Re: Trimming 'deadheads' (TREESAME 2nd parent) from revision walks?

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Sep 19, 2021, 23:44 UTC
Message-ID: <87k0jcb01k.fsf@evledraar.gmail.com>
In-Reply-To: <YUeImAqA0SZAdA2R@coredump.intra.peff.net>

On Sun, Sep 19 2021, Jeff King wrote:

Show 22 quoted lines

> On Sat, Sep 18, 2021 at 03:18:47PM +0100, Philip Oakley wrote:
>
>> Is there a method within `git rev-list` to trim side branch merges where
>> the merge's tree is identical to the first parent's commit-tree?
>> [...]
>> From my reading of the `rev-list` manual this is similar to the <paths>
>> TREESAME capability, but without specifying any paths (maybe just `.` ?).
>
> Yes, I'd just do "git log ." for this. I don't think there's another way
> to trigger simplification. In try_to_simplify_commit(), we bail early
> unless revs->prune is set, and that is set only by the presence of
> pathspecs or by --simplify-by-decoration.
>
>> * Is there a proper term for the treesame condition of the commit-tree
>> (as recorded in the commit object)?
>
> In a one-parent commit, I'd just call it an empty commit. For a merge,
> it is really I'd probably call it an "ours" merge, since one obvious way
> to get there is with "git merge -s ours" (of course you can also just
> resolve all conflicts in favor of one parent). I don't know of another
> name (besides treesame, of course, but that generally implies a
> particular scope of interest given by a pathspec).

Isn't it a "theirs" merge, not "ours"? Per the description Philip has:

    In the Git-for Windows repository, the previous releases are
    'deadheaded' by merging with the upstream git, and simply taking the
    upstream's tree unconditionally[...]

I.e. if you're taking your tree unconditionally it's -s ours, but -s theirs for theirs. Except of course for the small matter of us not having a "-s theirs" yet.

I had a WIP patch a while ago for a "-s theirs -X N", for what sounds like a similar use-case: https://lore.kernel.org/git/87sh7sdtc1.fsf@evledraar.gmail.com/