Use cached underlyingMatchType when normalizing applied match aliases

Also fixes underlyingMatchType to not use the resType of HKTypeLambdas
It should only be in `isMatch` used for `AliasingBounds`, not `isMatchAlias`

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

@@ -491,12 +491,10 @@ object Types extends TypeUtils {
     /** Does this application expand to a match type? */
     def isMatchAlias(using Context): Boolean = underlyingMatchType.exists
 
-    def underlyingMatchType(using Context): Type = stripped match {
+    def underlyingMatchType(using Context): Type = stripped match
       case tp: MatchType => tp
-      case tp: HKTypeLambda => tp.resType.underlyingMatchType
       case tp: AppliedType => tp.underlyingMatchType
       case _ => NoType
-    }
 
     /** Is this a higher-kinded type lambda with given parameter variances?
      *  These lambdas are used as the RHS of higher-kinded abstract types or
@@ -4681,35 +4679,23 @@ object Types extends TypeUtils {
 
     /** Exists if the tycon is a TypeRef of an alias with an underlying match type.
      *  Anything else should have already been reduced in `appliedTo` by the TypeAssigner.
+     *  May reduce several HKTypeLambda applications before the underlying MatchType is reached.
      */
     override def underlyingMatchType(using Context): Type =
       if ctx.period != validUnderlyingMatch then
         cachedUnderlyingMatch = superType.underlyingMatchType
         validUnderlyingMatch = validSuper
       cachedUnderlyingMatch
 
-    override def tryNormalize(using Context): Type = tycon.stripTypeVar match {
-      case tycon: TypeRef =>
-        def tryMatchAlias = tycon.info match
-          case AliasingBounds(alias) if isMatchAlias =>
-            trace(i"normalize $this", typr, show = true) {
-              MatchTypeTrace.recurseWith(this) {
-                alias.applyIfParameterized(args).tryNormalize
-                /* `applyIfParameterized` may reduce several HKTypeLambda applications
-                 * before the underlying MatchType is reached.
-                 * Even if they do not involve any match type normalizations yet,
-                 * we still want to record these reductions in the MatchTypeTrace.
-                 * They should however only be attempted if they eventually expand
-                 * to a match type, which is ensured by the `isMatchAlias` guard.
-                 */
-              }
-            }
-          case _ =>
-            NoType
-        tryCompiletimeConstantFold.orElse(tryMatchAlias)
-      case _ =>
-        NoType
-    }
+    override def tryNormalize(using Context): Type =
+      def tryMatchAlias =
+        if isMatchAlias then trace(i"normalize $this", typr, show = true):
+          if MatchTypeTrace.isRecording then
+            MatchTypeTrace.recurseWith(this)(superType.tryNormalize)
+          else
+            underlyingMatchType.tryNormalize
+        else NoType
+      tryCompiletimeConstantFold.orElse(tryMatchAlias)
 
     /** Is this an unreducible application to wildcard arguments?
      *  This is the case if tycon is higher-kinded. This means