nfc: provide reportDiag helper and simplify diagnostics

Author: inbelic

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -1857,8 +1857,6 @@ def err_hlsl_virtual_inheritance
     : Error<"virtual inheritance is unsupported in HLSL">;
 
 // HLSL Root Signature Parser Diagnostics
-def err_hlsl_unexpected_end_of_params
-    : Error<"expected %0 to denote end of parameters, or, another valid parameter of %1">;
 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<

clang/include/clang/Parse/ParseHLSLRootSignature.h

@@ -178,8 +178,8 @@ class RootSignatureParser {
   ///
   /// Returns true if there was an error reported.
   bool consumeExpectedToken(
-      RootSignatureToken::Kind Expected, unsigned DiagID = diag::err_expected,
-      RootSignatureToken::Kind Context = RootSignatureToken::Kind::invalid);
+      RootSignatureToken::Kind Expected,
+      std::optional<RootSignatureToken::Kind> Context = std::nullopt);
 
   /// Peek if the next token is of the expected kind and if it is then consume
   /// it.
@@ -195,6 +195,13 @@ class RootSignatureParser {
   /// StringLiterals
   SourceLocation getTokenLocation(RootSignatureToken Tok);
 
+  DiagnosticBuilder
+  reportDiag(unsigned DiagID,
+             std::optional<RootSignatureToken> Context = std::nullopt) {
+    RootSignatureToken Tok = Context.has_value() ? *Context : CurToken;
+    return getDiags().Report(getTokenLocation(Tok), DiagID);
+  }
+
 private:
   llvm::dxbc::RootSignatureVersion Version;
   SmallVector<RootSignatureElement> &Elements;