midx: fix bug that skips midx with alternates

The logic for constructing the linked list of multi-pack-indexes
in the object store is incorrect. If the local object store has
a multi-pack-index, but an alternate does not, then the list is
dropped.

Add tests that would have revealed this bug.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/midx.c b/midx.c
index 7fa75a37a3..0710c4c175 100644
--- a/midx.c
+++ b/midx.c
@@ -331,7 +331,7 @@ int midx_contains_pack(struct multi_pack_index *m, const char *idx_name)
 
 int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, int local)
 {
-	struct multi_pack_index *m = r->objects->multi_pack_index;
+	struct multi_pack_index *m;
 	struct multi_pack_index *m_search;
 	int config_value;
 
@@ -339,14 +339,15 @@ int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, i
 	    !config_value)
 		return 0;
 
-	for (m_search = m; m_search; m_search = m_search->next)
+	for (m_search = r->objects->multi_pack_index; m_search; m_search = m_search->next)
 		if (!strcmp(object_dir, m_search->object_dir))
 			return 1;
 
-	r->objects->multi_pack_index = load_multi_pack_index(object_dir, local);
+	m = load_multi_pack_index(object_dir, local);
 
-	if (r->objects->multi_pack_index) {
-		r->objects->multi_pack_index->next = m;
+	if (m) {
+		m->next = r->objects->multi_pack_index;
+		r->objects->multi_pack_index = m;
 		return 1;
 	}