bug#24193: 25.1; `window-min-size' fails for horizontal width when margins >= body text

[martin rudalics]

> 1. emacs -Q
> 2. in a frame 80 columns wide...
> 3. M-: (set-window-margins nil 20 20)
> 4. C-x 3
>      => "Window #<window 1 on *scratch*> too small for splitting (2)"
> 5. M-: (window-min-size nil t)
>      => 42
>
> Expected results:
>
> Window should split horizontally. Minimum window width should not be dictated 
by margin width.
>
> Actual results:
>
> Margin width dictates minimum window width and prevents window splitting.

Correct.  The Elisp manual states

 -- Function: window-min-size &optional window horizontal ignore
          pixelwise
     This function returns the minimum size of WINDOW.  WINDOW must be
     a valid window and defaults to the selected one.  The optional
     argument HORIZONTAL non-`nil' means to return the minimum number
     of columns of WINDOW; otherwise return the minimum number of
     WINDOW's lines.

     The return value makes sure that all components of WINDOW remain
     fully visible if WINDOW's size were actually set to it.  With
     HORIZONTAL `nil' it includes the mode and header line, the
     horizontal scroll bar and the bottom divider, if present.  With
     HORIZONTAL non-`nil' it includes the margins and fringes, the
     vertical scroll bar and the right divider, if present.

If you want to make a smaller window you have to explicitly specify its
size:

(defun split-window-right-ignore (&optional size)
  (interactive)
  (split-window-right (or size (/ (window-total-width) 2))))

(define-key ctl-x-map "3" 'split-window-right-ignore)

martin