GNU bug report logs - #1208
overlay after-string and adjacent overlays with same string

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Message #5 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Richard Stallman <rms <at> gnu.org>
To: emacs-pretest-bug <at> gnu.org
Subject: Two more overlay display bugs
Date: Sun, 19 Oct 2008 01:00:36 -0400

Here are bugs that were reported a year ago
which I think should not be forgotten.

To: bug-gnu-emacs <at> gnu.org
From: Joe Wells <jbw <at> macs.hw.ac.uk>
Date: Sat, 20 Oct 2007 06:32:19 +0100
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Subject: two display bugs involving interactions between after-string and
	display properties of adjacent overlays

Here are two more display bugs I found while trying to improve the
code in tex-fold.el in AUCTeX.

These bugs involve interactions between after-string and display
properties of adjacent overlays.

I'm assuming this macro in my reproduction code below:

  (defmacro test-in-fresh-buffer-and-window (&rest body)
    `(progn
       (delete-other-windows)
       (kill-buffer (get-buffer-create "xyzzy"))
       (let ((xyzzy-buf (get-buffer-create "xyzzy")))
         (set-buffer xyzzy-buf)
         (display-buffer xyzzy-buf)
         ,@body
         )))

BUG #1:  An overlay's after-string property that would appear at the
end of the buffer is not displayed, if the same overlay also has a
display property and an immediately preceding overlay also has an
after-string property.  (Putting extra characters at the end of the
buffer works around this bug.)

Reproduce with this expression:

  (test-in-fresh-buffer-and-window
   (insert "AB")
   (let ((o1 (make-overlay 1 2))
         (o2 (make-overlay 2 3)))
     (overlay-put o1 'after-string "1")
     (overlay-put o2 'after-string "2")
     (overlay-put o2 'display "b")
     ))

The above expression should display ?A1b2?.
The above expression wrongly actually displays ?A1b?.

BUG #2:  An overlay's display property and after-string property are
not displayed if an immediately following overlay shares the same Lisp
string as its display property.  (Using two distinct display strings
with identical contents works around the bug.)

Reproduce with this expression:

  (test-in-fresh-buffer-and-window
   (insert "ABCD")
   (let ((o1 (make-overlay 2 3))
         (o2 (make-overlay 3 4))
         (s #1=" "))
     (overlay-put o1 'after-string "1")
     (overlay-put o1 'display #1#)
     (overlay-put o2 'display #1#)))

The above expression should display ?A 1 D?.
The above expression wrongly actually displays ?A D?.

I hope these bug reports are helpful.

Joe

======================================================================
In GNU Emacs 22.1.1 (i686-pc-linux-gnu, GTK+ Version 2.8.20)
 of 2007-06-27 on artemis
Windowing system distributor `The X.Org Foundation', version 11.0.70000000
configured using `configure  '--prefix=/home/jbw/local2' '--enable-debug' '--disable-nls' '--with-x-toolkit=gtk' 'CFLAGS=-O0 -g3 -ggdb''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: en_US.UTF-8
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: jbw
  value of $LANG: nil
  locale-coding-system: utf-8
  default-enable-multibyte-characters: t

Minor modes in effect:
  TeX-source-specials-mode: t
  outline-minor-mode: t
  desktop-save-mode: t
  url-handler-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  auto-compression-mode: t
  temp-buffer-resize-mode: t
  size-indication-mode: t
  line-number-mode: t
  transient-mark-mode: t

Message #12 received at 1208-quiet <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: 1208-quiet <at> debbugs.gnu.org
Subject: Re: Two more overlay display bugs
Date: Sun, 19 Oct 2008 17:17:41 -0400

This was cloned from 1200, since 1200 contains two bugs.

> BUG #1:  An overlay's after-string property that would appear at the
> end of the buffer is not displayed, if the same overlay also has a
> display property and an immediately preceding overlay also has an
> after-string property.  (Putting extra characters at the end of the
> buffer works around this bug.)

This is fixed (see bug#1200).

> BUG #2:  An overlay's display property and after-string property are
> not displayed if an immediately following overlay shares the same Lisp
> string as its display property.  (Using two distinct display strings
> with identical contents works around the bug.)

This bug, 1208, is for this issue.

Message #15 received at 1208 <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: 1208 <at> debbugs.gnu.org
Subject: Re: bug#1208: overlay after-string and adjacent overlays with same string
Date: Sun, 19 Oct 2008 17:30:00 -0400

tags 1208 wontfix
stop

> BUG #2:  An overlay's display property and after-string property are
> not displayed if an immediately following overlay shares the same Lisp
> string as its display property.  (Using two distinct display strings
> with identical contents works around the bug.)

Tagging as wontfix based on the previous discussion:

http://lists.gnu.org/archive/html/bug-gnu-emacs/2008-02/msg00179.html

    This occurs because, as stated in the Emacs Lisp manual, all
    consecutive characters that have the same Lisp object as their
    `display' property are replaced as a single unit.  In this case, it's
    somewhat ambiguous what the behavior should be, but after looking at
    the code I think the behavior you suggest would be much more difficult
    to implement (and slower) than the current behavior.

    Furthermore, you can trivially obtain the behavior you want by making
    a copy of the string using copy-sequence, so that the two display
    strings are different Lisp objects.

    Therefore, let's leave this alone.

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