[PATCH 1/2] worktree: demonstrate data lost to auto-gc

[Johannes Schindelin <johannes.schindelin@gmx.de>]

When gc --auto is called in the presence of worktrees, it fails to take
*all* reflogs into account when trying to retain reachable objects, and as
a consequence data integrity goes pretty much to hell.

This patch provides a test case in the hopes that this bug gets fixed,
after an initial attempt has stalled for eight months already.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 t/t6500-gc.sh | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
index 1762dfa6a3..e24a4fb611 100755
--- a/t/t6500-gc.sh
+++ b/t/t6500-gc.sh
@@ -67,5 +67,44 @@ test_expect_success 'auto gc with too many loose objects does not attempt to cre
 	test_line_count = 2 new # There is one new pack and its .idx
 '
 
+trigger_auto_gc () {
+	# This is unfortunately very, very ugly
+	gdir="$(git rev-parse --git-common-dir)" &&
+	mkdir -p "$gdir"/objects/17 &&
+	touch "$gdir"/objects/17/17171717171717171717171717171717171717 &&
+	touch "$gdir"/objects/17/17171717171717171717171717171717171718 &&
+	git -c gc.auto=1 -c gc.pruneexpire=now -c gc.autodetach=0 gc --auto
+}
+
+test_expect_failure 'gc respects refs/reflogs in all worktrees' '
+	test_commit something &&
+	git worktree add worktree &&
+	(
+		cd worktree &&
+		git checkout --detach &&
+		# avoid implicit tagging of test_commit
+		echo 1 >something.t &&
+		test_tick &&
+		git commit -m worktree-reflog something.t &&
+		git rev-parse --verify HEAD >../commit-reflog &&
+		echo 2 >something.t &&
+		test_tick &&
+		git commit -m worktree-ref something.t &&
+		git rev-parse --verify HEAD >../commit-ref
+	) &&
+	trigger_auto_gc &&
+	git rev-parse --verify $(cat commit-ref)^{commit} &&
+	git rev-parse --verify $(cat commit-reflog)^{commit} &&
+
+	# Now, add a reflog in the top-level dir and verify that `git gc` in
+	# the worktree does not purge that
+	git checkout --detach &&
+	echo 3 >something.t &&
+	test_tick &&
+	git commit -m commondir-reflog something.t &&
+	git rev-parse --verify HEAD >commondir-reflog &&
+	(cd worktree && trigger_auto_gc) &&
+	git rev-parse --verify $(cat commondir-reflog)^{commit}
+'
 
 test_done
-- 
2.11.1.windows.1