Fix MethodExistsTypeSpecifyingExtension for union types

[staabm]

closes phpstan/phpstan#13272

[phpstan-bot]

This pull request has been marked as ready for review.

[staabm]

@liamduckett I just realized that the fix of this PR produces a false-positive (see the newly added testcase).
I do not yet know how to fix the initial problem without also regressing the other example.

just to let you know, as #4153 has the same problem

[staabm]

I think the we could build a better type in a TypeSpecifyingExtension if the TypeSpecifierContext would contain information, whether the context is always-terminating.

[liamduckett]

@liamduckett I just realized that the fix of this PR produces a false-positive (see the newly added testcase). I do not yet know how to fix the initial problem without also regressing the other example.

just to let you know, as #4153 has the same problem

Thanks. I'm not sure I understand the new test case (probably due to my inexperience) - why would $bar being narrowed here, be a problem?

[staabm]

the initial types were wrongly narrowed:

/** * @param 'quux'|'qux' $constUnion */ function fooBar(object $bar, string $constUnion): void {	if (!method_exists($bar, $constUnion)) {	throw new \Exception;	} // $bar does not have both methods, it has only either 'quux' or 'qux' but not both } 

---

while in the initial loop check example it is correct that $bar will have both methods at once:

foreach (['qux', 'quux'] as $method) {	assertType("'quux'|'qux'", $method);	if (!method_exists($bar, $method)) {	throw new \Exception;	} }