bug#23093: 25.0.92; Change for the worse: minibuffer completion window splits below rather that right

[N. Jackson]

Hi Martin,

At 19:47 +0100 on Tuesday 2016-03-22, martin rudalics wrote:

>> This change does not seem to me to be an improvement, as now far fewer
>> of the available completions are visible at once.
>
> Customizing ‘temp-buffer-max-height’ would fix that.

That seems a rather terrifying customization given that the current
value of `temp-buffer-max-height' is:

    (lambda
      (buffer)
      (if
          (and
           (display-graphic-p)
           (eq
            (selected-window)
            (frame-root-window)))
          (/
           (x-display-pixel-height)
           (frame-char-height)
           2)
        (/
         (-
          (frame-height)
          2)
         2)))

>> I suppose whether a "portrait" or "landscape" completions window is
>> better probably depends on the number and length of the completions and
>> also on the user's frame size, so presumably the splitting behaviour
>> should be a user option.
>
> It is.  Please customize ‘display-buffer-alist’ for the buffer named
> *Completions*.

This also doesn't seem a trivial customization; it involves alists of
alists, cons cells, regular expressions, functions.

This seems to be rather a lot to ask of the user just so they can get
back the Emacs 24 behaviour.

Instead, I was thinking more along the lines of a simple Boolean
variable called something like completions-window-prefer-split-right
with a default value of non-`nil' to give the old behaviour, and `nil'
would give the behaviour we're currently seeing in Emacs 25.