[clang] [clang] Catch missing format attributes (PR #70024)

[Aaron Puchert via cfe-commits]

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@@ -0,0 +1,143 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wmissing-format-attribute %s
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <uchar.h>
+#include <wchar.h>
+
+__attribute__((__format__ (__scanf__, 1, 4)))
+void f1(char *out, const size_t len, const char *format, ... /* args */)
+{
+    va_list args;
+    vsnprintf(out, len, format, args); // expected-warning {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f1'}}
+                                       // CHECK-FIXES: __attribute__((format(printf, 1, 4)))
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aaronpuchert wrote:

Shouldn't it be `__attribute__((format(printf, 3, 4)))`, since the format string is the third argument? The first argument is just the target buffer.

https://github.com/llvm/llvm-project/pull/70024