bug#13594: Planning Emacs-24.4

[martin rudalics]

> t was just a value to stop display-buffer searching down the action
> list. this seems enough to manage display-buffer via
> display-buffer-alist or the like.

It is not.  Returning t when calling `display-buffer' without may-fail
set doesn't improve anything.  And if my-fail is set, we can return nil
because the caller is prepared for it.  And you still don't handle the
case where a user doesn't want to see the buffer in the first place.

So please

(1) Provide two actions designators may-fail and do-fail, say.

(2) When may-fail is set and no window is found, return nil.  When
    may-fail is not set, return the most suitable window.

(3) When may-fail and do-fail are both set, break the

        (while (and functions (not window))
          (setq window (funcall (car functions) buffer alist)
                functions (cdr functions)))

    loop in `display-buffer' (for example, by having the function called
    return 'fail) and return nil.

martin