t6600: add clock-skew topologies and step counts for edge cases
Add topologies and tests exercising paint_down_to_common() under clock skew, where commit-date ordering (v1 commit-graph without corrected commit dates) violates the topological invariant that children are dequeued before parents: - se-*: side-exhaustion fires too early when one paint side fully drains from the queue while a low-date ancestor on the other side is still queued - se2-*: side-exhaustion returns a too-deep merge base because the correct (closer) base never receives both paint sides Also add step counts to the edge-case tests from the previous commit, a mixed finite/INFINITY generation topology exercising the transition from INFINITY-generation commits to graph-backed commits, and step counts for the grid-based merge-base test. Signed-off-by: Kristofer Karlsson <krka@spotify.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Kristofer Karlsson committed
Jul 11, 2026 at 13:27 UTC
b9bc40f1414642d8245a71c80e8396835c88b60c
1 file changed
+96
-2
t/t6600-test-reach.sh
+96
-2
@@ -140,6 +140,48 @@ test_expect_success 'setup' '
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git branch -f pi-X-br "$pi_x" &&
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git tag pi-X "$pi_x" &&
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+ # Clock-skew topology for side-exhaustion testing.
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+ # D is the correct merge base but has a higher committer date
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+ # than C (its child). With date ordering, D would be dequeued
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+ # before C, causing side-exhaustion to fire too early.
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+ # Generation ordering prevents this by visiting children
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+ # before parents regardless of dates.
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+ #
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+ # se-A (date 7000) --> se-C (date 3000) --> se-D (date 5000) --> se-root (date 4000)
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+ # se-B (date 6000) --> se-D
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+ #
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+ se_root=$(skew_commit 4000 se-root) &&
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+ se_D=$(skew_commit 5000 se-D -p "$se_root") &&
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+ se_C=$(skew_commit 3000 se-C -p "$se_D") &&
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+ se_A=$(skew_commit 7000 se-A -p "$se_C") &&
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+ se_B=$(skew_commit 6000 se-B -p "$se_D") &&
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+ git branch -f se-A "$se_A" &&
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+ git branch -f se-B "$se_B" &&
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+ git tag se-D "$se_D" &&
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+
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+ # Clock-skew topology with redundant ancestor for
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+ # side-exhaustion testing. MB1 is the correct merge base;
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+ # MB2 is its parent. A reaches MB2 via E (high date) and
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+ # MB1 via C (low date). B reaches MB1 via D. With date
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+ # ordering, side-exhaustion would fire before C is dequeued,
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+ # missing MB1. Generation ordering ensures both are found.
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+ #
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+ # se2-A (date 8000) --> se2-C (date 2000) --> se2-MB1 (date 5000) --> se2-MB2 (date 4000) --> se2-root (date 1000)
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+ # se2-A --> se2-E (date 6500) --> se2-MB2
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+ # se2-B (date 7000) --> se2-D (date 6000) --> se2-MB1
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+ #
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+ se2_root=$(skew_commit 1000 se2-root) &&
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+ se2_MB2=$(skew_commit 4000 se2-MB2 -p "$se2_root") &&
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+ se2_MB1=$(skew_commit 5000 se2-MB1 -p "$se2_MB2") &&
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+ se2_C=$(skew_commit 2000 se2-C -p "$se2_MB1") &&
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+ se2_D=$(skew_commit 6000 se2-D -p "$se2_MB1") &&
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+ se2_E=$(skew_commit 6500 se2-E -p "$se2_MB2") &&
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+ se2_A=$(skew_commit 8000 se2-A -p "$se2_C" -p "$se2_E") &&
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+ se2_B=$(skew_commit 7000 se2-B -p "$se2_D") &&
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+ git branch -f se2-A "$se2_A" &&
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+ git branch -f se2-B "$se2_B" &&
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+ git tag se2-MB1 "$se2_MB1" &&
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+
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git commit-graph write --reachable &&
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mv .git/objects/info/commit-graph commit-graph-full &&
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chmod u+w commit-graph-full &&
@@ -323,7 +365,8 @@ test_expect_success 'get_merge_bases_many:pending-stale' '
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echo "get_merge_bases_many(A,X):" &&
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git rev-parse ps-B
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} >expect &&
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- test_all_modes get_merge_bases_many
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+ test_all_modes get_merge_bases_many &&
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+ test_paint_down_steps 6 6 6 6
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'
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test_expect_success 'get_merge_bases_many:infinity-both-sides' '
@@ -337,7 +380,34 @@ test_expect_success 'get_merge_bases_many:infinity-both-sides' '
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echo "get_merge_bases_many(A,X):" &&
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git rev-parse pi-B
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} >expect &&
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- test_all_modes get_merge_bases_many
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+ test_all_modes get_merge_bases_many &&
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+ test_paint_down_steps 5 5 5 5
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+'
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+
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+test_expect_success 'setup mixed finite/INFINITY topology' '
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+ # Create a commit outside all saved commit-graph files so it always
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+ # has INFINITY generation, while its parent (ps-X) is in the graph
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+ # with a finite generation. Use the ps-* orphan topology so we do
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+ # not pollute the grid-based rev-list tests.
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+ git checkout ps-X &&
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+ test_env GIT_TEST_COMMIT_GRAPH= test_commit pm-INF
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+'
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+
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+test_expect_success 'get_merge_bases_many:mixed-finite-infinity' '
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+ # One tip (pm-INF) is outside the commit-graph with INFINITY
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+ # generation; the other (ps-B) is in the graph with finite
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+ # generation. The walk starts in the INFINITY region and crosses
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+ # into the finite region where side-exhaustion can fire.
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+ cat >input <<-\EOF &&
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+ A:pm-INF
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+ X:ps-B
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+ EOF
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+ {
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+ echo "get_merge_bases_many(A,X):" &&
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+ git rev-parse ps-X
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+ } >expect &&
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+ test_all_modes get_merge_bases_many &&
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+ test_paint_down_steps 3 3 3 3
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'
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test_expect_success 'merge-base --all commit-walk steps' '
@@ -347,6 +417,30 @@ test_expect_success 'merge-base --all commit-walk steps' '
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test_paint_down_steps 81 80 81 81
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'
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+test_expect_success 'merge-base --all with clock skew (side-exhaustion)' '
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+ # Verify correct merge base under clock skew. se-D (the
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+ # merge base) has a higher date than its child se-C.
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+ # Generation ordering ensures se-C is visited before se-D,
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+ # so P1 paint propagates correctly and se-D is found.
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+ >input &&
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+ git rev-parse se-D >expect &&
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+ run_all_modes git merge-base --all se-A se-B &&
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+ test_paint_down_steps 6 4 6 6
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+'
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+
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+test_expect_success 'merge-base --all with clock skew and redundant ancestor (side-exhaustion)' '
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+ # Verify correct merge base when clock skew could cause a
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+ # too-deep result. MB1 is the correct merge base; MB2 is
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+ # its ancestor. A reaches MB2 via E (high date) and MB1
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+ # via C (low date). Generation ordering ensures C is
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+ # visited before side-exhaustion fires, so MB1 is found
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+ # and remove_redundant correctly discards MB2.
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+ >input &&
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+ git rev-parse se2-MB1 >expect &&
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+ run_all_modes git merge-base --all se2-A se2-B &&
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+ test_paint_down_steps 8 7 8 8
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+'
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+
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test_expect_success 'reduce_heads' '
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cat >input <<-\EOF &&
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X:commit-1-10