Re: git format-patch lost the last part when branch merge

[Elijah Newren <newren@gmail.com>]

On Mon, Feb 22, 2021 at 3:03 PM Jeff King <peff@peff.net> wrote:
[...snip...]
>
> There are lots of ways to look at the diff of a merge. By default, `git
> show` will show a combined diff, which omits hunks where one side was
> taken verbatim, but otherwise shows what each side did.
>
> The diff shown in the link above is a diff against the first-parent
> (which you can also get locally with `git show --first-parent 582cd91`).
> One _could_ apply that diff onto the first parent to achieve the same
> tree as the merge plus all of the commits that got merged in. But it
> wouldn't make any sense to apply that (aside from conflict resolution,
> it would be redundant with all of the commits that format-patch just
> output!).
>
> You could imagine ways for format-patch to represent the conflict
> resolution done in a merge, but it's not quite trivial, and nobody has
> done it yet.

Are you referring to something like this (in the git.git repository)?

$ git show --oneline --remerge-diff 42342b3ee6
42342b3ee6 Merge branch 'ab/mailmap'
diff --git a/t/t4203-mailmap.sh b/t/t4203-mailmap.sh
index 1bce961e07..6fb18a34b0 100755
--- a/t/t4203-mailmap.sh
+++ b/t/t4203-mailmap.sh
@@ -257,16 +257,8 @@ test_expect_success 'No mailmap files, but configured' '

 test_expect_success 'setup mailmap blob tests' '
        git checkout -b map &&
-<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 60ecad090d (Merge branch 'ps/fetch-atomic')
        test_when_finished "git checkout main" &&
-       cat >just-bugs <<- EOF &&
-|||||||||||||||||||||||||||||||| 72c4083ddf
-       test_when_finished "git checkout master" &&
-       cat >just-bugs <<- EOF &&
-================================
-       test_when_finished "git checkout master" &&
        cat >just-bugs <<-\EOF &&
->>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 4e168333a8 (shortlog: remove
unused(?) "repo-abbrev" feature)
        Blob Guy <bugs@company.xx>
        EOF
        cat >both <<-EOF &&


I agree that representing the conflict done in a merge is more
difficult than it sounds, but if you mean what I think you mean then I
disagree with the "nobody has done it yet" half of your statement.
:-)

That said, I haven't attempted to tie this into format-patch in any
way, and have absolutely no plans to.  (And --remerge-diff hasn't been
submitted upstream, because it depends on ort, and that still needs
reviews...)