bug#28978: 26.0; Regression: separate, dedicated `*Completions*' frame no longer has parameter `minibuffer'

[martin rudalics]

> The problem is that (1) PREVIOUSLY, frame *Completions*
> had a nil `minibuffer' and (2) NOW, frame *Completions*
> has a `minibuffer' parameter whose value is the active
> minibuffer window (on the minibuffer frame).
>
> Does the problem description make more sense now?
> Sorry for the confusion.

It does so indeed.  The change and its motivation are:

        Fix semantics of 'minibuffer' frame parameter

        The 'minibuffer' frame parameter is now t for a normal frame
        (a frame with a root window plus a minibuffer window) and the
        frame's minibuffer window for a minibuffer-less frame (a frame
        whose minibuffer window is on another frame).  See also:
        https://lists.gnu.org/archive/html/emacs-devel/2016-07/msg01259.html

        * src/frame.c (make_frame, make_frame_without_minibuffer)
        (make_minibuffer_frame): When assigning the frame's minibuffer
        window also store corresponding 'minibuffer' frame parameter.
        (store_frame_param): Move the 'minibuffer' parameter checks to
        the beginning so we can silently override the value before it
        gets stored in the parameter alist.  Fix error handling.
        (Fframe_parameters): Return value of 'minibuffer' parameter
        unmodified.

        * lisp/frameset.el (frameset-filter-minibuffer): When the cdr of
        the parameter is a minibuffer window, save (minibuffer . nil)
        instead of (minibuffer . t).
        (frameset--reuse-frame): To find a non-minibuffer-only frame
        look out for a frame whose 'minibuffer' parameter is t instead
        of that frame's minibuffer window.
        (frameset-minibufferless-first-p): To find a minibuffer-less
        frame look out for a frame whose 'minibuffer' parameter is a
        window instead of nil.

martin