[clang] [Clang] allow `` `@$ `` in raw string delimiters in C++26 (PR #93216)

[Richard Smith via cfe-commits]

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@@ -2261,8 +2261,17 @@ bool Lexer::LexRawStringLiteral(Token &Result, const char *CurPtr,
 
   unsigned PrefixLen = 0;
 
-  while (PrefixLen != 16 && isRawStringDelimBody(CurPtr[PrefixLen]))
+  while (PrefixLen != 16 && isRawStringDelimBody(CurPtr[PrefixLen])) {
     ++PrefixLen;
+    if (!isLexingRawMode() &&
+        llvm::is_contained({'$', '@', '`'}, CurPtr[PrefixLen])) {
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zygoloid wrote:

There's an off-by-one error here: we're incrementing `PrefixLen` before checking the character, so this is checking the character *after* the one we just processed. Hence we don't diagnose `"@(foo)@"`, because the characters we look at are the `(` and `"` after the `@`s, not the `@`s themselves.

https://github.com/llvm/llvm-project/pull/93216