Nonsensical error when trying to use associated const in array #78189
Description
The following code:
trait ConstN {
const N: usize;
}
trait Array: ConstN {
fn array() -> [(); Self::N];
}
fn main() {}produces the following error:
error[E0599]: no associated item named `N` found for type parameter `Self` in the current scope
--> src/main.rs:6:30
|
6 | fn array() -> [(); Self::N];
| ^ associated item not found in `Self`
|
= help: items from traits can only be used if the type parameter is bounded by the trait
help: the following trait defines an item `N`, perhaps you need to add another supertrait for it:
|
5 | trait Array: ConstN + ConstN {
| ^^^^^^^^
error: aborting due to previous error
The error claims that Self::N doesn't exist, but then suggests adding a duplicate bound for the trait that defines it.
With #![feature(const_generics)], we get a more meaningful error:
error: constant expression depends on a generic parameter
--> src/main.rs:8:19
|
8 | fn array() -> [(); Self::N];
| ^^^^^^^^^^^^^
|
= note: this may fail depending on what value the parameter takes
We should try to emit this diagnostic (or something like it) regardless of whether or not #![feature(const_generics)] is enabled.