Clang flag -Wmissing-format-attribute doesn't catch missing attributes

[jstengleingithub]

GCC has a valuable flag -Wmissing-format-attribute which shows functions missing a format attribute. While Clang supports this flag, it currently doesn't do anything.
Code:

#include <stddef.h>
#include <string.h>
#include <stdarg.h>
#include <stdio.h>
void safe_snprintf(char *outstring, const size_t length, const char *format, ... /* args */);
void safe_snprintf(char *outstring, const size_t length, const char *format, ... /* args */)
{
    va_list args;
    va_start(args, format);
    if ((outstring != NULL) && (length > 0)) {
        vsnprintf(outstring, length, format, args);
        outstring[length - 1] = 0;
    }
    va_end(args);
}

GCC warning:

$ gcc -c -Wmissing-format-attribute test.c
test.c: In function 'safe_snprintf':
test.c:18:9: warning: function 'safe_snprintf' might be a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
         vsnprintf(outstring, length, format, args);
         ^~~~~~~~~
$ gcc --version
gcc (GCC) 8.4.1 20200928 (Red Hat 8.4.1-1)

Clang supports the flag but finds no issue:

$ ./clang -Wmissing-format-attribute -c ../../test.c
(no warning)
$ ./clang --version
Clang version 17.0.0  6ac13a798adae9a40023200dcaa6ed2e9fd9033a)