Reexported private functions cause linker errors

[alexcrichton]

If you have a library with this code:

pub use foo::bar;

mod foo {
  pub fn bar() {}
}

No one can use the bar function at the top-level. The reason for this is that we mark the function with an inline linkage, and LLVM then internalizes the symbol so no one else can use it.

After some digging, it looks like this is because it is not flagged as "reachable" in the reachability pass of the compiler. After taking a look at the code, the reachability pass is doing a lot of approximations about privacy, and it's not taking public re-exports into account.

I believe that the best solution is to instead use the output of the privacy pass of the compiler to initially seed the work list of the reachability pass. Reachability should know nothing about privacy, it should only have to perform the iterations necessary to create a set of reachable items from public items.

[alexcrichton]

As an example of where this can go wrong:

$ cat foo.rs
pub use foo::bar;

mod foo {
    pub fn bar() {}
}
$ cat bar.rs
extern mod foo;

fn main() {
    foo::bar();
}
$ rustc foo.rs --lib
warning: missing crate link meta `name`, using `foo` as default
warning: missing crate link meta `vers`, using `0.0` as default
warning: no debug symbols in executable (-arch x86_64)
$ rustc bar.rs -L.
warning: no debug symbols in executable (-arch x86_64)                                                              
$ ./bar
dyld: lazy symbol binding failed: Symbol not found: __ZN3foo3bar19h15bec6257b8bff78ak4v0.0E                         
  Referenced from: /Users/alex/code/rust-opt/./bar                                                                  
  Expected in: flat namespace                                                                                       

dyld: Symbol not found: __ZN3foo3bar19h15bec6257b8bff78ak4v0.0E                                                     
  Referenced from: /Users/alex/code/rust-opt/./bar                                                                  
  Expected in: flat namespace                                                                                       

zsh: trace trap  ./bar                                                                                              

[SiegeLord]

Is this the same issue affecting this code?

pub use internal::S;
mod internal
{
    pub struct S;
    impl S
    {
        pub fn test(&self) {}
    }
}

test.rc:(.text+0x39): undefined reference to `internal::S::test::he344781a19bc4532DkaI::v0.0'

[alexcrichton]

Checked to make sure, that test case fails on master and passes with this patch.