Description:
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Bug can seen here:

https://3v4l.org/m1HQ3

It affects all versions starting with 7.0.

If I copy the $_SESSION variable in another variable ($sessionCopy) and then I call session_decode, I do not expect $sessionCopy to be impacted by the call to $_SESSION.

Yet, in PHP 7.0+, $sessionCopy is also modified.

Test script:
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<?php

session_start();

// $_SESSION is empty so $oldSession is empty too now.
// I expect copy to be by value, not by reference so anything impacting $_SESSION should not impace $oldSession.
$oldSession = $_SESSION;

session_decode('id|i:1;');

var_dump($_SESSION);
var_dump($oldSession);

Expected result:
----------------
I expect $_SESSION and $oldSession to be different.


Actual result:
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In PHP 7+, $_SESSION and $oldSession are equal.