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

From: Junio C Hamano <[email-masked]>
Date: Thu, 11 May 2023 10:37:22 -0700

Sergey Organov <[email-masked]> 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.

"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.  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.

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.

THanks.