Re: so/diff-merges-more (was Re: What's cooking in git.git (Feb 2023, #01; Thu, 2))

[Glen Choo <chooglen@google.com>]

Sergey Organov <sorganov@gmail.com> writes:

>>   If the goal is to reduce typing, then we could add a different CLI
>>   flag that would behave like "-m -p", or we could teach "git diff" to
>>   accept proper single-character flags. Either of these options would be
>>   more discoverable and cleaner.
>
> The only drawback of this is that this leaves "-m" inconsistent with no
> apparent reason.
> [...]
> Then, out of curiosity, what do you think was the reason to change
> "--cc" behavior to match that of "-c"? To save typing? To me, changing
> "-m" accordingly is an improvement to the overall feel of git interface,
> the same way as changing "--cc" was.

FWIW, I agree that having an inconsistent "-m" is quite an eyesore, and
there isn't a particularly good reason for it.

The unfortunate reality of Hyrum's law is that some 'mistakes' or CLI
cleanups are difficult or even downright impossible to fix. I'd consider
"-m on its own does nothing" one of those.

> All you say is understood and are valid arguments, but then we will
> continue to face pretty valid confusion of why "-m" behaves differently
> from "-c/--cc/--remerge". I personally don't care, provided I get a way
> to make it behave sanely, and that's what "log.diffMerges-m-imply-p"
> patch does.

We could say, e.g.:

  "-m" is inconsistent, but we can't change it for backwards
  compatibility reasons. Please do not use it, use "-d" instead, because
  that is more sensible.

> As a kind of complaint, it was simple 1 patch from Junio once upon a
> time to change "--cc" to a sane behavior of implying -p, and now it
> takes rounds and rounds to do the same for -m. This is rather sad.

It is not because Junio has special privileges or anything of the sort,
though. My understanding is that it was just an accident that "-m"
_happened_ to be misused by enough people that we deemed that breakage
unacceptable, whereas "--cc" just _happened_ to be fixable.

FWIW, I might have also been on your side when we rolled back the first
"-m" implies "-p" change, but the consensus since then is that breaking
backwards compatibility just isn't worth it in this case, and it would
take a herculean effort to change that consensus. It might not be
completely impossible though, more on that later...

> Finally, event without "log.diffMerges-m-imply-p", the rest of the
> series still makes sense, so if the conclusion is to remove it, let's
> still merge the rest, please! Let me know, and I'll then remove the
> patch and will change documentation accordingly.

Oops. Sorry, I missed this the first time I read this message. This
alone should have warranted a response.

I'm not convinced that the series makes sense without
"log.diffMerges-m-imply-p":

* The main patch is

    diff-merges: implement [no-]hide option and log.diffMergesHide config

  which gives us a way to redefine "-m" as "--diff-merges=hide
  --diff-merges=on". However, we haven't seen any compelling reasons to
  use --diff-merges=hide [1]. I'm also fairly convinced that if we go
  back in time, "-m" wouldn't have the semantics of 'do nothing unless
  -p is also given', and I don't think we should immortalize a mistake
  by giving it an explicit option.

  All the other patches in their current form are dependent on this
  patch going in.

* diff-merges: support list of values for --diff-merges

  This only makes sense if we want to accept multiple values, which we
  don't without the main patch.

* diff-merges: issue warning on lone '-m' option
  diff-merges: improve --diff-merges documentation

  These are docs and UX cleanups as a result of the main patch.

_Maybe_ the number of lone "-m" users will shrink over time to the point
where we could make the switch? We could prepare for that by warning
that lone "-m" is a no-op now, but might imply "-p" at some point in the
future, and then after X amount of time, we might say that users have
had enough warning and actually change the default. I find this
unlikely, but not impossible. However, the patches don't prepare us for
this path, and that would deserve new patches and a different discussion
from what we've been having.

1. https://lore.kernel.org/git/kl6lilimepli.fsf@chooglen-macbookpro.roam.corp.google.com/