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Merge branch 'kk/commit-reach-find-all-fix' 

The early-exit optimization in 'paint_down_to_common()' has been
gated on the queue being generation-ordered, fixing a bug where
'git merge-base' (without '--all') could return incorrect results
on repositories with v1 commit graphs and clock skew.

* kk/commit-reach-find-all-fix:
  commit-reach: guard !FIND_ALL early exit with generation ordering check
  t6600: add test for merge-base early exit with clock skew
main
Junio C Hamano 2026-07-19 10:42:16 -07:00
parent a6d1c3516b ae68032a8d
commit 1950f4628e
2 changed files with 48 additions and 3 deletions
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10
commit-reach.c
View File

@ -108,11 +108,14 @@ static int paint_down_to_common(struct repository *r,
{ compare_commits_by_gen_then_commit_date }
};
int i;
int gen_ordered = 1;
timestamp_t last_gen = GENERATION_NUMBER_INFINITY;
struct commit_list **tail = result;

if (!min_generation && !corrected_commit_dates_enabled(r))
if (!min_generation && !corrected_commit_dates_enabled(r)) {
queue.pq.compare = compare_commits_by_commit_date;
gen_ordered = 0;
}

one->object.flags |= PARENT1;
if (!n) {
@ -147,11 +150,12 @@ static int paint_down_to_common(struct repository *r,
commit->object.flags |= RESULT;
tail = commit_list_append(commit, tail);
/*
* The queue is generation-ordered; no
* remaining common ancestor can be a
* When the queue is generation-ordered,
* no remaining common ancestor can be a
* descendant of this one.
*/
if (!(mb_flags & MERGE_BASE_FIND_ALL) &&
gen_ordered &&
generation < GENERATION_NUMBER_INFINITY)
break;
}

41
t/t6600-test-reach.sh
View File

@ -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 &&
@ -967,4 +1003,9 @@ test_expect_success 'merge-base without --all is one of --all results' '
grep -F -f single all
'

test_expect_success '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