Match and narrowing

AG5002 — match is not exhaustive: missing {missing}.

Default severity: error.

A match over a union or Result must handle every case the scrutinee can take; the checker computes the set of arms you covered and reports the ones missing. An unhandled case would fall through at runtime with no branch to run.

How to fix: add an arm for each listed missing case, or add a wildcard _ arm if a catch-all is genuinely what you want.

node main() {
  const r = compute()
  match (r) {
    is success(v) { print(v) }
    is failure(e) { print(e) }
  }
}

AG5003 — {name} here binds the value; it does not test the type. Did you mean p: {name} or is {name}?

Default severity: warning.

An un-guarded match arm whose left side is a bare name matches ANY value and binds it to that name — it never tests the type, even when the name is a type in scope. Writing Person => ... therefore does something very different from testing "is this a Person".

How to fix: to test the type and bind, write p: Person => ...; to test only, write is Person => ...; to genuinely bind whatever arrives, pick a name that is not a type.