display property with newline

[Stephen Berman]

When a display text property contains a newline and some characters
following the newline, the latter are not displayed when the display
property is at (or perhaps when it overlaps) (window-start).  To
reproduce: 

1. emacs -Q

2. Type "test " 17 times, i.e., enough to make the line of text longer
than fill-column.

3. Put the cursor on column 70 and type
   `M-: (put-text-property (1- (point)) (point) 'display " \n     ")'
(the display string here is one space + a newline + five spaces, but
it is only important that it contain a newline and a following
character).

Now the buffer displays the following, where `|' marks the left
fringe, and the cursor is still on column 70, indicated by `^':

|test test test test test test test test test test test test test test 
|     test test test 
      ^

4. Type M-: (scroll-up 1); now the buffer displays the following,
where again `|' marks the left fringe, and the cursor is still on
column 70, indicated by `^':

|test test test
 ^

A variant of this bug is seen by doing steps 1-3 and then reducing the
frame height (e.g. by dragging the mouse) one line at a time until the
window contains just one line (plus the mode line and the minibuffer),
at which point the text is displayed as in step 4.
 

Another example:
a. emacs -Q
b. Type " " (i.e., space)
c. Type M-: (put-text-property (1- (point)) (point) 'display "\n***"),
so that the buffer displays this:
|
|***
 ^
d. Now typing M-: (scroll-up 1) yields an "End of buffer" error, but
clicking the down arrow in the scroll bar (at least with the GTK+
toolkit) once makes the "***" disappear and the cursor get vertically
centered in the window.  (If you put the cursor after "***" and then
click the down arrow in the scroll bar, "***" still vanishes but the
cursor is now at the top of the window.)


The first example can also be reproduced with emacs -nw -Q, however,
the resulting display after step 4 is different:
|t test
 ^

This bug also exists in the released Emacs 22.1 and appears to exist
already in 21.3, though there the behavior is somewhat different, due
I think to additional bugs that have been fixed in Emacs 22.


In GNU Emacs 22.1.50.3 (i686-pc-linux-gnu, GTK+ Version 2.10.6)
 of 2007-06-03 on escher
Windowing system distributor `The X.Org Foundation', version 11.0.70199902
configured using `configure  '--with-x-toolkit=gtk''

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

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t

Recent input:
<help-echo> C-x b t <return> M-x c o l u m <tab> <return> 
t e s t SPC C-a C-k C-y C-y C-y C-y C-y C-y C-y C-y 
C-y C-y C-y C-y C-y C-y C-y C-y C-y M-x r e p o r <tab> 
<return>

Recent messages:
("emacs" "-Q")
For information about the GNU Project and its goals, type C-h C-p.
Column-Number mode enabled
Mark set [17 times]
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