TypeDoesNotContainType - psalm still considers a property always null even if it may be set in called method

[sad-spirit]

Issue #5231 was closed, but only the "simplified" code example was actually fixed.

The code I posted originally still triggers the error with latest psalm:
https://psalm.dev/r/2afe4e3c4b

ERROR: TypeDoesNotContainType - 26:23 - Type null for $this->pairFirst is always null
ERROR: TypeDoesNotContainType - 40:13 - Type null for $this->pairFirst is always null

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/2afe4e3c4b

<?php
class UnicodeUnescaper
{
    /**
     * First codepoint of Unicode surrogate pair
     * @var int|null
     */
    private $pairFirst;

    public function unescapeUnicode(string $escaped): string
    {
        $this->pairFirst = null;
        $unescaped       = '';

        foreach (
            preg_split(
                "/(\\\\(?:\\\\|[0-9a-fA-F]{4}|\\+[0-9a-fA-F]{6}))/",
                $escaped,
                -1,
                PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE
            ) ?: [] as $part
        ) {
            if ('\\' === $part[0] && '\\' !== $part[1]) {
                $unescaped .= $this->handlePossibleSurrogatePairs(hexdec(ltrim($part, '\\+')));

            } elseif (null !== $this->pairFirst) {
                break;

            } elseif ('\\' === $part[0]) {
                $unescaped .= '\\';

            } elseif (false !== strpos($part, '\\')) {
                throw new Exception('Invalid Unicode escape');

            } else {
                $unescaped .= $part;
            }
        }

        if (null !== $this->pairFirst) {
            throw new Exception('Unfinished Unicode surrogate pair');
        }

        return $unescaped;
    }

    private function handlePossibleSurrogatePairs(int $codepoint): string
    {
        $utf8              = '';
        $isSurrogateFirst  = 0xD800 <= $codepoint && 0xDBFF >= $codepoint;
        $isSurrogateSecond = 0xDC00 <= $codepoint && 0xDFFF >= $codepoint;

        if ((null !== $this->pairFirst) !== $isSurrogateSecond) {
            throw new Exception("Invalid Unicode surrogate pair");
        } elseif (null !== $this->pairFirst) {
            $utf8 = 'pair';
            $this->pairFirst = null;
        } elseif ($isSurrogateFirst) {
            $this->pairFirst = $codepoint;
        } else {
            $utf8 = 'symbol';
        }

        return $utf8;
    }
}

// this will trigger an Exception psalm claims cannot be triggered
(new UnicodeUnescaper())->unescapeUnicode('wrong: \\db99');

Psalm output (using commit 3f4bb25):

ERROR: TypeDoesNotContainType - 26:23 - Type null for $this->pairFirst is always null

ERROR: TypeDoesNotContainType - 40:13 - Type null for $this->pairFirst is always null

[muglug]

Sorry! Your example, simplified again: https://psalm.dev/r/3d9228342e

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/3d9228342e

<?php
class A
{
    private ?int $foo = null;

    public function bar(): void
    {
        $this->foo = null;
        
        while (rand(0, 1)) {
            if (rand(0, 1)) {
                $this->setFoo();
            } elseif ($this->foo !== null) {
                break;
            }
        }

        if (null !== $this->foo) {}
    }

    private function setFoo(): void
    {
        $this->foo = 5;
    }
}

Psalm output (using commit 3f4bb25):

ERROR: TypeDoesNotContainType - 13:23 - Type null for $this->foo is always null

ERROR: TypeDoesNotContainType - 18:13 - Type null for $this->foo is always null