Existence checks are missing in switch/pattern matching when using that

[ruby-random]

This code:

-> | foo? => 42

Produces this compiled output:

// Generated by LiveScript 1.4.0
(function(){
  switch (false) {
  case typeof foo == 'undefined' || foo === null:
    return 42;
  }
});

However, if you mention that in the return clause:

-> | foo? => that

It will compile to this:

// Generated by LiveScript 1.4.0
(function(){
  var that;
  switch (false) {
  case (that = foo) == null:
    return that;
  }
});

Note missing checks for foo existence, so this code will die with ReferenceError when foo is not defined, and it shouldn't happen.

[misterfish]

Indeed this can be seen even more easily like this:

if a?
    console.log that # => ReferenceError

PR #895 might fix this.

---

if a?
    console.log that

var that;
if (typeof a != 'undefined' && a !== null && (that = a, true)) {
  console.log(that);
}

---

if not a?
    console.log that

var that;
if ((that = undefined) || typeof a == 'undefined' || a === null) {
  console.log(that);
}

---

a = 10
if a?
    console.log that

var a;
a = 10;
if ((that = a) != null) {
  console.log(that);
}

---

a = 10
if not a?
    console.log that

var a;
a = 10;
if ((that = a) == null) {
  console.log(that);
}

---

The switch and while variants should work as well, and forms such as

if a? and not b?
    that

work the same as before I believe.

Any other cases to think about? :)