[clang] [HLSL][RootSignature] Implement Lexing of DescriptorTables (PR #122981)

[Chris B via cfe-commits]

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@@ -0,0 +1,194 @@
+#include "clang/Parse/ParseHLSLRootSignature.h"
+
+namespace clang {
+namespace hlsl {
+
+// Lexer Definitions
+
+static bool IsNumberChar(char C) {
+  // TODO(#126565): extend for float support exponents
+  return isdigit(C); // integer support
+}
+
+bool RootSignatureLexer::LexNumber(RootSignatureToken &Result) {
+  // NumericLiteralParser does not handle the sign so we will manually apply it
+  bool Negative = Buffer.front() == '-';
+  bool Signed = Negative || Buffer.front() == '+';
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llvm-beanz wrote:

I have a grammar question here. Is the `-` or `+` part of the numeric literal token, or is it better (as in C++), that the unary operator be its own token? The reason I ask, is that if you look at the C++ (& HLSL) grammar leading `-` is a unary operator, _not_ part of the numeric literal token string. This is why the Clang parser really only supports parsing positive numbers, the negation is a modifier.

Where this becomes relevant is a few lines below where you emit the `err_hlsl_expected_number_literal`, that's really an error that should be coming from _parsing_ not lexing because you're combining adjacent tokens and recognizing that the grammar requires a number follow the sign token.

https://github.com/llvm/llvm-project/pull/122981