builtin/pack-refs: introduce new "--auto" flag

Calling git-pack-refs(1) will unconditionally cause it to pack all
requested refs regardless of the current state of the ref database. For
example:

  - With the "files" backend we will end up rewriting the complete
    "packed-refs" file even if only a single ref would require
    compaction.

  - With the "reftable" backend we will end up always compacting all
    tables into a single table.

This behaviour can be completely unnecessary depending on the backend
and is thus wasteful.

With the introduction of the `PACK_REFS_AUTO` flag in the preceding
commit we can improve this and let the backends decide for themselves
whether to pack refs in the first place. Expose this functionality via a
new "--auto" flag in git-pack-refs(1), which mirrors the same flag in
both git-gc(1) and git-maintenance(1).

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/t/t0610-reftable-basics.sh b/t/t0610-reftable-basics.sh
index a53d1dc493..6de7529575 100755
--- a/t/t0610-reftable-basics.sh
+++ b/t/t0610-reftable-basics.sh
@@ -387,6 +387,40 @@ test_expect_success 'pack-refs: compaction raises locking errors' '
 	test_cmp expect err
 '
 
+test_expect_success 'pack-refs: auto compaction' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+
+		test_commit A &&
+
+		# The tables should have been auto-compacted, and thus auto
+		# compaction should not have to do anything.
+		ls -1 .git/reftable >tables-expect &&
+		test_line_count = 4 tables-expect &&
+		git pack-refs --auto &&
+		ls -1 .git/reftable >tables-actual &&
+		test_cmp tables-expect tables-actual &&
+
+		# Lock all tables write some refs. Auto-compaction will be
+		# unable to compact tables and thus fails gracefully, leaving
+		# the stack in a sub-optimal state.
+		ls .git/reftable/*.ref |
+		while read table
+		do
+			touch "$table.lock" || exit 1
+		done &&
+		git branch B &&
+		git branch C &&
+		rm .git/reftable/*.lock &&
+		test_line_count = 5 .git/reftable/tables.list &&
+
+		git pack-refs --auto &&
+		test_line_count = 1 .git/reftable/tables.list
+	)
+'
+
 test_expect_success 'pack-refs: prunes stale tables' '
 	test_when_finished "rm -rf repo" &&
 	git init repo &&