Re: Simple isearch concerns

[Gregory Heytings <gregory@heytings.org>]

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Thanks again for your detailed comments!

Here is the new patch.  As you will see, it is possible to put nil in the 
cdr of the symbol property, in which case the search direction does not 
change, but I would not recommend to do that: I tried it, and the 
resulting behavior is not what one would expect, very often the match 
doesn't change at all.  Therefore I did not mention that possibility in 
the manual.

Also, there's a condition-case around the funcall, to catch beginning of 
buffer / end of buffer errors.

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From c5855569efdcd5af20ea37609ece3f0eef9c4f3d Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Fri, 8 Apr 2021 22:30:07 +0000
Subject: [PATCH] New user option to scroll isearch matches

* lisp/isearch.el (isearch-allow-match-scroll): New user option.
(isearch-pre-command-hook): Handle the new option.

* etc/NEWS: Mention the new user option.

* doc/emacs/search.texi: Document the new user option.
---
 doc/emacs/search.texi | 22 ++++++++++++++++++++++
 etc/NEWS              | 10 ++++++++++
 lisp/isearch.el       | 41 ++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 72 insertions(+), 1 deletion(-)

diff --git a/doc/emacs/search.texi b/doc/emacs/search.texi
index f3c42bcea7..59e2841611 100644
--- a/doc/emacs/search.texi
+++ b/doc/emacs/search.texi
@@ -587,6 +587,14 @@ Not Exiting Isearch
 an incremental search.  This feature is disabled if
 @code{isearch-allow-scroll} is @code{nil} (which it is by default).
 
+@vindex isearch-allow-match-scroll
+  Likewise, if you change the variable @code{isearch-allow-match-scroll}
+to a non-@code{nil} value, this enables the use of the keyboard scrolling
+commands @kbd{M-<}, @kbd{M->}, @kbd{C-v} and @kbd{M-v}, to move
+respectively to the first occurrence of the current search string in
+the buffer, the last one, the first one after the current window,
+and the last one before the current window.
+
 @item Motion Commands
 @cindex motion commands, during incremental search
 When @code{isearch-yank-on-move} is customized to @code{shift},
@@ -598,6 +606,20 @@ Not Exiting Isearch
 search string without using the shift key for cursor motion commands,
 but it applies only for certain motion command that have the
 @code{isearch-move} property on their symbols.
+
+@cindex motion commands, during incremental search, change
+  When @code{isearch-allow-match-scroll} is non-@code{nil}, it
+is also possible to change the effect of motion commands during
+incremental search, by modifying the @code{isearch-match-scroll}
+property of their symbols.  For example, to make @kbd{C-p} and
+@kbd{C-n} move to the previous and next line and restart Isearch
+forward and backward respectively, you can put the following
+lines in your init file (@pxref{Init File}):
+
+@example
+(put 'next-line 'isearch-match-scroll '(next-line . forward))
+(put 'previous-line 'isearch-match-scroll '(previous-line . backward))
+@end example
 @end table
 
 @node Isearch Minibuffer
diff --git a/etc/NEWS b/etc/NEWS
index d3a8748ded..4d4b2f48e1 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -367,6 +367,16 @@ trying to be non-destructive.
 This command opens a new buffer called "*Memory Report*" and gives a
 summary of where Emacs is using memory currently.
 
++++
+** New user option 'isearch-allow-match-scroll'.
+When this option is set, the commands 'beginning-of-buffer',
+'end-of-buffer', 'scroll-up-command' and 'scroll-down-command' move
+respectively to the first occurrence of the current search string
+in the buffer, the last one, the first one after the current window,
+and the last one before the current window.  Additionally, users can
+change the meaning of other motion commands during Isearch by using
+their 'isearch-match-scroll' property.
+
 ** Outline
 
 +++
diff --git a/lisp/isearch.el b/lisp/isearch.el
index 4b4f44bdff..ca3baf5eee 100644
--- a/lisp/isearch.el
+++ b/lisp/isearch.el
@@ -2866,12 +2866,37 @@ isearch-allow-scroll
 However, you cannot scroll far enough that the current match is
 no longer visible (is off screen).  But if the value is `unlimited'
 that limitation is removed and you can scroll any distance off screen.
-If nil, scrolling commands exit Isearch mode."
+If nil, scrolling commands exit Isearch mode.
+See also the related option `isearch-allow-match-scroll'."
   :type '(choice (const :tag "Scrolling exits Isearch" nil)
                  (const :tag "Scrolling with current match on screen" t)
                  (const :tag "Scrolling with current match off screen" unlimited))
   :group 'isearch)
 
+(put 'beginning-of-buffer 'isearch-match-scroll
+     '((lambda () (goto-char (point-min))) . forward))
+(put 'end-of-buffer 'isearch-match-scroll
+     '((lambda () (goto-char (point-max))) . backward))
+(put 'scroll-up-command 'isearch-match-scroll
+     '((lambda () (goto-char (window-end))) . forward))
+(put 'scroll-down-command 'isearch-match-scroll
+     '((lambda () (goto-char (window-start)) (recenter nil t)) . backward))
+
+(put 'next-line 'isearch-match-scroll '(next-line . forward))
+(put 'previous-line 'isearch-match-scroll '(previous-line . backward))
+
+(defcustom isearch-allow-match-scroll nil
+  "Whether scrolling to another match is allowed during incremental search.
+If non-nil, the four scrolling commands `beginning-of-buffer',
+`end-of-buffer', `scroll-up-command' and `scroll-down-command' move
+respectively to the first first occurrence of the current search string in
+the buffer, the last one, the first one after the current window, and the
+last one before the current window.
+See also the related option `isearch-allow-scroll'."
+  :type '(choice (const :tag "Off" nil)
+                 (const :tag "On" t))
+  :group 'isearch)
+
 (defcustom isearch-allow-prefix t
   "Whether prefix arguments are allowed during incremental search.
 If non-nil, entering a prefix argument will not terminate the
@@ -2973,6 +2998,20 @@ isearch-pre-command-hook
      ;; Optionally edit the search string instead of exiting.
      ((eq search-exit-option 'edit)
       (setq this-command 'isearch-edit-string))
+     ;; Handle match scrolling functions.
+     ((and isearch-allow-match-scroll
+           (symbolp this-command)
+           (get this-command 'isearch-match-scroll))
+      (let* ((property (get this-command 'isearch-match-scroll))
+             (function (car property))
+             (direction (or (cdr property)
+                            (if isearch-forward 'forward 'backward))))
+        (setq isearch-just-started t)
+        (condition-case nil
+            (funcall function)
+          (error nil))
+        (isearch-repeat direction)
+        (setq this-command 'ignore)))
      ;; Handle a scrolling function or prefix argument.
      ((or (and isearch-allow-prefix
                (memq this-command '(universal-argument universal-argument-more
-- 
2.30.2