Generic extern fns (former crust functions) cause an ICE

[pcwalton]

This is because they're *u8, so trans sees no substs and it won't monomorphize it. Then it calls type_of on a ty param and ICEs.

I think maybe crust functions should have to have explicit type parameter substitutions.

[nikomatsakis]

I expect this will work out fine once they have proper types.

[nikomatsakis]

Not critical for 0.6; removing milestone

[catamorphism]

Reproduced with 0252c30. Nominating for milestone 5, production-ready.

[graydon]

these are not foreign, they're callbacks-to-rust. title's wrong.

[graydon]

accepted for production-ready milestone

[emberian]

@pcwalton @catamorphism do you have a testcase?

[MicahChalmer]

As requested by @jdm when he closed my dupe of this (sorry about that), here's a bit of code that reproduces the ICE on the current master:

fn with_type_params<T>() { }

extern fn foo<T>() {
    with_type_params::<T>();
}

fn main() {
    let _a:*u8 = foo;
}

Not that this should actually compile, since it's trying to the generic foo without its type parameter--but I'd expect a normal compiler error message rather than an ICE.

A question: if this bug gets fixed, is it expected that this code would work if let _a:*u8 = foo were replaced with, for instance, let _a:*u8 = foo::<int>? As of now, it still doesn't compile, though it doesn't ICE in that case--instead it complains that foo doesn't take type parameters, even though it does.

[brson]

cc #10353

[pnkfelix]

accepted for P-backcompat-lang (under assumption we will just disallow this construction).

[alexcrichton]

Closed by 8f3f666