Imported Upstream version 3.6.0

Former-commit-id: da6be194a6b1221998fc28233f2503bd61dd9d14

mcs/errors/cs0609.cs

@@ -0,0 +1,22 @@
+// CS0609: Cannot set the `IndexerName' attribute on an indexer marked override
+// Line: 15
+
+using System.Runtime.CompilerServices;
+
+class BaseClass {
+        protected virtual bool this[int index] {
+                get {
+                        return true;
+                }
+        }
+}
+
+class DerivedClass: BaseClass {
+        [IndexerName("Error")]
+        protected override bool this[int index] {
+                get {
+                        return false;
+                }
+        }
+}
+