pack-objects: turn off bitmaps when we see --shallow lines

Reachability bitmaps do not work with shallow operations,
because they cache a view of the object reachability that
represents the true objects. Whereas a shallow repository
(or a shallow operation in a repository) is inherently
cutting off the object graph with a graft.

We explicitly disallow the use of bitmaps in shallow
repositories by checking is_repository_shallow(), and we
should continue to do that. However, we also want to
disallow bitmaps when we are serving a fetch to a shallow
client, since we momentarily take on their grafted view of
the world.

It used to be enough to call is_repository_shallow at the
start of pack-objects.  Upload-pack wrote the other side's
shallow state to a temporary file and pointed the whole
pack-objects process at this state with "git --shallow-file",
and from the perspective of pack-objects, we really were
in a shallow repo.  But since b790e0f (upload-pack: send
shallow info over stdin to pack-objects, 2014-03-11), we do
it differently: we send --shallow lines to pack-objects over
stdin, and it registers them itself.

This means that our is_repository_shallow check is way too
early (we have not been told about the shallowness yet), and
that it is insufficient (calling is_repository_shallow is
not enough, as the shallow grafts we register do not change
its return value). Instead, we can just turn off bitmaps
explicitly when we see these lines.

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

1 files changed, 1 insertions, 0 deletions

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index de36c60ca1..2c60ddf4a8 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2498,6 +2498,7 @@ static void get_object_list(int ac, const char **av)
 				if (get_sha1_hex(line + 10, sha1))
 					die("not an SHA-1 '%s'", line + 10);
 				register_shallow(sha1);
+				use_bitmap_index = 0;
 				continue;
 			}
 			die("not a rev '%s'", line);