I have to say it's expected behavior

see: https://github.com/laruence/php-src/blob/master/Zend/tests/debug_info.phpt

or at least a expected side affect

Hi Laruence,

Sorry, I don't understand what you mean. The tests don't cover the case when the key is empty.

The issue also doesn't manifest when the empty key isn't the first element i.e. this:

<?php 

class A{
    function __debugInfo(){
        return [
            
            "foo" => 'bar',
            '' => 'bar',
        ];
    }
}


print_r(new A);

?>

works fine.

$ sapi/cli/php -n -d error_reporting=-1 /tmp/1.php
A Object
(
    [foo] => bar
    [
Notice: Illegal member variable name in /tmp/1.php on line 14
] => bar
)

the problem is, we use \0class_name\0property_name for private properties.

so, \0 has a special meaning if it's the lead char.

Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

Reading the \0 is a bug, as that's past the end of the string (well, greater than the length variable).

The bug isn't saying that strings starting with \0 should be accepted. It's saying that it shouldn't even get that far.

Basically, the check at http://lxr.php.net/xref/PHP_TRUNK/Zend/zend_compile.c#1242 should also include a check against name->len:

    if (name->len == 0 || name->val[0] != '\0') {