Avoid using `snprintf(3)` in case `MRB_DISABLE_STDIO`; fix #3714

mrbgems/mruby-string-ext/src/string.c

@@ -602,17 +602,25 @@ mrb_str_upto(mrb_state *mrb, mrb_value beg)
       all_digits_p(RSTRING_PTR(beg), RSTRING_LEN(beg)) &&
       all_digits_p(RSTRING_PTR(end), RSTRING_LEN(end))) {
     mrb_int min_width = RSTRING_LEN(beg);
-    mrb_int max_width = RSTRING_LEN(end);
     mrb_int bi = mrb_int(mrb, mrb_str_to_inum(mrb, beg, 10, FALSE));
     mrb_int ei = mrb_int(mrb, mrb_str_to_inum(mrb, end, 10, FALSE));
-    mrb_value str = mrb_str_new(mrb, NULL, max_width);
     int ai = mrb_gc_arena_save(mrb);
-    char *buf = RSTRING_PTR(str);
 
     while (bi <= ei) {
+      mrb_value ns, str;
+
       if (excl && bi == ei) break;
-      snprintf(buf, max_width+1, "%.*" MRB_PRId, (int)min_width, bi);
-      mrb_yield(mrb, block, mrb_str_new(mrb, buf, strlen(buf)));
+      ns = mrb_format(mrb, "%S", mrb_fixnum_value(bi));
+      if (min_width > RSTRING_LEN(ns)) {
+        str = mrb_str_new(mrb, NULL, min_width);
+        memset(RSTRING_PTR(str), '0', min_width-RSTRING_LEN(ns));
+        memcpy(RSTRING_PTR(str)+min_width-RSTRING_LEN(ns),
+               RSTRING_PTR(ns), RSTRING_LEN(ns));
+      }
+      else {
+        str = ns;
+      }
+      mrb_yield(mrb, block, str);
       mrb_gc_arena_restore(mrb, ai);
       bi++;
     }