_ outside digits

Built from the repository at commit a8614dc.

A _ in an integer literal must stand between two digits, as in 1_000_000.

Why

A _ only groups digits so that long numbers are easy to read. A doubled or trailing _ groups nothing, so it is more likely a typo than a choice.

Broken

fn main() {
    let n = 1__000
    print(n)
}

What sisu says

error[E0008]: `_` must sit between digits
 --> E0008.sisu:2:14
  |
2 |     let n = 1__000
  |              ^

sisu: 1 error
sisu: for more on a code, run `sisu explain <code>`: E0008

Fixed

fn main() {
    let n = 1_000
    print(n)
}