When adding a packfile to it store we add it both to the list and map of
packfiles, but we don't append it to the most-recently-used list of
packs. We do know to add the packfile to the MRU list as soon as we
access any of its objects, but in between we're being inconistent. It
doesn't help that there are some subsystems that _do_ add the packfile
to the MRU after having added it, which only adds to the confusion.

Refactor the code so that we unconditionally add packfiles to the MRU
when adding them to a packfile store.

Note that this does not allow us to drop `packfile_store_prepare_mru()`
just yet: while the MRU list is already populated with all packs now,
the order in which we add these packs is indeterministic for most of the
part. So by first calling `sort_pack()` on the other packfile list and
then re-preparing the MRU list we inherit its sorting.

Signed-off-by: Patrick Steinhardt <redacted>
---
 midx.c     | 2 --
 packfile.c | 1 +
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/midx.c b/midx.c
index 8022be9a45e..24e1e721754 100644
--- a/midx.c
+++ b/midx.c

@@ -462,8 +462,6 @@ int prepare_midx_pack(struct multi_pack_index *m,
 		    m->pack_names[pack_int_id]);
 	p = packfile_store_load_pack(r->objects->packfiles,
 				     pack_name.buf, m->source->local);
-	if (p)
-		packfile_list_append(&m->source->odb->packfiles->mru, p);
 	strbuf_release(&pack_name);
 
 	if (!p) {

diff --git a/packfile.c b/packfile.c
index f8158c1aa52..79d2b27c42c 100644
--- a/packfile.c
+++ b/packfile.c

@@ -871,6 +871,7 @@ void packfile_store_add_pack(struct packfile_store *store,
 		pack_open_fds++;
 
 	packfile_list_prepend(&store->packs, pack);
+	packfile_list_append(&store->mru, pack);
 
 	strmap_put(&store->packs_by_path, pack->pack_name, pack);
 }

-- 
2.51.2.997.g839fc31de9.dirty