gc: add --expire-to option

[adlternative]

I want to perform a "safe" garbage collection for the Git repository
on the server, which avoids data corruption issues caused by
concurrent pushes during git GC. To achieve this, I currently need to
use git repack --cruft --expire-to=<dir> and git prune
in combination. However, it would be simpler if we could directly use
--expire-to=<dir> with the git-gc command.

cc: [email protected]
cc: [email protected]
cc: [email protected]

[adlternative]

/submit

[gitgitgadget]

Submitted as [email protected]

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[gitgitgadget]

There are issues in commit 4254269:
fix(gc): make --prune=now compatible with --expire-to
Lines in the body of the commit messages should be wrapped between 60 and 76 characters.
Indented lines, and lines without whitespace, are exempt

[gitgitgadget]

Submitted as [email protected]

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[gitgitgadget]

On the Git mailing list, ZheNing Hu wrote (reply to this):

ZheNing Hu via GitGitGadget <[email protected]> 于2024年12月31日周二 10:18写道：
>
> From: ZheNing Hu <[email protected]>
>
> This commit extends the functionality of `git gc`
> by adding a new option, `--expire-to=<dir>`. Previously,
> this feature was implemented in `git repack` (see 91badeb),
> allowing users to specify a directory where unreachable and
> expired cruft packs are stored during garbage collection.
> However, users had to run `git repack --cruft --expire-to=<dir>`
> followed by `git prune` to achieve similar results within `git gc`.
>
> By introducing `--expire-to=<dir>` directly into `git gc`,
> we simplify the process for users who wish to manage their
> repository's cleanup more efficiently. This change involves
> passing the `--expire-to=<dir>` parameter through to `git repack`,
> making it easier for users to set up a backup location for cruft
> packs that will be pruned.
>
> Signed-off-by: ZheNing Hu <[email protected]>
> ---
>  Documentation/git-gc.txt | 6 ++++++
>  builtin/gc.c             | 6 +++++-
>  t/t6500-gc.sh            | 6 ++++++
>  3 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/git-gc.txt b/Documentation/git-gc.txt
> index 370e22faaeb..b4c0cf02972 100644
> --- a/Documentation/git-gc.txt
> +++ b/Documentation/git-gc.txt
> @@ -69,6 +69,12 @@ be performed as well.
>         the `--max-cruft-size` option of linkgit:git-repack[1] for
>         more.
>
> +--expire-to=<dir>::
> +       When packing unreachable objects into a cruft pack, write a cruft
> +       pack containing pruned objects (if any) to the directory `<dir>`.
> +       See the `--expire-to` option of linkgit:git-repack[1] for
> +       more.
> +
>  --prune=<date>::
>         Prune loose objects older than date (default is 2 weeks ago,
>         overridable by the config variable `gc.pruneExpire`).
> diff --git a/builtin/gc.c b/builtin/gc.c
> index d52735354c9..77904694c9f 100644
> --- a/builtin/gc.c
> +++ b/builtin/gc.c
> @@ -136,6 +136,7 @@ struct gc_config {
>         char *prune_worktrees_expire;
>         char *repack_filter;
>         char *repack_filter_to;
> +       char *repack_expire_to;
>         unsigned long big_pack_threshold;
>         unsigned long max_delta_cache_size;
>  };
> @@ -441,6 +442,8 @@ static void add_repack_all_option(struct gc_config *cfg,
>                 if (cfg->max_cruft_size)
>                         strvec_pushf(&repack, "--max-cruft-size=%lu",
>                                      cfg->max_cruft_size);
> +               if (cfg->repack_expire_to)
> +                       strvec_pushf(&repack, "--expire-to=%s", cfg->repack_expire_to);
>         } else {
>                 strvec_push(&repack, "-A");
>                 if (cfg->prune_expire)
> @@ -675,7 +678,6 @@ struct repository *repo UNUSED)
>         const char *prune_expire_sentinel = "sentinel";
>         const char *prune_expire_arg = prune_expire_sentinel;
>         int ret;
> -
>         struct option builtin_gc_options[] = {
>                 OPT__QUIET(&quiet, N_("suppress progress reporting")),
>                 { OPTION_STRING, 0, "prune", &prune_expire_arg, N_("date"),
> @@ -694,6 +696,8 @@ struct repository *repo UNUSED)
>                            PARSE_OPT_NOCOMPLETE),
>                 OPT_BOOL(0, "keep-largest-pack", &keep_largest_pack,
>                          N_("repack all other packs except the largest pack")),
> +               OPT_STRING(0, "expire-to", &cfg.repack_expire_to, N_("dir"),
> +                          N_("pack prefix to store a pack containing pruned objects")),
>                 OPT_END()
>         };
>
> diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
> index ee074b99b70..d4b0653a9b7 100755
> --- a/t/t6500-gc.sh
> +++ b/t/t6500-gc.sh
> @@ -339,6 +339,12 @@ test_expect_success 'gc.maxCruftSize sets appropriate repack options' '
>         test_subcommand $cruft_max_size_opts --max-cruft-size=3145728 <trace2.txt
>  '
>
> +test_expect_success '--expire-to sets appropriate repack options' '
> +       mkdir expired &&
> +       GIT_TRACE2_EVENT=$(pwd)/trace2.txt git -C cruft--max-size gc --cruft --expire-to=./expired/pack &&
> +       test_subcommand $cruft_max_size_opts --expire-to=./expired/pack <trace2.txt
> +'
> +
>  run_and_wait_for_gc () {
>         # We read stdout from gc for the side effect of waiting until the
>         # background gc process exits, closing its fd 9.  Furthermore, the
> --
> gitgitgadget
>

Hi, Jeff King, could you come and help take a look at this patch?
I would be very grateful if you have time!

ZheNing Hu