Fix #8933: Fix eta expansion when comparing hk types

Author: odersky

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

@@ -497,7 +497,7 @@ class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] w
             if (base.typeSymbol == cls2) return true
           }
           else if tp1.isLambdaSub && !tp1.isAnyKind then
-            return recur(tp1, EtaExpansion(cls2.typeRef))
+            return recur(tp1, EtaExpansion(tp2))
         fourthTry
     }
 

tests/pos/i8933.scala

@@ -0,0 +1,15 @@
+trait Foo[F[_]]
+
+trait Top {
+  type F[X]
+  def foo: Foo[F]
+}
+
+trait Left extends Top
+
+trait Right extends Top {
+  trait F[X]
+  def foo: Foo[F] = new Foo[F] {}
+}
+
+class Bottom extends Left with Right