Error occur in completion-setup-function()

[Hideyuki SHIRAI]

Hello,

I think that found a bug at completion-setup-function() in
simple.el. Please try this code and type 'tab'. 

(let ()
  (setq test-map (make-sparse-keymap))
  (define-key test-map "\t" 'test-completion)
  (define-key test-map "\C-m" 'exit-minibuffer)

  (defun test-completion ()
    (interactive)
    (with-output-to-temp-buffer
        "*tmp*"
      (display-completion-list nil)))

  (read-from-minibuffer "Type TAB: " nil test-map))


Such an error occurs, 

Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
  +(nil 0)
  (let* ((common-string-length ...) (element-start ...) (element-common-end 
...) (maxp ...)) (while (and element-start ...) (when ... ... ...) (setq 
element-start ...) (if element-start ...)))
  (progn (let* (... ... ... ...) (while ... ... ... ...)))
  (if completion-base-size (progn (let* ... ...)))
  (when completion-base-size (let* (... ... ... ...) (while ... ... ... ...)))
  (save-current-buffer (set-buffer standard-output) <<snip>>
  (with-current-buffer standard-output (completion-list-mode) <<snip>>
  (let ((mainbuf ...) (mbuf-contents ...)) <<snip>>
  completion-setup-function()
  run-hooks(completion-setup-hook)
  display-completion-list(nil)
  (with-output-to-temp-buffer "*tmp*" (display-completion-list nil))
  test-completion()


By the way, emacs-21.3 worked. To my thinking, 

(defun completion-setup-function ()
  <<snip>>
      (when completion-base-size
        (let* ((common-string-length
                (- (length mbuf-contents) completion-base-size))
               (element-start (next-single-property-change
                               (point-min)
                               'mouse-face))
               (element-common-end
                (+ (or element-start nil) common-string-length))
                                     ~~~
that 0, point-min() or minibuffer-prompt-end() is correct of
this `nil'.
  
-- 
Hideyuki SHIRAI