[PATCH v4 3/3] gc: add gc.repackFilter config option

[Christian Couder <christian.couder@gmail.com>]

A previous commit has implemented `git repack --filter=<filter-spec>` to
allow users to remove objects that are available on a promisor remote
but that they don't want locally.

Users might want to perform such a cleanup regularly at the same time as
they perform other repacks and cleanups, so as part of `git gc`.

Let's allow them to configure a <filter-spec> for that purpose using a
new gc.repackFilter config option.

Now when `git gc` will perform a repack with a <filter-spec> configured
through this option and not empty, the repack process will be passed a
corresponding `--filter=<filter-spec>` argument.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 Documentation/config/gc.txt |  9 +++++++++
 builtin/gc.c                |  6 ++++++
 t/t6500-gc.sh               | 19 +++++++++++++++++++
 3 files changed, 34 insertions(+)

diff --git a/Documentation/config/gc.txt b/Documentation/config/gc.txt
index 38fea076a2..9359136f14 100644
--- a/Documentation/config/gc.txt
+++ b/Documentation/config/gc.txt
@@ -130,6 +130,15 @@ or rebase occurring.  Since these changes are not part of the current
 project most users will want to expire them sooner, which is why the
 default is more aggressive than `gc.reflogExpire`.
 
+gc.repackFilter::
+	When repacking, use the specified filter to omit certain
+	objects from the resulting packfile. WARNING: this could
+	easily corrupt the current repo and lose data if ANY of the
+	omitted objects hasn't been already pushed to a remote. Be
+	very careful about objects that might have been created
+	locally! See the `--filter=<filter-spec>` option of
+	linkgit:git-repack[1].
+
 gc.rerereResolved::
 	Records of conflicted merge you resolved earlier are
 	kept for this many days when 'git rerere gc' is run.
diff --git a/builtin/gc.c b/builtin/gc.c
index 02455fdcd7..bf28619723 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -52,6 +52,7 @@ static timestamp_t gc_log_expire_time;
 static const char *gc_log_expire = "1.day.ago";
 static const char *prune_expire = "2.weeks.ago";
 static const char *prune_worktrees_expire = "3.months.ago";
+static char *repack_filter;
 static unsigned long big_pack_threshold;
 static unsigned long max_delta_cache_size = DEFAULT_DELTA_CACHE_SIZE;
 
@@ -161,6 +162,8 @@ static void gc_config(void)
 	git_config_get_ulong("gc.bigpackthreshold", &big_pack_threshold);
 	git_config_get_ulong("pack.deltacachesize", &max_delta_cache_size);
 
+	git_config_get_string("gc.repackfilter", &repack_filter);
+
 	git_config(git_default_config, NULL);
 }
 
@@ -346,6 +349,9 @@ static void add_repack_all_option(struct string_list *keep_pack)
 
 	if (keep_pack)
 		for_each_string_list(keep_pack, keep_one_pack, NULL);
+
+	if (repack_filter && *repack_filter)
+		strvec_pushf(&repack, "--filter=%s", repack_filter);
 }
 
 static void add_repack_incremental_option(void)
diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
index d9acb63951..b1492b521a 100755
--- a/t/t6500-gc.sh
+++ b/t/t6500-gc.sh
@@ -56,6 +56,7 @@ test_expect_success 'gc -h with invalid configuration' '
 '
 
 test_expect_success 'gc is not aborted due to a stale symref' '
+	test_when_finished "rm -rf remote client" &&
 	git init remote &&
 	(
 		cd remote &&
@@ -202,6 +203,24 @@ test_expect_success 'one of gc.reflogExpire{Unreachable,}=never does not skip "e
 	grep -E "^trace: (built-in|exec|run_command): git reflog expire --" trace.out
 '
 
+test_expect_success 'gc.repackFilter launches repack with a filter' '
+	test_when_finished "rm -rf server client" &&
+	test_create_repo server &&
+	git -C server config uploadpack.allowFilter true &&
+	git -C server config uploadpack.allowAnySHA1InWant true &&
+	test_commit -C server 1 &&
+	git clone --bare --no-local server client &&
+	git -C client config remote.origin.promisor true &&
+	git -C client rev-list --objects --all --missing=print >objects &&
+	test $(grep -c "^?" objects) = 0 &&
+
+	GIT_TRACE=$(pwd)/trace.out git -C client -c gc.repackFilter=blob:none -c repack.writeBitmaps=false -c gc.pruneExpire=now gc &&
+
+	grep -E "^trace: (built-in|exec|run_command): git repack .* --filter=blob:none ?.*" trace.out &&
+	git -C client rev-list --objects --all --missing=print >objects &&
+	test $(grep -c "^?" objects) = 1
+'
+
 prepare_cruft_history () {
 	test_commit base &&
 
-- 
2.39.0.59.g395bcb85bc.dirty