Surprising flow-analysis of `switch` statements

[eernstg]

The rule about switch statements is here. Consider the following example:

enum Enum { one, two }

void main() {
  Enum e = Enum.one;
  num n;
  switch (e) {
    case Enum.one: n = 1; break;
    case Enum.two: n = 2; break;
  }
  print(n.isEven);
}

The switch statement rule might need a few adjustments (saying something about default, and handling the situation where there is no default and the last case has no break;), but I would in any case expect the rule to promote n to int after the switch statement. The actual flow analysis does not reach that conclusion, so the analyzer reports an error on n.isEven, showing that n has type num.

@stereotype441, what do you think?