is_refname_available(): use dirname in first loop

In the first loop (over prefixes of refname), use dirname to keep
track of the current prefix. This is not an improvement in itself, but
in a moment we will start using dirname for a role where a
NUL-terminated string is needed.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>

refs.c

@@ -878,26 +878,30 @@ static int is_refname_available(const char *refname,
 	const char *slash;
 	int pos;
 	struct strbuf dirname = STRBUF_INIT;
+	int ret = 0;
 
 	/*
 	 * For the sake of comments in this function, suppose that
 	 * refname is "refs/foo/bar".
 	 */
 
+	strbuf_grow(&dirname, strlen(refname) + 1);
 	for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
+		/* Expand dirname to the new prefix, not including the trailing slash: */
+		strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);
+
 		/*
 		 * We are still at a leading dir of the refname (e.g.,
 		 * "refs/foo"; if there is a reference with that name,
 		 * it is a conflict, *unless* it is in skip.
 		 */
-		pos = search_ref_dir(dir, refname, slash - refname);
+		pos = search_ref_dir(dir, dirname.buf, dirname.len);
 		if (pos >= 0) {
 			/*
 			 * We found a reference whose name is a proper
 			 * prefix of refname; e.g., "refs/foo".
 			 */
-			struct ref_entry *entry = dir->entries[pos];
-			if (skip && string_list_has_string(skip, entry->name)) {
+			if (skip && string_list_has_string(skip, dirname.buf)) {
 				/*
 				 * The reference we just found, e.g.,
 				 * "refs/foo", is also in skip, so it
@@ -910,10 +914,11 @@ static int is_refname_available(const char *refname,
 				 * "refs/foo"). So we can stop looking
 				 * now and return true.
 				 */
-				return 1;
+				ret = 1;
+				goto cleanup;
 			}
-			error("'%s' exists; cannot create '%s'", entry->name, refname);
-			return 0;
+			error("'%s' exists; cannot create '%s'", dirname.buf, refname);
+			goto cleanup;
 		}
 
 
@@ -922,14 +927,16 @@ static int is_refname_available(const char *refname,
 		 * the next component. So try to look up the
 		 * directory, e.g., "refs/foo/".
 		 */
-		pos = search_ref_dir(dir, refname, slash + 1 - refname);
+		strbuf_addch(&dirname, '/');
+		pos = search_ref_dir(dir, dirname.buf, dirname.len);
 		if (pos < 0) {
 			/*
 			 * There was no directory "refs/foo/", so
 			 * there is nothing under this whole prefix,
 			 * and we are OK.
 			 */
-			return 1;
+			ret = 1;
+			goto cleanup;
 		}
 
 		dir = get_ref_dir(dir->entries[pos]);
@@ -943,10 +950,9 @@ static int is_refname_available(const char *refname,
 	 * names are in the "refs/foo/bar/" namespace, because they
 	 * *do* conflict.
 	 */
-	strbuf_addstr(&dirname, refname);
+	strbuf_addstr(&dirname, refname + dirname.len);
 	strbuf_addch(&dirname, '/');
 	pos = search_ref_dir(dir, dirname.buf, dirname.len);
-	strbuf_release(&dirname);
 
 	if (pos >= 0) {
 		/*
@@ -960,15 +966,21 @@ static int is_refname_available(const char *refname,
 		dir = get_ref_dir(entry);
 		data.skip = skip;
 		sort_ref_dir(dir);
-		if (!do_for_each_entry_in_dir(dir, 0, nonmatching_ref_fn, &data))
-			return 1;
+		if (!do_for_each_entry_in_dir(dir, 0, nonmatching_ref_fn, &data)) {
+			ret = 1;
+			goto cleanup;
+		}
 
 		error("'%s' exists; cannot create '%s'",
 		      data.conflicting_refname, refname);
-		return 0;
+		goto cleanup;
 	}
 
-	return 1;
+	ret = 1;
+
+cleanup:
+	strbuf_release(&dirname);
+	return ret;
 }
 
 struct packed_ref_cache {