Fix #16654 and partially fix #16583

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -1007,7 +1007,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
       case tp1: MatchType =>
         def compareMatch = tp2 match {
           case tp2: MatchType =>
-            isSameType(tp1.scrutinee, tp2.scrutinee) &&
+            isSameType(tp1.scrutinee.widenSkolem, tp2.scrutinee.widenSkolem) &&
             tp1.cases.corresponds(tp2.cases)(isSubType)
           case _ => false
         }

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1373,7 +1373,7 @@ object Types {
           Atoms.Range(set, set)
         else Atoms.Unknown
 
-      dealias match
+      dealias.normalized match
         case tp: SingletonType =>
           tp.underlying.atoms match
             case as @ Atoms.Range(lo, hi) =>
@@ -1456,7 +1456,7 @@ object Types {
       deskolemizer(this)
 
     /** The result of normalization using `tryNormalize`, or the type itself if
-     *  tryNormlize yields NoType
+     *  tryNormalize yields NoType
      */
     final def normalized(using Context): Type = {
       val normed = tryNormalize
@@ -4478,7 +4478,15 @@ object Types {
           case MatchAlias(alias) =>
             trace(i"normalize $this", typr, show = true) {
               MatchTypeTrace.recurseWith(this) {
-                alias.applyIfParameterized(args.map(_.normalized)).tryNormalize
+                alias.applyIfParameterized(args.map(_.normalized)) match
+                  case mt @ MatchType(bound, scrutinee, cases) =>
+                    val scrutinee1 = scrutinee.widenSkolem
+                    if scrutinee1 ne scrutinee then
+                      mt.derivedMatchType(bound, scrutinee.widenSkolem, cases).normalized
+                    else
+                      mt.tryNormalize
+                  case mt =>
+                    mt.tryNormalize
               }
             }
           case _ =>
@@ -4946,7 +4954,7 @@ object Types {
           trace(i"reduce match type $this $hashCode", matchTypes, show = true) {
             def matchCases(cmp: TrackingTypeComparer): Type =
               val saved = ctx.typerState.snapshot()
-              try cmp.matchCases(scrutinee.normalized, cases)
+              try cmp.matchCases(scrutinee.normalized.widenSkolem, cases)
               catch case ex: Throwable =>
                 handleRecursive("reduce type ", i"$scrutinee match ...", ex)
               finally
@@ -6045,7 +6053,7 @@ object Types {
         case _ =>
           if args.exists(isRange) then
             if variance > 0 then
-              tp.derivedAppliedType(tycon, args.map(rangeToBounds)) match
+              tp.derivedAppliedType(tycon, args.map(rangeToBounds))(using ctx.addMode(Mode.AllowLambdaWildcardApply)) match
                 case tp1: AppliedType if tp1.isUnreducibleWild && ctx.phase != checkCapturesPhase =>
                   // don't infer a type that would trigger an error later in
                   // Checking.checkAppliedType; fall through to default handling instead

tests/pos/16583.scala

@@ -0,0 +1,15 @@
+import scala.compiletime.constValueTuple
+
+val ll0: Tuple3["one", "two", "three"] = constValueTuple[("one", "two", "three")]
+val ll1 = constValueTuple[("one", "two", "three")].toList
+val ll3: List["one" | ("two" | ("three" | Nothing))] = constValueTuple[("one", "two", "three")].toList
+val ll4: List["one" | ("two" | "three")] = constValueTuple[("one", "two", "three")].toList
+
+inline def labels[Labels <: Tuple](using ev: Tuple.Union[Labels] <:< String): List[String] =
+  val tmp = constValueTuple[Labels].toList
+  ev.substituteCo( tmp )
+
+def test = labels[("one", "two", "three")]
+
+def toList(x: Tuple): List[Tuple.Union[x.type]] = ???
+def test2[Labels <: Tuple] = toList((???): Labels)

tests/pos/16654.scala

@@ -0,0 +1,7 @@
+def toCsvFlat[A <: Product](a: A)(using m: scala.deriving.Mirror.ProductOf[A]) = {
+  def flatTuple(any: Any): Tuple = any match
+    case p: Product => p.productIterator.map(flatTuple).foldLeft(EmptyTuple: Tuple)(_ ++ _)
+    case a          => Tuple1(a)
+
+  val tuple = flatTuple(Tuple.fromProductTyped(a)).toList
+}