multi-pack-index: avoid writing to global in option callback

We declare the --object-dir option like:

  OPT_CALLBACK(0, "object-dir", &opts.object_dir, ...);

but the pointer to opts.object_dir is completely unused. Instead, the
callback writes directly to a global. Which fortunately happens to be
opts.object_dir. So everything works as expected, but it's unnecessarily
confusing.

Instead, let's have the callback write to the option value pointer that
has been passed in. This also quiets a -Wunused-parameter warning (since
we don't otherwise look at "opt").

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

builtin/multi-pack-index.c

@@ -56,11 +56,12 @@ static struct opts_multi_pack_index {
 static int parse_object_dir(const struct option *opt, const char *arg,
 			    int unset)
 {
-	free(opts.object_dir);
+	char **value = opt->value;
+	free(*value);
 	if (unset)
-		opts.object_dir = xstrdup(get_object_directory());
+		*value = xstrdup(get_object_directory());
 	else
-		opts.object_dir = real_pathdup(arg, 1);
+		*value = real_pathdup(arg, 1);
 	return 0;
 }