bug#40808: 27.0.91; inaccuracy in isearch-lazy-count

[Juri Linkov]

>> But there is still one corner case I'm worried about:
>> isearch-lazy-count still counts matches that can't be opened
>> and can't be visited, such as hidden links in org-mode.
>>
>> To not count them we need to bind 'search-invisible' to 'open'
>> in isearch-lazy-highlight-search, but the problem is that
>> isearch-filter-predicate and isearch-range-invisible will
>> temporarily open them, whereas we need just to check
>> whether they can be opened.
>>
>> So in the following patch I added a new variable isearch-check-overlays
>> that could instruct isearch-range-invisible to not open overlays
>> when it's non-nil that means we need only to check them, not open:
>
> Fine with me, but please make this change on master, not on emacs-27.

Right decision, because org-mode is broken anyway, and this fix won't make
it better.  A test case that demonstrates the problem in org-mode:

0. emacs -Q
1. visit emacs/etc/ORG-NEWS
2. isearch for "http": C-s http C-s C-s C-s ...

it eventually stops at org links where "http" is invisible, such as

  [[https://orgmode.org/worg/library-of-babel.html][here]]

The problem is that org-mode puts the text property 'invisible'
only when the link is scrolled into view, I guess it puts the property
using font-lock.

So at least in emacs-27 now it consistently counts all matches
ignoring their visibility.