Private type exposed in public without a warning

[kvark]

Here is the code:

pub mod foo {
    mod sub {
        pub struct Bar;
    }
    
    use sub::Bar;
    
    pub struct Foo {
        pub bar: Bar,
    }
}

//use foo::Bar; // this errors for `Bar` being private

I expected to see this happen (compile error):

Private type sub::Bar exposed in public signature of Foo::bar

Instead, this happened: compiles just fine.
Trying to use the type fails, since it's private

Meta

Tested on stable 1.44.0 and nightly of 1.46.0

playground link

[cuviper]

Sometimes this is done intentionally, like the Sealed trait here:
https://rust-lang.github.io/api-guidelines/future-proofing.html

[Dylan-DPC]

Closing this as it is intended and not sure if there's anything that can be done here

[petrochenkov]

This is now addressed by a lint called unnameable_types (#48054), but that lint is allowed by default.