Allow 'M-<' in the minibuffer to behave more logically

* doc/lispref/minibuf.texi (Completion Commands)
(Text from Minibuffer): Document it.

* lisp/minibuffer.el (minibuffer-beginning-of-buffer): New command
(bug#3447).
(map): Bind it.

doc/lispref/minibuf.texi

@@ -333,6 +333,9 @@ default, it makes the following bindings:
 @item @key{RET}
 @code{exit-minibuffer}
 
+@item @key{M-<}
+@code{minibuffer-beginning-of-buffer}
+
 @item @kbd{C-g}
 @code{abort-recursive-edit}
 
@@ -1248,6 +1251,14 @@ combines this keymap with either @code{minibuffer-local-completion-map}
 or @code{minibuffer-local-must-match-map}.
 @end defvar
 
+@defvar minibuffer-beginning-of-buffer-movement
+If non-@code{nil}, the @kbd{M-<} command will move to the end of the
+prompt if point is after the end of the prompt.  If point is at or
+before the end of the prompt, move to the start of the buffer.  If
+this variable is @code{nil}, the command behaves like
+@code{beginning-of-buffer}.
+@end defvar
+
 
 @node High-Level Completion
 @subsection High-Level Completion Functions

etc/NEWS

@@ -617,6 +617,12 @@ list the contents of such directories when completing file names.
 
 ** Minibuffer
 
++++
+*** A new variable, 'minibuffer-beginning-of-buffer-movement', has
+been introduced to allow controlling how the 'M-<' command works in
+the minibuffer.  If non-nil, point will move to the end of the prompt
+(if point is after the end of the prompt).
+
 ---
 *** Minibuffer now uses 'minibuffer-message' to display error messages
 at the end of the active minibuffer.

lisp/minibuffer.el

@@ -2233,6 +2233,7 @@ The completion method is determined by `completion-at-point-functions'."
 
 (let ((map minibuffer-local-map))
   (define-key map "\C-g" 'abort-recursive-edit)
+  (define-key map "\M-<" 'minibuffer-beginning-of-buffer)
   (define-key map "\r" 'exit-minibuffer)
   (define-key map "\n" 'exit-minibuffer))
 
@@ -2529,6 +2530,14 @@ such as making the current buffer visit no file in the case of
 `set-visited-file-name'."
   :type 'boolean)
 
+(defcustom minibuffer-beginning-of-buffer-movement nil
+  "Control how the `M-<' command in the minibuffer behaves.
+If non-nil, the command will go to the end of the prompt (if
+point is after the end of the prompt).  If nil, it will behave
+like the `beginning-of-buffer' command."
+  :version "27.1"
+  :type 'boolean)
+
 ;; Not always defined, but only called if next-read-file-uses-dialog-p says so.
 (declare-function x-file-dialog "xfns.c"
                   (prompt dir &optional default-filename mustmatch only-dir-p))
@@ -3589,6 +3598,33 @@ See `completing-read' for the meaning of the arguments."
     (when file-name-at-point
       (insert file-name-at-point))))
 
+(defun minibuffer-beginning-of-buffer (&optional arg)
+  "Move to the logical beginning of the minibuffer.
+This command behaves like `beginning-of-buffer', but if point is
+after the end of the prompt, move to the end of the prompt.
+Otherwise move to the start of the buffer."
+  (declare (interactive-only "use `(goto-char (point-min))' instead."))
+  (interactive "^P")
+  (when (or (consp arg)
+            (region-active-p))
+    (push-mark))
+  (goto-char (cond
+              ;; We want to go N/10th of the way from the beginning.
+              ((and arg (not (consp arg)))
+	       (+ (point-min) 1
+		  (/ (* (- (point-max) (point-min))
+                        (prefix-numeric-value arg))
+                     10)))
+              ;; Go to the start of the buffer.
+              ((or (null minibuffer-beginning-of-buffer-movement)
+                   (<= (point) (minibuffer-prompt-end)))
+	       (point-min))
+              ;; Go to the end of the minibuffer.
+              (t
+               (minibuffer-prompt-end))))
+  (when (and arg (not (consp arg)))
+    (forward-line 1)))
+
 (provide 'minibuffer)
 
 ;;; minibuffer.el ends here