Fine-grained NS modifier key settings (bug#38296)

For the ns-KEY-modifier and ns-right-KEY-modifier variables, KEY
being 'control', 'command', 'alternate' and 'function', allow
values on the form (:ordinary SYMBOL :function :SYMBOL :mouse SYMBOL),
so that the key can be used for different modifiers (or none) in
different contexts.  This is particularly useful for using the macOS
Option key for extended character entry while still using it as an
Emacs modifier for function keys and mouse clicks.

* src/nsterm.m (mod_of_kind, right_mod, nil_or_none): Helper functions.
(EV_MODIFIERS2): Add KIND argument.
(EV_MODIFIERS): Adapt call to EV_MODIFIERS2.
(ns_get_shifted_character): Use correct event kind for modifiers.
(ns-alternate-modifier, ns-right-alternate-modifier)
(ns-command-modifier, ns-right-command-modifier)
(ns-control-modifier, ns-right-control-modifier)
(ns-function-modifier): Rewrite doc strings for new data format.
(QCordinary, QCfunction, QCmouse): Define symbols.
* lisp/cus-start.el: Conform to new data types.
* doc/emacs/macos.texi (Mac / GNUstep Basics)
(Mac / GNUstep Customization): Improved documentation.
* etc/NEWS: Mention the change.

1 files changed, 6 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index eb32d70f571..98a35206225 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -3273,6 +3273,12 @@ Previously it was supported only in the Cygwin-w32 build.
 ** Emacs now handles key combinations involving the macOS "command"
 and "option" modifier keys more correctly.
 
+** MacOS modifier key behaviour is now more adjustable.
+The behaviour of the macOS "Option", "Command", "Control" and
+"Function" keys can now be specified separately for use with
+ordinary keys, function keys and mouse clicks.  This allows using them
+in their standard macOS way for composing characters.
+
 ** The special handling of 'frame-title-format' on NS where setting it
 to 't' would enable the macOS proxy icon has been replaced with a
 separate variable, 'ns-use-proxy-icon'.  'frame-title-format' will now