_dump($s[$o] ?? 'z');
</PHP>
we get the following:
<PHP>
bool(false)
Fatal error: Uncaught TypeError: Cannot access offset of type stdClass on string
</PHP>

As this likely points to a bug, and to normalize the behaviour with the null coalesced operator,
we propose to emit the following warning when using an invalid offset type for a string offset:

<blockquote>
Warning: Cannot access offset of type TYPE on string
</blockquote>

<doodle title="Warn when using invalid offset types when checking string offsets with isset()/empty()?" auth="girgias" voteType="single" closed="true">
   * Yes
   * No
</doodle>


===== Backward Incompatible Changes =====

For PHP 8.5 additional warnings will be emitted.
The promotions of warnings to the appropriate <php>Error</php> will happen no earlier than PHP 9.
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