[clang] [clang][Parser] Warn when the body of expansion statement is not a compound statement (PR #209229)

[via cfe-commits]

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@@ -457,6 +457,9 @@ def err_expansion_stmt_requires_cxx2c : Error<
   "expansion statements are only supported in C++2c">;
 def err_for_template : Error<
   "'for template' is invalid; use 'template for' instead">;
+def ext_expansion_stmt_requires_braced_body : ExtWarn<
+  "ISO C++ requires a compound statement to be the body of expansion statement">,
+  InGroup<DiagGroup<"expansion-stmt-braced-body">>, DefaultIgnore;
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Sirraide wrote:

Isn’t `ExtWarn<>` + `DefaultIgnore` just `Extension<>`?

https://github.com/llvm/llvm-project/pull/209229