Merge pull request #6306 from dotty-staging/fix-5101

Fix #5101: add test (fixed in #6001)

Author: liufengyun

tests/neg/i5101.check

@@ -0,0 +1,2 @@
+[137..139..142] in i5101.scala
+Not found: A0

tests/neg/i5101.scala

@@ -0,0 +1,14 @@
+object Bar {
+  trait A
+  case class A0(foo: Int) extends A
+}
+
+object Foo {
+  import Bar.A
+
+  def buzz(a: A) = {
+    a match {
+      case A0(_) =>     // error
+    }
+  }
+}