Call to function is_string with string will always evaluate to true

[emodric]

Hi,

I have Treat PHPDoc types as certain option turned off, and the following piece of code fails:

https://phpstan.org/r/5dd76406-fbfc-4134-8158-c859505a05fc

Disabling checkAlwaysTrueCheckTypeFunctionCall option, actually removes the error message, but that doesn't seem correct to me.

If I configured PHPStan so that PHPDoc types are not certain, then by all reasoning, the code in question should be fine without disabling checkAlwaysTrueCheckTypeFunctionCall.

[emodric]

Another example: https://phpstan.org/r/1b095cf7-2a8b-43ca-994e-32d01c8aa60a