Imported Upstream version 5.8.0.22

Former-commit-id: df344e34b07851d296efb3e6604c8db42b6f7aa3

mcs/tests/test-pattern-09.cs

@@ -0,0 +1,33 @@
+using System.Collections.Generic;
+
+class Expr
+{
+	public int Field;
+}
+
+static class X
+{
+	public static IEnumerable<int> Test (Expr expr)
+	{
+		object exprCur = expr;
+		if (exprCur is Expr list) {
+			yield return list.Field;
+		}
+	}
+
+	public static IEnumerable<string> Test2 (int? expr)
+	{
+		int? exprCur = expr;
+		while (exprCur != null) {
+			if (exprCur is int list) {
+				yield return list.ToString ();
+			}
+		}
+	}	
+
+	public static void Main ()
+	{
+		Test (null);
+		Test2 (3);
+	}
+}