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t6600: add test for merge-base early exit with clock skew 

Add a topology where the correct merge base (M2) has a lower
committer date than its ancestor (M1) due to clock skew.  With a
v1 commit graph (topological levels only, no corrected commit
dates), paint_down_to_common() falls back to commit-date ordering.
In that mode, M1 pops before M2, acquires both paint sides, and
the !FIND_ALL early exit fires -- returning the wrong merge base.

Mark the test as test_expect_failure to document the bug; the next
commit will fix it.

Signed-off-by: Kristofer Karlsson <krka@spotify.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
jch
Kristofer Karlsson 2026-06-29 13:19:20 +00:00 committed by Junio C Hamano
parent 93e5b1680e
commit 18cf52c8a5
1 changed files with 41 additions and 0 deletions
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41
t/t6600-test-reach.sh
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@ -49,6 +49,42 @@ test_expect_success 'setup' '
git tag -a -m "$x-$i" tag-$x-$i commit-$x-$i || return 1
done
done &&
# Build a topology with clock skew to test the !FIND_ALL early
# exit in paint_down_to_common(). M2 is the correct merge base
# of P1 and P2, but its ancestor M1 has a higher committer date
# due to clock skew. With date-only ordering (v1 commit graph
# without corrected commit dates), M1 pops from the queue first,
# gets both paint sides, and the early exit fires before M2 is
# ever visited.
#
# P1 P2 @7000
# | / \
# A B D @6000
# / \ | |
# | M2--+ | @2000 (correct merge base)
# \ | |
# M1--------+ @5000 (clock skew: date > M2)
# |
# root @1000
#
git checkout --orphan skew-orphan &&
skew_tree=$(git mktree </dev/null) &&
skew_commit () {
GIT_COMMITTER_DATE="@$1 +0000" GIT_AUTHOR_DATE="@$1 +0000" \
git commit-tree -m "$2" "$skew_tree" $3 $4 $5 $6
} &&
skew_root=$(skew_commit 1000 root) &&
skew_M1=$(skew_commit 5000 M1 -p "$skew_root") &&
skew_M2=$(skew_commit 2000 M2 -p "$skew_M1") &&
skew_A=$(skew_commit 6000 A -p "$skew_M1" -p "$skew_M2") &&
skew_B=$(skew_commit 6000 B -p "$skew_M2") &&
skew_D=$(skew_commit 6000 D -p "$skew_M1") &&
skew_P1=$(skew_commit 7000 P1 -p "$skew_A") &&
skew_P2=$(skew_commit 7000 P2 -p "$skew_B" -p "$skew_D") &&
git branch -f skew-P1 "$skew_P1" &&
git branch -f skew-P2 "$skew_P2" &&
git tag skew-M2 "$skew_M2" &&

git commit-graph write --reachable &&
mv .git/objects/info/commit-graph commit-graph-full &&
chmod u+w commit-graph-full &&
@ -922,4 +958,9 @@ test_expect_success 'merge-base without --all is one of --all results' '
grep -F -f single all
'

test_expect_failure 'merge-base without --all, clock skew, v1 commit-graph' '
git rev-parse skew-M2 >expect &&
merge_base_all_modes skew-P1 skew-P2
'

test_done