Re: Suggested experimental test

[Dmitry Gutov]

On 25.03.2021 21:30, Yuri Khan wrote:
> On Thu, 25 Mar 2021 at 20:20, Dmitry Gutov <dgutov@yandex.ru> wrote:
>
> > But C-c doesn't have a dedicated keymap, so solving this seems like the
> > first step. What could we do?
> >
> >     (kbd (format "%s C-l" ctl-c-key-sequence) 'some-command)
> >
> > Or maybe create a bogus ctrl-c keymap and then make sure to refer to its
> > binding with something like
> >
> >     (kbd "[C-c] C-l" 'some-command)
> >
> > ...I'm not sure, ideas welcome.
>
> How about this:
>
> * Introduce a virtual key, let’s call it <mode-specific>. Let’s
> specifically *not* name it <key-formerly-known-as-C-c>.
> * Have all modes use that as the prefix key for mode-specific
> commands, instead of C-c.
> * In the default configuration, translate C-c to <mode-specific>.
>
> Proof of concept:
>
>      $ emacs -Q
>
>      (define-key help-mode-map (kbd "<mode-specific> <mode-specific>")
>                  #'help-follow-symbol)
>      (define-key help-mode-map (kbd "<mode-specific> C-b") #'help-go-back)
>      (define-key help-mode-map (kbd "<mode-specific> C-f") #'help-go-forward)
>      (define-key key-translation-map (kbd "<menu>") (kbd "<mode-specific>"))
>      ;; C-x C-e all of the above
>
>      (define-key help-mode-map (kbd "C-c C-c") nil)
>      (define-key help-mode-map (kbd "C-c C-b") nil)
>      (define-key help-mode-map (kbd "C-c C-f") nil)
>      (define-key help-mode-map (kbd "C-c") nil)
>      ;; should be unneeded after all modes convert
>
>      (global-set-key (kbd "C-c") #'copy-region-as-kill)
>      (global-set-key (kbd "C-v") #'cua-paste)
>
>      <f1> m C-x o
>      ;; I’m now in a *Help* buffer listing currently enabled modes
>
>      <f1> b
>      ;; I’m now in a *Help* buffer listing bindings
>
>      <menu> C-b
>      ;; I’m back to modes
>
>      <menu> C-f
>      ;; I’m back to bindings
>
>      S-<down> S-<down> S-<down> C-c
>      C-x o C-v
>      ;; I have a copy of a few lines from *Help* in my *scratch*

This is a solid proposal. We can go with it, especially if we don't mind 
the key sequence ergonomics in keymaps, as well as backward incompatibility.

Perhaps we could instead do something with key-translation-map (or one 
of its friends) that works on existing keymaps?

The use of 'menu-item' allows us to filter based on whether the key is 
first in the sequence:

(define-key key-translation-map (kbd "<menu>") (kbd "C-c"))
(define-key key-translation-map (kbd "C-c")
  `(menu-item "" ,(kbd "<C-c-translated>")
              :filter my--head-of-sequence-p))
(global-set-key (kbd "<C-c-translated>") 'kill-ring-save)

(defun my--head-of-sequence-p (cmd)
  (if (> (length (this-command-keys-vector)) 1)
      (kbd "C-c")
    cmd))

This seems backward-compatible enough, but the main downside is that 
Emacs now says 'C-c-' in the echo area when you hit <menu>. Which must 
be confusing to the main target audience.