Multiple extern functions with differing signatures cause LLVM to throw an assertion

[Blei]

See the following code:

mod a {
    extern {
        fn my_fn(a: *u8);
    }
}

mod b {
    extern {
        fn my_fn(a: *u16);
    }
}

fn main() { }

Compiling it causes the following error:

Assertion failed: isa<X>(Val) && "cast<Ty>() argument of incompatible type!", file c:/Users/philii/rust/src/llvm/include/llvm/Support/Casting.h, line 231

I am not sure what the correct handling of this case should be. One easy solution would be to disallow multiple declarations of the same extern function in the same crate.

[brson]

nominating production ready

[brson]

there may be another issue open on this. it's been a known problem for a long time

[brson]

Dupe of #1866