bug#54380: 29.0.50; Unexpected nil value of 'rest' in 'balance-windows-2'

[martin rudalics <rudalics@gmx.at>]

If the code had used a term like say 'number-of-resizable-children' we
might have been able to avoid this bug in the first place.  Too bad ...

 > Attempting to use ‘balance-windows’ in a frame displaying many
 > windows, two of which are displaying buffers which both have the
 > buffer-local variable ‘window-size-fixed’ set to t, fails with the
 > error “Wrong type argument: number-or-marker-p, nil”.  This error is
 > produced by line 5765 of window.el, “(while (and sub (> rest 0))”.  It
 > appears that the code in this function always expects ‘rest’ to have a
 > non-nil value, but in this case ‘rest’ is nil. Modifying line 5765 to
 > read “(while (and sub rest (> rest 0))” so that it checks ‘rest’ is
 > non-nil before attemping to call ‘>’ seems to fix it.  I haven’t
 > attached a patch as a patch for a one-line diff seems excessive, but
 > if it would be useful, I can provide one.

Thanks for the report.  The bug is a consequence of the following
sequence of steps in 'balance-windows-2':

- If an internal window has only fixed-size children, we eventually set
   'number-of-children' to zero here

	    (setq number-of-children (1- number-of-children))

- We set 'rest' only if 'number-of-children' is greater zero here

     (when (> number-of-children 0)
       (setq rest (% total-sum number-of-children))

- We ask for the value of 'rest' when a window has at least one child as

   (let* (...
          (first (window-child window))

     (setq sub first)
     (while (and sub (> rest 0))

I checked in a fix, please try with latest master.

Thanks again, martin