Re: [PATCH 0/2] commit-reach: fix !FIND_ALL early exit with v1 commit graph

[Junio C Hamano <gitster@pobox.com>]

"Kristofer Karlsson via GitGitGadget" <gitgitgadget@gmail.com>
writes:

> Fixes a bug introduced by 93e5b1680e (commit-reach: early exit
> paint_down_to_common for single merge-base, 2025-04-10) where git merge-base
> can return the wrong result.
>
> The bug requires all of the following to trigger:
>
>  1. A v1 commit graph (topological levels only, no corrected commit dates).
>     Generation v2 with corrected commit dates has been the default since
>     2021, so only repos that have not rewritten their commit graph in over
>     four years would be affected.
>  2. git merge-base without --all (the common case, but --all is unaffected
>     because it disables the early exit).
>  3. A topology with clock skew: the correct merge base has a lower committer
>     date than one of its ancestors that is also a common ancestor. With date
>     ordering, the deeper ancestor pops first and the early exit fires before
>     the correct result is found.
>
> This two-patch series:
>
>  1. Adds a test demonstrating the bug (clock-skew topology where the correct
>     merge base has a lower date than its ancestor)
>  2. Fixes it by tracking whether the queue is generation-ordered and gating
>     the early exit on that flag

Where should this new "gen_ordered" flag go in the world with
kk/merge-base-exhaustion topic merged in?  Does it also belong
to the paint_state struct or can it be on-stack independent variable
to the function?