Conditional return type + Union Types = unexpected result

[LastDragon-ru]

Bug report

If we have something like

/**
 * @return ($b is A ? ANode : ($b is B ? BNode : CNode))
 */
public function b(A|B|C $b): ANode|BNode|CNode {
    return match(true) {
        $b instanceof A => new ANode(),
        $b instanceof B => new BNode(),
        default => new CNode(),
     };
}

PHPStan will resolve the return type of b() as b(A) => ANode, b(B) => BNode which are expected. But for b(A|B) it will report that the return type is ANode|BNode|CNode. This is not true, the type should be ANode|BNode.

Code snippet that reproduces the problem

https://phpstan.org/r/9d568b79-afd0-48b3-a379-50127980fbb5

Expected output

ANode|BNode

Did PHPStan help you today? Did it make you happy in any way?

Yep 😋

[ondrejmirtes]

Fixed: phpstan/phpstan-src#2641

[github-actions]

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