log_backend.h missing include for UTIL_CAT in LOG_BACKEND_DEFINE macro

[JeffLangballe]

Describe the bug
When trying to define a logging backend with LOG_BACKEND_DEFINE, I get errors relating to the macro expansion of LOG_BACKEND_DEFINE even though all of the arguments for the macro are correct.

To Reproduce
Create and compile a source file to create a logging backend as such

#include <logging/log_backend.h>// Include only this

... function declarations ...

static struct log_backend_api my_api = {
	.put = put,
	.put_sync_string = put_sync_string,
	.put_sync_hexdump = put_sync_hexdump,
	.dropped = dropped,
	.panic = panic,
	.init = init,
};

LOG_BACKEND_DEFINE(my_log, my_api, true);

Yields many errors and warnings upon compilation. It looks like the UTIL_CAT macro is not defined so the compiler thinks we're doing a function declaration.

Expected behavior
The LOG_BACKEND_DEFINE macro should compile and behave if all of its arguments are correct. log_backend.h should include the necessary headers (in this case, sys/util.h) for its implementation.

Impact
To fix I can include the missing sys/util.h header in log_backend.h so that UTIL_CAT is defined. Alternatively, I can include that same header in my logger backend source or include another log_*.h file which includes it like log_core.h.

Screenshots or console output

/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:77:16: warning: parameter names (without types) in function declaration
  static struct log_backend_control_block UTIL_CAT(backend_cb_, _name) = \
                ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:77:16: error: function 'UTIL_CAT' is initialized like a variable
  static struct log_backend_control_block UTIL_CAT(backend_cb_, _name) = \
                ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:79:3: error: field name not in record or union initializer
   .active = false,            \
   ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:79:3: note: (near initialization for 'UTIL_CAT')
   .active = false,            \
   ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
In file included from /mnt/c/Dev/ncs/zephyr/include/sys/atomic.h:12:0,
                 from /mnt/c/Dev/ncs/zephyr/include/logging/log_msg.h:9,
                 from /mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:9,
                 from /mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:1:
/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:79:13: error: invalid initializer
   .active = false,            \
             ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:79:13: note: (near initialization for 'UTIL_CAT')
   .active = false,            \
             ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
In file included from /mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:1:0:
/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:80:3: error: field name not in record or union initializer
   .id = 0,             \
   ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:80:3: note: (near initialization for 'UTIL_CAT')
   .id = 0,             \
   ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:80:9: warning: excess elements in scalar initializer
   .id = 0,             \
         ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:80:9: note: (near initialization for 'UTIL_CAT')
   .id = 0,             \
         ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
/mnt/c/Dev/ncs/zephyr/include/logging/log_backend.h:85:19: error: 'backend_cb_' undeclared here (not in a function); did you mean 'log_backend_get'?
   .cb = &UTIL_CAT(backend_cb_, _name),          \
                   ^
/mnt/c/Dev/designblocksstandalone/applets/cloud/src/cloud_log_backend.c:46:1: note: in expansion of macro 'LOG_BACKEND_DEFINE'
 LOG_BACKEND_DEFINE(cloud_log, cloud_api, true);
 ^~~~~~~~~~~~~~~~~~
```

[carlescufi]

@JeffLangballe does it work if you add:
#include <sys/util.h>
as the first line?