unapply loses stable prefix when in pattern position

[EugeneFlesselle]

Compiler version

3.5.0-RC1

Minimized code

trait Wrap:
  type Value
  val value: Value

object Wrap:
  def unapply(w: Wrap): Some[w.Value] = Some(w.value)

object Test:
  val w: Wrap = ???

  val Some(n1) = Wrap.unapply(w)
  val _: w.Value = n1 // ok

  val Wrap(n2) = w
  val _: w.Value = n2 // Error Found: (Test.n2 : Wrap#Value)

Expectation

Expected no errors

[EugeneFlesselle]

In (w: w.type) match case Wrap(n) => ... we type the pattern with a selector type of Wrap, i.e. we have lost the reference to w.type. This is due to a widening in typedMatch:

scala3/compiler/src/dotty/tools/dotc/typer/Typer.scala

Lines 1974 to 1976 in e2dfea3

	val selType = rawSelectorTpe match
	case c: ConstantType if tree.isInline => c
	case otherTpe => otherTpe.widen

adapting this fixes the issue, but causes a bunch of other tests to fail.