privacy exposure bug when struct has field(s) *and* an impl

[pnkfelix]

This was fun one for isolating the parameters where it does and does not occur.

The code (a.rs):

mod a {
    #[cfg(hide_payload)]      struct S;
    #[cfg(not(hide_payload))] struct S { p: () }

    #[cfg(not(hide_impl))]    impl S { }
}

struct Expose;
impl Expose {
    #[cfg(not(hide_payload))] pub fn expose(&self) -> a::S { a::S { p: () } }
    #[cfg(hide_payload)]      pub fn expose(&self) -> a::S { a::S }
}

fn main() {
    let _s = Expose.expose();
}

So, S is not pub in a, so it should not be possible to access it from main.

But, out of the box, the above compiles and runs:

% rustc --version
/Users/fklock/opt/rust-dbg/bin/rustc 0.9-pre (4dded43 2013-11-17 23:41:25 -0800)
host: x86_64-apple-darwin
% rustc a.rs
%

If you remove either the payload or the impl, the privacy checker will flag an error:

% rustc --cfg hide_payload a.rs
a.rs:11:61: 11:65 error: struct `S` is inaccessible
a.rs:11     #[cfg(hide_payload)]      pub fn expose(&self) -> a::S { a::S }
                                                                     ^~~~
error: aborting due to previous error
task 'rustc' failed at 'explicit failure', /Users/fklock/Dev/Mozilla/rust.git/src/libsyntax/diagnostic.rs:101
task '<main>' failed at 'explicit failure', /Users/fklock/Dev/Mozilla/rust.git/src/librustc/lib.rs:396

% rustc --cfg hide_impl a.rs
a.rs:10:54: 10:58 error: type `S` is private
a.rs:10     #[cfg(not(hide_payload))] pub fn expose(&self) -> a::S { a::S { p: () } }
                                                              ^~~~
error: aborting due to previous error
task 'rustc' failed at 'explicit failure', /Users/fklock/Dev/Mozilla/rust.git/src/libsyntax/diagnostic.rs:101
task '<main>' failed at 'explicit failure', /Users/fklock/Dev/Mozilla/rust.git/src/librustc/lib.rs:396

[pnkfelix]

(The fact that the error messages are different is a little bit of a red flag to me.)

[alexcrichton]

Agreed, something funky is going on here.

[alexcrichton]

As mentioned in #10548, I believe that this is all a similar bug as this program:

mod a {
    struct S;
    impl S { }
}

fn foo(_: a::S) {
}

fn main() {}

This should not compile, but it does.