[PATCH v5 8/8] gc: add `gc.repackFilterTo` config option

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

A previous commit implemented the `gc.repackFilter` config option
to specify a filter that should be used by `git gc` when
performing repacks.

Another previous commit has implemented
`git repack --filter-to=<dir>` to specify the location of the
packfile containing filtered out objects when using a filter.

Let's implement the `gc.repackFilterTo` config option to specify
that location in the config when `gc.repackFilter` is used.

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

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 Documentation/config/gc.txt | 11 +++++++++++
 builtin/gc.c                |  4 ++++
 t/t6500-gc.sh               | 13 ++++++++++++-
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/Documentation/config/gc.txt b/Documentation/config/gc.txt
index 2153bde7ac..466466d6cc 100644
--- a/Documentation/config/gc.txt
+++ b/Documentation/config/gc.txt
@@ -150,6 +150,17 @@ gc.repackFilter::
 	objects into a separate packfile.  See the
 	`--filter=<filter-spec>` option of linkgit:git-repack[1].
 
+gc.repackFilterTo::
+	When repacking and using a filter, see `gc.repackFilter`, the
+	specified location will be used to create the packfile
+	containing the filtered out objects. **WARNING:** The
+	specified location should be accessible, using for example the
+	Git alternates mechanism, otherwise the repo could be
+	considered corrupt by Git as it migh not be able to access the
+	objects in that packfile. See the `--filter-to=<dir>` option
+	of linkgit:git-repack[1] and the `objects/info/alternates`
+	section of linkgit:gitrepository-layout[5].
+
 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 9b0984f301..1b7c775d94 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -62,6 +62,7 @@ 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 char *repack_filter_to;
 static unsigned long big_pack_threshold;
 static unsigned long max_delta_cache_size = DEFAULT_DELTA_CACHE_SIZE;
 
@@ -172,6 +173,7 @@ static void gc_config(void)
 	git_config_get_ulong("pack.deltacachesize", &max_delta_cache_size);
 
 	git_config_get_string("gc.repackfilter", &repack_filter);
+	git_config_get_string("gc.repackfilterto", &repack_filter_to);
 
 	git_config(git_default_config, NULL);
 }
@@ -361,6 +363,8 @@ static void add_repack_all_option(struct string_list *keep_pack)
 
 	if (repack_filter && *repack_filter)
 		strvec_pushf(&repack, "--filter=%s", repack_filter);
+	if (repack_filter_to && *repack_filter_to)
+		strvec_pushf(&repack, "--filter-to=%s", repack_filter_to);
 }
 
 static void add_repack_incremental_option(void)
diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
index 232e403b66..e412cf8daf 100755
--- a/t/t6500-gc.sh
+++ b/t/t6500-gc.sh
@@ -203,7 +203,6 @@ test_expect_success 'one of gc.reflogExpire{Unreachable,}=never does not skip "e
 '
 
 test_expect_success 'gc.repackFilter launches repack with a filter' '
-	test_when_finished "rm -rf bare.git" &&
 	git clone --no-local --bare . bare.git &&
 
 	git -C bare.git -c gc.cruftPacks=false gc &&
@@ -215,6 +214,18 @@ test_expect_success 'gc.repackFilter launches repack with a filter' '
 	grep -E "^trace: (built-in|exec|run_command): git repack .* --filter=blob:none ?.*" trace.out
 '
 
+test_expect_success 'gc.repackFilterTo store filtered out objects' '
+	test_when_finished "rm -rf bare.git filtered.git" &&
+
+	git init --bare filtered.git &&
+	git -C bare.git -c gc.repackFilter=blob:none \
+		-c gc.repackFilterTo=../filtered.git/objects/pack/pack \
+		-c repack.writeBitmaps=false -c gc.cruftPacks=false gc &&
+
+	test_stdout_line_count = 1 ls bare.git/objects/pack/*.pack &&
+	test_stdout_line_count = 1 ls filtered.git/objects/pack/*.pack
+'
+
 prepare_cruft_history () {
 	test_commit base &&
 
-- 
2.42.0.rc1.8.ga52e3a71db