print_r() results in warning: unexpected NAN value was coerced to string

[ausi]

Description

The following code:

<?php
print_r([NAN]);

Resulted in this output:

Warning: unexpected NAN value was coerced to string in /in/IW2fE on line 3
Array
(
    [0] => NAN
)

But I expected this output instead:

Array
(
    [0] => NAN
)

This warning got introduced in #19573 but I don’t think affecting print_r() was intended as this function is supposed to “Print human-readable information about a variable”.
The related functions var_dump() and var_export() are not affected by this warning.

PHP Version

PHP 8.5.8 (cli) (built: Jul  1 2026 03:46:27) (NTS)
Copyright (c) The PHP Group
Built by Homebrew
Zend Engine v4.5.8, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.8, Copyright (c), by Zend Technologies

Operating System

MacOS 26.6.2