bug#31325: 27.0.50; PROPOSAL: introduce a new function to recenter without redisplaying the frame

[John Shahid]

martin rudalics <rudalics@gmx.at> writes:

>> * window.c (recenter): add a new REDISPLAY argument to allow the
>
> Please capitalize the word after the colon ...
>
>>   caller to control the redisplay behavior. `recenter' will only
>
> .. and use two spaces when beginning a new sentence.
>
> Thank you, martin

Fixed in the attached patch.

Cheers,

>From c945faf3774ea8d331ced94b80422dfaebd83018 Mon Sep 17 00:00:00 2001
From: John Shahid <jvshahid@gmail.com>
Date: Thu, 28 Jun 2018 09:13:45 -0400
Subject: [PATCH] Add a new argument to `recenter' to allow finer control of
 redisplay

* window.c (recenter): Add a new REDISPLAY argument to allow the
  caller to control the redisplay behavior.  `recenter' will only
  redisplay the frame if this new arg and `recenter-redisplay' are
  both non-nil.
* window.el (recenter-top-bottom): pass an extra non-nil argument to
  `recenter' to force a redisplay
---
 doc/lispref/windows.texi | 12 +++++++-----
 etc/NEWS                 |  5 +++++
 lisp/window.el           | 10 +++++-----
 src/window.c             | 20 +++++++++++---------
 4 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/doc/lispref/windows.texi b/doc/lispref/windows.texi
index 5497759595..9740bbebf2 100644
--- a/doc/lispref/windows.texi
+++ b/doc/lispref/windows.texi
@@ -4138,7 +4138,7 @@ Textual Scrolling
 only if point is already on that position do they signal an error.
 @end defopt
 
-@deffn Command recenter &optional count
+@deffn Command recenter &optional count redisplay
 @cindex centering point
 This function scrolls the text in the selected window so that point is
 displayed at a specified vertical position within the window.  It does
@@ -4152,8 +4152,9 @@ Textual Scrolling
 
 If @var{count} is @code{nil} (or a non-@code{nil} list),
 @code{recenter} puts the line containing point in the middle of the
-window.  If @var{count} is @code{nil}, this function may redraw the
-frame, according to the value of @code{recenter-redisplay}.
+window.  If @var{count} is @code{nil} and @var{redisplay} is
+non-@code{nil}, this function may redraw the frame, according to the
+value of @code{recenter-redisplay}.
 
 When @code{recenter} is called interactively, @var{count} is the raw
 prefix argument.  Thus, typing @kbd{C-u} as the prefix sets the
@@ -4181,8 +4182,9 @@ Textual Scrolling
 
 @defopt recenter-redisplay
 If this variable is non-@code{nil}, calling @code{recenter} with a
-@code{nil} argument redraws the frame.  The default value is
-@code{tty}, which means only redraw the frame if it is a tty frame.
+@code{nil} @var{count} argument and non-@code{nil} @var{redisplay}
+argument redraws the frame.  The default value is @code{tty}, which
+means only redraw the frame if it is a tty frame.
 @end defopt
 
 @deffn Command recenter-top-bottom &optional count
diff --git a/etc/NEWS b/etc/NEWS
index 12757f61d2..8adb962120 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -658,6 +658,11 @@ manual for more details.
 
 * Lisp Changes in Emacs 27.1
 
++++
+** The function 'recenter' accepts an additional optional argument.
+If the optional second argument is nil, recenter will not redisplay
+the frame regardless of the value of 'recenter-redisplay'.
+
 +++
 ** New functions 'major-mode-suspend' and 'major-mode-restore'.
 Use them when switching temporarily to another major mode, e.g. for
diff --git a/lisp/window.el b/lisp/window.el
index fdd510401d..6d9d8bdcd2 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -8778,15 +8778,15 @@ recenter-top-bottom
           (min (max 0 scroll-margin)
                (truncate (/ (window-body-height) 4.0)))))
       (cond ((eq recenter-last-op 'middle)
-            (recenter))
+            (recenter nil t))
            ((eq recenter-last-op 'top)
-            (recenter this-scroll-margin))
+            (recenter this-scroll-margin t))
            ((eq recenter-last-op 'bottom)
-            (recenter (- -1 this-scroll-margin)))
+            (recenter (- -1 this-scroll-margin) t))
            ((integerp recenter-last-op)
-            (recenter recenter-last-op))
+            (recenter recenter-last-op t))
            ((floatp recenter-last-op)
-            (recenter (round (* recenter-last-op (window-height))))))))))
+            (recenter (round (* recenter-last-op (window-height))) t)))))))
 
 (define-key global-map [?\C-l] 'recenter-top-bottom)
 
diff --git a/src/window.c b/src/window.c
index 81fd7f2b47..a966e99ca8 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5898,22 +5898,23 @@ displayed_window_lines (struct window *w)
 }
 
 
-DEFUN ("recenter", Frecenter, Srecenter, 0, 1, "P",
+DEFUN ("recenter", Frecenter, Srecenter, 0, 2, "P",
        doc: /* Center point in selected window and maybe redisplay frame.
 With a numeric prefix argument ARG, recenter putting point on screen line ARG
 relative to the selected window.  If ARG is negative, it counts up from the
 bottom of the window.  (ARG should be less than the height of the window.)
 
-If ARG is omitted or nil, then recenter with point on the middle line of
-the selected window; if the variable `recenter-redisplay' is non-nil,
-also erase the entire frame and redraw it (when `auto-resize-tool-bars'
-is set to `grow-only', this resets the tool-bar's height to the minimum
-height needed); if `recenter-redisplay' has the special value `tty',
-then only tty frames are redrawn.
+If ARG is omitted or nil, then recenter with point on the middle line
+of the selected window; if REDISPLAY & `recenter-redisplay' are
+non-nil, also erase the entire frame and redraw it (when
+`auto-resize-tool-bars' is set to `grow-only', this resets the
+tool-bar's height to the minimum height needed); if
+`recenter-redisplay' has the special value `tty', then only tty frames
+are redrawn.
 
 Just C-u as prefix means put point in the center of the window
 and redisplay normally--don't erase and redraw the frame.  */)
-  (register Lisp_Object arg)
+  (Lisp_Object arg, Lisp_Object redisplay)
 {
   struct window *w = XWINDOW (selected_window);
   struct buffer *buf = XBUFFER (w->contents);
@@ -5933,7 +5934,8 @@ and redisplay normally--don't erase and redraw the frame. 
 */)
 
   if (NILP (arg))
     {
-      if (!NILP (Vrecenter_redisplay)
+      if (!NILP (redisplay)
+         && !NILP (Vrecenter_redisplay)
          && (!EQ (Vrecenter_redisplay, Qtty)
              || !NILP (Ftty_type (selected_frame))))
        {
-- 
2.18.0