[PATCH 5/9] midx: fix bug that skips midx with alternates

[Derrick Stolee]

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 <dsto...@microsoft.com>
---
 midx.c                      | 11 ++++++-----
 t/t5319-multi-pack-index.sh | 17 +++++++++++++++++
 2 files changed, 23 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;
        }
 
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index ae1d5d4592..4b6e2825a6 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -149,6 +149,23 @@ test_expect_success 'repack removes multi-pack-index' '
 
 compare_results_with_midx "after repack"
 
+test_expect_success 'multi-pack-index and alternates' '
+       git init --bare alt.git &&
+       echo $(pwd)/alt.git/objects >.git/objects/info/alternates &&
+       echo content1 >file1 &&
+       altblob=$(GIT_DIR=alt.git git hash-object -w file1) &&
+       git cat-file blob $altblob &&
+       git rev-list --all
+'
+
+compare_results_with_midx "with alternate (local midx)"
+
+test_expect_success 'multi-pack-index in an alternate' '
+       mv .git/objects/pack/* alt.git/objects/pack
+'
+
+compare_results_with_midx "with alternate (remote midx)"
+
 
 # usage: corrupt_data <file> <pos> [<data>]
 corrupt_data () {
-- 
2.18.0.118.gd4f65b8d14