review: add test to denote consistent comma behaviour

Author: inbelic

clang/test/SemaHLSL/RootSignature.hlsl

@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -x hlsl -fsyntax-only %s -verify
+
+// expected-no-diagnostics
+
+// Test that we have consistent behaviour for comma parsing. Namely:
+// - a single trailing comma is allowed after any parameter
+// - a trailing comma is not required
+
+[RootSignature("CBV(b0, flags = DATA_VOLATILE,), DescriptorTable(Sampler(s0,),),")]
+void maximum_commas() {}
+
+[RootSignature("CBV(b0, flags = DATA_VOLATILE), DescriptorTable(Sampler(s0))")]
+void minimal_commas() {}