E4171

Compiler diagnostic name: last_regex_case_must_be_catchall.

The catch-all case in a lexmatch or lexscan expression must be the last case.

Once a catch-all branch is reached, later regex cases can never be selected.

Erroneous example

///|
pub fn match_text(text : String) -> Unit {
  lexmatch text with longest {
    _ => ()
    re"^abc$" => ()
  }
}

The _ branch appears before another regex case.

Suggestion

Move the catch-all branch to the end. If the expression has no catch-all case at all, see E4224.

///|
pub fn match_text(text : String) -> Unit {
  lexmatch text with longest {
    re"^abc$" => ()
    _ => ()
  }
}