Re: How to avoid infinite recursion in ZLE widgets

[Daniel Shahaf <d.s@xxxxxxxxxxxxxxxxxx>]

Peter Slížik wrote on Wed, 23 Sep 2020 10:34 +0200:
> Hello,
> 
> I'd like to replicate the functionality found in some text editors - namely
> that if you press a single or double quote, the editor inserts two of them
> and places the cursor inside the pair.
> 
> With some necessary checks for word boundaries, etc. left out, the solution
> looks rather trivial:
> 
> function insert-single-quotes() {
>     zle self-insert "''"    # that's "_'_'_"
>     zle backward-char
> }  
> 
> zle -N insert-single-quotes
> bindkey "'" insert-single-quotes    # that's "_'_"
> 
> However, this solution creates infinite recursion (a single quote bound to
> insert a single quote).

No, it doesn't.  I tried in «zsh -f» and it inserts a single quote
without moving the cursor.

It inserts _one_ quote, rather than two, because self-insert ignores
its positional arguments and the widget was bound to «'».

> 1. How to prevent the recursion?

Always open a new shell for testing.

> Is self-insert the right widget for this task?

You could also use «zle .self-insert», or even modify $LBUFFER and
$RBUFFER directly («LBUFFER+=\'; RBUFFER=\'$RBUFFER»).

(Incidentally, I guess you may also want to check whether ${RBUFFER}
starts with a single quote, but that's no longer a zsh question but
a business logic question.)

> 2. I played with zle -U. What are the use cases for zle self-insert and zle
> -U?

«zle -U foo» subjects the «f», «o», and «o» to bindkey mappings.  For
instance, «bindkey -s x y» followed by «zle -U x» would insert «y».

«self-insert» appends one character to the buffer.

> 3. I tried to avoid the recursion by using "zle -K .safe -U text", but it
> ended with "too many arguments for -K". How is zle -K expected to be used?

As «zle -K foo» without further arguments.  You can do something like this:

    {
        readonly save_KEYMAP=$KEYMAP
        zle -K .safe
        ⋮
    } always {
        zle -K $save_KEYMAP
    }

But see above about $LBUFFER.

Cheers,

Daniel