E0093

Warning name: unknown_constr_pat_on_exhaustive_type

A Type::.. pattern is used with an enum that is not marked #non_exhaustive. Closed enums have no unknown future constructor for this pattern to match, so the pattern is meaningless.

Erroneous example

///|
pub(all) enum Status {
  Ready
  Busy
}

///|
pub fn describe(status : Status) -> String {
  match status {
    Ready => "ready"
    Busy => "busy"
    Status::.. => "unknown"
  }
}

Suggestion

Remove the Type::.. case from a closed enum match. If the enum is a public extension point whose defining package may add constructors in future releases, mark its declaration with #non_exhaustive, match every currently known constructor explicitly, and keep Type::.. as the final compatibility case.

///|
#non_exhaustive
pub(all) enum Status {
  Ready
  Busy
}

///|
pub fn describe(status : Status) -> String {
  match status {
    Ready => "ready"
    Busy => "busy"
    Status::.. => "unknown"
  }
}