bug#54027: Wishlist: Support full CSI u specification for terminal input

[Eli Zaretskii <eliz@gnu.org>]

> From: Alex Hutcheson <alexhutcheson@google.com>
> Date: Sun, 27 Feb 2022 13:53:56 -0500
> Cc: 54027@debbugs.gnu.org
> 
> My thinking is that it's very low-cost to support all possible encodings, 
> even if it's unlikely that a terminal would actually send them.
> 
> Using your example:
> \e[65;5u
> Would be a valid way to encode C-a according to the spec at 
> http://www.leonerd.org.uk/hacks/fixterms/
> 
> Most terminals will not encode it that way, and will instead send ^A, 
> but it would be nice to support it gracefully if a terminal happens to 
> send C-a encoded that way.
> 
> In addition, the "just support all inputs encoded this way" approach
> seems simpler to understand and maintain than an approach that
> distinguishes between key combinations that have an existing 
> alternative encoding and those that don't.
> The entries in the keymap won't be referenced unless Emacs actually
> receives matching input, so the cost of having entries for additional
> combinations seems fairly minimal.
> 
> Maybe I'm misunderstanding keymap performance or some other
> important parameter, though?

Let's add Stefan to this discussion.

Stefan, any comments or thoughts?

> 
> On Sun, Feb 27, 2022 at 1:38 PM Eli Zaretskii <eliz@gnu.org> wrote:
> 
>  > From: Alex Hutcheson <alexhutcheson@google.com>
>  > Date: Sun, 27 Feb 2022 13:21:20 -0500
>  > Cc: 54027@debbugs.gnu.org
>  > 
>  > We basically need to support the cross-product of:
>  > modifier combinations x ASCII characters
> 
>  No, AFAIU we only need to support keys+modifiers that are not
>  otherwise supported already.  E.g., C-a is already supported, so we
>  don't need to add it, and similarly many other combinations are
>  already supported.  Or what am I missing?
> 
> -- 
> Alex Hutcheson
> alexhutcheson@google.com