bug#38296: Allow Option key to be modifier for non-char key and mouse events

[Alan Third <alan@idiocy.org>]

On Mon, Nov 25, 2019 at 08:15:31PM +0100, Mattias Engdegård wrote:
> 21 nov. 2019 kl. 22.12 skrev Alan Third <alan@idiocy.org>:
> 
> > Do you think this functionality will only be required for the
> > alt/option key or will there be a demand to add it for command too? In
> > my experience the characters available via command are rather more
> > obscure, but I’ve little experience with non‐UK keyboards.
> 
> Looking at Mitsuharu Yamamoto's Mac port made me change my mind: it
> solves the problem by allowing the variables to have values on the
> form (:ordinary SYMBOL :function SYMBOL :mouse SYMBOL), defining
> each modifier key separately for ordinary keys, function keys and
> mouse events.

I had wondered about doing something like this, but not as flexible.
Is this the exact interface used by the Mac port? I’m not keen on the
word ‘ordinary’, but there’s no use in us doing something different.

> This is more flexible, and turned out to be rather simple to
> implement, so I think this is better than adding variables. I did it
> for all ns-KEY-modifier and ns-right-KEY-modifier variables (KEY
> being control, command, alternate and function), since it seemed
> silly not to. The relevant macOS-specific documentation was improved
> as well.

Thanks, it looks good to me. I’ve got a few nitpicks re. the
documentation:

+The modifiers themselves can be customised;

I think that should be a colon at the end, not a semi‐colon, although
my grasp of semi‐colon use is tenuous at best.

+The value of each variable is either a symbol, describing the key for
+any purpose, or a list on the form
                         ^
                        of

+@key{Option} key in macOS is normally used for composing additional

I would remove the word ‘normally’. I think it’s redundant since we’re
already talking about ‘standard behaviour’.

Unless anyone else has objections I don’t see any reason not to push
this.
-- 
Alan Third