bug#39822: 27.0.90; Cannot set *Completions* buffer height using display-buffer-alist

[Davor Rotim]

Testing with 'emacs -Q' and the following snippet:

(add-to-list 'display-buffer-alist
             '("\\*Completions\\*"
               (display-buffer-in-side-window)
               (window-height . 0.05)
               (side . bottom)
               (slot . 0)
               (window-parameters . ((no-other-window . t)))))

Seems like the 'window-height' parameter is being ignored and I'm unable
to set the height for the *Completions* window this way.

Switching window direction to 'left' or 'right' and setting
'window-width' instead of height seems to be working with this altered
snippet:

(add-to-list 'display-buffer-alist
             '("\\*Completions\\*"
               (display-buffer-in-side-window)
               (window-width . 0.05)
               (side . right)
               (slot . 0)
               (window-parameters . ((no-other-window . t)))))

The 'window-height' parameter gets ignored only when specifying the
'top' or 'bottom' side.


In GNU Emacs 27.0.90 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.14, cairo 
version 1.17.3)
 of 2020-02-28 built on nostromo
Repository revision: 696ee02c3a40cf0e19f963cfaf8004ca42f7e897
Repository branch: emacs-27
Windowing system distributor 'The X.Org Foundation', version 11.0.12007000
System Description: Arch Linux

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark set
(("\\*Completions\\*" (display-buffer-in-side-window) (window-width . 0.05) 
(side . right) (slot . 0) (window-parameters (no-other-window . t))))
Quit
Configured using:
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Major mode: Lisp Interaction

Minor modes in effect:
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Load-path shadows:
None found.

Features:
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Memory information:
((conses 16 44881 10781)
 (symbols 48 6003 1)
 (strings 32 15441 1795)
 (string-bytes 1 513956)
 (vectors 16 9962)
 (vector-slots 8 129161 9124)
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 (buffers 1000 11))