repack: add `repack.honorpackkeep` config varjk/repack-honor-pack-keep

The git-repack command always passes `--honor-pack-keep`
to pack-objects. This has traditionally been a good thing,
as we do not want to duplicate those objects in a new pack,
and we are not going to delete the old pack.

However, when bitmaps are in use, it is important for a full
repack to include all reachable objects, even if they may be
duplicated in a .keep pack. Otherwise, we cannot generate
the bitmaps, as the on-disk format requires the set of
objects in the pack to be fully closed.

Even if the repository does not generally have .keep files,
a simultaneous push could cause a race condition in which a
.keep file exists at the moment of a repack. The repack may
try to include those objects in one of two situations:

  1. The pushed .keep pack contains objects that were
     already in the repository (e.g., blobs due to a revert of
     an old commit).

  2. Receive-pack updates the refs, making the objects
     reachable, but before it removes the .keep file, the
     repack runs.

In either case, we may prefer to duplicate some objects in
the new, full pack, and let the next repack (after the .keep
file is cleaned up) take care of removing them.

This patch introduces an option to disable the
`--honor-pack-keep` option.  It is not triggered by default,
even when pack.writeBitmaps is turned on, because its use
depends on your overall packing strategy and use of .keep
files.

Note that this option just disables the pack-objects
behavior. We still leave packs with a .keep in place, as we
do not necessarily know that we have duplicated all of their
objects.

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

2 files changed, 15 insertions, 1 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 499a3c4360..ed98e91ed8 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2128,6 +2128,14 @@ repack.usedeltabaseoffset::
 	"false" and repack. Access from old Git versions over the
 	native protocol are unaffected by this option.
 
+repack.honorPackKeep::
+	If set to false, include objects in `.keep` files when repacking
+	via `git repack`. Note that we still do not delete `.keep` packs
+	after `pack-objects` finishes. This means that we may duplicate
+	objects, but this makes the option safe to use when there are
+	concurrent pushes or fetches. This option is generally only
+	useful if you have set `pack.writeBitmaps`. Defaults to true.
+
 rerere.autoupdate::
 	When set to true, `git-rerere` updates the index with the
 	resulting contents after it cleanly resolves conflicts using
diff --git a/builtin/repack.c b/builtin/repack.c
index 239f278fac..b4439edf26 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -9,6 +9,7 @@
 #include "argv-array.h"
 
 static int delta_base_offset = 1;
+static int honor_pack_keep = 1;
 static char *packdir, *packtmp;
 
 static const char *const git_repack_usage[] = {
@@ -22,6 +23,10 @@ static int repack_config(const char *var, const char *value, void *cb)
 		delta_base_offset = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "repack.honorpackkeep")) {
+		honor_pack_keep = git_config_bool(var, value);
+		return 0;
+	}
 	return git_default_config(var, value, cb);
 }
 
@@ -190,10 +195,11 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 
 	argv_array_push(&cmd_args, "pack-objects");
 	argv_array_push(&cmd_args, "--keep-true-parents");
-	argv_array_push(&cmd_args, "--honor-pack-keep");
 	argv_array_push(&cmd_args, "--non-empty");
 	argv_array_push(&cmd_args, "--all");
 	argv_array_push(&cmd_args, "--reflog");
+	if (honor_pack_keep)
+		argv_array_push(&cmd_args, "--honor-pack-keep");
 	if (window)
 		argv_array_pushf(&cmd_args, "--window=%u", window);
 	if (window_memory)