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

[martin rudalics]

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