index is not an integer constant expression when using const fn argument

[oli-obk]

#![feature(const_fn)]
const fn test(x: usize) -> i32 {
    [42;5][x]
}
fn main () {
    let _ = test(5);
}

I guess we cannot const evaluate the index anymore but must translate it with llvm's constant evaluator, because it might only be available as a value we got from a static. But then I'm not sure how to do the range check.

Nope, that's not a problem. Is there any reason not to thin out trans/consts down to the point where it's just a thin wrapper around const_eval + translation of ConstVal to ValueRef?

I mean after #25570 (const indexing), since after that I think the const_eval is feature-equivalent with the const translator.

[eefriedman]

const_eval currently can't return an address as a result (needed to evaluate e.g. const I: &'static u32 = &1).

Granted, that isn't a fundamental issue.

[oli-obk]

right. That would be solvable by adding a ConstVal::Ref variant.

[oli-obk]

This now ices with thread 'main' panicked at 'index out of bounds: the len is 5 but the index is 5'

[Mark-Simulacrum]

No longer ICEs or errors. E-needstest.