rust/tests/ui/const-generics/issues/issue-90455.rs
Esteban Küber 6b24fdf811 Provide structured suggestion for unconstrained generic constant
```
error: unconstrained generic constant
  --> $DIR/const-argument-if-length.rs:18:10
   |
LL |     pad: [u8; is_zst::<T>()],
   |          ^^^^^^^^^^^^^^^^^^^
   |
help: try adding a `where` bound
   |
LL | pub struct AtLeastByte<T: ?Sized> where [(); is_zst::<T>()]: {
   |                                   ++++++++++++++++++++++++++
```

Detect when the constant expression isn't `usize` and suggest casting:

```
error: unconstrained generic constant
 --> f300.rs:6:10
  |
6 |     bb::<{!N}>();
  |          ^^^^
-Ztrack-diagnostics: created at compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs:3539:36
  |
help: try adding a `where` bound
  |
5 | fn b<const N: bool>() where [(); {!N} as usize]: {
  |                       ++++++++++++++++++++++++++
```

Fix #122395.
2024-03-21 00:03:59 +00:00

14 lines
292 B
Rust

//@ run-rustfix
#![feature(generic_const_exprs, adt_const_params)]
#![allow(incomplete_features, dead_code)]
struct FieldElement<const N: &'static str> {
n: [u64; num_limbs(N)],
//~^ ERROR unconstrained generic constant
}
const fn num_limbs(_: &str) -> usize {
0
}
fn main() {}