pack-bitmap: return multiple packs via `reuse_partial_packfile_from_bitmap()`

Further prepare for enabling verbatim pack-reuse over multiple packfiles
by changing the signature of reuse_partial_packfile_from_bitmap() to
populate an array of `struct bitmapped_pack *`'s instead of a pointer to
a single packfile.

Since the array we're filling out is sized dynamically[^1], add an
additional `size_t *` parameter which will hold the number of reusable
packs (equal to the number of elements in the array).

Note that since we still have not implemented true multi-pack reuse,
these changes aren't propagated out to the rest of the caller in
builtin/pack-objects.c.

In the interim state, we expect that the array has a single element, and
we use that element to fill out the static `reuse_packfile` variable
(which is a bog-standard `struct packed_git *`). Future commits will
continue to push this change further out through the pack-objects code.

[^1]: That is, even though we know the number of packs which are
  candidates for pack-reuse, we do not know how many of those
  candidates we can actually reuse.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/pack-bitmap.c b/pack-bitmap.c
index c75a83e9cc..4d5a484678 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -2001,7 +2001,8 @@ static int bitmapped_pack_cmp(const void *va, const void *vb)
 }
 
 void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
-					struct packed_git **packfile_out,
+					struct bitmapped_pack **packs_out,
+					size_t *packs_nr_out,
 					struct bitmap **reuse_out)
 {
 	struct repository *r = the_repository;
@@ -2069,7 +2070,8 @@ void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
 	 * need to be handled separately.
 	 */
 	bitmap_and_not(result, reuse);
-	*packfile_out = packs[0].p;
+	*packs_out = packs;
+	*packs_nr_out = packs_nr;
 	*reuse_out = reuse;
 }