Switch to making baseType consider annotations

Author: dwijnand

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

@@ -2222,8 +2222,13 @@ object SymDenotations {
           case tp @ AppliedType(tycon, args) =>
             def computeApplied = {
               btrCache(tp) = NoPrefix
+              extension (tp: Type) def typeSymbol2: Symbol = tp match
+                case tp: TypeRef     => tp.symbol
+                case tp: TypeVar     => tp.underlying.typeSymbol2
+                case tp: AppliedType => tp.underlying.typeSymbol2
+                case _               => NoSymbol
               val baseTp =
-                if (tycon.typeSymbol eq symbol) tp
+                if (tycon.typeSymbol2 eq symbol) tp
                 else (tycon.typeParams: @unchecked) match {
                   case LambdaParam(_, _) :: _ =>
                     recur(tp.superType)

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

@@ -2402,7 +2402,7 @@ object Types {
 
     private def argDenot(param: TypeSymbol)(using Context): Denotation = {
       val cls = param.owner
-      val args = prefix.widenDealias.baseType(cls).argInfos
+      val args = prefix.baseType(cls).argInfos
       val typeParams = cls.typeParams
 
       def concretize(arg: Type, tparam: TypeSymbol) = arg match {

compiler/test/dotc/pos-test-pickling.blacklist

@@ -21,7 +21,6 @@ i15181.scala
 i15922.scala
 t5031_2.scala
 i16997.scala
-argDenot-alpakka.scala
 
 # Tree is huge and blows stack for printing Text
 i7034.scala