bug#59130: Inconsistent behaviour with key-translation-map

bug#59130: Inconsistent behaviour with key-translation-map

[João Guerra]

It's possible to remap keys into other keys or sequence of keys via
key-translation-map
(https://www.gnu.org/software/emacs/manual/html_node/elisp/Translation-Keymaps.html).

For example,

setting
(define-key key-translation-map (kbd "<apps>") (kbd "C-x C-f"))
and pressing <apps> will execute command find-file,

setting
(define-key key-translation-map (kbd "<apps>") (kbd "C-x"))
and pressing <apps> C-f will execute command find-file.

However, setting
(define-key key-translation-map (kbd "<apps>") (kbd "C-x @ h"))
and pressing <apps> p will not execute H-p.

(C-x @ h adds prefix hyper
https://www.gnu.org/software/emacs/manual/html_node/emacs/Modifier-Keys.html)

Is this an issue or as expected?

bug#59130: Inconsistent behaviour with key-translation-map

[Eli Zaretskii]

> From: João Guerra <joca.bt@gmail.com>
> Date: Tue, 8 Nov 2022 20:37:36 +0100
> 
> It's possible to remap keys into other keys or sequence of keys via
> key-translation-map
> (https://www.gnu.org/software/emacs/manual/html_node/elisp/Translation-Keymaps.html).
> 
> For example,
> 
> setting
> (define-key key-translation-map (kbd "<apps>") (kbd "C-x C-f"))
> and pressing <apps> will execute command find-file,
> 
> setting
> (define-key key-translation-map (kbd "<apps>") (kbd "C-x"))
> and pressing <apps> C-f will execute command find-file.
> 
> However, setting
> (define-key key-translation-map (kbd "<apps>") (kbd "C-x @ h"))
> and pressing <apps> p will not execute H-p.
> 
> (C-x @ h adds prefix hyper
> https://www.gnu.org/software/emacs/manual/html_node/emacs/Modifier-Keys.html)
> 
> Is this an issue or as expected?

Adding Stefan to CC, in the hope that he knows the answer.

bug#59130: Inconsistent behaviour with key-translation-map

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>> However, setting
>> (define-key key-translation-map (kbd "<apps>") (kbd "C-x @ h"))
>> and pressing <apps> p will not execute H-p.
>> 
>> (C-x @ h adds prefix hyper
>> https://www.gnu.org/software/emacs/manual/html_node/emacs/Modifier-Keys.html)
>> 
>> Is this an issue or as expected?

It's expected because the remapping of `C-x @ h` to a hyper prefix is
done with:

    (define-key function-key-map [?\C-x ?@ ?h] 'event-apply-hyper-modifier)

and `function-key-map` is applied *before* `key-translation-map` and hence
doesn't apply to the result of `key-translation-map` remapping.

    (define-key input-decode-map (kbd "<apps>") (kbd "C-x @ h"))

might work, OTOH, since `input-decode-map` applies before those
other two.

Note that `event-apply-hyper-modifier` has various limitations
(e.g. you can't use `?\C-x ?@ ?h ?\C-x ?@ ?m a` to make a `H-M-a` event)
so even if the above works it may not satisfy all your use cases.


        Stefan

bug#59130: Inconsistent behaviour with key-translation-map

[João Guerra]

> Note that `event-apply-hyper-modifier` has various limitations
> (e.g. you can't use `?\C-x ?@ ?h ?\C-x ?@ ?m a` to make a `H-M-a` event)
> so even if the above works it may not satisfy all your use cases.

Thanks for the clarification. Indeed I can do (define-key
key-translation-map (kbd "<apps>") #'event-apply-hyper-modifier).
However it has the limitations you described, as I cannot use Meta or
other modifiers with it.

Any suggestions on how to support this via lisp with something like
event-apply-hyper-modifier or hiperify (the example in the manual)?

bug#59130: Inconsistent behaviour with key-translation-map

[João Guerra]

After some analysis it looks like what I want to do cannot be done
totally in lisp. I'll just define hyper via xdb. Please close this
issue.

bug#59130: Inconsistent behaviour with key-translation-map

[Eli Zaretskii]

> From: João Guerra <joca.bt@gmail.com>
> Date: Thu, 10 Nov 2022 22:15:28 +0100
> Cc: 59130@debbugs.gnu.org, Stefan Monnier <monnier@iro.umontreal.ca>
> 
> After some analysis it looks like what I want to do cannot be done
> totally in lisp. I'll just define hyper via xdb. Please close this
> issue.

Thanks, closed.