id128: introduce ID128_UUID_STRING_MAX for sizing UUID buffers

src/libsystemd/sd-id128/id128-util.c

@@ -11,7 +11,7 @@
 #include "io-util.h"
 #include "stdio-util.h"
 
-char *id128_to_uuid_string(sd_id128_t id, char s[37]) {
+char *id128_to_uuid_string(sd_id128_t id, char s[static ID128_UUID_STRING_MAX]) {
         unsigned n, k = 0;
 
         assert(s);

src/libsystemd/sd-id128/id128-util.h

@@ -8,7 +8,9 @@
 #include "hash-funcs.h"
 #include "macro.h"
 
-char *id128_to_uuid_string(sd_id128_t id, char s[37]);
+#define ID128_UUID_STRING_MAX 37
+
+char *id128_to_uuid_string(sd_id128_t id, char s[static ID128_UUID_STRING_MAX]);
 
 bool id128_is_valid(const char *s) _pure_;