Fix #6322: normalize types in baseType

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

@@ -1751,9 +1751,11 @@ object SymDenotations {
           Stats.record("computeBaseType, total")
           Stats.record(s"computeBaseType, ${tp.getClass}")
         }
+        val normed = tp.tryNormalize
+        if (normed.exists) return recur(normed)
+
         tp match {
           case tp @ TypeRef(prefix, _) =>
-
             def foldGlb(bt: Type, ps: List[Type]): Type = ps match {
               case p :: ps1 => foldGlb(bt & recur(p), ps1)
               case _ => bt
@@ -1794,7 +1796,6 @@ object SymDenotations {
             computeTypeRef
 
           case tp @ AppliedType(tycon, args) =>
-
             def computeApplied = {
               btrCache.put(tp, NoPrefix)
               val baseTp =
@@ -1812,8 +1813,8 @@ object SymDenotations {
 
           case tp: TypeParamRef =>  // uncachable, since baseType depends on context bounds
             recur(ctx.typeComparer.bounds(tp).hi)
-          case tp: TypeProxy =>
 
+          case tp: TypeProxy =>
             def computeTypeProxy = {
               val superTp = tp.superType
               val baseTp = recur(superTp)
@@ -1827,7 +1828,6 @@ object SymDenotations {
             computeTypeProxy
 
           case tp: AndOrType =>
-
             def computeAndOrType = {
               val tp1 = tp.tp1
               val tp2 = tp.tp2
@@ -1851,6 +1851,7 @@ object SymDenotations {
 
           case JavaArrayType(_) if symbol == defn.ObjectClass =>
             this.typeRef
+
           case _ =>
             NoType
         }

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

@@ -1,12 +1,15 @@
 i1812.scala
 i1867.scala
 i3067.scala
-matchtype.scala
 t247.scala
 t2712-5.scala
 t284-pos.scala
 t3249
 t3486
 t3612.scala
-typelevel0.scala
 reference
+
+# Match types
+typelevel0.scala
+matchtype.scala
+6322.scala

tests/pos/6322.scala

@@ -0,0 +1,24 @@
+object Test {
+  final class A
+  final class B
+  final class C
+
+  trait F1[T1] {
+    def apply(x: T1): Unit
+  }
+
+  type F[N] = N match {
+    case A => F1[String]
+    case B => F[A]
+    case C => F[B]
+  }
+
+  val s1: F[A] = ???
+  s1.apply("A")
+
+  val s2: F[B] = ???
+  s2.apply("B")
+
+  val s3: F[C] = ???
+  s3.apply("C")
+}