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

[Daniel Rodríguez Troitiño 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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drodriguez wrote:

I did not know about those options. I will try to change the test to work like that.

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?

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