var a=function(){var x=0;return (function(){return x;})};

[zaoqi-unsafe]

var a=function(){var x=0;return (function(){return x;})};
a()();

typedef short int16_t;

struct a_func_t {
    int16_t (*func)(struct a_func_t *);
    int16_t x;
};

static struct a_func_t * (*a)();
int16_t func(int16_t x)
{
    return x;

}
struct a_func_t * a_func()
{
    int16_t x;
    x = 0;
    return (func);

}

int main(void) {
    a = a_func;
    a()(x);

    return 0;
}

[zaoqi-unsafe]

jdoodle.c: In function 'a_func':
jdoodle.c:18:12: warning: returning 'int16_t (*)(int16_t)' {aka 'short int (*)(short int)'} from a function with incompatible return type 'struct a_func_t *' [-Wincompatible-pointer-types]
     return (func);
            ^
jdoodle.c: In function 'main':
jdoodle.c:24:9: error: 'x' undeclared (first use in this function)
     a()(x);
         ^
jdoodle.c:24:9: note: each undeclared identifier is reported only once for each function it appears in
jdoodle.c:24:5: error: called object is not a function or function pointer
     a()(x);
     ^