Suggested experimental test

[Gregory Heytings <gregory@heytings.org>]

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>
> This concludes our first experimental test on the devel branch.  The 
> amount of feedback wasn't overwhelming, but we did get some -- and I 
> guess the `M-o' command wasn't very popular, so I'm not really that 
> surprised.
>
> So I think it was a moderately successful experiment, and we should use 
> this way of trying out user interface changes more.
>

May I suggest the attached, slightly more controversial, experimental 
test?

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From 8282fa547f79230a112da9e4e49c4149d4c31f7f Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Fri, 19 Mar 2021 18:51:49 +0000
Subject: [PATCH] * lisp/loadup.el: Change the 'C-o' ('open-line') binding
 experimentally

---
 lisp/loadup.el | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/lisp/loadup.el b/lisp/loadup.el
index 4a0b8f508c..02808365f0 100644
--- a/lisp/loadup.el
+++ b/lisp/loadup.el
@@ -477,6 +477,40 @@
 
 \f
 
+(define-key global-map "\C-o" #'free-ctl-o)
+
+(defun free-ctl-o ()
+  (interactive)
+  (setq prefix-arg current-prefix-arg)
+  (message "Repeat C-o to insert newlines after point, or type C-h or ? for help")
+  (let ((map (make-sparse-keymap)))
+    (define-key map (kbd "C-o") #'open-line)
+    (define-key map (kbd "C-h") #'free-ctl-o-explain)
+    (define-key map (kbd "?") #'free-ctl-o-explain)
+    (set-transient-map map t)))
+
+(defun free-ctl-o-explain ()
+  (interactive)
+  (switch-to-buffer "*Change to C-o*")
+  (let ((inhibit-read-only t))
+    (erase-buffer)
+    (insert "[Type `q' to exit this buffer.]\n\n"
+            "We've disabled the normal `C-o' binding for a month (until April\n"
+            "23th, 2021) in the development version of GNU Emacs, while keeping\n"
+            "the `open-line' command that was bound to `C-o' on repeated `C-o'.\n\n"
+            "If this change doesn't annoy too many people, the plan is to leave\n"
+            "the `C-o' key unbound, except when it is repeated, for usage by\n"
+            "third-party packages.\n\n"
+            "If you wish to restore the `C-o' binding, you can put the following\n"
+            "in your .emacs or .emacs.d/init.el file:\n\n"
+            "(global-set-key (kbd \"C-o\") #'open-line)\n\n"
+            "If you wish to protest this change, please send you thoughts to the\n"
+            "emacs-devel@gnu.org mailing list.\n"))
+  (goto-char (point-min))
+  (special-mode))
+
+\f
+
 (if dump-mode
     (let ((output (cond ((equal dump-mode "pdump") "emacs.pdmp")
                         ((equal dump-mode "dump") "emacs")
-- 
2.30.1