bug#33838: 27.0.50; lazy-highlight fails with a quick key sequence

bug#33838: 27.0.50; lazy-highlight fails with a quick key sequence

[Juri Linkov]

Quickly typing `C-s C-s' to repeat the last search in a file with long
wrapped lines sometimes fails to lazy-highlight other matches.

This is because the condition in isearch-lazy-highlight-new-loop relies on
the return value of `(sit-for 0)' and when there is input pending like the
second `C-s' keystroke unprocessed due to the large file size with long
lines, it doesn't start a new lazy-highlight loop.

I noticed this problem only after starting to use lazy-count that fails
to count matches.  Before that, there was no clear indication that
lazy-highlight failed in such cases.

I doubt that relying on its return value was intentional, so I propose
the following fix:

diff --git a/lisp/isearch.el b/lisp/isearch.el
index dd0973d4ea..5876e70305 100644
--- a/lisp/isearch.el
+++ b/lisp/isearch.el
@@ -3661,7 +3661,7 @@ isearch-lazy-highlight-new-loop
 search string to change or the window to scroll).  It is also used
 by other Emacs features."
   (when (and (null executing-kbd-macro)
-             (sit-for 0)         ;make sure (window-start) is credible
+             (progn (sit-for 0) t) ;make sure (window-start) is credible
              (or (not (equal isearch-string
                              isearch-lazy-highlight-last-string))
                  (not (memq (selected-window)

bug#33838: 27.0.50; lazy-highlight fails with a quick key sequence

[Juri Linkov]

> Quickly typing `C-s C-s' to repeat the last search in a file with long
> wrapped lines sometimes fails to lazy-highlight other matches.
>
> This is because the condition in isearch-lazy-highlight-new-loop relies on
> the return value of `(sit-for 0)' and when there is input pending like the
> second `C-s' keystroke unprocessed due to the large file size with long
> lines, it doesn't start a new lazy-highlight loop.

I realized that sit-for here is for a reason to not try running
isearch-lazy-highlight-new-loop on every keypress.  The problem is that
when the first `C-s' is ignored (in this case isearch-string is an empty
string and isearch-lazy-highlight-last-string is the last search string),
for the second `C-s', isearch-string is equal to isearch-lazy-highlight-last-string
from the last search, so a new loop is not initiated.

A proper fix would be to reset isearch-lazy-highlight-last-string
on exiting Isearch, so it won't affect the next search:

diff --git a/lisp/isearch.el b/lisp/isearch.el
index dd0973d4ea..d2c1c150b5 100644
--- a/lisp/isearch.el
+++ b/lisp/isearch.el
@@ -1357,6 +1357,7 @@ isearch-done
   (setq minibuffer-message-timeout isearch-original-minibuffer-message-timeout)
   (isearch-dehighlight)
   (lazy-highlight-cleanup lazy-highlight-cleanup)
+  (setq isearch-lazy-highlight-last-string nil)
   (let ((found-start (window-group-start))
 	(found-point (point)))
     (when isearch-window-configuration

bug#33838: 27.0.50; lazy-highlight fails with a quick key sequence

[Juri Linkov]

> A proper fix would be to reset isearch-lazy-highlight-last-string
> on exiting Isearch, so it won't affect the next search:

Pushed to master and closed.