bug#25751: Query replace lazy highlighting

[Juri Linkov <juri@linkov.net>]

>>> > I think the problem is not that we remove the highlight and add it
>>> > anew, the problem is that there's a redisplay cycle in between the
>>> > removal and the following addition.  The fact that setting
>>> > lazy-highlight-initial-delay alleviates the problem to some extent,
>>> > but still leaves the flicker tells me that there's a call to sit-for
>>> > or some such somewhere in the code that processes replacements, and
>>> > the removal and addition of the highlight are on two different sides
>>> > of that sit-for call.  One possible solution would be to remove the
>>> > highlight and add it without triggering redisplay, then I'd expect the
>>> > flicker to go away.
>>> >
>>> > Does this make sense?
>>>
>>> This feature is called _lazy_ highlighting where _lazy_ implies that it's
>>> intended to highlight matches much later after a lot of redisplay cycles.
>>
>> You could still leave the "lazy" part, if you both remove and re-add
>> the overlays after the idle delay.  IOW, the important thing is not to
>> have redisplay between removal and addition of the highlight.
>
> That's an option too, and here is the tested patch (it sets
> lazy-highlight-max-at-a-time to nil to avoid redisplay between
> lazy iterations):

Installed and closed.