Imported Upstream version 5.10.0.71

Former-commit-id: 65f7f4344e4c1c5e42628faefa5b9d36955387d1

mcs/errors/cs1644-59.cs

@@ -0,0 +1,13 @@
+// CS1644: Feature `readonly references' cannot be used because it is not part of the C# 7.0 language specification
+// Line: 9
+// Compiler options: -langversion:7
+
+class X
+{
+	int i;
+
+	ref readonly int Test ()
+	{
+		return ref i;
+	}
+}