can reach `pub` items within `priv mod`s

[ben0x539]

I'm not sure I entirely grok visibility rules, but the following seems to compile when I don't think it should.

priv mod foo {
    priv mod bar {
        pub fn f() {}
    }   
}   

fn main() {
    foo::bar::f();
}   

[thestinger]

I don't think priv does anything on mod, it's just a parser flaw.

[ILyoan]

Still reproducible.

[toddaaro]

Was able to reproduce that this compiles, but also not sure if it is a bug. @pcwalton can you look at this?

[alexcrichton]

Nominating for well-defined.

I think that this is another case where it'd be awesome to have resolve rules actually written down somewhere. Currently it sounds like it's still "whatever resolve does".

[graydon]

accepted for production-ready milestone

[pnkfelix]

Sub-bug of #6143

[pnkfelix]

Also, there is relevant short discussion on #8215 : namely, assuming we adopt the rule stated by @bblum as "pub items in a non-pub mod are visible to the rest of the crate, but not visible to users outside the crate", then the above code is not a bug, if I understand correctly.

(However, this example also demonstrates that bblum's rule is not compatible with the fifth condition listed by @alexcrichton: "Any local-crate path which goes outside the bounds of [conditions 3 and 4] will only resolve if each component of the path is pub. For example I could reach into a child's private mod's pub items, but not the child's private mod's non-pub items." Again, that's assuming I understand correctly.)

[alexcrichton]

I'm closing this in favor of #8215. This specific issue would be fixed by those rules, and otherwise the validity of this code will be determined by the decision on that bug.