Poor diagnostic: "length depth must be less than 0", but it mustn't

[jonas-schievink]

#![feature(macro_metavar_expr)]

macro_rules! metavar {
    ( $i:expr ) => {
        ${length(0)}
    };
}

const _: i32 = metavar!(0);

errors with:

error: length depth must be less than 0
 --> src/main.rs:5:10
  |
5 |         ${length(0)}
  |          ^^^^^^^^^^^

However, passing -1 as the depth is rejected with:

error: meta-variable expression depth must be a literal
 --> src/main.rs:5:11
  |
5 |         ${length(-1)}
  |           ^^^^^^

error: expected expression, found `$`
  --> src/main.rs:5:9
   |
5  |         ${length(-1)}
   |         ^ expected expression

[compiler-errors]

Am I mistaken or is this fixed on nightly?

[jonas-schievink]

Ah, it looks like you have to invoke the macro for the error to happen. Updated the example to reflect that.