Default parameters in interop setters are allowed

[gzm0]

The two following definitions compile, but probably shouldn't:

trait JS extends js.Object {
  def a_=(x: Int = 1): Unit = js.native
}

class A {
  @JSExport
  def a_=(x: Int = 1): Unit = ???
}

[gzm0]

@sjrd, please confirm this.

[sjrd]

The raw JS type variant should definitely not compile (the compiler wouldn't know what to do with a call site x.a_=()!)

For the exports, well ... Tough question. The default would bear no meaning for the export, but could in theory be used by Scala code. I would say forbid it. (If this is really what the author wants, they can declare an overload that is not exported.)

[gzm0]

I would say forbid it.

I agree. It is something that should not occur in Scala code either. And the overload (or a second method) is a reasonable workaround if one really needs it.

[gzm0]

I assume we'll emit a warning for this in the 0.6.x series, right?

[sjrd]

Yep, I guess we have to make it a warning.

We should also emit a compile error for a call site x.a_=(). (Currently it would likely silently produce invalid IR with a leftover UndefinedParam() or something like that.)

[sjrd]

Fixed in 7cacc30