RE: C-x C-f in two frames -> "user minibuffer while in minibuffer": Bug?

[Drew Adams]

    If I open a second frame, then do C-x C-f in one of them and press
    tab so that the window is split and I get a *Completions* buffer in
    one frame, and when I then select the second frame and do a C-x C-f
    there, I don't get another *Completions* buffer there, but an error
    message that appears in the first frame:

    "Command attempted to use minibuffer while in minibuffer"

    This happens with standard settings, on the GNU/Linux port as well as
    on Carbon, no matter what display-buffer-reuse-frames is.
    Is that a bug?

Others have explained what's happening wrt minibuffer input. Here's some
more info that might help:

The *Completions* buffer is a bit special, in that its input is directed to
the minibuffer. When it is in a separate frame, the frame focus needs to be
redirected to the minibuffer explicitly, I've found. I do this:

;; Use `my-display-*Completions*-frame' to display *Completions* buffer
(add-to-list
  'special-display-buffer-names
  (list "*Completions*" 'my-display-*Completions*-frame))

(defun my-display-*Completions*-frame (buf &optional args)
  "Display *Completions* buffer in its own frame.
`special-display-function' is used to do the actual displaying.
Completion input events are redirected to `my-minibuffer-frame'."
  (let (return-window)
    (setq return-window
          (select-window (funcall special-display-function buf args)))
    (raise-frame)
    (redirect-frame-focus (selected-frame) my-minibuffer-frame)
    return-window))

The key line is the second-to-last: redirect-frame-focus.

The value of variable `my-minibuffer-frame' is a standalone minibuffer
(only) frame. (For the complete code, see
http://www.emacswiki.org/elisp/oneonone.el. See also
http://www.emacswiki.org/elisp/elect-mbuf.el for code that removes the
*Completions* frame when you are done with it.)

HTH,

  Drew