[HLSL][RootSignature] Make keywords case-insensitive

- from dxc testing, it was shown that keywords could be specified in a
case-insensitive manner. the current implementation was case sensitive

Author: Finn Plummer

clang/lib/Lex/LexHLSLRootSignature.cpp

@@ -95,7 +95,7 @@ RootSignatureToken RootSignatureLexer::LexToken() {
 
   // Define a large string switch statement for all the keywords and enums
   auto Switch = llvm::StringSwitch<TokenKind>(TokSpelling);
-#define KEYWORD(NAME) Switch.Case(#NAME, TokenKind::kw_##NAME);
+#define KEYWORD(NAME) Switch.CaseLower(#NAME, TokenKind::kw_##NAME);
 #define ENUM(NAME, LIT) Switch.CaseLower(LIT, TokenKind::en_##NAME);
 #include "clang/Lex/HLSLRootSignatureTokenKinds.def"
 

clang/unittests/Lex/LexHLSLRootSignatureTest.cpp

@@ -120,6 +120,36 @@ TEST_F(LexHLSLRootSignatureTest, ValidLexAllTokensTest) {
   CheckTokens(Lexer, Tokens, Expected);
 }
 
+TEST_F(LexHLSLRootSignatureTest, ValidCaseInsensitiveKeywordsTest) {
+  // This test will check that we can lex keywords in an case-insensitive
+  // manner
+  const llvm::StringLiteral Source = R"cc(
+    DeScRiPtOrTaBlE
+
+    CBV srv UAV sampler
+    SPACE visibility FLAGS
+    numDescriptors OFFSET
+  )cc";
+  auto TokLoc = SourceLocation();
+  hlsl::RootSignatureLexer Lexer(Source, TokLoc);
+
+  SmallVector<hlsl::RootSignatureToken> Tokens;
+  SmallVector<hlsl::TokenKind> Expected = {
+      hlsl::TokenKind::kw_DescriptorTable,
+      hlsl::TokenKind::kw_CBV,
+      hlsl::TokenKind::kw_SRV,
+      hlsl::TokenKind::kw_UAV,
+      hlsl::TokenKind::kw_Sampler,
+      hlsl::TokenKind::kw_space,
+      hlsl::TokenKind::kw_visibility,
+      hlsl::TokenKind::kw_flags,
+      hlsl::TokenKind::kw_numDescriptors,
+      hlsl::TokenKind::kw_offset,
+  };
+
+  CheckTokens(Lexer, Tokens, Expected);
+}
+
 TEST_F(LexHLSLRootSignatureTest, ValidLexPeekTest) {
   // This test will check that we the peek api is correctly used
   const llvm::StringLiteral Source = R"cc(