Uninformative error message for use of non-const expression in fixed-size array type

[sdleffler]

I was messing with macros and came across the error message "error: no type for local variable 10 [E0513]". The following code will reproduce the error using the Rust playground, on Stable, Beta, and Nightly channels:

fn main() {
    let v: usize = 2;
    let x: [i32; v] = [0, 1];
}

I would have expected an error message such as "expected constant expression, found non-constant expression." It looks like an easy fix, but I imagine E0513 can occur in other situations as well. Replacing let v: usize in the above code sample with const v: usize will compile and run just fine.

[nagisa]

You cannot use constant expressions in type context either. (apparently I misremembered and confused it with some other thing) I agree, though, that the error message is pretty bad.

[oli-obk]

there's actually a FIXME for it https://github.com/rust-lang/rust/blob/219eca11b044de3644b3e9101124513c1a842b09/src/test/compile-fail/non-constant-expr-for-fixed-len-vec.rs

[oli-obk]

dupe of #24414