* lisp/isearch.el (isearch-lazy-highlight): New choice ‘all-windows’.

(isearch-lazy-highlight-update): Check it to decide whether to apply
overlays only on the selected window.

* lisp/follow.el (follow-mode): Set isearch-lazy-highlight to ‘all-windows’.
(Bug#17453, bug#21092)

2 files changed, 13 insertions, 4 deletions

diff --git a/lisp/follow.el b/lisp/follow.el
index 3ad4f108902..db3b2821a56 100644
--- a/lisp/follow.el
+++ b/lisp/follow.el
@@ -427,6 +427,9 @@ Keys specific to Follow mode:
         (add-hook 'replace-update-post-hook 'follow-post-command-hook nil t)
         (add-hook 'ispell-update-post-hook 'follow-post-command-hook nil t)
 
+        (when isearch-lazy-highlight
+          (setq-local isearch-lazy-highlight 'all-windows))
+
         (setq window-group-start-function 'follow-window-start)
         (setq window-group-end-function 'follow-window-end)
         (setq set-window-group-start-function 'follow-set-window-start)
diff --git a/lisp/isearch.el b/lisp/isearch.el
index d0fb15ec641..699d6eaf730 100644
--- a/lisp/isearch.el
+++ b/lisp/isearch.el
@@ -285,8 +285,13 @@ are `word-search-regexp' \(`\\[isearch-toggle-word]'), `isearch-symbol-regexp'
   "Controls the lazy-highlighting during incremental search.
 When non-nil, all text in the buffer matching the current search
 string is highlighted lazily (see `lazy-highlight-initial-delay'
-and `lazy-highlight-interval')."
-  :type 'boolean
+and `lazy-highlight-interval').
+
+When multiple windows display the current buffer, the
+highlighting is displayed only on the selected window, unless
+this variable is set to the symbol `all-windows'."
+  :type '(choice boolean
+                 (const :tag "On, and applied to all windows" all-windows))
   :group 'lazy-highlight
   :group 'isearch)
 
@@ -3298,8 +3303,9 @@ Attempt to do the search exactly the way the pending Isearch would."
                           ;; 1000 is higher than ediff's 100+,
                           ;; but lower than isearch main overlay's 1001
                           (overlay-put ov 'priority 1000)
-                          (overlay-put ov 'face 'lazy-highlight)))
-                          ;(overlay-put ov 'window (selected-window))))
+                          (overlay-put ov 'face 'lazy-highlight)
+                          (unless (eq isearch-lazy-highlight 'all-windows)
+                            (overlay-put ov 'window (selected-window)))))
                       ;; Remember the current position of point for
                       ;; the next call of `isearch-lazy-highlight-update'
                       ;; when `lazy-highlight-max-at-a-time' is too small.