bug#44533: 27.1; Mac special key modifiers not functioning as expected

[Alan Third]

On Tue, Nov 10, 2020 at 08:09:03PM +0800, YH Tan wrote:
> 
> 
> > On Nov 10, 2020, at 19:11, Alan Third <alan@idiocy.org> wrote:
> > 
> > On Mon, Nov 09, 2020 at 11:23:13PM +0800, YH Tan wrote:
> >> The functioning of certain special key modifiers doesn't seem to work as
> >> expected in 27.1.
> >> 
> >> For example, when I do:
> >> 
> >> (setq mac-left-option-modifier 'nil)
> >            ^^^^
> >> 
> >> nothing happens to the left option key, which retains its meta function. 
> > 
> > You should be using mac-option-modifier, not mac-left-option-modifier.
> 
> This would reset both option keys. I would like to retain meta on the right. 

mac-left-option-modifier has no special function on the NS port of
Emacs. It may on the Mac port, but I don't think so. I recommend you
review the documentation (C-h i m emacs i ns-alternate-modifier).

> > This actually sounds suspiciously like you've remapped fn as option in
> > the system preferences. The fn key has some strange behaviours when
> > used with "control" keys like the arrows.
> > 
> 
> Yes. I do have: 
> 
> (setq mac-function-modifier 'meta)
> 
> which maps function to meta. You mean this can actually interfere
> with the right-option meta key? I’ve been using the same setup for
> previous versions of emacs without problem.

We reworked the keyboard handling for Emacs 27 because there were a
lot of strange behaviours.

I've attached a patch, it's for the master branch but is easily
adapted for Emacs 27.

Assuming this works I'd like to apply it to Emacs 27, but I'm not 100%
sure it won't break anything, so perhaps it's best to put it in master
first and back-port to Emacs 27 when/if we're happy with it.
-- 
Alan Third

0001-Fix-error-with-fn-key-in-NS-port-bug-44533.patch
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