Re: [PATCH] Fix Werror=format-diag with --disable-nls.

[Martin Sebor <msebor@gmail.com>]

On 1/20/22 10:03, Jakub Jelinek wrote:
> On Thu, Jan 20, 2022 at 09:56:59AM -0700, Martin Sebor wrote:
>>> With normal -Wformat I see all expected warnings in:
>>> char *foo (const char *) __attribute__((format_arg(1)));
>>> void bar (const char *, ...) __attribute__((format(printf, 1, 2)));
>>
>> -Wformat-diag is internal to GCC and needs one of the GCC-internal
>> attributes to enable, like __gcc_cxxdiag__, for example like this:
>>
>>    __attribute__ ((format (__gcc_cxxdiag__, 1, 2)))
>>    void bar (const char *, ...);
>>
>> With that it triggers in all the same instances as -Wformat below
>> (as near I can tell for a modified test case).
> 
> Glad to hear that, but then I don't understand why we didn't warn on
> cp/error.cc before Martin L.'s change when --disable-nls wasn't used.

Good question!  There does seem to be some strange interplay between
parentheses and -Wformat for __gcc_cdiag__ functions in the C++ front
end:

__attribute__ ((format (__gcc_cxxdiag__, 1, 2)))
void bar (const char *, ...);

void
baz (int x)
{
   bar (x ? "<%s" : "%i", x);           // -Wformat-diag
   bar ((x ? "<%s" : "%i"), x);         // silence
   bar ((x ? ("<%s") : ("%i")), x);     // silence
}

The C front end warns on all three calls.

With attribute printf both the C and C++ front ends issue a -Wformat
for all three calls as expected (passing an int to %s).

Martin