nfc: improve error message for non-zero flag diagnostic

- we shouldn't pass in a string to the diagnostic, instead we should
define the string properly and provide better context

Author: inbelic

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -1856,5 +1856,6 @@ def err_hlsl_unexpected_end_of_params
 def err_hlsl_rootsig_repeat_param : Error<"specified the same parameter '%0' multiple times">;
 def err_hlsl_rootsig_missing_param : Error<"did not specify mandatory parameter '%0'">;
 def err_hlsl_number_literal_overflow : Error<"integer literal is too large to be represented as a 32-bit %select{signed |}0 integer type">;
+def err_hlsl_rootsig_non_zero_flag : Error<"non-zero integer literal specified for flag value">;
 
 } // end of Parser diagnostics

clang/lib/Parse/ParseHLSLRootSignature.cpp

@@ -76,7 +76,7 @@ std::optional<RootFlags> RootSignatureParser::parseRootFlags() {
   // Handle the edge-case of '0' to specify no flags set
   if (tryConsumeExpectedToken(TokenKind::int_literal)) {
     if (!verifyZeroFlag()) {
-      getDiags().Report(CurToken.TokLoc, diag::err_expected) << "'0'";
+      getDiags().Report(CurToken.TokLoc, diag::err_hlsl_rootsig_non_zero_flag);
       return std::nullopt;
     }
   } else {
@@ -538,7 +538,7 @@ RootSignatureParser::parseDescriptorRangeFlags() {
   // Handle the edge-case of '0' to specify no flags set
   if (tryConsumeExpectedToken(TokenKind::int_literal)) {
     if (!verifyZeroFlag()) {
-      getDiags().Report(CurToken.TokLoc, diag::err_expected) << "'0'";
+      getDiags().Report(CurToken.TokLoc, diag::err_hlsl_rootsig_non_zero_flag);
       return std::nullopt;
     }
     return DescriptorRangeFlags::None;

clang/unittests/Parse/ParseHLSLRootSignatureTest.cpp

@@ -616,7 +616,7 @@ TEST_F(ParseHLSLRootSignatureTest, InvalidNonZeroFlagsTest) {
   hlsl::RootSignatureParser Parser(Elements, Lexer, *PP);
 
   // Test correct diagnostic produced
-  Consumer->setExpected(diag::err_expected);
+  Consumer->setExpected(diag::err_hlsl_rootsig_non_zero_flag);
   ASSERT_TRUE(Parser.parse());
 
   ASSERT_TRUE(Consumer->isSatisfied());