Re: `isearch-complete1' should use `completion-at-point' or `completion-in-region' (was: bug#39015)

[Juri Linkov]

> Not sure why in the first place `isearch-complete1' uses some custom
> auto-completion implementation that is different from a conventional 
> solution, perhaps historical reasons.  Thus, I believe that reusing either
> `completion-at-point' or `completion-in-region' to implement that
> functionality is much better in the long run.  This would also allow 
> packages, which customize completion behavior, to hook into `isearch'
> auto-completion as well.  See also [1] for example.
>
> [1] https://github.com/abo-abo/swiper/issues/1882

Indeed, Isearch uses custom completion for historical reasons,
and there is no reason for this anymore.

But there is one thing I don't understand: how packages prefer to hook
into auto-completion?  Is it enough to convert `isearch-complete1' to
just `completing-read' in the minibuffer activated by `isearch-edit-string'?