[PATCH 00/10] gc: enable cruft packs by default

This series graduates `gc.cruftPacks` out of `feature.experimental` and enables it by default, meaning that a bare `git gc` will generate a cruft pack.

The main benefits are described in detail in the second to last patch, but a brief summary is that:

  - cruft packs avoid an issue where repositories with many unreachable
    objects that were written too recently to be pruned causes an
    explosion of loose object files

  - cruft packs allow pairs of unreachable objects with similar content
    to delta with each other since they can be represented in a single
    pack instead of as individual loose objects.

Cruft packs have been in the tree for the vast majority of the past calendar year, and have been in use at GitHub for even longer without issue.

The series is structured as follows:

  - The first two patches are cleanup.
  - The third patches fixes an oversight where the code for `git gc`'s
    `--keep-largest-pack` option would incorrectly consider cruft packs.
  - The next five patches are test preparation.
  - Then the substantive patch, to actually graduate `gc.cruftPacks` and
    enable it by default.
  - The final patch is some cleanup that can only take place towards the
    end of the series.

Cruft packs have been a success for us at GitHub, and I am really excited to get it in the hands of more users by default.

Thanks in advance for your review.

-Taylor

Taylor Blau (10):
  pack-write.c: plug a leak in stage_tmp_packfiles()
  builtin/repack.c: fix incorrect reference to '-C'
  builtin/gc.c: ignore cruft packs with `--keep-largest-pack`
  t/t5304-prune.sh: prepare for `gc --cruft` by default
  t/t9300-fast-import.sh: prepare for `gc --cruft` by default
  t/t6500-gc.sh: refactor cruft pack tests
  t/t6500-gc.sh: add additional test cases
  t/t6501-freshen-objects.sh: prepare for `gc --cruft` by default
  builtin/gc.c: make `gc.cruftPacks` enabled by default
  repository.h: drop unused `gc_cruft_packs`

 Documentation/config/feature.txt |   3 -
 Documentation/config/gc.txt      |  12 +--
 Documentation/git-gc.txt         |  12 +--
 Documentation/gitformat-pack.txt |   4 +-
 builtin/gc.c                     |   8 +-
 builtin/repack.c                 |   2 +-
 pack-write.c                     |  14 ++--
 repo-settings.c                  |   4 +-
 repository.h                     |   1 -
 t/t5304-prune.sh                 |  28 +++----
 t/t6500-gc.sh                    | 136 ++++++++++++++++---------------
 t/t6501-freshen-objects.sh       |  10 +--
 t/t9300-fast-import.sh           |  13 +--
 13 files changed, 121 insertions(+), 126 deletions(-)