E4216

Compiler diagnostic name: lexscan_catchall_binder_not_supported.

A lexscan catch-all case uses a binder pattern.

lexscan consumes input only when a regex matches. The final catch-all also handles end of input, so it does not bind a matched substring. Use _ for that case and bind text with as on the regex cases that need it. This also applies when the target is an in-memory @lexbuf.StringScanner.

Erroneous example

///|
pub fn next_token(lexbuf : @lexbuf.Lexbuf) -> String {
  lexscan lexbuf {
    (re"^[a-z]+" as word) => word.to_owned()
    rest => rest.to_owned()
  }
}

Suggestion

Replace the catch-all binder with _.

///|
pub fn next_token(lexbuf : @lexbuf.Lexbuf) -> String {
  lexscan lexbuf {
    (re"^[a-z]+" as word) => word.to_owned()
    _ => "end"
  }
}