Imported Upstream version 5.10.0.47

Former-commit-id: d0813289fa2d35e1f8ed77530acb4fb1df441bc0

mcs/errors/cs8178-2.cs

@@ -0,0 +1,20 @@
+// CS8178: `await' cannot be used in an expression containing a call to `X.this[int]' because it returns by reference
+// Line: 12
+
+using System.Threading.Tasks;
+
+class X
+{
+	int x;
+
+	async Task Test ()
+	{
+		Foo (ref this [await Task.FromResult (1)]);
+	}
+
+	ref int this [int arg] => ref x;
+
+	static void Foo (ref int arg)
+	{
+	}
+}