emacs-27 b77f6af: ERC right stamps: also use latest buffer's window's width (Bug#44140)

[Amin Bandali]

branch: emacs-27
commit b77f6af24e9193a4f70622cda6d641c58e885c22
Author: Olivier Certner <olce.emacs@certner.fr>
Commit: Amin Bandali <bandali@gnu.org>

    ERC right stamps: also use 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 | 51 +++++++++++++++++++++++++++++++++------------------
 1 file changed, 33 insertions(+), 18 deletions(-)

diff --git a/lisp/erc/erc-stamp.el b/lisp/erc/erc-stamp.el
index 0714800..b9adce6 100644
--- a/lisp/erc/erc-stamp.el
+++ b/lisp/erc/erc-stamp.el
@@ -192,6 +192,11 @@ or `erc-send-modify-hook'."
                                 (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 erc-timestamp-last-inserted nil
   "Last timestamp inserted into the buffer.")
 (make-variable-buffer-local 'erc-timestamp-last-inserted)
@@ -267,27 +272,32 @@ property to get to the POSth 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'.
-
-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."
+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-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
+    (forward-char -1)                   ; before the last newline
     (let* ((str-width (string-width string))
+           window                  ; used in computation of `pos' only
           (pos (cond
                 (erc-timestamp-right-column erc-timestamp-right-column)
                 ((and (boundp 'erc-fill-mode)
@@ -295,10 +305,15 @@ be printed just before the window-width."
                       (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