Unreachable code assertions for .NET

The roslyn C# compiler is unfortunately not the brightest when it comes to detecting that code cannot be reached, and will throw errors in cases like this:

enum PossibleValues {
	One,
	Two,
}

...
Foo foo;
if (value == PossibleValues.One) {
	foo = value1;
}
else if (value == PossibleValues.Two) {
	foo = value2;
}

//Refuses to compile with the compiler complaining that foo has a possibly
//undefined value, even though we know that's not the case:
foo.bar();

This nuget consists of just the definition for a single exception, UnreachableException. Throwing UnreachableException will force the compiler to let the code through:

Foo foo;
if (value == PossibleValues.One) {
	foo = value1;
}
else if (value == PossibleValues.Two) {
	foo = value2;
}
else {
	throw new UnreachableException();
}

//compiles OK this time:
foo.bar();

This is no substitute for proper compiler awareness of unreachable code, as if at some point in the future a new value PossibleValues.Three is added to the enum, the code will still compile and then a UnreachableException() will be thrown at runtime when that branch of the if condition is taken. A proper compiler would compile the first example above and then refuse to compile it when PossibleValues.Three is added to the enum.