bug#35389: 27.0.50; [PATCH] Emacs on macOS sets mouse-wheel variables directly

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 10 May 2019 22:25:31 +0100
> From: Alan Third <alan@idiocy.org>
> Cc: Robert Pluim <rpluim@gmail.com>, 35389@debbugs.gnu.org,
> 	npostavs@gmail.com
> 
> > Why does that system configuration need a different default to begin
> > with?  In general, having different defaults on different systems is
> > not a good idea.
> 
> macOS 10.7+ handles wheel scrolling differently from how other systems
> handle it. If we stick with the defaults then it becomes
> uncontrollably fast, the current defaults make it feel similar to X,
> Windows, etc.
> 
> IIRC, fixing it in C is probably possible, but not as straight forward
> as just changing the defaults. There was discussion of it in Emacs
> devel at the time and only one person objected, but later changed
> their mind.

Could there be some internal variable, either in Lisp or in C, which
we then would use in the default value, as some unit, instead of just
number of wheel turns and number of lines?  Then we could set that
internal variable to different values, but keep the customization the
same in those internally-defined units.  I think that would be
somewhat cleaner, if possible and reasonable, because we'd be able to
document the customization in these units in a platform-independent
way.

If that's impractical, then I guess we'll have to live with this
inconsistency, although I personally consider it a slippery slope.  At
the very least it should be documented, in NEWS if not in the manual.

> > Also, the original patch mentioned a specific version of appkit,
> > whereas this one is more general, AFAIU.  Wouldn't that cause trouble
> > or surprise elsewhere?
> 
> We still support macOS 10.6, which behaves similarly to X and Windows.
> Changing the defaults for it would result in unexpected behaviour.

Are you saying that testing the OS version and testing the appkit
version yield the same result in this case?  Or are you saying that
testing the appkit version is simply incorrect?  Because that was my
concern.

Thanks.