I think we should be able to prune a case statement that will never be reached, but please correct me if I'm wrong.

Consider this case:

import 'fruits.dart';

main() {
  var fruit = new Apple(8);
  fruit.bite();

  var inSeason = chooseFruit('FALL');
}

Fruit chooseFruit(String season) {
  switch (season) {
    case "FALL":
      return new Apple(10);
    case "SUMMER":
      return new Orange(20);
  }
}

and over in fruits.dart:

library fruits;

abstract class Fruit {
  final num yummy;
  int numBites = 0;

  Fruit(this.yummy);

  bite() {
    numBites += 1;
  }
}

class Apple extends Fruit {
  Apple(yummy) : super(yummy);
}

class Orange extends Fruit {
  Orange(yummy) : super(yummy);
}

The generated code:

$$.Apple = {"": "Fruit;yummy,numBites"};

$$.Orange = {"": "Fruit;yummy,numBites"};

// Bound closures
Isolate.$finishClasses($$, $, null);
$$ = null;

$.main = function() {
  $.Apple$(8).bite$0();
  $.chooseFruit("FALL");
};

$.chooseFruit = function(season) {
  switch (season) {
    case "FALL":
      return $.Apple$(10);
    case "SUMMER":
      return $.Orange$(20);
  }
};

$.Apple$ = function(yummy) {
  return new $.Apple(yummy, 0);
};

$.Orange$ = function(yummy) {
  return new $.Orange(yummy, 0);
};

My assumption was, that because I always pass in 'FALL' to chooseFruit, the compiler would know that I never want an Orange, and can prune out the Orange class and its case clause.