When using for+let, the loop variable isn't available in the when clause

[vendethiel]

exemple:

for let k in v when k
  ...

result:

var i$, ref$, len$;
for (i$ = 0, len$ = (ref$ = v).length; i$ < len$; ++i$) {
  if (k) {
    (fn$.call(this, ref$[i$]));
  }
}
function fn$(k){
  throw Error('unimplemented');
}

expected:

var i$, ref$, len$;
for (i$ = 0, len$ = (ref$ = v).length; i$ < len$; ++i$) {
  var k = ref$[i$];
  if (k) {
    (fn$.call(this, k));
  }
}
function fn$(k){
  throw Error('unimplemented');
}

[rhendric]

Turns out this is slightly narrower; the actual issue only occurs when the loop variable is the entirety of the when clause. for let k in v when k > 0 works as expected.

[vendethiel]

Actually there's another bug underneath:

for let {}:k in v when k > 0
  ...

gives

var i$, ref$, len$;
for (i$ = 0, len$ = (ref$ = v).length; i$ < len$; ++i$) {
  if (k > 0) {
    (fn$.call(this, ref$[i$]));
  }
}
function fn$(){
  throw Error('unimplemented');
}