add extra default visibility testcase

- also catches a small error for no clauses edge case

Author: inbelic

clang/lib/Parse/ParseHLSLRootSignature.cpp

@@ -219,7 +219,7 @@ bool RootSignatureParser::ParseDescriptorTable() {
     HasComma = !TryConsumeExpectedToken(TokenKind::pu_comma);
   }
 
-  if (HasComma)
+  if (HasComma && Table.NumClauses != 0)
     return ReportError(); // report 'comma' denotes a required extra item
 
   if (ConsumeExpectedToken(TokenKind::pu_r_paren))

clang/unittests/Parse/ParseHLSLRootSignatureTest.cpp

@@ -142,7 +142,8 @@ TEST_F(ParseHLSLRootSignatureTest, ParseValidDTClausesTest) {
               | Descriptors_Static_Keeping_Buffer_Bounds_Checks
       ),
       visibility = Shader_Visibility_Pixel
-    )
+    ),
+    DescriptorTable()
   )cc";
 
   TrivialModuleLoader ModLoader;
@@ -158,7 +159,7 @@ TEST_F(ParseHLSLRootSignatureTest, ParseValidDTClausesTest) {
   RootSignatureParser Parser(Elements, Tokens);
 
   ASSERT_FALSE(Parser.Parse());
-  ASSERT_EQ((int)Elements.size(), 5);
+  ASSERT_EQ((int)Elements.size(), 6);
 
   // Test default values are set correctly
   RootElement Elem = Elements[0];
@@ -212,6 +213,12 @@ TEST_F(ParseHLSLRootSignatureTest, ParseValidDTClausesTest) {
   ASSERT_EQ(Elem.Table.NumClauses, (uint32_t)4);
   ASSERT_EQ(Elem.Table.Visibility, ShaderVisibility::Pixel);
 
+  // Test generated DescriptorTable start has correct default values
+  Elem = Elements[5];
+  ASSERT_EQ(Elem.Tag, RootElement::ElementType::DescriptorTable);
+  ASSERT_EQ(Elem.Table.NumClauses, (uint32_t)0);
+  ASSERT_EQ(Elem.Table.Visibility, ShaderVisibility::All);
+
   delete PP;
 }