Octopus? Really? Interesting...

Guys,

So, I brain-wedged a merge here just now and was surprised to see that a simple fetch-n-merge yielded an octopus merge. I was expecting a fast-forward. So I went back and reviewed. What actually happend was this:

    $ git checkout master
    $ git fetch origin
    # check it out... looks great ... let's merge it
    $ git merge master origin/master
    merge performed by octopus.

Oh, yeah.  Duh.  I did name two branches.  Feh.

Couple questions:

    Is it ever NOT the case, that if you are on one
    branch ("master") and name it as a "to be merged"
    branch along with some others, that we can simplify
    the request by noting that it is the same as the
    current "to be merged into" target branch?

    Other than creating a log message with "merged
    by octopus", will this merge be content-identical
    to the obvious simplified merge?

Thanks, jdl

Jon Loeliger <jdl@freescale.com> writes:

Yes we can, but "filter ancestors out from the remotes" computation does not happen before the merge strategy is chosen.

I think octopus actually tries to be careful not to run the read-tree 3-way merge when merging a true ancestor (see ll.77-87 in git-merge-octopus.sh, but see below), so the resulting tree should be identical to "-s resolve" merge.

But that does not mean the user's wish to record such a commit as one ancestor should not be honored, and I think there actually is a benign bug there. Due to the "Already up-to-date with $SHA1" part, the codepath that says "Fast forwarding to:" never actually triggers, so in practice we end up dropping any true ancestor from the parent list of the resulting merge. That contradicts the comment in ll.77-87 that suggests we try not to outsmart the user who told us to create such an octopus for unfathomable reason ;-)