Re: baffled again

> tony.luck@intel.com writes:
>
> > So I have another anomaly in my GIT tree.  A patch to
> > back out a bogus change to arch/ia64/hp/sim/boot/bootloader.c
> > in my release branch at commit
> >
> >  62d75f3753647656323b0365faa43fc1a8f7be97
> >
> > appears to have been lost when I merged the release branch to
> > the test branch at commit
> >
> >  0c3e091838f02c537ccab3b6e8180091080f7df2
>
>     : siamese; git cat-file commit 0c3e091838f02c537ccab3b6e8180091080f7df2
>     tree 61a407356d1e897e0badea552ce69e657cab6108
>     parent 7ffacc1a2527c219b834fe226a7a55dc67ca3637
>     parent a4cce10492358b33d33bb43f98284c80482037e8
>     author Tony Luck <tony.luck@intel.com> 1124808655 -0700
>     committer Tony Luck <tony.luck@intel.com> 1124808655 -0700
>
>     Pull release into test branch
>
> So I pulled 7ffacc and a4cce1 from your repository and started
> digging from there.  7ffacc was the head of "test" branch back
> then, and a4cce1 was the head of "release" branch.  I checked
> out 7ffacc in the repository and pulled a4cce1 into it, using
> the GIT with the "optimum merge-base" patch.
>
>     : siamese; git pull . aegl-release
>     Packing 0 objects
>     Unpacking 0 objects
>
>     * committish: a4cce10492358b33d33bb43f98284c80482037e8	refs/heads/aegl-release from .
>     Trying to find the optimum merge base.
>     Trying to merge a4cce10492358b33d33bb43f98284c80482037e8 into 7ffacc1a2527c219b834fe226a7a55dc67ca3637 using c1ffb910f7a4e1e79d462bb359067d97ad1a8a25.
>     Simple merge failed, trying Automatic merge
>     Auto-merging arch/ia64/sn/kernel/io_init.c.
>     Committed merge db376974c0aebb9e99e5cd0bce21088c6a9d927c
>      arch/ia64/hp/sim/boot/boot_head.S |    2 +-
>      1 files changed, 1 insertions(+), 1 deletions(-)
>
> It is using c1ffb9 as the merge base.  The problematic path
> in the three trees involved are:
>
> : siamese; git ls-tree -r aegl-test-7ffacc1a | grep arch/ia64/hp/sim/boot/bootloader.c
> 100644 blob a7bed60b69f9e8de9a49944e22d03fb388ae93c7	arch/ia64/hp/sim/boot/bootloader.c
> : siamese; git ls-tree -r aegl-release-a4cce1 | grep arch/ia64/hp/sim/boot/bootloader.c
> 100644 blob 51a7b7b4dd0e7c5720683a40637cdb79a31ec4c4	arch/ia64/hp/sim/boot/bootloader.c
> : siamese; git ls-tree -r aegl-c1ffb9 | grep arch/ia64/hp/sim/boot/bootloader.c
> 100644 blob 51a7b7b4dd0e7c5720683a40637cdb79a31ec4c4	arch/ia64/hp/sim/boot/bootloader.c
>
> So the file did not change between the merge base and release,
> and test had the change.  merge-cache picked the one in the test
> release.  Your guess in the other message hits the mark.
>
> I wonder what _other_ candidates these two commits have in
> common and what would have happened if they were used as the
> base instead?
>
>     : siamese; git merge-base -a aegl-test-7ffacc1a aegl-release-a4cce1
>     f6fdd7d9c273bb2a20ab467cb57067494f932fa3
>     3a931d4cca1b6dabe1085cc04e909575df9219ae
>     c1ffb910f7a4e1e79d462bb359067d97ad1a8a25
>
> You can check what variant of the file each of these commits
> contain.
>
> What is happening is:
>
> * the problematic patch 4aec0f is one before 3a931d.  Among the
>   three merge-base candidates, only 3a931d contains teh wrongly
>   patched version.
>
> * the problematic change 4aec0f patch introduces is part of test
>   branch, because it was pulled via release.
>
> * the tip of release being merged into test has this patch
>   reverted, and the file is exactly the same as before 4aec0f
>   patch.
>
> So three-way trivial merge algorithm says, "hey, the file did
> not change between common ancestor and release but it is
> different in test, so the one in the test branch must be the
> merge result."
>
> This does not have much to do with which common ancestor
> merge-base chooses.  Sorry, I am not sure what is the right way
> to resolve this offhand.