This is correct behavior too. Being public means that your declaration is shown to clients in other modules. They have to be able to see all the types involved!

(The compiler has to assume the typealias is meaningful; it won't just blindly throw it away.)

@belkadan Does meaningful here mean "the typealias can be substituted with the type it refers to without violating the access level of that type"?

I still don't quite get why an inaccessible typealias can't be thrown away for the consumer in favor of the type it refers to if that type is accessible for the user.
For instance, the developer wants to use an alias for a complex public type within the module for readability, but doesn't want to expose that alias to the consumer. I know this isn't a strong use case, but even so, does it really make sense for functions and types to become inaccessible just because a typealias in their signature is itself inaccessible?

There's no way for the compiler to tell the difference between "I'm using this for my convenience" and "I'm trying to show this to users but forgot it was internal". Right now there's a consistent rule, if restrictive. If you're interested in changing this, bring it up on the Swift Evolution forums.

How could I miss that...Of course, the user might want to do the opposite. Thank you.