[clang] [Clang][Lex] Implement CWG3013: Error if #embed parameters were defined as macros (PR #224769)

[Mariya Podchishchaeva via cfe-commits]

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@@ -922,6 +928,24 @@ bool Preprocessor::HandleIdentifier(Token &Identifier) {
   if (const MacroDefinition MD = getMacroDefinition(&II)) {
     const auto *MI = MD.getMacroInfo();
     assert(MI && "macro definition with no macro info?");
+    // C++ [cpp.pre]/p4, [cpp.cond]/p9: if one of the pp-tokens of a #embed
+    // directive (or a has-embed-expression) is the identifier limit, prefix,
+    // suffix, or if_empty and that identifier is defined as a macro, the
+    // program is ill-formed.
+    //
+    // Thus, do not continue processing if compiling for C++. C doesn't have
+    // this restriction however, so only issue a warning for C if -Wc++-compat
+    // is enabled.
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Fznamznon wrote:

I find it weird that C++ diverges from C anyhow for a feature that new. Does it actually? That is not good

https://github.com/llvm/llvm-project/pull/224769