Fix commit-graph v1 regression in v2.55.0#954
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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>
When paint_down_to_common() falls back to commit-date ordering (for v1 commit graphs without corrected commit dates), the !FIND_ALL early exit incorrectly fires. The exit assumes the queue is generation- ordered, so the first RESULT commit found must be the shallowest. With date ordering this is not guaranteed: a closer merge base with a lower committer date (clock skew) may still be in the queue behind deeper commits. Add a gen_ordered flag that is cleared when the date fallback fires, and require it for the early exit. Update the test from the previous commit to test_expect_success. Signed-off-by: Kristofer Karlsson <krka@spotify.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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paint_down_to_common() regression in v2.55.0
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I love it when my PR Checks fail for reasons that are totally outside my control...</s> |
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Oops. By resolving the merge conflicts via 44992e5, I accidentally updated the branch in |
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Junio has marked Kristofer's
paint_down_to_common()fix fornext(lore), but the topic has not yet graduated tomaster. This PR is a backport ontovfs-2.55.0, queued while upstream finishes cooking.The regression was introduced by git/git@93e5b1680e (merged as git/git@6390da42c7) and first shipped in v2.55.0, which is why the base here is
vfs-2.55.0. That commit added a fast-path early exit inpaint_down_to_common()predicated on the priority queue being generation-ordered. The predicate holds under the generation-then-date ordering, but the same function falls back to plain commit-date ordering when!min_generation && !corrected_commit_dates_enabled(r), which is true whenever the loaded commit-graph lacks a GDAT chunk (i.e. a v1 graph). Under that fallback the early exit is unsound: with clock skew, a closer merge base can sit behind deeper commits in the queue, andgit merge-base(without--all) can silently return a non-best answer. The tip commit git/git@ae68032a8d0 threads agen_orderedflag through and gates the early exit on it.The reason microsoft/git in particular needs to carry this promptly, rather than wait the usual weeks for upstream graduation, is Scalar.
set_recommended_config()pinscommitGraph.generationVersion=1(scalar.c:191), and that pin is applied on everyscalar clone,scalar register, andscalar reconfigure. Stolee introduced it in 18580f020d1 as a deliberate but temporary compatibility measure for existing enlistments with v1 graphs on disk, with the accompanyingDocumentation/scalar.adocnote calling out that v2 is preferred and the pin is expected to change once the upgrade story solidifies. Every Scalar-managed enlistment on microsoft/git 2.55.x therefore lands on exactly the broken code path, and Scalar's target audience (Office monorepos and external adopters) is precisely the large-monorepo, many-active-branches cohort Kristofer's original optimization was aimed at in the first place.