Hi!

I found myself in a similar situation with an experimental package I've
been working on, mode-line-keyboard [1]. In this package I need to ignore
event, like key down, all together. My solution is to bind functions to
input-event-map that calls `read-key` recursively, as I found that
returning nil breaks a key sequence. I just realised that I haven't tried
[] so I might need to revisit this.

Anyway, I found the key map handing in Emacs really confusing. To help me
out I put together a companion package, keymap-logger [2], that logs most
things that is passed to and transformed by the various keymaps like
input-key-map and key-translation-map. Maybe it can help you to gain some
insight of what is going on.

    -- Anders

[1]: https://github.com/Lindydancer/mode-line-keyboard
[2]: https://github.com/Lindydancer/keymap-logger



On Thu, Dec 13, 2018 at 8:11 PM Yuri Khan <yurivkhan@gmail.com> wrote:

> Hello emacs-devel,
>
> I am trying to implement an input-decode-map for the Kitty terminal
> emulator [1], specifically, for its full keyboard mode extension [2].
> This would solve one of the two major deficiences of Emacs in a
> terminal emulator, namely, the inability to distinguish many
> keystrokes. (The other one, lack of full color, is also solved by
> Kitty, with the right terminfo modifications.)
>
> In the full keyboard mode, the terminal passes to the application
> *all* keystrokes, in a very machine-friendly format. That is, for
> events other than character input (i.e. normal characters, shifted
> characters, Enter, Tab, and Backspace), it sends an escape sequence
> containing a key code, a modifier bit mask, and whether the key was
> pressed, released, or autorepeated.
>
> This is a bit too much for an application such as Emacs; in
> particular, it is not interested in key release events, or events
> regarding modifier keys.
>
> To give an example, Kitty sends the sequence “ESC _ K p A B b ESC \”
> for the event “Left Alt pressed”.
>
> I can get Emacs to ignore this sequence by doing this:
>
>     (define-key input-decode-map "\e_KpABb\e\\" [])
>
> However, input decoding is accompanied by echoing the current key
> sequence prefix, and when the sequence is complete, Emacs clears the
> echo area. With key release events, this happens *a lot*. This is
> suboptimal because sometimes Emacs asks a question in the echo area
> and waits for a key.
>
> For example, when the user presses C-x C-c, (kill-emacs) may ask
> whether to save files. Then the release event for C-c comes, and the
> echo area is cleared.
>
> Is there a way to turn off echoing for prefixes of sequences matched
> against input-decode-map, so that echoing still works for “manual” key
> sequences but not sequences sent by the terminal?
>
> If not, would such an option be considered useful?
>
>
> [1]: https://sw.kovidgoyal.net/kitty/
> [2]:
> https://sw.kovidgoyal.net/kitty/protocol-extensions.html#keyboard-handling
>
>