[lang-team-minutes] private-in-public rules

[petrochenkov]

@nikomatsakis

I think I would like to see a system where we have some minimal amount of hard errors and then use lints for the rest. Specifically, I imagine lints for:

• marking something as pub that is not reachable from crate root (per the new modules RFC)
• marking something as pub that references things that are not pub (this is now a hard error)

e.g., functions that return private types, public trait impls that re-export private types

That's pretty much the plan.
I wanted to implement the second item without an RFC, it's on my work queue for months already (the queue is moving rarely these days).
I'll prioritize this then and write an RFC, type privacy needs documentation anyway.

@nikomatsakis

simply lint against pub use foo::PrivateThing

@aturon

But it would not be a hard error to re-export a type with greater visibility than what was originally stated for it.

This can't be done without undesirable consequences (either completely out-of-place hacks or breaking globs), privacy is pretty ingrained into the import resolution algorithm.
As I mentioned previously "private and cannot be reexported" is actually a "this pub use doesn't reexport anything" error in disguise.