bug#56815: 29.0.50; Isearch lazy-highlight highlights too much when truncate-lines is in effect

[Gregory Heytings]

> Moreover, isearch.el could use some special-purpose algorithm for 
> looking for visible matches in this case.  For example, as soon as 
> posn-at-point tells us a match is to the right of the window's right 
> edge, isearch.el could go to the beginning of the next line and continue 
> from there, instead of checking all the subsequent matches on the same 
> line (with a result that is known in advance).  This way, we will 
> probably have even fewer matches, and the search will be faster, except 
> for very large values of hscroll.

And you really think it's TRT to add such a special-purpose algorithm for 
that very specific "long-and-truncated lines" case everywhere in Emacs? 
Because isearch is just one example, there are many other places where you 
will similarly need to reduce the portion of the buffer that will be 
considered by the command to the portion of the buffer that is actually 
visible on screen.