Optimization: Unreachable break added when throwing in switch cases

[dpatti]

Example Coffee:

switch foo
  when "bar"
    throw Error("bar")
  when "baz"
    true

Compiles to:

switch (foo) {
  case "bar":
    throw Error("bar");
    break;
  case "baz":
    true;
}

Which, while valid, throws off some linters because the break statement is unreachable.

[nickdima]

Why are you linting the generated javascript?

[dpatti]

Because the tooling for JavaScript surpasses the tooling for CoffeeScript. We use a combination of coffeelint and jshint for this reason.

That said, I don't think our choice of linting tools is entirely relevant. CoffeeScript already omits the break statement if the when block contains a return statement, so it should similarly omit it if there is a throw statement.

[lydell]

Seems like checking for throw needs to be added on this line.

[msonnabaum]

Same thing happens when the return value is either assigned, or the return value of the switch statement is also the return of a function.

b = switch
    when a > 10
      "greater than 10"
    when a < 10
      if a > 5
        "greater than five"
      else
        "less than five"
    else
      "is 10"

var b;

b = (function() {
  switch (false) {
    case !(a > 10):
      return "greater than 10";
    case !(a < 10):
      if (a > 5) {
        return "greater than five";
      } else {
        return "less than five";
      }
      break;
    default:
      return "is 10";
  }
})();