GNU bug report logs - #802
before-string property has no effect if display property is empty

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Message #3 received at quiet <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: quiet <quiet <at> debbugs.gnu.org>
Subject: before-string property has no effect if display property is empty
Date: Wed, 27 Aug 2008 16:25:53 -0400

Package: emacs
Version: 22.1
Severity: minor

(Filing a report for an old item from FOR-RELEASE.)

http://lists.gnu.org/archive/html/bug-gnu-emacs/2007-09/msg00094.html
http://lists.gnu.org/archive/html/emacs-devel/2007-09/msg01816.html

Summary:
    
    The documentation leads me to believe that the before-string and
    display properties of an overlay should be orthogonal.  However, the
    before-string is not displayed if the display property is the empty
    string.
    
    Reproduce by evaluating this code:
    
      (let ((buf (get-buffer-create "foo")))
        (with-current-buffer buf
          (display-buffer buf)
          (erase-buffer)
          (dolist (o (overlays-in (point-min) (point-max)))
            (delete-overlay o))
          (insert "ABC")
          (let ((o (make-overlay 2 3))
                (s (make-string 3 ?X)))
            (overlay-put o 'display "")
            (overlay-put o 'before-string s))))
    
    You will see the 'foo' window pop up and in the window you will see
    'AC'.  I expected that instead 'AXXXC' would be shown.

Message #10 received at 802-done <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Chong Yidong <cyd <at> stupidchicken.com>
To: 802-done <at> debbugs.gnu.org
Subject: Re: before-string property has no effect if display property is empty
Date: Sat, 27 Jun 2009 00:25:08 -0400

> The documentation leads me to believe that the before-string and
> display properties of an overlay should be orthogonal.  However, the
> before-string is not displayed if the display property is the empty
> string.

>   (let ((buf (get-buffer-create "foo")))
>     (with-current-buffer buf
>       (display-buffer buf)
>       (erase-buffer)
>       (dolist (o (overlays-in (point-min) (point-max)))
>         (delete-overlay o))
>       (insert "ABC")
>       (let ((o (make-overlay 2 3))
>             (s (make-string 3 ?X)))
>         (overlay-put o 'display "")
>         (overlay-put o 'before-string s))))

> You will see the 'foo' window pop up and in the window you will see
> 'AC'.  I expected that instead 'AXXXC' would be shown.

This bug is already fixed in current CVS (and in the Emacs 23.1 branch).

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