Bug report

Using docker version ghcr.io/phpstan/phpstan:latest, but verified with sandbox:

• with or without strict
• with or without bleeding edge
• Level 9

The middle item of a chained assignment appears to be uncertain, while the left item is known.

Not sure if there's some syntax here I should be using instead..

Code snippet that reproduces the problem

https://phpstan.org/r/e21ee227-0d57-484d-8aac-d028662bc06b

<?php declare(strict_types = 1);

/**
* @return array{id: int}|null
*/

function maybeNull(){
	if ((rand(3)%2) != 0) {
		return ['id' => 1];
	}
	return null;
}

/**
* @return void
*/
function foo(){
	if (!is_null($a = $b = maybeNull())){
		echo $a['id'];
		echo $b['id']; // 20 "Offset 'id' does not exist on array{id: int}|null."
	}
}

Adding extra parens doesn't seem to affect it: https://phpstan.org/r/3bd843c3-6b01-49f1-a714-6829e82b4cab

	if (!is_null($a = ($b = maybeNull()))){

Adding a third chained assignment appears to indicate only the leftmost one is known: https://phpstan.org/r/00c89cf0-196a-483a-8fb7-42d6658c520e

	if (!is_null($a = $b = $c = maybeNull())){
		echo $a['id'];
		echo $b['id']; // 20 "Offset 'id' does not exist on array{id: int}|null."
		echo $c['id']; // 21 "Offset 'id' does not exist on array{id: int}|null."
	}

Expected output

No errors

Actual output

20 | Offset 'id' does not exist on array{id: int}\|null.