Re: Can we clarify the purpose of `git diff -s`?

From: Sergey Organov <sorganov@gmail.com>
Date: May 11, 2023, 18:04 UTC
Message-ID: <87lehu219c.fsf@osv.gnss.ru>
In-Reply-To: <xmqqwn1ewyzx.fsf@gitster.g>

Junio C Hamano <gitster@pobox.com> writes:

Show 29 quoted lines

> Sergey Organov <sorganov@gmail.com> writes:
>
>> I entirely agree with your conclusion: obviously, -s (--silent) and
>> --no-patch are to be different for UI to be even remotely intuitive, and
>> I'd vote for immediate fix of --no-patch semantics even though it's a
>> backward-incompatible change.
>
> I forgot to write about this part.
>
> tl;dr.  While I do not think the current "--no-patch" that turns off
> things other than "--patch" is intuitive, an "immediate" change is
> not possible.  Let's do one fix at a time.
>
> The behaviour came in the v1.8.4 days with a series that was merged
> by e2ecd252 (Merge branch 'mm/diff-no-patch-synonym-to-s',
> 2013-07-22), which
>
>  * made "--no-patch" a synonym for "-s";
>
>  * fixed "-s --patch", in which the effect of "-s" got stuck and did
>    not allow the patch output to be re-enabled again with "--patch";
>
>  * updated documentation to explain "--no-patch" as a synonym for
>    "-s".
>
> While it is very clear that the intent of the author was to make it
> a synonym for "-s" and not a "feature-wise enable/disable" option,
> that is what we've run with for the past 10 years.  You identified
> bugs related the "-s got stuck" problem and we recently fixed that.

I wonder, why this intention of the author has not been opposed at that time is beyond my understanding, sorry! What exactly did it bring to make --no-patch a synonym for -s? Not only it's illogical, it's even not useful as being more lengthy.

Probably nobody actually cared at that time, me thinks.

>
> "Should --no-patch be changed" can be treated as a separate issue,
> and whenever we can treat two things separately, I want to do so, to
> keep the potential blast radius smaller.

Sure it's a separate change. When I said "immediate" I meant that there is no need for some transition measures like config variables, not that it is to be included in the "fix -s".

Show 20 quoted lines

> That way, if an earlier change turns out OK but the other change
> causes severe regression, we can only revert or rework the latter. An
> exception is if committing to one change (e.g. "fix '-s'") makes the
> other change (e.g. "redefine --no-patch") impossible, but we all know
> it is not the case here. I gave an outline of how to go about it in
> the log message of that "fix '-s'" patch.
>
> I do not think it will break established use cases too badly to fix
> the behaviour of "-s" so that it does not get stuck.  We saw an
> existing breakage in one test, but asking the owners of scripts that
> make the same mistake of assuming "-s" gets stuck for some but not
> other options to fix that assumption based on an earlier faulty
> implementation is much easier.
>
> But "git diff --stat --patch --no-patch", which suddenly starts
> showing diffstat after you make "--no-patch" no longer a synonym for
> "-s", has a much larger potential to break the existing workflows.
> And I do not think asking the users who followed the documented
> "--no-patch is a synonym for -s" to change their script because we
> decided to make "--no-patch" no longer a synonym is much harder.

Why somebody would use --no-patch instead of -s when she means -s? Is't it obvious that

   git diff --stat --patch -s

is not only shorter but dramatically more clear than

   git diff --stat --patch --no-patch

???

Taking this into account, I'd predict no breakage at all.

> So, no, I do not think we can immediately "fix".  I do not think
> anybody knows if it can be done "immediately" or needs a careful
> planning to transition, and I offhand do not know if it is even
> possible to transition without fallout.

This has been expected, and this is one of the things that stops me from trying to "fix" anything in the Git UI recently. I think that perfectly legit carefulness from the maintainer to be conservative in accepting of such changes goes a bit too far, sorry!

Thanks, -- Sergey Organov