Re: [PATCH v3] gc: add `--expire-to` option

>
> "ZheNing Hu via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
> > From: ZheNing Hu <adlternative@gmail.com>
> >
> > 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.
>
> Today I do not have enough time to do my usual commit log message
> critique.  Please use "git show -s --format=reference" when
> referring to an earlier commit.
>

> > Note: When git-gc is used with both `--cruft` and `--expire-to`,
> > it does not pass `-a` to git-repack to delete all unreachable
> > objects as `git gc --prune=now` originally did. Instead, it
> > generates a cruft pack in the directory specified by expire-to.
>
> Is this less important than "we added --expire-to to gc that is
> passed down to underlying repack" in the previous paragraph?
>

> Not removing the unreachables too early with "repack -a" is an
> essential part of the design of this new feature to allow us not to
> lose the cruft objects, so I was a bit surprised that this was
> described as a "Note:".
>

> > 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.
>
> Does "When packing unreachable objects into a cruft pack" mean that
> this option is only meaningful with "--cruft"?  As "--cruft" is on
> by default, is it an error to pass "--no-cruft" when you use this
> option?
>

> > diff --git a/builtin/gc.c b/builtin/gc.c
> > index d52735354c9..8656e1caff0 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;
> >  };
> > @@ -432,7 +433,8 @@ static int keep_one_pack(struct string_list_item *item, void *data UNUSED)
> >  static void add_repack_all_option(struct gc_config *cfg,
> >                                 struct string_list *keep_pack)
> >  {
> > -     if (cfg->prune_expire && !strcmp(cfg->prune_expire, "now"))
> > +     if (cfg->prune_expire && !strcmp(cfg->prune_expire, "now")
> > +             && !(cfg->cruft_packs && cfg->repack_expire_to))
> >               strvec_push(&repack, "-a");
>
> Hmph.  When "--expire-to=<there>" is given, we are dropping these
> unreachable objects right away, but we said "--no-cruft", then we
> say "repack -a".  If we have both "--cruft" and "--expire-to=<there>",
> then ...
>
> >       else if (cfg->cruft_packs) {
> >               strvec_push(&repack, "--cruft");
> > @@ -441,6 +443,8 @@ 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);
>
> ... we do the usual "repack --cruft --expire-to=<there>" in the next
> block.
>
> > @@ -675,7 +679,6 @@ 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"),
>
> OK.
>
> > @@ -694,6 +697,8 @@ 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()
> >       };
>
> OK.
>
> > 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
> > +'
>
> As "--cruft" is on by default, the command line does not have to
> have it, but being explicit is good.
>
> Should we also see what happens when "--no-cruft" is given?
>