bug#53126: 29.0.50; [PATCH] Lazy highlight/count when reading query-replace string, etc.

[Augusto Stoffel <arstoffel@gmail.com>]

On Sat,  8 Jan 2022 at 20:59, Juri Linkov <juri@linkov.net> wrote:

> Strange, I expected that the lazy-count feature applied to query-replace
> should do a different thing - when querying about replacing the current match,
> it should show the number of current match and the number of total matches.
> The latter number should be updated after every replacement.
>

That would be handy too.  I haven't checked how the `perform-replace'
loop works, but wouldn't this require a hook into the lazy count
procedure --- precisely what my patch introduces through the new
variable `isearch-lazy-count-display-function'?

> But your patches are intended for a different feature - highlighting
> of matches in the buffer while entering an input string in the minibuffer.
>
> I wonder how many users need this feature, when it's easy to construct
> a query-replace string using highlighting/counting in isearch-mode,
> then type M-%
> (isearch-query-replace) that invokes query-replace with the
> query-replace string.
>

Sure, this alternative method works.  But somehow it's not the way I
usually start a replace, and I think there's nothing wrong with that
preference :-)

> Perhaps better to ask on emacs-devel if anyone needs this feature.

We can ask.  But note that the bulk of the patch has a fairly general
purpose, namely to read a regexp with live preview of the matches.
There's probably a couple extra uses for this.