Named Tuple key validation not applied to Tuple[] syntax

[aherlihy]

From #23155

Compiler version

3.7.2-RC1-bin-SNAPSHOT

Minimized code

Seems no named tuple key validation occurs at all when not using the explicit syntax:

  val explicit: (_1: Int, _1: Int) = ??? // error, both for the duplicate and "_1" cannot be a named tuple selector because clashes with regular tuple selectors
  val viaTupleN: NamedTuple.NamedTuple[Tuple2["_1", "_1"], Tuple2[Int, Int]] = ??? //  no error
  val viaTupleExpl: NamedTuple.NamedTuple[("_1", "_1"), (Int, Int)] = ??? // no error
  val viaCons: NamedTuple.NamedTuple["_1" *: "_1" *: EmptyTuple, Int *: Int *: EmptyTuple] = ???  // no error

Do we want to ensure we're checking for any key name restrictions on the desugared tuples, or document that the NamedTuple syntax shouldn't be used in user code directly?

[aherlihy]

After discussion with the compiler team this works as intended.