bug#21468: 24.5; When next-line (visual) crosses overlay with before-string="\n" point goes to column 0

[Noam Postavsky <npostavs@users.sourceforge.net>]

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On 10/10/15, Eli Zaretskii <eliz@gnu.org> wrote:
>> Date: Fri, 9 Oct 2015 19:34:43 -0400
>> From: Noam Postavsky <npostavs@users.sourceforge.net>
>> - On a truncated line with the overlay, move-end-of-line skips to the
>> next line. (I tried to avoid this by only adding the stretched space
>> when it's going to be visible. But that just made things worse
>> (looping in the display engine))
>>
>> - When at the end of line, next-line goes to the end-of-line instead
>> of staying on the same column.
>
> Are these caused by the 'cursor' property, i.e. do not happen if that
> property is not used?

They're not caused by the 'cursor' property, although it makes the 2nd
case more visually surprising.

>
> In any case, I'd appreciate a short self-contained test case for each
> of these two issues, as I'm not sure I understand what's going on.
>

Using attached 21468-overlay.el

The 1st case:

   emacs -Q -l 21468-overlay.el -f 21468-test-eol-skip

then hit C-e. Point lands at the end of line 19 instead of the end of
line 18 where it started.

The 2nd case

   emacs -Q -l 21468-overlay.el -f 21468-test-eol-col-movement

then hit C-e C-n. Point lands at the end of line 8 instead of line 8,
column 33 which is what happens when there is no overlay.

[-- Attachment #2: 21468-overlay.el --]
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(defconst +file-name+ load-file-name)
(defun 21468-put-overlay-at-line (line)
  (goto-line line)
  (let ((ov (make-overlay (line-beginning-position) (line-end-position)))
        (face (list :overline "red" :underline "green")))
    (overlay-put ov 'face face)
    (overlay-put ov 'after-string
                 (propertize "\s" 'face face
                             'display (list 'space :align-to
                                            `(+ (,(window-body-width nil t))
                                                ,(window-hscroll)))
                             'cursor t))))
(defun 21468-test-eol-skip ()
  (find-file +file-name+)
  (setq truncate-lines t)
  ;; line 18 is truncated (assuming window width < 200)
  (21468-put-overlay-at-line 18)
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  )

(defun 21468-test-eol-col-movement ()
  (find-file +file-name+)
  (21468-put-overlay-at-line 7))