Malformed \u escape

Built from the repository at commit a8614dc.

\u is followed by 1 to 6 hexadecimal digits in braces: \u{E4}. A missing brace, no digits, more than 6 digits or a character that is not a hexadecimal digit is an error, reported over the escape as far as it reaches.

Why

Without the braces, \uE4 would not say where the number ends. Six digits are enough for every code point, which stops at 10FFFF.

Broken

fn main() {
    let c = '\uE4'
    print(c)
}

What sisu says

error[E0090]: malformed `\u` escape
 --> E0090.sisu:2:14
  |
2 |     let c = '\uE4'
  |              ^^
  |
  = help: write `\u{` and 1 to 6 hex digits, then `}`

sisu: 1 error
sisu: for more on a code, run `sisu explain <code>`: E0090

Fixed

fn main() {
    let c = '\u{E4}'
    print(c)
}