Superfluous error message for a private pub use

[bfops]

This causes an error:

mod foo {}

mod bar {
  pub use foo; // error: `foo` is private, and cannot be reexported
}

Since foo is no more accessible than it was before, this doesn't seem like an actual instance of E0365.

[jonas-schievink]

I think this is intentional, but a better error message (maybe an additional note or help) seems useful since this often confuses people

[cgaebel]

I want to use this to refer to f and g as mod1::f, mod1::g in my crate, but export them as mod2::f and mod2::g for external use.

Regardless of my intentions, no "decrease of privacy" or other morally objectionable things are happening here. It's just an error message triggering in a case it's not needed.

[petrochenkov]

Long story short: 1) this works as intended, because reasons RFC 136 says so 2) wait for an implementation of RFC 1422 and write

mod foo {}

mod bar {
  pub(super) use foo;
}

Links:
rust-lang/rfcs#136
rust-lang/rfcs#200
https://github.com/rust-lang/meeting-minutes/blob/master/weekly-meetings/2014-09-16.md#rfc-public-items
#28450
rust-lang/rfcs#1422