False exhaustivity warning when unapply return type is a tuple defined using *:

[eejbyfeldt]

Compiler version

3.6.2

Minimized code

object Test {
  sealed trait Expr[T]

  case class Person(name: String, age: Int)
  object PP {
    def unapply(e: Expr[Person]): String *: Int *: EmptyTuple = ???
  }

  val expr: Expr[Person] = ???
  expr match {
    case PP(str, _) => ???
  }
}

Output

-- [E029] Pattern Match Exhaustivity Warning: scala3_bug.scala:10:2 
10 |  expr match {
   |  ^^^^
   |  match may not be exhaustive.
   |
   |  It would fail on pattern case: PP()
   |------------------------------------------------------------------------------------------
   | Explanation (enabled by `-explain`)
   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   | There are several ways to make the match exhaustive:
   |  - Add missing cases as shown in the warning
   |  - If an extractor always return Some(...), write Some[X] for its return type
   |  - Add a case _ => ... at the end to match all remaining cases
    ------------------------------------------------------------------------------------------
1 warning found

Expectation

The code should compile without warnings.

[eejbyfeldt]

If the unapply is changed to

    def unapply(e: Expr[Person]): (String, Int) = ???

the warnings goes away. Also if the code is changed to do a match on Person instead of Expr[Person] like

object Test {
  case class Person(name: String, age: Int)
  object PP {
    def unapply(e: Person): String *: Int *: EmptyTuple = ???
  }

  val expr: Person = ???
  expr match {
    case PP(str, _) => ???
  }
}

then there is also no warning.