From mboxrd@z Thu Jan  1 00:00:00 1970
Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail
From: Juri Linkov <juri@linkov.net>
Newsgroups: gmane.emacs.bugs
Subject: bug#51590: follow-mode is broken with header-line and tab-line
Date: Thu, 04 Nov 2021 19:29:28 +0200
Organization: LINKOV.NET
Message-ID: <86pmrf3l9m.fsf_-_@mail.linkov.net>
References: <86bl31xfl9.fsf@mail.linkov.net> <83h7ctgk93.fsf@gnu.org>
Mime-Version: 1.0
Content-Type: multipart/mixed; boundary="=-=-="
Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214";
	logging-data="16029"; mail-complaints-to="usenet@ciao.gmane.io"
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (x86_64-pc-linux-gnu)
Cc: 51590@debbugs.gnu.org
To: Eli Zaretskii <eliz@gnu.org>
Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Thu Nov 04 18:40:30 2021
Return-path: <bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org>
Envelope-to: geb-bug-gnu-emacs@m.gmane-mx.org
Original-Received: from lists.gnu.org ([209.51.188.17])
	by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)
	(Exim 4.92)
	(envelope-from <bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org>)
	id 1migj0-00040Y-CA
	for geb-bug-gnu-emacs@m.gmane-mx.org; Thu, 04 Nov 2021 18:40:30 +0100
Original-Received: from localhost ([::1]:49076 helo=lists1p.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.90_1)
	(envelope-from <bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org>)
	id 1migiy-00032M-BL
	for geb-bug-gnu-emacs@m.gmane-mx.org; Thu, 04 Nov 2021 13:40:28 -0400
Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:44908)
 by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)
 (Exim 4.90_1) (envelope-from <Debian-debbugs@debbugs.gnu.org>)
 id 1migha-0002Rg-M1
 for bug-gnu-emacs@gnu.org; Thu, 04 Nov 2021 13:39:04 -0400
Original-Received: from debbugs.gnu.org ([209.51.188.43]:60003)
 by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128)
 (Exim 4.90_1) (envelope-from <Debian-debbugs@debbugs.gnu.org>)
 id 1mighZ-0001hP-Mt
 for bug-gnu-emacs@gnu.org; Thu, 04 Nov 2021 13:39:02 -0400
Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2)
 (envelope-from <Debian-debbugs@debbugs.gnu.org>) id 1mighZ-0001V8-Jc
 for bug-gnu-emacs@gnu.org; Thu, 04 Nov 2021 13:39:01 -0400
X-Loop: help-debbugs@gnu.org
Resent-From: Juri Linkov <juri@linkov.net>
Original-Sender: "Debbugs-submit" <debbugs-submit-bounces@debbugs.gnu.org>
Resent-CC: bug-gnu-emacs@gnu.org
Resent-Date: Thu, 04 Nov 2021 17:39:01 +0000
Resent-Message-ID: <handler.51590.B51590.16360474905671@debbugs.gnu.org>
Resent-Sender: help-debbugs@gnu.org
X-GNU-PR-Message: followup 51590
X-GNU-PR-Package: emacs
Original-Received: via spool by 51590-submit@debbugs.gnu.org id=B51590.16360474905671
 (code B ref 51590); Thu, 04 Nov 2021 17:39:01 +0000
Original-Received: (at 51590) by debbugs.gnu.org; 4 Nov 2021 17:38:10 +0000
Original-Received: from localhost ([127.0.0.1]:43314 helo=debbugs.gnu.org)
 by debbugs.gnu.org with esmtp (Exim 4.84_2)
 (envelope-from <debbugs-submit-bounces@debbugs.gnu.org>)
 id 1miggk-0001TO-2I
 for submit@debbugs.gnu.org; Thu, 04 Nov 2021 13:38:10 -0400
Original-Received: from relay12.mail.gandi.net ([217.70.178.232]:47977)
 by debbugs.gnu.org with esmtp (Exim 4.84_2)
 (envelope-from <juri@linkov.net>)
 id 1miggT-0001S1-RS; Thu, 04 Nov 2021 13:38:08 -0400
Original-Received: (Authenticated sender: juri@linkov.net)
 by relay12.mail.gandi.net (Postfix) with ESMTPSA id EF6D6200003;
 Thu,  4 Nov 2021 17:37:46 +0000 (UTC)
In-Reply-To: <83h7ctgk93.fsf@gnu.org> (Eli Zaretskii's message of "Wed, 03 Nov
 2021 20:35:36 +0200")
X-BeenThere: debbugs-submit@debbugs.gnu.org
X-Mailman-Version: 2.1.18
Precedence: list
X-BeenThere: bug-gnu-emacs@gnu.org
List-Id: "Bug reports for GNU Emacs,
 the Swiss army knife of text editors" <bug-gnu-emacs.gnu.org>
List-Unsubscribe: <https://lists.gnu.org/mailman/options/bug-gnu-emacs>,
 <mailto:bug-gnu-emacs-request@gnu.org?subject=unsubscribe>
List-Archive: <https://lists.gnu.org/archive/html/bug-gnu-emacs>
List-Post: <mailto:bug-gnu-emacs@gnu.org>
List-Help: <mailto:bug-gnu-emacs-request@gnu.org?subject=help>
List-Subscribe: <https://lists.gnu.org/mailman/listinfo/bug-gnu-emacs>,
 <mailto:bug-gnu-emacs-request@gnu.org?subject=subscribe>
Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org
Original-Sender: "bug-gnu-emacs"
 <bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org>
Xref: news.gmane.io gmane.emacs.bugs:218913
Archived-At: <http://permalink.gmane.org/gmane.emacs.bugs/218913>

