non_exhaustive_switch_statement

The type '{0}' isn't exhaustively matched by the switch cases since it doesn't match the pattern '{1}'.

The analyzer produces this diagnostic when a switch statement switching over an exhaustive type is missing a case for one or more of the possible values that could flow through it.

The following code produces this diagnostic because the switch statement doesn't have a case for the value E.three, and E is an exhaustive type:

enum E { one, two, three }

void f(E e) {
  switch (e) {
    case E.one:
    case E.two:
  }
}

Add a case for each of the constants that aren't currently being matched:

enum E { one, two, three }

void f(E e) {
  switch (e) {
    case E.one:
    case E.two:
      break;
    case E.three:
  }
}

If the missing values don't need to be matched, then add a default clause or a wildcard pattern:

enum E { one, two, three }

void f(E e) {
  switch (e) {
    case E.one:
    case E.two:
      break;
    default:
  }
}

But be aware that adding a default clause or wildcard pattern will cause any future values of the exhaustive type to also be handled, so you will have lost the ability for the compiler to warn you if the switch needs to be updated.