Merge pull request #8475 from dotty-staging/fix-#5699

Fix #5699: Add regression test

Author: liufengyun

tests/pos/i5699.scala

@@ -0,0 +1,5 @@
+def test = {
+  type M = { type T[+A] } & { type T[-A] }
+  val M: M = ().asInstanceOf[M]
+  M: M
+}