Variable marked as always defined, even though it might be unset

[icatalina]

Bug report

This seems like a regression from 1.5.3, we didn't have this issue before.

$whereParts = [];

if (!$foo['a']) {
    $whereParts[] = 'something';
}

if (!$foo['b']) {
    $count = 3;
    $whereParts[] = 'example';
}

if (empty($whereParts)) {
    return [];
}

return isset($count) ? $count : 0;

$count is marked as always defined, it can clearly be unset.

Code snippet that reproduces the problem

https://phpstan.org/r/81e9327a-136e-4a7f-908e-b571c173d32c

Expected output

No error

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[icatalina]

Ok, after a bit more digging, in 1.5.3 this code doesn't report:

public function sayHello(array $foo): void
{
    $whereParts = [];

    if (!$foo['a']) {
        $whereParts[] = 'something';
    }

    if (!$foo['b']) {
        $count = 3;
        // notice the 2 pushes to the array
        $whereParts[] = 'example';
        $whereParts[] = 'bar';
    }

    if (empty($whereParts)) {
        return [];
    }

    return isset($count) ? $count : 0;
}

but the original does

[phpstan-bot]

@icatalina After the latest push in 1.8.x, PHPStan now reports different result with your code snippet:

@@ @@
-22: Variable $count in isset() always exists and is not nullable.
+No errors

[icatalina]

👏

[herndlm]

Ondrej most likely wants a regression test for it before closing it :)

[github-actions]

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