using generic functions with a foreign ABI doesn't work

[thestinger]

extern "C" fn foo<T>() {}

fn main() {
    let _ = foo::<int>;
}

task 'rustc' failed at 'assertion failed: f.abis.is_rust() || f.abis.is_intrinsic()', /build/rust-git/src/rust/src/librustc/middle/trans/monomorphize.rs:176

Use case, if you're curious: https://github.com/thestinger/rust-core/blob/master/core/thread.rs#L30

[emberian]

I'm wondering if that assertion can just be removed. Are there any fundamental problems with generics with foreign ABI? I can't think of any. (cc @pcwalton @nikomatsakis ?)

[brson]

Generic functions will be called differently for every type, and that doesn't map to C except in some limited circumstances. This could rather be a proper compiler error - I'm kind of surprised this bug still exists.

[thestinger]

@brson: It's useful to be able to write a generic function and obtain function pointers to specific monomorphized instances though. It should be possible to do this and ask that the function use the C ABI.

[thestinger]

@cmr: it's definitely not as simple as removing the assertion

[brson]

Nominating.

[pnkfelix]

Current thinking is to put in a proper error message now (as in, don't add support in the short term for 1.0).

Then post 1.0 we can backward-compatibly extend rustc to add support for this.

Accepted for P-high for the error message.

[nrc]

taking, for the error message

[emberian]

There's no ICE anymore, but this is still an issue.

[emberian]

Eh, opening a new issue.