Fields of private structures should be private by default

[alexcrichton]

It was brought up recently that the rules for field privacy aren't quite as they were intended to be. Currently, fields are public by default, and you explicitly make them private. In the originally envisioned world, this was only true of pub structs. Private structs would have private-by-default.

This essentially means that the default visibility of fields inherits the visibility of the struct. I would also like to go so far as to disallow pub on fields of a private structure.

Nominating

[huonw]

Would resolving #10573 by disallowing private things in public type signatures stop this from mattering?

[alexcrichton]

It would, but it's also unclear on what the resolution of #10573 should be I think.

[huonw]

Oh, maybe pub use would mean that this still needs to be handled explicitly.

pub use Foo = Bar;

struct Bar {
    can_users_of_foo_see_this: int
}

[alexcrichton]

Good point! We have had a lot of bad luck in the past with inherited visibility, but technically this would bring structs in lines with enums, so maybe ok?

Sounds like we shouldn't deny pub field: type on a priv struct, but the fields should still be private by default.

[pnkfelix]

Accepted for P-backcompat-lang