TypeDoesNotContainxy after on isset after unset in a loop

[blizzz]

Minimal example: https://psalm.dev/r/cd3ebd7a1c

If there is a variable containing an instance of something that might get unset in a loop, Psalm complains when checking with isset().

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/cd3ebd7a1c

<?php

class A { 
    function noop(): void {
        sleep(0);
    }
}

$a = new A();
while(true) {
    if(!isset($a)) {
        exit(0);
    }
    $a->noop();
    unset($a);
}

Psalm output (using commit 1afce4d):

ERROR: TypeDoesNotContainNull - 11:9 - Cannot resolve types for $a - A does not contain null

[orklah]

Note for whoever will work on this in the future: TMixed takes an optional parameter inside_loop. This is used to allow overriding TMixed when it's generate by calling isset() on an empty array. We probably need to generate the same TMixed with inside loop when we encounter an unset instead of setting the variable to null. The loop may automatically recover from this