/in/double_list.c: In function 'append':
/in/double_list.c:106:1: error: expected ';' before ':' token
 :
 ^
/in/double_list.c:128:1: error: expected declaration or statement at end of input
 }
 ^
/in/double_list.c:104:40: error: unused variable 'node' [-Werror=unused-variable]
  node_t* a = malloc(sizeof(node_t)), * node=*head_ref;
                                        ^~~~
cc1: all warnings being treated as errors