replace a non-working #error statement with a working _Static_assert statement

[edmund-huber]

The following doesn't work like the author intended:

#define WIFI_INIT_CONFIG_DEFAULT #error Wifi is disabled in config, WIFI_INIT_CONFIG_DEFAULT will not work

Instead of making the compiler print "Wifi is disabled in config,.." and exit, it causes a long confusing error like:

$DELETED/esp-idf/components/esp32/include/esp_wifi.h:138:34: error: stray '#' in program
 #define WIFI_INIT_CONFIG_DEFAULT #error Wifi is disabled in config, WIFI_INIT_CONFIG_DEFAULT will not work
                                  ^
$DELETED/main/./wifi_task.c:37:43: note: in expansion of macro 'WIFI_INIT_CONFIG_DEFAULT'
     wifi_init_config_t wifi_init_config = WIFI_INIT_CONFIG_DEFAULT();
                                           ^
$DELETED/esp-idf/components/esp32/include/esp_wifi.h:138:35: error: 'error' undeclared (first use in this function)
 #define WIFI_INIT_CONFIG_DEFAULT #error Wifi is disabled in config, WIFI_INIT_CONFIG_DEFAULT will not work
                                   ^
$DELETED/main/./wifi_task.c:37:43: note: in expansion of macro 'WIFI_INIT_CONFIG_DEFAULT'
     wifi_init_config_t wifi_init_config = WIFI_INIT_CONFIG_DEFAULT();
                                           ^
$DELETED/esp-idf/components/esp32/include/esp_wifi.h:138:35: note: each undeclared identifier is reported only once for each function it appears in
 #define WIFI_INIT_CONFIG_DEFAULT #error Wifi is disabled in config, WIFI_INIT_CONFIG_DEFAULT will not work
                                   ^
$DELETED/main/./wifi_task.c:37:43: note: in expansion of macro 'WIFI_INIT_CONFIG_DEFAULT'
     wifi_init_config_t wifi_init_config = WIFI_INIT_CONFIG_DEFAULT();
                                           ^
$DELETED/esp-idf/components/esp32/include/esp_wifi.h:138:41: error: expected ',' or ';' before 'Wif'
 #define WIFI_INIT_CONFIG_DEFAULT #error Wifi is disabled in config, WIFI_INIT_CONFIG_DEFAULT will not work
                                         ^
$DELETED/main/./wifi_task.c:37:43: note: in expansion of macro 'WIFI_INIT_CONFIG_DEFAULT'
     wifi_init_config_t wifi_init_config = WIFI_INIT_CONFIG_DEFAULT();

To me, it seems that if anyone includes esp_wifi.h without enabling wifi in the config, then that is an error. I can't imagine a situation where someone wants wifi struct definitions without intending to use wifi, but it's a possibility. Does anyone do that?

[igrr]

IIRC the idea was to error out only if this macro was actually used in the program. Usage of esp_wifi_* functions would cause linker error, so that's the only remaining definition to check.
Maybe defining WIFI_INIT_CONFIG_DEFAULT to a {0}; _Static_assert(0, "please enable wifi in menuconfig to use esp_wifi.h"); would do the trick?

[edmund-huber]

Yeah, it's clear what the intent of the original code was, but my first question I suppose is whether that makes sense at all. Why would one include "wifi.h" if they didn't intend for wifi to be enabled? :P

What you suggested with _Static_assert worked, so maybe we can just do that.

[projectgus]

Cherry-picked in 0aab67f, thanks