unapply cannot return generic tuples

[nicolasstucki]

Compiler version

3.1.0

Minimized example

object Bar:
  def unapply(x: Any): Int *: Int *: EmptyTuple = ??? // Works it returns a `Tuple2[Int, Int]`

def test =
  "" match
    case Bar(a, b) =>

Output

10 |    case Bar(a, b) =>
   |         ^^^^^^^^^
   |         Wrong number of argument patterns for Bar; expected: ()

Expectation

Should be supported.

[dwijnand]

This doesn't work because Tuple's product arity is 0 ("expected: ()"). I guess we need to teach productArity to walk the type to count the arity.

[nicolasstucki]

It seems that in the example of #13968 we do calculate the arity correctly. We should see how it is handled there and why it was not done here.

[dwijnand]

Duplicate of #11008