Inconsistency with member selection of generic tuples with know TupleN

[nicolasstucki]

Compiler version

3.1.0

Minimized code

def f[T <: Tuple2[Int, Int]](tup: T): T = tup

def test: Unit =
  (1, 2)._1
  f((1, 2))._1

  (1 *: 2 *: EmptyTuple)._1 // error: `*:` does not have a member `_1` based on our current encoding it is considered ok
  f(1 *: 2 *: EmptyTuple)._1 // error: should not fail as `f` returns a subtype of `Tuple2` and should have the member `_1`
  f[Int *: Int *: EmptyTuple](1 *: 2 *: EmptyTuple)._1 // error

  f[Int *: Int *: EmptyTuple]((1, 2))._1 // error
  f[Tuple2[Int, Int]](1 *: 2 *: EmptyTuple)._1

Output

-- [E008] Not Found Error: Foo.scala:7:25 --------------------------------------
7 |  (1 *: 2 *: EmptyTuple)._1 // error: `*:` does not have a member `_1` based on our current encoding it is considered ok
  |  ^^^^^^^^^^^^^^^^^^^^^^^^^
  |  value _1 is not a member of (Int, Int)
-- [E008] Not Found Error: Foo.scala:8:26 --------------------------------------
8 |  f(1 *: 2 *: EmptyTuple)._1 // error: should not fail as `f` returns a subtype of `Tuple2` and should have the member `_1`
  |  ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |  value _1 is not a member of (Int, Int)
-- [E008] Not Found Error: Foo.scala:9:52 --------------------------------------
9 |  f[Int *: Int *: EmptyTuple](1 *: 2 *: EmptyTuple)._1 // error
  |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |  value _1 is not a member of Int *: Int *: EmptyTuple
-- [E008] Not Found Error: Foo.scala:11:38 -------------------------------------
11 |  f[Int *: Int *: EmptyTuple]((1, 2))._1 // error
   |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |  value _1 is

Expectation

Ideally, they should all work.

[nicolasstucki]

The main issue is that Tuple2[Int, Int] <:< Int *: Int *: EmptyTuple because we extend Tuple2 explicitly and from another side we also assume that Int *: Int *: EmptyTuple <:< Tuple2[Int, Int]; therefore Tuple2[Int, Int] =:= Int *: Int *: EmptyTuple. But Int *: Int *: EmptyTuple does not have access to the members of Tuple2[Int, Int]. This creates inconsistency depending on how/when we check for the members.