alternates: provide helper for allocating alternate

Allocating a struct alternate_object_database is tricky, as
we must over-allocate the buffer to provide scratch space,
and then put in particular '/' and NUL markers.

Let's encapsulate this in a function so that the complexity
doesn't leak into callers (and so that we can modify it
later).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 6 deletions

diff --git a/sha1_name.c b/sha1_name.c
index faf873cf7f..98152a68ba 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -86,12 +86,7 @@ static void find_short_object_filename(int len, const char *hex_pfx, struct disa
 		 * alt->name/alt->base while iterating over the
 		 * object databases including our own.
 		 */
-		const char *objdir = get_object_directory();
-		size_t objdir_len = strlen(objdir);
-		fakeent = xmalloc(st_add3(sizeof(*fakeent), objdir_len, 43));
-		memcpy(fakeent->base, objdir, objdir_len);
-		fakeent->name = fakeent->base + objdir_len + 1;
-		fakeent->name[-1] = '/';
+		fakeent = alloc_alt_odb(get_object_directory());
 	}
 	fakeent->next = alt_odb_list;