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

[via cfe-commits]

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@@ -1117,6 +1118,31 @@ 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 (DoubleUnderscore)
+        break; // Cannot be repeated.
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Sirraide wrote:

This is presumably because there currently is only one suffix that uses the `DoubleUnderscore` flag, so the other flags that also get set when `__wb` is parsed (e.g. `HasSize`) would be enough to disallow repetition here, from what I can tell. I’d still keep `DoubleUnderscore` in case we decide to add more literal suffixes that contain double underscores.

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