bug in line-move-ignore-invisible behavior

[Eric Ding]

This bug report will be sent to the Free Software Foundation,
 not to your local site managers!!
Please write in English, because the Emacs maintainers do not have
translators to read other languages for them.

In GNU Emacs 20.7.1 (i386-redhat-linux-gnu, X toolkit)
 of Tue Jun 13 2000 on porky.devel.redhat.com
configured using `configure  --mandir=/usr/man --infodir=/usr/info
--prefix=/usr --libexecdir=/usr/lib --sharedstatedir=/var --with-gcc --with-pop
--with-x-toolkit i386-redhat-linux-gnu'

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

Load the following file in emacs, then evaluate the expressions one at
a time:

;; comment line 1
;; comment line 2
;; comment line 3
;; comment line 4
;; comment line 5

(set (make-local-variable 'line-move-ignore-invisible) t)

(add-text-properties (progn (goto-char (point-min)) (forward-line 4) (point))
                     (progn (forward-line) (point))
                     '(invisible t))

(add-text-properties (progn (goto-char (point-min)) (point))
                     (progn (forward-line 2) (point))
                     '(invisible t))

;; end of file

After the second expression's evaluated, the line ";; comment line 5"
disappears, and cursor movement ignores that line as expected.  After
the third expression's evaluated, the top two lines disappear as
expected, so that the top of the buffer looks like:

;; comment line 3
;; comment line 4

and the cursor is at the beginning of the first line.  Move the cursor
down one line, no problem.  Move it back up a line, though, and emacs
signals an error:

        Wrong type argument: integer-or-marker-p, nil

This bug is in both emacs 20.7 and emacs 21.1.

Eric

Recent input:
M-x r e p o tab o r backspace backspace r t - e m a 
c s - b u g return

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