Linker library order is important

[vadimcn]

Let's say I have 3 modules main.rs, a.rs and b.rs, and two external libraries libfoo.a and libbar.a, and that libbar depends on symbols defined in libfoo.

main.rs

mod a;
mod b;
fn main() {}

a.rs

#[link(name = "foo")]
extern {}

b.rs

#[link(name = "bar")]
#[link(name = "foo")]
extern {}

Because rustc de-dupes the list of external libraries, it will pass to linker only -lfoo -lbar. However gnu linker does not look for unresolved symbols in libraries it had already processed, so it will fail to resolve libbar's references to libfoo. The correct command line would have been -lfoo -lbar -lfoo.

Rustc should not de-duplicate the list of libraries. Furthermore, I think it should guarantee that libs will appear in the same order on the linker command line as they did in the source file.

[alexcrichton]

Another possible solution could be link(name = "foo", priority = "100") where the default priority is N and they're sorted lowest to highest, but it does seem odd that we're de-duping the libraries.

[sanxiyn]

Did #12688 fix this?

[alexcrichton]

It did indeed, a test was checked in as well.