[clang] [BitInt] Expose a _BitInt literal suffix in C++ (PR #86586)

[Richard Smith via cfe-commits]

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@@ -1117,19 +1118,37 @@ NumericLiteralParser::NumericLiteralParser(StringRef TokSpelling,
       if (isImaginary) break;   // Cannot be repeated.
       isImaginary = true;
       continue;  // Success.
+    case '_':
+      if (isFPConstant)
+        break; // Invalid for floats
+      if (HasSize)
+        break;
+      if (possibleBitInt)
+        break; // Cannot be repeated.
+      if (LangOpts.CPlusPlus && s[1] == '_') {
+        // Scan ahead to find possible rest of BitInt suffix
+        for (const char *c = s; c != ThisTokEnd; ++c) {
+          if (*c == 'w' || *c == 'W') {
+            possibleBitInt = true;
+            ++s;
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zygoloid wrote:

FYI, per CWG1810 / [over.literal]/1, it's now IFNDR rather than UB:

> Some literal suffix identifiers are reserved for future standardization; see [usrlit.suffix]. A declaration whose literal-operator-id uses such a literal suffix identifier is ill-formed, no diagnostic required.

... but that doesn't make a difference here. (The "NDR" part is just to allow implementations to permit the standard library to declare these literal operators.)

https://github.com/llvm/llvm-project/pull/86586