Adapt refutability warning in Space engine to named tuples

Fixes scala#22899

Author: odersky

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -279,7 +279,7 @@ object SpaceEngine {
     || unappResult <:< ConstantType(Constant(true)) // only for unapply
     || (unapp.symbol.is(Synthetic) && unapp.symbol.owner.linkedClass.is(Case))  // scala2 compatibility
     || unapplySeqTypeElemTp(unappResult).exists // only for unapplySeq
-    || isProductMatch(unappResult, argLen)
+    || isProductMatch(unappResult.stripNamedTuple, argLen)
     || extractorMemberType(unappResult, nme.isEmpty, NoSourcePosition) <:< ConstantType(Constant(false))
     || unappResult.derivesFrom(defn.NonEmptyTupleClass)
     || unapp.symbol == defn.TupleXXL_unapplySeq // Fixes TupleXXL.unapplySeq which returns Some but declares Option

tests/warn/i22899.scala

@@ -0,0 +1,27 @@
+case class CaseClass(a: Int)
+
+object ProductMatch_CaseClass {
+  def unapply(int: Int): CaseClass = CaseClass(int)
+}
+
+object ProductMatch_NamedTuple {
+  def unapply(int: Int): (a: Int) = (a = int)
+}
+
+object NameBasedMatch_CaseClass {
+  def unapply(int: Int): Some[CaseClass] = Some(CaseClass(int))
+}
+
+object NameBasedMatch_NamedTuple {
+  def unapply(int: Int): Some[(a: Int)] = Some((a = int))
+}
+
+object Test {
+  val ProductMatch_CaseClass(a = x1) = 1    // ok, was pattern's type (x1 : Int) is more specialized than the right hand side expression's type Int
+  val ProductMatch_NamedTuple(a = x2) = 2   // ok, was pattern binding uses refutable extractor `org.test.ProductMatch_NamedTuple`
+  val NameBasedMatch_CaseClass(a = x3) = 3  // ok, was pattern's type (x3 : Int) is more specialized than the right hand side expression's type Int
+  val NameBasedMatch_NamedTuple(a = x4) = 4 // ok, was pattern's type (x4 : Int) is more specialized than the right hand side expression's type Int
+
+  val CaseClass(a = x5) = CaseClass(5)      // ok, was pattern's type (x5 : Int) is more specialized than the right hand side expression's type Int
+  val (a = x6) = (a = 6)                    // ok
+}