bug#69738: Followup

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 15 Apr 2024 10:15:55 +0000
> From: rameiko87@posteo.net
> Cc: 69738@debbugs.gnu.org
> 
> > So please show a minimal
> > recipe for reproducing this, after applying the patch I sent, and
> > starting from "emacs -Q -nw".  There's probably something I'm missing.
> 
> emacs -nw -Q (FRAME 1 IS SCRATCH)
> C-x 5 2
> M-x load-file PATCH
> M-x rmail (FRAME 2 IS RMAIL)
> M-: (setq rmail-mail-new-frame t)
> C-x 5 2
> C-x b *Messages* (FRAME 3 IS MESSAGES)
> C-x 5 o (BACK TO FRAME 2)
> m (NEW MAIL OPENS ON FRAME 4)
> C-u - C-x 5 o (THIS IS WHAT THE PATCH DOES, REVERTING BACK TO FRAME 1 
> WHICH IS SCRATCH AND NOT RMAIL)
> 
> Does it make sense?

I guess it does, although it evidently breaks the expectations of
Rmail.  Please try a more thorough patch below.

> Curiously, replacing the last line by C-c C-k kills the draft but 
> doesn't change the frame (note that I applied the patch). I deduce that 
> rmail-mail-return is not called by C-c C-k... Am I doing something 
> wrong?

It looks like "C-c C-k" (implemented in message.el) was not intended
to return to the original buffer.

diff --git a/lisp/mail/rmail.el b/lisp/mail/rmail.el
index d422383..437f120 100644
--- a/lisp/mail/rmail.el
+++ b/lisp/mail/rmail.el
@@ -3684,7 +3684,12 @@ rmail-start-mail
 				   other-headers)
   (let ((switch-function
 	 (cond (same-window nil)
-	       (rmail-mail-new-frame 'switch-to-buffer-other-frame)
+	       (rmail-mail-new-frame
+                (progn
+                  ;; Record the frame from which we invoked this command.
+                  (modify-frame-parameters (selected-frame)
+				           '((rmail-orig-frame . t)))
+                  'switch-to-buffer-other-frame))
 	       (t 'switch-to-buffer-other-window)))
 	yank-action)
     (if replybuffer
@@ -3714,6 +3719,11 @@ rmail-start-mail
 	  (modify-frame-parameters (selected-frame)
 				   '((mail-dedicated-frame . t)))))))
 
+(defun rmail--find-orig-rmail-frame ()
+  (car (filtered-frame-list
+        (lambda (frame)
+          (eq (frame-parameter frame 'rmail-orig-frame) t)))))
+
 (defun rmail-mail-return (&optional newbuf)
   "Try to return to Rmail from the mail window.
 If optional argument NEWBUF is specified, it is the Rmail buffer
@@ -3755,9 +3765,19 @@ rmail-mail-return
    ;; probably wants to delete it now.
    ((display-multi-frame-p)
     (delete-frame))
-   ;; The previous frame is where normally they have the Rmail buffer
-   ;; displayed.
-   (t (other-frame -1))))
+   (t
+    ;; Try to find the original Rmail frame and make it the top frame.
+    (let ((fr (selected-frame))
+          (orig-fr (rmail--find-orig-rmail-frame)))
+      (if orig-fr
+          (progn
+            (modify-frame-parameters orig-fr '((rmail-orig-frame . nil)))
+            (select-frame-set-input-focus orig-fr))
+        ;; If we cannot find the frame from which we started, punt, and
+        ;; display the previous frame, which is where they normally have
+        ;; the Rmail buffer displayed.
+        (other-frame -1))
+      (delete-frame fr)))))
 
 (defun rmail-mail ()
   "Send mail in another window.