bug#8725: 23.2; imenu--split-menu should not deliver surprises

[dino chiesa]

imenu--split-menu sorts the menu structure, placing breakout menus at
the top.  This seems arbitrary, surprising, and unnecessary. 
 
A reasonable sorting behavior would be to sort in the order in which the
menu items were found - that is to say, leave the order the way it was
on entry to the defun.  Another reasonable sorting behavior would be to
sort menu items lexicographically.  This defun does neither of those
things but rather applies the arbitrary decision to put items with
submenus at the top. Why?
 
This is not consistent with good UI design. It makes for a confusing
menu, in which the order of items doesn't correspond to *anything* useful.
 
Also, this behavior is not avoidable. Though imenu allows specification
of a sort function for menbu items, the arbitrary sorting described
above happens whether or not a custom sort function is provided. The
only way around this is to advise or redefine imenu--split-menu.
 
To fix this, in imenu.el , redefine imenu--split-menu to remove the offending
arbitrariness:
 
    (defun imenu--split-menu (menulist title)
      (let ((menulist (copy-sequence menulist))
            keep-at-top tail)
        (if (memq imenu--rescan-item menulist)
            (setq keep-at-top (list imenu--rescan-item)
                  menulist (delq imenu--rescan-item menulist)))
        ;; DPC - ban menu fascism!
        ;; (setq tail menulist)
        ;; (dolist (item tail)
        ;;   (when (imenu--subalist-p item)
        ;;     (push item keep-at-top)
        ;;     (setq menulist (delq item menulist))))
        (if imenu-sort-function
            (setq menulist (sort menulist imenu-sort-function)))
        (if (> (length menulist) imenu-max-items)
            (setq menulist
                  (mapcar
                   (lambda (menu)
                     (cons (format "From: %s" (caar menu)) menu))
                   (imenu--split menulist imenu-max-items))))
        (cons title
              (nconc (nreverse keep-at-top) menulist))))
 
 
In GNU Emacs 23.2.1 (i386-mingw-nt6.1.7601)
 of 2010-05-08 on G41R2F1
Windowing system distributor `Microsoft Corp.', version 6.1.7601
configured using `configure --with-gcc (3.4) --no-opt --cflags -Ic:/xpm/include'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
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  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: ENU
  value of $XMODIFIERS: nil
  locale-coding-system: cp1252
  default enable-multibyte-characters: t
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  tooltip-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
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