On Sat, Jan 29, 2022 at 8:04 AM Elijah Newren [off-list ref] wrote:

On Wed, Jan 26, 2022 at 12:48 AM Christian Couder
[off-list ref] wrote:

quoted

On Sat, Jan 22, 2022 at 10:56 PM Elijah Newren via GitGitGadget
[off-list ref] wrote:

quoted

quoted

Stuff intentionally NOT included, but which others seemed to feel strongly
about; they'd need to convince me more on these:

 * Any form of diff output[1]

It's not a big issue for me to not include them right now as long as
it's possible to add cli options later that add them.

My main concern is just that `merge-tree` remain a low-level tool and
have machine-parseable output.  I was a little worried that both you
and Dscho wanted everything on stdout rather than in separate files,
as the <Informational messages> part of the output is rather
free-form.  But since it's at the end, and has a machine-parseable
beginning, it can just be slurped in and we're all good.  The diff
output raises my eyebrow because I'm worried we're losing this
property.  If there are clear usecases for adding more output, and we
can do so without losing this machine-parseable property, I don't have
a problem with adding an option for it.

That's ok for me for now. I will certainly not work on adding options
for diff output without any usecase.

One analogy we might use here is that `git merge` provides a diffstat
at the end.  What you're asking is more than a diffstat, but might be
considered similar-ish in nature.

quoted

The reason is
that I think in many cases when there are conflicts, the conflicts
will be small and the user will want to see them.

I'm a little worried about the assumption here that conflict size is
measurable and visible via diffs.  That might be true in some cases,
but a UI written with that assumption is going to be very confusing
when hitting cases where that assumption does not hold.  For example:

  * What if there is a binary file conflict, or a modify/delete or
rename/delete conflict, or failed-to-merge submodule conflict, or a
file location conflict? (For these, there is no diff relative to the
first parent and hence this conflict would have no diff output for
it)?
  * What if there was a simple file/directory conflict?  A diff would
show a rename (even when neither side did any renames), but not any
conflict markers.
  * What if there was a rename/rename conflict (both sides renamed
same file differently) or a distinct types conflict?  The former
results in three different conflicting files, none of them with
conflict markers, while the latter results in two different
conflicting files both without conflict markers?  Showing individual
per-file diffs totally loses all context here -- it'll show no-diff
for one of the files, and totally new additions for the ones.

In those cases we just tell users that they cannot resolve those
conflicts in the user interface, see the following doc:

https://docs.gitlab.com/ee/user/project/merge_requests/conflicts.html#conflicts-you-can-resolve-in-the-user-interface

Such a problem statement just seems fraught with edge cases to me, and
suggests that the problem statement might be in need of revisiting.

Users understand that some kinds of conflicts cannot yet be resolved
using a user interface. Maybe we will be able to make improvements so
that more kinds of conflicts can be resolved in a UI in the future
though. That's why a flexible and extensible output could help.

Don't read this as me closing the door on the possibility of diffs;
I'm not trying to do that.  I'm listing my misgivings about how I
think they might be used (i.e. be careful if you're headed down this
path as you might be digging yourself a never-ending support hole).
You can also think of my comments as feedback to consider and address
when you propose a future feature addition for adding diffs.  If/when
you propose such a feature, we'd probably be able to dive more into
specifics and usecases at that time, which may or may not circumvent
my concerns.

I know that diffs, or any new single feature, will likely not be a
silver bullet.

quoted

So it would be
simpler to just have an option to show any conflict right away, rather
than have the user launch another command (a diff-tree against which
tree and with which options?).

Um, this part I'm not sure I get.  I thought the reason for the diffs
was performance -- you knew you wanted the diffs, and you wanted it
done as part of the same process.  But why would this be simpler?

In the commit message of 4/12 you show an example of using it in simple scripts:

NEWTREE=$(git merge-tree --write-tree $BRANCH1 $BRANCH2)
test $? -eq 0 || die "There were conflicts..."
...

So I think it would be simpler for someone interested in seeing the
conflicts, like a script writer, or maybe someone using it manually
for example as a dry run before performing a merge, to be able to get
them right away from the command rather than to have to use another
command (which means finding the right command, arguments and options
for that) to get them.

Your patch series included three different diffs, and the emails you
pointed me at suggested all kinds of configurability.  That suggests
the merge-tree command would have to take the exact same options the
user would supply to diff, and thus would have to be told all the same
options, right?  I don't see how this removes any complexity at all
for the user.

Unless...is the request in some way similar to merge's diffstat where
there is always a very specific type of diff that is wanted and you
aren't envisioning much flexibility in what kind of diff or what to
diff against -- is that where the simplification comes from?

Well I just think the default diff output could be tailored for the
most likely usecases and options made available later for more
advanced usecases or users.