confusing error with 'extern crate'

[comex]

a.rs:

#![crate_type = "dylib"]
pub trait Foo {}

b.rs:

mod c;
fn main() {}

c.rs:

extern crate a;
use a::Foo;

Ran rustc a.rs, then rustc b.rs -L.. The result is a confusing error:

c.rs:2:9: 2:10 error: unresolved import. maybe a missing `extern crate a`?
c.rs:2     use a::Foo;

rustc 0.11-pre-nightly (d35804e 2014-04-18 00:01:22 -0700)

[SiegeLord]

It's unclear what you mean by 'useless'. You seem to imply that it is unusable, which is not the case (to use from it you need to do, e.g., use self::a::Foo in c.rs). It is, however, unused if you uncomment the use statement, but I imagine you could want to link to a crate for some side-effect (e.g. the other crate could bring some C libraries which are used in a way invisible to rustc).

The wrong use error is bizarre though in this case.

[comex]

I see. Some people in #rust seemed to think that it was unusable, but I guess that's wrong. I've edited the bug to refer to the confusing error.

[frewsxcv]

visiting for triage

The error message is slightly different now with the latest rust

/t/triage $ cat a.rs
#![crate_type = "dylib"]
pub trait Foo {}

/t/triage $ cat b.rs
mod c;
fn main() {}

/t/triage $ cat c.rs
extern crate a;
use a::Foo;

/t/triage $ rustc a.rs
/t/triage $ rustc b.rs -L.
c.rs:2:5: 2:6 error: unresolved import `a::Foo`. Did you mean `self::a`?
c.rs:2 use a::Foo;
           ^
error: aborting due to previous error

/t/triage $ rustc --version
rustc 1.0.0-nightly (1d00c545e 2015-01-30 19:56:34 +0000)

[Gankra]

Looks fixed to me.