bug#47215: 28.0.50; Let M-x switch between M-x and M-X

[Felician Nemeth <felician.nemeth@gmail.com>]

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Lars Ingebrigtsen <larsi@gnus.org> writes:

> Felician Nemeth <felician.nemeth@gmail.com> writes:
>
>>> I'm not quite sure how to implement this, though -- we basically end up
>>> in `completing-read', and `execute-extended-command-for-buffer' would
>>> have to define an `M-x' binding there, I guess...  and then somehow call
>>> `read-extended-command' with the text already in the minibuffer.
>>>
>>> Anybody got an idea as to how to implement this without rewriting
>>> `read-extended-command' completely?
>>
>> The execute-extended-commands have two undocumented optional arguments
>> (command-name and typed).  What are they used for?
>>
>> Anyway, following the fallback logic of `ido-find-file', I was able to
>> rebind `M-x' and save the content of the minibuffer with a non-standard
>> exit from `execute-extended-command'.  Maybe the ugly code below can
>> give ideas to someone more knowledgeable.
>
> Thanks -- I was wondering more about the situation where you've typed
>
> M-X foo|bar
>
> (| for point)
>
> and then hit `M-x' because you want to switch to the other mode.
> Ideally, `M-x' should do that, and also preserve the text the user has
> typed, and the cursor position.  I don't see an obvious simple way to do
> that... 

I've discovered that the initial-input argument of `completing-read` can
be written as (STRING . POSITION).  The attached patch makes use of it
and shows a simple implementation of my original wish.

However, the patch creates code duplication.  Also, I don't know how it
copes with recursive editing: maybe it's not a good idea to rebind M-x
when `enable-recursive-minibuffers' is t.  Finally, the docstring says
initial-input is deprecated.

I'm happy to work on the patch if you guide me to the right direction,
but this time I'd rather receive a fish instead of being taught how to
fish :)


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diff --git a/lisp/simple.el b/lisp/simple.el
index c48e644345..1bd8ba5993 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -1949,7 +1949,46 @@ read-extended-command-predicate
                         command-completion-default-include-p)
                  (function :tag "Other function")))
 
-(defun read-extended-command ()
+(defun execute-extended-command--cycle ()
+  (interactive)
+  (throw 'cycle
+         (cons 'cycle (cons (minibuffer-contents)
+                            (- (point) (minibuffer-prompt-end))))))
+
+(defun read-extended-command (&optional prompt)
+  (let ((minibuffer-local-must-match-map minibuffer-local-must-match-map)
+        (read-extended-command-predicate read-extended-command-predicate)
+        initial-input ret)
+    (define-key minibuffer-local-must-match-map
+      (kbd "M-x") #'execute-extended-command--cycle)
+    (while (not ret)
+      (setq ret (catch 'cycle
+                  (read-extended-command-1 prompt initial-input)))
+      (when (and (consp ret) (eq 'cycle (car ret)))
+        ;; Cycle to the next setting.  There's only two, so it's easy to do.
+        (if read-extended-command-predicate
+            (setq prompt "M-x "
+                  read-extended-command-predicate nil)
+          (let ((keymaps
+                  ;; The major mode's keymap and any active minor modes.
+                  (cons
+                   (current-local-map)
+                   (mapcar
+                    #'cdr
+                    (seq-filter
+                     (lambda (elem)
+                       (symbol-value (car elem)))
+                     minor-mode-map-alist)))))
+            (setq prompt "M-X ")
+            (setq read-extended-command-predicate
+                  (lambda (symbol buffer)
+                    (or (command-completion-using-modes-p symbol buffer)
+                        (where-is-internal symbol keymaps))))))
+        (setq initial-input (cdr ret))
+        (setq ret nil)))
+    ret))
+
+(defun read-extended-command-1 (prompt initial-input)
   "Read command name to invoke in `execute-extended-command'.
 This function uses the `read-extended-command-predicate' user option."
   (let ((buffer (current-buffer)))
@@ -1976,8 +2015,8 @@ read-extended-command
 		              (cons def (delete def all))
 		            all)))))
       ;; Read a string, completing from and restricting to the set of
-      ;; all defined commands.  Don't provide any initial input.
-      ;; Save the command read on the extended-command history list.
+      ;; all defined commands.  Save the command read on the
+      ;; extended-command history list.
       (completing-read
        (concat (cond
 	        ((eq current-prefix-arg '-) "- ")
@@ -1994,9 +2033,7 @@ read-extended-command
 	       ;; but actually a prompt other than "M-x" would be confusing,
 	       ;; because "M-x" is a well-known prompt to read a command
 	       ;; and it serves as a shorthand for "Extended command: ".
-               (if (memq 'shift (event-modifiers last-command-event))
-	           "M-X "
-	         "M-x "))
+               (or prompt "M-x "))
        (lambda (string pred action)
          (if (and suggest-key-bindings (eq action 'metadata))
 	     '(metadata
@@ -2013,7 +2050,7 @@ read-extended-command
                          (funcall read-extended-command-predicate sym buffer)
                        (error (message "read-extended-command-predicate: %s: %s"
                                        sym (error-message-string err))))))))
-       t nil 'extended-command-history))))
+       t initial-input 'extended-command-history))))
 
 (defun command-completion-using-modes-p (symbol buffer)
   "Say whether SYMBOL has been marked as a mode-specific command in BUFFER."
@@ -2241,7 +2278,7 @@ execute-extended-command-for-buffer
              (or (command-completion-using-modes-p symbol buffer)
                  (where-is-internal symbol keymaps)))))
      (list current-prefix-arg
-           (read-extended-command)
+           (read-extended-command "M-X ")
            execute-extended-command--last-typed)))
   (with-suppressed-warnings ((interactive-only execute-extended-command))
     (execute-extended-command prefixarg command-name typed)))