Fix #7107: Avoid assertion that gets invalidated by illegal code

Author: odersky

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

@@ -1361,7 +1361,8 @@ object Types {
       case tp: TypeRef =>
         if (tp.info.isInstanceOf[TempClassInfo]) {
           tp.recomputeDenot()
-          assert(!tp.info.isInstanceOf[TempClassInfo])
+            // We usually should have `!tp.info.isInstanceOf[TempClassInfo]` here, but
+            // this can be falsified for code with illegal cyclic references. See neg/i7107.scala.
         }
         tp.info.parents
       case tp: TypeProxy =>

tests/neg/i7107.scala

@@ -0,0 +1,2 @@
+trait F[T] { type X }
+object Rec extends F[Rec.X] // error: X is not a member of Rec