Confusing error when metavariable expressions are used outside of reptitions

[repnop]

Currently when a metavariable expression is used outside of any repetitions, it produces a somewhat cryptic error message instead of saying its not within a repetitions, example:

#![feature(macro_metavar_expr)]

macro_rules! f {
    ($n:ident) => {
        ${length()};
    }
}

fn main() {
    f!(a);
}

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

[steffahn]

@rustbot label requires-nightly F-macro-metavar-expr

[c410-f3r]

This issue was fixed ~1 month ago