Unicode identifiers

identifiers.rs

#![allow(uncommon_codepoints)]

fn main() {
    // Plank's constant
    let ℏ = 1.054571817e-34;
    // The rust mascot
    let 🦀 = "Ferris";
}

Output of rustc

error: Ferris cannot be used as an identifier
 --> foo.rs:5:9
  |
5 |     let 🦀 = "Ferris";
  |         ^^ help: try using their name instead: `ferris`

error: aborting due to previous error