Consider aliases of Any as top

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

@@ -255,7 +255,7 @@ object Types extends TypeUtils {
     /** Is this type exactly `Any`, or a type lambda ending in `Any`? */
     def isTopOfSomeKind(using Context): Boolean = dealias match
       case tp: TypeLambda => tp.resType.isTopOfSomeKind
-      case _ => isExactlyAny
+      case _ => dealias.isExactlyAny
 
     def isBottomType(using Context): Boolean =
       if ctx.mode.is(Mode.SafeNulls) && !ctx.phase.erasedTypes then hasClassSymbol(defn.NothingClass)

tests/pos/i19610.min1.scala

@@ -0,0 +1,9 @@
+final case class Wrap[T <: U](first: A[T])(using A[T] <:< A[N])
+sealed trait A[+T]
+type U = Any
+type N = Nothing
+
+@main def main = {
+  // Error: Cannot prove that A[U] <:< A[N].
+  Wrap(new A[N] {})
+}

tests/pos/i19610.orig.scala

@@ -0,0 +1,12 @@
+// Error: Cannot prove that A[U] <:< A[N].
+def res1: Unit = Wrap(new A[N]{})
+
+// Adding the obvious type argument to Wrap makes it compile just fine.
+def res2: Unit = Wrap[N](new A[N]{})
+
+final case class Wrap[T <: U](first: A[T])(using A[T] <:< A[N])
+
+sealed trait A[+T]
+
+type U = Any
+type N = Nothing

tests/pos/i19610.scala

@@ -0,0 +1,14 @@
+type Top = Any
+type Bot = Nothing
+
+sealed trait Cov[+A]
+
+final case class Wrap1[B <: Top](first: Cov[B])(using Cov[B] <:< Cov[Bot])
+final case class Wrap2[B <: Any](first: Cov[B])(using Cov[B] <:< Cov[Bot])
+
+class Test:
+  def t10 = Wrap1/* */(new Cov[Bot] {}) // error: Cannot prove that Cov[Top] <:< Cov[Bot]
+  def t11 = Wrap1[Bot](new Cov[Bot] {}) // ok
+
+  def t20 = Wrap2/* */(new Cov[Bot] {}) // ok
+  def t21 = Wrap2[Bot](new Cov[Bot] {}) // ok