Incorrect missing initializer warning in anonymous structure in union

[Kristine]

GCC incorrectly reports structure elements as uninitialized when -Wextra is used. This appears to be specific to anonymous structures in unions.

You can easily reproduce this by creating a file called test.c (see contents below) and compiling with this command:
arm-none-eabi-gcc -mcpu=cortex-m4 -mthumb -Wextra -std=c99 -c -o "test.o" -x c "test.c"

When test.c is compiled, I get this warning even though api_version_major is clearly initialized:
test.c:18:5: warning: missing initializer for field 'api_version_major' of 'struct <anonymous>' [-Wmissing-field-initializers]
     .api_version_major = 1,
     ^
test.c:11:17: note: 'api_version_major' declared here
         uint8_t api_version_major;

File contents of test.c:

#include <stdint.h>

typedef union st_version
{
    uint32_t version_id;
    struct
    {
        uint8_t code_version_minor;
        uint8_t code_version_major;
        uint8_t api_version_minor;
        uint8_t api_version_major;
    };
} version_t;

static const version_t version =
{
    .api_version_minor = 1,
    .api_version_major = 1,
    .code_version_major = 1,
    .code_version_minor = 0
};

[Tejas Belagod (belagod-tejas)]

Hi Kristine,

What gcc version are you using?

Thanks,
Tejas.

[Kristine (kjassman)]

Hi Tejas,

I was using 4.9 2015q3. Sorry, I should have tested the latest version before reporting. I just tried version 5.3 2016q1 and this is fixed. You can close this.

Thanks,
Kristine