Non-exhaustive 'when' statements will be prohibited since 1.7

Reports a non-exhaustive when statements that will lead to compilation error since 1.7.

Motivation types:

Problematic/meaningless usage patterns need to be discouraged/blocked (e.g. counterintuitive behaviors)
- Code is error-prone
Inconsistency in the design (things are done differently in different contexts)

Impact types:

Compilation. Some code that used to compile won't compile any more
- There were cases when such code worked with no exceptions
  - Some such code could compile without any warnings

More details: KT-47709: Make when statements with enum, sealed, and Boolean subjects exhaustive by default

The quick-fix adds the missing else -> {} branch.

Example:

sealed class Base {
    class A : Base()
    class B : Base()
}

fun test(base: Base) {
    when (base) {
        is Base.A -> ""
    }
}

After the quick-fix is applied:

sealed class Base {
    class A : Base()
    class B : Base()
}

fun test(base: Base) {
    when (base) {
        is Base.A -> ""
        else -> {}
    }
}

This inspection only reports if the Kotlin language level of the project or module is 1.6 or higher.

Inspection Details
Available in:	IntelliJ IDEA 2023.3, Qodana for JVM 2023.3
Plugin:	Kotlin, @snapshot@

Last modified: 13 July 2023