Call dealias after stripping type variables for tupleElementTypesUpTo

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

@@ -83,7 +83,8 @@ class TypeUtils:
           case _ =>
             if defn.isTupleClass(tp.typeSymbol) && !normalize then Some(tp.dealias.argInfos)
             else None
-      recur(self.stripTypeVar, bound)
+      val stripped = if normalize then self.stripTypeVar.dealias else self.stripTypeVar // keep error reporting aliased
+      recur(stripped, bound)
 
     /** Is this a generic tuple but not already an instance of one of Tuple1..22? */
     def isGenericTuple(using Context): Boolean =

tests/pos/i22643.scala

@@ -0,0 +1,48 @@
+import language.experimental.namedTuples
+
+
+
+object ExhibitB:
+
+  trait JoinB[A <: Tuple, B <: Tuple]:
+    type NTB = NamedTuple.NamedTuple[Tuple.Concat[A, B], (String, Int)]
+    val ntB: NTB = ???
+
+  val joinB: JoinB[Tuple1["nameB"], Tuple1["ageB"]] = ???
+
+  joinB.ntB.nameB    // works
+
+
+object ExhibitC:
+
+  type A = Tuple1["nameC"]
+  type B = Tuple1["ageC"]
+
+  type NamesC = Tuple.Concat[A, B]
+  type NTC = NamedTuple.NamedTuple[NamesC, (String, Int)]
+  val ntC: NTC = ???
+
+  ntC.nameC   // works
+
+
+object ExhibitD:
+
+  trait JoinD[A, B]:
+    type NamesD = (A, B)
+    type NTD = NamedTuple.NamedTuple[NamesD, (String, Int)]
+    val ntD: NTD = ???
+
+  val joinD: JoinD["nameD", "ageD"] = ???
+
+  joinD.ntD.nameD    // works
+
+object ExhibitA:
+
+  trait JoinA[A <: Tuple, B <: Tuple]:
+    type NamesA = Tuple.Concat[A, B]
+    type NTA = NamedTuple.NamedTuple[NamesA, (String, Int)]
+    val ntA: NTA = ???
+
+  val joinA: JoinA[Tuple1["nameA"], Tuple1["ageA"]] = ???
+
+  joinA.ntA.nameA    // fixed

tests/pos/i22645a.scala

@@ -0,0 +1,44 @@
+import language.experimental.namedTuples
+object ExhibitA:  //  fails
+
+  class SelectableNT[N <: Tuple] extends Selectable:
+    def selectDynamic(name: String) = ???
+    type Names = Tuple.Map[N, [X] =>> X]
+    type Fields = NamedTuple.NamedTuple[Names, (String, Int)]
+
+  val x = new SelectableNT[("name", "age")]
+  x.name  // fails
+
+
+object ExhibitB:  //  works
+
+  class SelectableNT[N <: Tuple] extends Selectable:
+    def selectDynamic(name: String) = ???
+    type Fields = NamedTuple.NamedTuple[N, (String, Int)]
+
+  val x = new SelectableNT[("name", "age")]
+  x.name
+
+
+object ExhibitC:  // works
+
+  class SelectableNT[N <: Tuple] extends Selectable:
+    def selectDynamic(name: String) = ???
+    type Fields = NamedTuple.NamedTuple[N, (String, Int)]
+
+  type N = ("name", "age")
+  val x = new SelectableNT[N]
+  x.name
+
+
+object ExhibitD:  // works
+
+  class SelectableNT[N <: Tuple] extends Selectable:
+    def selectDynamic(name: String) = ???
+    type Fields = NamedTuple.NamedTuple[N, (String, Int)]
+
+  type N = ("name", "age")
+  type Names = Tuple.Map[N, [X] =>> X]
+  val x = new SelectableNT[Names]
+  x.name
+