Setting arbitrary windows as frame's minibuffer

[Akio Burns <akioburns@icloud.com>]

I would like to set an arbitrary window as the frame's minibuffer so that I may position the minibuffer adjacent to the focused window when it is invoked rather that at the bottom of the frame.

After removing the validation in frame.c

    	  if (!MINI_WINDOW_P (XWINDOW (val)))
    	    error ("The `minibuffer' parameter does not specify a valid minibuffer window");

I tried setting the frame's minibuffer with

    (set-frame-parameter (selected-frame) 'minibuffer (selected-window))

This works for the first minibuffer invocation. Unfortunately, once the minibuffer quits/closes Emacs becomes stuck trying to resize the window and the minibuffer visually migrates back to the bottom of the frame.

Given that minibuffer window can be placed in a separate frame, it seems to me this should not be difficult. Am I missing something simple that would permit arbitrary minibuffer positioning?

—Akio