[clang] [llvm] [HLSL][RootSignature] Implement Parsing of Descriptor Tables (PR #122982)

[Finn Plummer via cfe-commits]

================
@@ -93,6 +96,108 @@ class RootSignatureLexer {
   }
 };
 
+class RootSignatureParser {
+public:
+  RootSignatureParser(SmallVector<llvm::hlsl::rootsig::RootElement> &Elements,
+                      RootSignatureLexer &Lexer, DiagnosticsEngine &Diags);
+
+  /// Iterates over the provided tokens and constructs the in-memory
+  /// representations of the RootElements.
+  ///
+  /// The return value denotes if there was a failure and the method will
+  /// return on the first encountered failure, or, return false if it
+  /// can sucessfully reach the end of the tokens.
+  bool Parse();
+
+private:
+  // Root Element helpers
+  bool ParseRootElement();
+  bool ParseDescriptorTable();
+  bool ParseDescriptorTableClause();
+
+  /// Helper dispatch method
+  ///
+  /// These will switch on the Variant kind to dispatch to the respective Parse
+  /// method and store the parsed value back into Ref.
+  ///
+  /// It is helpful to have a generalized dispatch method so that when we need
+  /// to parse multiple optional parameters in any order, we can invoke this
+  /// method
+  bool ParseParam(llvm::hlsl::rootsig::ParamType Ref);
+
+  // Parse as many optional parameters as possible in any order
+  bool ParseOptionalParams(
+      llvm::SmallDenseMap<TokenKind, llvm::hlsl::rootsig::ParamType> &RefMap);
+
+  // Common parsing helpers
----------------
inbelic wrote:

I restructured the comments a bit so I don't think this applies anymore.

https://github.com/llvm/llvm-project/pull/122982