Better error message for generic_const_exprs inference failure

[atsuzaki]

Fixes #90531

This code:

#![feature(generic_const_exprs)] fn foo<const N: usize>(_arr: [u64; N + 1]) where [u64; N + 1]: {} fn main() { let arr = [5; 5]; foo(arr); }

Will now emit the following error:

warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes --> test.rs:1:12 | 1 | #![feature(generic_const_exprs)] | ^^^^^^^^^^^^^^^^^^^ | = note: `#[warn(incomplete_features)]` on by default = note: see issue #76560 <https://github.com/rust-lang/rust/issues/76560> for more information error[E0284]: type annotations needed --> test.rs:8:7 | 8 | foo(arr); | ^^^ cannot infer the value of the const parameter `N` declared on the function `foo` | note: required by a bound in `foo` --> test.rs:3:56 | 3 | fn foo<const N: usize>(_arr: [u64; N + 1]) where [u64; N + 1]: {} | ^^^^^ required by this bound in `foo` help: consider specifying the generic argument | 8 | foo::<N>(arr); | +++++ error: aborting due to previous error; 1 warning emitted

cc: @lcnr thanks a lot again for the help on this

[rust-highfive]

r? @cjgillot

(rust-highfive has picked a reviewer for you, use r? to override)

[lcnr]

Thanks ❤️

r? @lcnr

@bors r+ rollup

[bors]

📌 Commit 96d34dc has been approved by lcnr

It is now in the queue for this repository.