bug#44140: Updated patch

[Olivier Certner <olce.emacs@certner.fr>]

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Patch slightly edited (commit message, doc text) and rebased on top of a 
recent 'master'. Ready to apply. Easy to backport to 27 as well.

-- 
Olivier Certner

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From 3658345e21d65c1c4e72ec7a7d90e0dcf08f1f7f Mon Sep 17 00:00:00 2001
From: Olivier Certner <olce.emacs@certner.fr>
Date: Tue, 6 Jul 2021 12:35:43 +0200
Subject: [PATCH] ERC right stamps: Use also latest buffer's window's width
 (Bug#44140)

* lisp/erc/erc-stamp.el (erc-insert-timestamp-right): Use latest
buffer's window's width to position the timestamp, if both
`erc-timestamp-right-column' and `erc-fill-column' are not set (or
`erc-fill-mode' is off).  This is what the documentation says, but was
not implemented.  Also fix the bug of using selected window's width
instead of the (or some) window showing the buffer.  The latest
window's width is saved in `erc-timestamp-last-window-width' and used
when the buffer is no more shown.  In case the buffer was never shown,
which I'm not sure can happen, either use `fill-column' if set, or
give up on aligning and just output the timestamp (modulo the kludge)
right after message text.  While here, fix the off by one calculation
of point start when the reference is the window's width.
---
 lisp/erc/erc-stamp.el | 44 ++++++++++++++++++++++++++++---------------
 1 file changed, 29 insertions(+), 15 deletions(-)

diff --git a/lisp/erc/erc-stamp.el b/lisp/erc/erc-stamp.el
index 31de9e8069..4cf744549d 100644
--- a/lisp/erc/erc-stamp.el
+++ b/lisp/erc/erc-stamp.el
@@ -181,6 +181,11 @@ erc-add-timestamp
 				 (list (lambda (_window _before dir)
 					 (erc-echo-timestamp dir ct))))))))
 
+(defvar-local erc-timestamp-last-window-width nil
+  "Stores the width of the last window that showed the current
+buffer. This is used by `erc-insert-timestamp-right' when the
+current buffer is not shown in any window.")
+
 (defvar-local erc-timestamp-last-inserted nil
   "Last timestamp inserted into the buffer.")
 
@@ -250,27 +255,32 @@ erc-fill-column
 
 (defun erc-insert-timestamp-right (string)
   "Insert timestamp on the right side of the screen.
-STRING is the timestamp to insert.  The function is a possible value
-for `erc-insert-timestamp-function'.
+STRING is the timestamp to insert.  This function is a possible
+value for `erc-insert-timestamp-function'.
 
-If `erc-timestamp-only-if-changed-flag' is nil, a timestamp is always
-printed.  If this variable is non-nil, a timestamp is only printed if
-it is different from the last.
+If `erc-timestamp-only-if-changed-flag' is nil, a timestamp is
+always printed.  If this variable is non-nil, a timestamp is only
+printed if it is different from the last.
 
-If `erc-timestamp-right-column' is set, its value will be used as the
-column at which the timestamp is to be printed.  If it is nil, and
-`erc-fill-mode' is active, then the timestamp will be printed just
-before `erc-fill-column'.  Otherwise, if the current buffer is
-shown in a window, that window's width is used.  If the buffer is
-not shown, and `fill-column' is set, then the timestamp will be
-printed just `fill-column'.  As a last resort, the timestamp will
-be printed just before the window-width."
+If `erc-timestamp-right-column' is set, its value will be used as
+the column at which the timestamp is to be printed.  If it is
+nil, and `erc-fill-mode' is active, then the timestamp will be
+printed just before `erc-fill-column'.  Otherwise, if the current
+buffer is shown in a window, that window's width is used as the
+right boundary.  In case multiple windows show the buffer, the
+width of the most recently selected one is used.  If the buffer
+is not shown, the timestamp will be printed just before the
+window width of the last window that showed it.  If the buffer
+was never shown, and `fill-column' is set, it will be printed
+just before `fill-column'.  As a last resort, timestamp will be
+printed just after each line's text (no alignment)."
   (unless (and erc-timestamp-only-if-changed-flag
 	       (string-equal string erc-timestamp-last-inserted))
     (setq erc-timestamp-last-inserted string)
     (goto-char (point-max))
     (forward-char -1);; before the last newline
     (let* ((str-width (string-width string))
+           window ; Used in 'pos' computation only
 	   (pos (cond
 		 (erc-timestamp-right-column erc-timestamp-right-column)
 		 ((and (boundp 'erc-fill-mode)
@@ -278,10 +288,14 @@ erc-insert-timestamp-right
 		       (boundp 'erc-fill-column)
 		       erc-fill-column)
 		  (1+ (- erc-fill-column str-width)))
+                 ((setq window (get-buffer-window nil t))
+                  (setq erc-timestamp-last-window-width (window-width window))
+                  (- erc-timestamp-last-window-width str-width))
+                 (erc-timestamp-last-window-width
+		  (- erc-timestamp-last-window-width str-width))
 		 (fill-column
 		  (1+ (- fill-column str-width)))
-		 (t
-		  (- (window-width) str-width 1))))
+                 (t (current-column))))
 	   (from (point))
 	   (col (current-column)))
       ;; The following is a kludge used to calculate whether to move
-- 
2.30.0