Unsound generic tuple type test

[nicolasstucki]

The following two matches succeed when they should not. Tuple, NonEmptyTuple, *: erase to Object or Product and therefore the test is performed on those classes.

("a": Any) match
    case _: Tuple => assert(false)
    case _ => // ok

  case class Foo(a: Int)

  (Foo(1): Any) match
    case a: (_ *: _) => a.tail
    case _ => // ok

As these classes do not exist at runtime we should handle them as abstract types which would yield the unchecked warning. This approach could be combined with TypeTest to provide a type test that does the correct checks at runtime.

[nicolasstucki]

Minimized to

  assert(((): Any).isInstanceOf[Tuple])
  assert((1, 2).isInstanceOf[Tuple])
  assert((1, 2, 3).isInstanceOf[Tuple])
  assert(!"".isInstanceOf[Tuple]) // fail
  assert(!Some("").isInstanceOf[Tuple]) // fail

  assert(!((): Any).isInstanceOf[NonEmptyTuple])
  assert((1, 2).isInstanceOf[NonEmptyTuple])
  assert((1, 2, 3).isInstanceOf[NonEmptyTuple])
  assert(!("": Any).isInstanceOf[NonEmptyTuple])
  assert(!(Some(""): Any).isInstanceOf[NonEmptyTuple]) // fail

  assert(!((): Any).isInstanceOf[_ *: _])
  assert((1, 2).isInstanceOf[_ *: _])
  assert((1, 2, 3).isInstanceOf[_ *: _])
  assert(!("": Any).isInstanceOf[_ *: _])
  assert(!(Some(""): Any).isInstanceOf[_ *: _]) // fail

All these assertions should pass

[nicolasstucki]

Maybe we could erase instance tests on tuples in the following way

x.isInstanceOf[NonEmptyTuple]

isInstanceOfNonEmptyTuple(x)

// In scala.runtime.Tuple
def isInstanceOfNonEmptyTuple(x: Any): Boolean = 
  x.isInstanceOf[Tuple1[_]] 
  || x.isInstanceOf[Tuple2[_, _]] 
  || ... 
  || x.isInstanceOf[Tuple22[_, ..., _]] 
  ||  x.isInstanceOf[TupleXXL] || 

[nicolasstucki]

We also have a similar issue with asInstanceOf

[nicolasstucki]

This is a blocker for #9049