Turn on this rule to flag when expressions that do not check that all cases are covered when the subject is an enum or sealed class and the when expression is used as a statement. When this happens it's unclear what was intended when an unhandled case is reached. It is better to be explicit and either handle all cases or use a default else statement to cover the unhandled cases.

Noncompliant Code

enum class Color {
    RED,
    GREEN,
    BLUE
}

fun whenOnEnumFail(c: Color) {
    when(c) {
        Color.BLUE -> {}
        Color.GREEN -> {}
    }
}

Compliant Code

enum class Color {
    RED,
    GREEN,
    BLUE
}

fun whenOnEnumCompliant(c: Color) {
    when(c) {
        Color.BLUE -> {}
        Color.GREEN -> {}
        Color.RED -> {}
    }
}

fun whenOnEnumCompliant2(c: Color) {
    when(c) {
        Color.BLUE -> {}
        else -> {}
    }
}

Options

• allowElseExpression (default: True)

  whether else can be treated as a valid case for enums and sealed classes