Badly worded note for non-constant array length

[durka]

let len = 42;
let arr = [0; len];

rustc 1.0.0 - 1.11.0: error: expected constant integer for repeat count, found variable
rustc 1.12.0 - 1.15.0: non-constant path in constant expression
rustc 1.16.0 - present: non-constant used with constant

Can we have the first one back please?

[cbreeden]

To clarify, the problem is in the note:

rustc 1.17.0 (56124baa9 2017-04-24)
error[E0435]: attempt to use a non-constant value in a constant
 --> <anon>:3:19
  |
3 |     let arr = [0; len];
  |                   ^^^ non-constant used with constant

error: aborting due to previous error

[kennytm]

Note introduced in #35858, using the exact wording from #35801.

Rust 1.12 fully transitioned to MIR, which made the repeat count no longer special, thus losing the special error message.

I think the note should be reworded to "non-constant used as constant".

[Mark-Simulacrum]

The error message today speaks the truth and does so quite well. Closing.

error[E0435]: attempt to use a non-constant value in a constant
 --> test.rs:3:19
  |
3 |     let arr = [0; len];
  |                   ^^^ non-constant used with constant

error: aborting due to previous error(s)

[durka]

The span label is still pretty nonsensical.

[Mark-Simulacrum]

Okay, I'll reopen. Can you provide the exact wording you'd expect? (I personally don't really see any point for a span label, but ... ).

[durka]

Either remove the label or just "non-constant value" seems to make more sense to me. It's the "with constant" that is weird IMO.

[durka]

I'll PR.

[JeffCarpenter]

I just came here after googling attempt to use a non-constant value in a constant: non-constant value and want to say that the first error message is a lot easier to understand!