--=-=-=
Content-Type: text/plain

retitle 51590 follow-mode is broken with header-line and tab-line
quit

>> The most low-level function of follow-mode is follow-calc-win-end.
>> When global-tab-line-mode is enabled, follow-calc-win-end
>> returns the same values as when global-tab-line-mode is disabled.
>
> Can you step through that function and see which part is misbehaving
> there?
>
>> I don't understand what more low-level function doesn't take
>> into account the height of the tab-line.  Maybe the problem is
>> in pos-visible-in-window-p?  Or maybe different values returned
>> by window-inside-pixel-edges and window-end?
>
> I don't know the answer, but I see that header-line-format is
> mentioned in one place in follow.el, and that is not a good sign...

Indeed, I tested with the header-line, and it has the same problem,
so retitled this bug report.

After trial and error, I arrived to the following patch that completely
fixes these problems.  However, I can't explain how it works.


--=-=-=
Content-Type: text/x-diff
Content-Disposition: inline; filename=follow-line-height.patch

diff --git a/lisp/follow.el b/lisp/follow.el
index b64f4cb734..327c66d5ff 100644
--- a/lisp/follow.el
+++ b/lisp/follow.el
@@ -679,6 +679,7 @@ follow-scroll-down
 	     (goto-char start)
 	     (vertical-motion (- (- (window-height win)
 				    (if header-line-format 2 1)
+				    (if tab-line-format 2 1)
 				    next-screen-context-lines)))
 	     (set-window-start win (point))
 	     (goto-char start)
@@ -946,8 +947,10 @@ follow-calc-win-end
 used."
   (let* ((win (or win (selected-window)))
 	 (edges (window-inside-pixel-edges win))
-	 (ht (- (nth 3 edges) (nth 1 edges)))
-	 (last-line-pos (posn-point (posn-at-x-y 0 (1- ht) win))))
+	 (ht (+ (- (nth 3 edges) (nth 1 edges))
+		(window-header-line-height win)
+		(window-tab-line-height win)))
+	 (last-line-pos (posn-point (posn-at-x-y 0 (- ht 1) win))))
     (if (pos-visible-in-window-p last-line-pos win)
 	(let ((end (window-end win t)))
 	  (list end (pos-visible-in-window-p (point-max) win)))

--=-=-=--