[HLSL][RootSignature] Handle an empty root signature

- Define the Parser struct
- Model RootElements as a variant of the different types
- Create a basic test case for unit testing

Author: inbelic

clang/include/clang/Parse/ParseHLSLRootSignature.h

@@ -22,6 +22,8 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
 
+#include "llvm/Frontend/HLSL/HLSLRootSignature.h"
+
 namespace clang {
 namespace hlsl {
 
@@ -93,6 +95,27 @@ 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:
+  SmallVector<llvm::hlsl::rootsig::RootElement> &Elements;
+  RootSignatureLexer &Lexer;
+  DiagnosticsEngine &Diags;
+
+  RootSignatureToken CurToken;
+};
+
 } // namespace hlsl
 } // namespace clang
 

clang/lib/Parse/ParseHLSLRootSignature.cpp

@@ -1,5 +1,7 @@
 #include "clang/Parse/ParseHLSLRootSignature.h"
 
+using namespace llvm::hlsl::rootsig;
+
 namespace clang {
 namespace hlsl {
 
@@ -168,5 +170,20 @@ std::optional<RootSignatureToken> RootSignatureLexer::PeekNextToken() {
   return Result;
 }
 
+// Parser Definitions
+
+RootSignatureParser::RootSignatureParser(SmallVector<RootElement> &Elements,
+                                         RootSignatureLexer &Lexer,
+                                         DiagnosticsEngine &Diags)
+    : Elements(Elements), Lexer(Lexer), Diags(Diags) {}
+
+bool RootSignatureParser::Parse() {
+  // Handle edge-case of empty RootSignature()
+  if (Lexer.EndOfBuffer())
+    return false;
+
+  return true;
+}
+
 } // namespace hlsl
 } // namespace clang

clang/unittests/Parse/ParseHLSLRootSignatureTest.cpp

@@ -24,6 +24,7 @@
 #include "gtest/gtest.h"
 
 using namespace clang;
+using namespace llvm::hlsl::rootsig;
 
 namespace {
 
@@ -312,4 +313,26 @@ TEST_F(ParseHLSLRootSignatureTest, InvalidLexRegNumberTest) {
   ASSERT_FALSE(Consumer->IsSatisfied());
 }
 
+// Valid Parser Tests
+
+TEST_F(ParseHLSLRootSignatureTest, ValidParseEmptyTest) {
+  const llvm::StringLiteral Source = R"cc()cc";
+
+  TrivialModuleLoader ModLoader;
+  auto PP = CreatePP(Source, ModLoader);
+  auto TokLoc = SourceLocation();
+
+  hlsl::RootSignatureLexer Lexer(Source, TokLoc, *PP);
+  SmallVector<RootElement> Elements;
+  hlsl::RootSignatureParser Parser(Elements, Lexer, Diags);
+
+  // Test no diagnostics produced
+  Consumer->SetNoDiag();
+
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ((int)Elements.size(), 0);
+
+  ASSERT_TRUE(Consumer->IsSatisfied());
+}
+
 } // anonymous namespace

llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h

@@ -0,0 +1,30 @@
+//===- HLSLRootSignature.h - HLSL Root Signature helper objects -----------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file This file contains helper objects for working with HLSL Root
+/// Signatures.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_FRONTEND_HLSL_HLSLROOTSIGNATURE_H
+#define LLVM_FRONTEND_HLSL_HLSLROOTSIGNATURE_H
+
+#include <variant>
+
+namespace llvm {
+namespace hlsl {
+namespace rootsig {
+
+// Models RootElement
+using RootElement = std::variant<std::monostate>;
+
+} // namespace rootsig
+} // namespace hlsl
+} // namespace llvm
+
+#endif // LLVM_FRONTEND_HLSL_HLSLROOTSIGNATURE_H