strv: introduce strv_extendf_with_size()

src/basic/strv.c

@@ -906,7 +906,7 @@ void strv_print_full(char * const *l, const char *prefix) {
                 printf("%s%s\n", strempty(prefix), *s);
 }
 
-int strv_extendf(char ***l, const char *format, ...) {
+int strv_extendf_with_size(char ***l, size_t *n, const char *format, ...) {
         va_list ap;
         char *x;
         int r;
@@ -918,7 +918,7 @@ int strv_extendf(char ***l, const char *format, ...) {
         if (r < 0)
                 return -ENOMEM;
 
-        return strv_consume(l, x);
+        return strv_consume_with_size(l, n, x);
 }
 
 char* startswith_strv(const char *s, char * const *l) {

src/basic/strv.h

@@ -56,7 +56,8 @@ static inline int strv_extend(char ***l, const char *value) {
 int strv_extend_many_internal(char ***l, const char *value, ...);
 #define strv_extend_many(l, ...) strv_extend_many_internal(l, __VA_ARGS__, POINTER_MAX)
 
-int strv_extendf(char ***l, const char *format, ...) _printf_(2,3);
+int strv_extendf_with_size(char ***l, size_t *n, const char *format, ...) _printf_(3,4);
+#define strv_extendf(l, ...) strv_extendf_with_size(l, NULL, __VA_ARGS__)
 
 int strv_push_with_size(char ***l, size_t *n, char *value);
 static inline int strv_push(char ***l, char *value) {