Is the fact that foo (a: b, dx) is an illegal coffeescript error in an interpreter or part of a language?

Question

in coffeescript, the following code is legal

foo (a: b, d)

foo ({a: b}, dx)

foo (a: b, (dx))

But for some reason

foo (a: b, dx)

is illegal. I believe this should be either because there is ambiguity here that I do not see, or the interpreter is overly vigilant.

Answer 1

it turns out that this is a previously reported coffeescript error