Re: address@hidden: part of display property on before-string property is not displayed]

[YAMAMOTO Mitsuharu]

>>>>> On Wed, 03 Oct 2007 22:02:17 -0400, Richard Stallman <address@hidden> 
>>>>> said:

> [I sent this message twice but did not get a response.]

> Would someone please fix this and ack?

> ------- Start of forwarded message -------
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>       autolearn=failed version=3.1.0
> To: address@hidden
> From: Joe Wells <address@hidden>
> Date: Tue, 18 Sep 2007 23:04:11 +0100
> MIME-Version: 1.0
> Content-Type: text/plain; charset=utf-8
> Subject: part of display property on before-string property is not displayed

> When a string is the display property of a portion of a before-string
> property of an overlay, part of the display property can disappear.
> In this case the first character of the display property does not get
> shown.

> 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 (copy-sequence "DEF")))
>         (put-text-property 1 2 'display "123" s)
>         (overlay-put o 'display "Y")
>         (overlay-put o 'before-string s))))

> You will see the ?foo? window pop up and in the window you will see
> ?AD23FYC?.  I expected that instead ?AD123FYC? would be shown.

> This seems like a bug.

A suspicious part is at line 4240 in xdisp.c (line numbers are those
in the EMACS_22_BASE branch):

  3906  handle_single_display_spec (it, spec, object, position,
  3907                              display_replaced_before_p)

  4222        if (STRINGP (value))
  4223          {
  4224            if (SCHARS (value) == 0)
  4225              {
  4226                pop_it (it);
  4227                return -1;  /* Replaced by "", i.e. nothing.  */
  4228              }
  4229            it->string = value;
  4230            it->multibyte_p = STRING_MULTIBYTE (it->string);
  4231            it->current.overlay_string_index = -1;
  4232            IT_STRING_CHARPOS (*it) = IT_STRING_BYTEPOS (*it) = 0;
  4233            it->end_charpos = it->string_nchars = SCHARS (it->string);
  4234            it->method = GET_FROM_STRING;
  4235            it->stop_charpos = 0;
  4236            it->string_from_display_prop_p = 1;
  4237            /* Say that we haven't consumed the characters with
  4238               `display' property yet.  The call to pop_it in
  4239               set_iterator_to_next will clean this up.  */
  4240            *position = start_pos;
  4241          }

where `position' points to it->current.string_pos when
handle_single_display_spec above is called while processing a
`display' property in a overlay string, and thus line 4240 overrides
the effect of line 4232.

  3784  handle_display_prop (it)

  3792    if (STRINGP (it->string))
  3793      {
  3794        object = it->string;
  3795        position = &it->current.string_pos;
  3796      }
  3797    else
  3798      {
  3799        XSETWINDOW (object, it->w);
  3800        position = &it->current.pos;
  3801      }

  3855        int ret = handle_single_display_spec (it, prop, object, position, 
0);

I guess the reason to pretend as if the `display' property were not
processed yet at line 4240 is to process overlay strings at the start
position of the `display' property later.  If this guess is correct,
then this adjustment would be necessary only when processing a
`display' property within a buffer text.

Could someone more familiar with redisplay check if the following
patch DTRT?

                                     YAMAMOTO Mitsuharu
                                address@hidden

Index: src/xdisp.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/xdisp.c,v
retrieving revision 1.1149.2.11
diff -c -p -r1.1149.2.11 xdisp.c
*** src/xdisp.c 9 Oct 2007 01:28:33 -0000       1.1149.2.11
--- src/xdisp.c 11 Oct 2007 07:04:31 -0000
*************** handle_single_display_spec (it, spec, ob
*** 4237,4249 ****
          /* Say that we haven't consumed the characters with
             `display' property yet.  The call to pop_it in
             set_iterator_to_next will clean this up.  */
!         *position = start_pos;
        }
        else if (CONSP (value) && EQ (XCAR (value), Qspace))
        {
          it->method = GET_FROM_STRETCH;
          it->object = value;
!         *position = it->position = start_pos;
        }
  #ifdef HAVE_WINDOW_SYSTEM
        else
--- 4237,4252 ----
          /* Say that we haven't consumed the characters with
             `display' property yet.  The call to pop_it in
             set_iterator_to_next will clean this up.  */
!         if (!STRINGP (it->stack[it->sp - 1].string))
!           it->current.pos = start_pos;
        }
        else if (CONSP (value) && EQ (XCAR (value), Qspace))
        {
          it->method = GET_FROM_STRETCH;
          it->object = value;
!         it->position = start_pos;
!         if (!STRINGP (it->stack[it->sp - 1].string))
!           it->current.pos = start_pos;
        }
  #ifdef HAVE_WINDOW_SYSTEM
        else
*************** handle_single_display_spec (it, spec, ob
*** 4257,4263 ****
          /* Say that we haven't consumed the characters with
             `display' property yet.  The call to pop_it in
             set_iterator_to_next will clean this up.  */
!         *position = start_pos;
        }
  #endif /* HAVE_WINDOW_SYSTEM */
  
--- 4260,4267 ----
          /* Say that we haven't consumed the characters with
             `display' property yet.  The call to pop_it in
             set_iterator_to_next will clean this up.  */
!         if (!STRINGP (it->stack[it->sp - 1].string))
!           it->current.pos = start_pos;
        }
  #endif /* HAVE_WINDOW_SYSTEM */