[clang] [Sema] -Wformat: warn about C23 %b %B when not in C23 language mode (PR #126694)

[Mariya Podchishchaeva via cfe-commits]

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@@ -0,0 +1,41 @@
+// RUN: %clang_cc1 -std=c17 -DPRE_C23 -fsyntax-only -verify -isystem %S/Inputs %s
+// RUN: %clang_cc1 -std=c23 -DPOST_C23 -fsyntax-only -verify -isystem %S/Inputs %s
+
+#include <stdarg.h>
+#include <stddef.h>
+
+int printf(const char *restrict, ...);
+
+#if PRE_C23
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Fznamznon wrote:

> Not sure what you mean a "compat warning". Do you mean that instead of saying "invalid conversion specifier 'b'" it should say something like "'b' is not valid before C23" or similar wording?

Something like this but please disregard this comment since I wasn't thinking about it being a problem of standard library when writing this. This https://github.com/llvm/llvm-project/pull/126694#issuecomment-2651125203 should be considered instead.

https://github.com/llvm/llvm-project/pull/126694