Source that is not valid UTF-8

Built from the repository at commit a8614dc.

A source file must be text in UTF-8. The error points at the first byte that is not.

Why

Sisu reads every source file as UTF-8, so that a column and a string mean the same thing in every editor. A file saved in another encoding, such as Latin-1, stores a character like é as a byte that UTF-8 does not allow there.

Broken

The file below, saved in Latin-1:

fn main() {
    // café
    print(1)
}

What sisu says

error[E0072]: source is not valid UTF-8
 --> E0072.sisu:2:11
  |
2 |     // caf�
  |           ^
  |
  = help: save the file as UTF-8

sisu: 1 error
sisu: for more on a code, run `sisu explain <code>`: E0072

Fixed

The same file, saved in UTF-8:

fn main() {
    // café
    print(1)
}