Re: scratch/backend-completion aaaa016056 2/2: Speed it up

[Stefan Monnier <monnier@iro.umontreal.ca>]

> diff --git a/lisp/external-completion.el b/lisp/external-completion.el
> index da3a986b8c..25e94e540b 100644
> --- a/lisp/external-completion.el
> +++ b/lisp/external-completion.el
> @@ -104,8 +104,10 @@ taking a (STRING POINT) as arguments.  The default is to set to
>           `(external-completion-allc . ,(if pred (seq-filter pred all) all))))
>        (`(boundaries . ,_) nil)
>        (_
> -       (let ((all (funcall lookup string (length string))))
> -         (complete-with-action action all string pred))))))
> +       ;; FIXME: Stefan had a call to `lookup' and
> +       ;; `complete-with-action' again here, but that just seems to
> +       ;; slow down things for no good reason, so I took it out.
> +       ))))

The code was definitely needed for some cases like `try-completion`
and `all-completions` (e.g. to make sure we only return completion
of the `string` *prefix* as callers of those functions expect and to
make sure we obey `pred`).

But I'm surprised it made things slow: this code should only be involved
when the user choose some *other* completion style, so could you check
which method of the completion table was invoked?

Maybe we should only use that code when `action` is one of `t` or `nil`?


        Stefan