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Bug #78513 compact('0') (any int) will generate an array with inaccessible key
Submitted: 2019-09-08 18:51 UTC Modified: 2021-07-19 13:16 UTC
Avg. Score:4.5 ± 0.5
Reproduced:2 of 2 (100.0%)
Same Version:1 (50.0%)
Same OS:1 (50.0%)
From: Assigned:
Status: Open Package: Arrays related
PHP Version: Irrelevant OS: Linux/Any
Private report: No CVE-ID: None
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 [2019-09-08 18:51 UTC]
compact('0') (or any other number) will generate an array with inaccessible keys if a variable with that value is defined.

I can't think of any reason to actually do this in real code, but I'd also expect all functions to return arrays with accessible keys.

Note that ext/opcache/Optimizer/zend_func_info.c may need to be changed depending on how this is fixed, to add MAY_BE_ARRAY_KEY_LONG.


I'd suggest limiting the fix to development php versions(php 7.4/8.0). was a similar issue with inaccessible array keys, but had a different cause (casting object to array)

Test script:
call_user_func(function () {
    ${0} = 'value';
    $result = compact('0');

Expected result:
Should emit the following output, with an integer array key (0, not '0') that can be accessed.

  0 => 'value'

Alternatively, it could throw/return an error value.

Actual result:
php test.php
array (
  '0' => 'value',
)Notice: Undefined offset: 0 in /home/tyson/test.php on line 6


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 [2019-09-09 07:58 UTC]
There's a larger underlying issue here:

${0} = 'value';
var_dump($GLOBALS[0]); // Notice: Undefined offset: 0

Only works on HHVM an PHP < 5.0.

Same for the other way around:

$GLOBALS[0] = 'value';
var_dump(${0}); // Notice: Undefined variable: 0
 [2021-07-19 13:16 UTC]
Also, the fix would introduce a BC break: <>.
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