Invalid refutable pattern warning with Tuple

[Adam-Vandervorst]

Compiler version

3.2.1-RC1-bin-20220904-b5fea82-NIGHTLY

Minimized code

While investigating , I noticed *:-tuples in unapply return raise refutable pattern warnings.

class Foo

object Foo:
//  def unapply(f: Foo): (Int, Int) = ???  // does not raise a warning
  def unapply(f: Foo): Int *: Int *: EmptyTuple = ???

@main def example =
  val Foo(x, y) = new Foo
  println(x)

Output

  val Foo(x, y) = new Foo
      ^^^^^^^^^^^^^^^^^^^
pattern binding uses refutable extractor `tuple_refutable_pattern_issue.this.Foo`

If this usage is intentional, this can be communicated by adding `: @unchecked` after the expression,
which may result in a MatchError at runtime.
This patch can be rewritten automatically under -rewrite -source 3.2-migration.

Expectation

No warning, as this can not result in a MatchError at runtime.

[mbovel]

Seems like the snippet compiles with 3.1.3 but not 3.2.0:

$ scala-cli compile --server=false --scala-version=3.1.3 refutable_pattern_tuple.scala
$ scala-cli compile --server=false --scala-version=3.2.0 refutable_pattern_tuple.scala
-- Warning: /Users/mbovel/scala-snippets/refutable_pattern_tuple.scala:7:9 -----
7 |  val Foo(x, y) = new Foo
  |      ^^^^^^^^^^^^^^^^^^^
  |pattern binding uses refutable extractor `Foo`
  |
  |If this usage is intentional, this can be communicated by adding `: @unchecked` after the expression,
  |which may result in a MatchError at runtime.
  |This patch can be rewritten automatically under -rewrite -source 3.2-migration.
1 warning found

So this is probably a regression. I am wondering if this is related to https://github.com/lampepfl/dotty/issues/15650.

[mbovel]

Related: https://github.com/lampepfl/dotty/issues/15990.