E0076

Warning name: lexmatch_first_match

Using lexmatch with first-match semantics is deprecated.

This warning is emitted for lexmatch expressions that use the default first-match strategy, including lexmatch ... with first. Prefer regex match expressions for ordinary regex checks in new code.

Erroneous example

///|
fn classify(input : String) -> String {
  lexmatch input {
    "if" => "keyword"
    _ => "other"
  }
}

///|
test {
  ignore(classify)
}

Suggestion

Rewrite first-match lexmatch code with a regex match expression when possible. If you specifically need lexer-style longest-match behavior, make that explicit with lexmatch ... with longest.

///|
fn classify(input : String) -> String {
  if input =~ re"^if$" {
    "keyword"
  } else {
    "other"
  }
}

///|
test {
  ignore(classify)
}