[PATCH v2 1/2] gc: add `--expire-to` option

["ZheNing Hu via GitGitGadget" <gitgitgadget@gmail.com>]

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.

Signed-off-by: ZheNing Hu <adlternative@gmail.com>
---
 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
-- 
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