Bug report

After upgrading to phpstan 2.1.18, I get this error:

Property name for mixed must be a string, but 'example_one'|'example_two' was given.
         🪪  property.nameNotString

example snippet:

...
$field = $condition ? 'example_one' : 'example_two';
$result = $object->$field;

I believe those are both strings. Probably it does not recognize specific literals as strings?

This happened in:

php: 8.4
phpstan: 2.1.18
level: 1

Code snippet that reproduces the problem

https://phpstan.org/r/1bc5bdd8-63ae-4f3f-8fd5-605998483ed1

Expected output

Both strings should be valid as strings, expected no error.

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