tree ae534d0cd0aa0bf3cb24650098106d45e8632d9a
parent fa23090b0c5cc27d0720535e27236fef9b409efb
author Taylor Blau <me@ttaylorr.com> 1653088672 -0400
committer Junio C Hamano <gitster@pobox.com> 1653605306 -0700

builtin/pack-objects.c: --cruft without expiration

Teach `pack-objects` how to generate a cruft pack when no objects are
dropped (i.e., `--cruft-expiration=never`). Later patches will teach
`pack-objects` how to generate a cruft pack that prunes objects.

When generating a cruft pack which does not prune objects, we want to
collect all unreachable objects into a single pack (noting and updating
their mtimes as we accumulate them). Ordinary use will pass the result
of a `git repack -A` as a kept pack, so when this patch says "kept
pack", readers should think "reachable objects".

Generating a non-expiring cruft packs works as follows:

  - Callers provide a list of every pack they know about, and indicate
    which packs are about to be removed.

  - All packs which are going to be removed (we'll call these the
    redundant ones) are marked as kept in-core.

    Any packs the caller did not mention (but are known to the
    `pack-objects` process) are also marked as kept in-core. Packs not
    mentioned by the caller are assumed to be unknown to them, i.e.,
    they entered the repository after the caller decided which packs
    should be kept and which should be discarded.

    Since we do not want to include objects in these "unknown" packs
    (because we don't know which of their objects are or aren't
    reachable), these are also marked as kept in-core.

  - Then, we enumerate all objects in the repository, and add them to
    our packing list if they do not appear in an in-core kept pack.

This results in a new cruft pack which contains all known objects that
aren't included in the kept packs. When the kept pack is the result of
`git repack -A`, the resulting pack contains all unreachable objects.

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