GNU bug report logs - #1200
Two more overlay display bugs

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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 1200-done <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: 1200-done <at> debbugs.gnu.org
Subject: Re: bug#1200: Two more overlay display bugs
Date: Sun, 19 Oct 2008 17:11:12 -0400

Richard Stallman wrote (on Sun, 19 Oct 2008 at 01:00 -0400):

> 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 was fixed in Emacs 22.3. The relevant change is

2008-03-31  Chong Yidong  <cyd <at> stupidchicken.com>

        * xdisp.c (next_overlay_string): Don't set
        overlay_strings_at_end_processed_p if we're currently reading
        from a display string.

> 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.)

I have split this into a separate bug.

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