-Wmissing-field-initializers false positive with compound literals

[Richard Sandiford]

Alexey Neyman <stilor@att.net> writes:
> Hi all,
>
> I've encountered a weird behavior of -Wmissing-field-initializers option 
> (which is a part of -Wextra) regarding structure initializers that 
> contain compound literals as initializers for some of their fields. 
> Reproduced with all GCC versions from 4.8.5 to 11.2.
>
> Consider the following test case:
>
> struct foo {
>         const char *a1;
>         const char * const *a2;
>         void *a3;
>         void *a4;
> };
>
> const char *aux[] = { "y", 0 };
>
> struct foo a = {
>         .a1 = "x",
> #if defined(CASE1)
>         .a2 = (const char * const []){ "y", 0 },
> #elif defined(CASE2)
>         .a2 = aux,
> #elif defined(CASE3)
>         .a2 = 0,
> #elif defined(CASE4)
>         /* .a2 not initialized */
> #elif defined(CASE5)
>         .a2 = (const char * const []){ "y", 0 },
>         .a3 = 0,
> #endif
> };
>
> struct foo b = {
>         .a2 = (const char * const []){ "y", 0 },
>         .a1 = "x",
> };
>
> CASE1 gives a warning about 'a3' field being initialized, despite the 
> manual stating that named field initializers should prevent this warning 
> from being generated. CASE2 initializes the field to point to an 
> explicitly defined array, and it works with no warnings. CASE3 uses a 
> constant as an initializer and also works without warnings. CASE5 
> initializes the field 'a3' and produces no warnings about the next 
> field, 'a4'.
>
> Reversing the order of the 'a1' and 'a2' initializers (as in the 'b' 
> variable) also does not produce a warning. It seems that the warning is 
> only produced if the last initialized field in a structure uses a 
> compound literal.
>
> Looks like a bug to me; please confirm that I should file it into GCC's 
> bugzilla.

Yeah, I agree it's a bug.  I think it's likely to be the same underlying
issue as PR82283, so I've copied the example there (hope you don't mind).

Thanks,
Richard