[PATCH 0/3] Implement filtering repacks

[Christian Couder <christian.couder@gmail.com>]

Earlier this year, John Cai sent 2 versions of a patch series to
implement `git repack --filter=<filter-spec>`:

https://lore.kernel.org/git/pull.1206.git.git.1643248180.gitgitgadget@gmail.com/

We tried to "sell" it as a way to use partial clone on a Git server to
offload large blobs to, for example, an http server, while using
multiple promisor remotes on the client side.

Even though it is still our end goal, it seems a bit far fetched for
now and unnecessary as `git repack --filter=<filter-spec>` could be
useful on the client side too.

For example one might want to clone with a filter to avoid too many
space to be taken by some large blobs, and one might realize after
some time that a number of the large blobs have still be downloaded
because some old branches referencing them were checked out. In this
case a filtering repack could remove some of those large blobs.

Some of the comments on the patch series that John sent were related
to the possible data loss and repo corruption that a filtering repack
could cause. It's indeed true that it could be very dangerous, and we
agree that improvements were needed in this area.

To address this, in the patch 2/3 introducing --filter, we warn users
launching such a repack on the command line and ask them if they
really want to do it. If such a repack is not launched from a
terminal, we die().

A new patch 3/3, though, introduces --force to allow users to launch
such a repack without a terminal and without having to confirm it on
the command line.

Patch 1/3 is a preparatory patch.

In short, this small patch series tries to reboot the previous one
with a focus on the client side and a focus on safety.

Thanks to John Cai, who worked on the previous versions, and to
Jonathan Nieder, Jonathan Tan and Taylor Blau, who recently discussed
this with me at the Git Merge and Contributor Summit.

Christian Couder (3):
  pack-objects: allow --filter without --stdout
  repack: add --filter=<filter-spec> option
  repack: introduce --force to force filtering

 Documentation/git-repack.txt | 17 ++++++++++++++
 builtin/pack-objects.c       |  6 +----
 builtin/repack.c             | 44 ++++++++++++++++++++++++++++++------
 t/t7700-repack.sh            | 20 ++++++++++++++++
 4 files changed, 75 insertions(+), 12 deletions(-)

-- 
2.38.0.4.g7f9724c7bf.dirty