Package: emacs;
Reported by: JD Smith <jdtsmith <at> gmail.com>
Date: Wed, 20 Aug 2025 01:40:02 UTC
Severity: normal
Found in version 30.2.50
Done: Eli Zaretskii <eliz <at> gnu.org>
View this message in rfc822 format
From: Eli Zaretskii <eliz <at> gnu.org> To: "J.D. Smith" <jdtsmith <at> gmail.com> Cc: 79275 <at> debbugs.gnu.org Subject: bug#79275: 30.2.50; overlay line-prefix display property fighting with text display property Date: Thu, 21 Aug 2025 21:13:58 +0300
> From: "J.D. Smith" <jdtsmith <at> gmail.com>
> Cc: 79275 <at> debbugs.gnu.org
> Date: Wed, 20 Aug 2025 11:06:20 -0400
>
> Eli Zaretskii <eliz <at> gnu.org> writes:
>
> >> From: JD Smith <jdtsmith <at> gmail.com>
> >> Date: Tue, 19 Aug 2025 21:39:38 -0400
> >>
> >> An overlay which applies a line-prefix (e.g. to set the fringe) across several lines conflicts with underlying text which has a replacing display property set. Evaluate the following in the *scratch* buffer, with at least 3 blank lines at the top of the buffer.
> >>
> >> (progn
> >> (delete-all-overlays)
> >> (let ((ov (make-overlay 1 4)))
> >> (overlay-put ov 'line-prefix (propertize "SHOULDNOTSEETHIS" 'display
> >> '(left-fringe right-triangle success))))
> >> (put-text-property 2 3 'display ">testing fringe display"))
> >>
> >> The result is very strange: the SHOULDNOTSEETHIS prefix string appears (sans fringe display), but then vanishes on the next redisplay. Some (well-balanced) fight between overlay line-prefix display and normal display properties seems to be occurring.
> >
> > Thanks.
> >
> > One of the redisplay optimizations we use couldn't cope with this
> > tricky situation (a line-prefix immediately followed by a display
> > string at the beginning of a line), and needs to be disabled in this
> > case.
> >
> > Does the patch below give good results?
>
> Yes it does, thanks. There still appears to be another corner case,
> however. If the conflict occurs at the /beginning/ of the overlay:
>
> (progn
> (delete-all-overlays)
> (let ((ov (make-overlay 1 4)))
> (overlay-put ov 'line-prefix (propertize "SHOULDNOTSEETHIS" 'display
> '(left-fringe right-triangle success))))
> (put-text-property 1 2 'display ">testing fringe display")) ;; changed from 2->3 to 1->2
>
> SHOULDNOTSEETHIS still appears (and remains). That situation is what
> actually motivated the report.
Please try the patch below, I hope it fixes both of the situations you
described.
diff --git a/src/xdisp.c b/src/xdisp.c
index 2691296..b8088f6 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -7261,6 +7261,8 @@ push_it (struct it *it, struct text_pos *position)
p->from_disp_prop_p = it->from_disp_prop_p;
++it->sp;
+ it->string_from_prefix_prop_p = false;
+
/* Save the state of the bidi iterator as well. */
if (it->bidi_p)
bidi_push_it (&it->bidi_it);
@@ -22657,8 +22659,23 @@ #define GIVE_UP(X) return 0
/* Give up if the row starts with a display property that draws
on the fringes, since that could prevent correct display of
line-prefix and wrap-prefix. */
- if (it.sp > 1
+ if ((it.sp > 1
&& it.method == GET_FROM_IMAGE && it.image_id == -1)
+ /* Give up if there's a line/wrap-prefix property on buffer
+ text, and the row begins with a display or overlay string.
+ This is because in that case the iterator state produced by
+ init_to_row_end is already set to the display/overlay
+ string, and thus cannot be used to display the prefix
+ before the display/overlay string. */
+ || (it.sp == 1
+ && it.method == GET_FROM_STRING
+ && !it.string_from_prefix_prop_p
+ && (!NILP (Fget_char_property (make_fixnum (IT_CHARPOS (it)),
+ Qline_prefix,
+ it.w->contents))
+ || !NILP (Fget_char_property (make_fixnum (IT_CHARPOS (it)),
+ Qwrap_prefix,
+ it.w->contents)))))
GIVE_UP (26);
start_pos = it.current.pos;
@@ -24710,15 +24727,29 @@ cursor_row_p (struct glyph_row *row)
/* Push the property PROP so that it will be rendered at the current
- position in IT. Return true if PROP was successfully pushed, false
- otherwise. Called from handle_line_prefix to handle the
- `line-prefix' and `wrap-prefix' properties. */
+ position in IT. FROM_BUFFER non-zero means the property was found on
+ buffer text, even though IT is set to iterate a string.
+ Return true if PROP was successfully pushed, false otherwise.
+ Called from handle_line_prefix to handle the `line-prefix' and
+ `wrap-prefix' properties. */
static bool
-push_prefix_prop (struct it *it, Lisp_Object prop)
+push_prefix_prop (struct it *it, Lisp_Object prop, int from_buffer)
{
- struct text_pos pos =
- STRINGP (it->string) ? it->current.string_pos : it->current.pos;
+ struct text_pos pos;
+
+ if (STRINGP (it->string))
+ {
+ if (from_buffer) /* a string, but prefix property from buffer */
+ pos = it->current.string_pos;
+ else /* a string and prefix property from string */
+ pos.charpos = pos.bytepos = 0; /* we have yet to iterate that string */
+ }
+ else /* a buffer and prefix property from buffer */
+ pos = it->current.pos;
+
+ bool phoney_display_string =
+ from_buffer && STRINGP (it->string) && it->string_from_display_prop_p;
eassert (it->method == GET_FROM_BUFFER
|| it->method == GET_FROM_DISPLAY_VECTOR
@@ -24737,6 +24768,13 @@ push_prefix_prop (struct it *it, Lisp_Object prop)
it->position not yet set when this function is called. */
push_it (it, &pos);
+ /* Reset this flag, since it is not relevant (comes from a display
+ string that follows iterator position). If we don't do that, any
+ display properties on the prefix string will be ignored. The call
+ to pop_it when we are done with the prefix will restore the flag. */
+ if (phoney_display_string)
+ it->string_from_display_prop_p = false;
+
if (STRINGP (prop))
{
if (SCHARS (prop) == 0)
@@ -24794,7 +24832,7 @@ push_prefix_prop (struct it *it, Lisp_Object prop)
#endif /* HAVE_WINDOW_SYSTEM */
else
{
- pop_it (it); /* bogus display property, give up */
+ pop_it (it); /* bogus prefix property, give up */
return false;
}
@@ -24806,11 +24844,14 @@ push_prefix_prop (struct it *it, Lisp_Object prop)
static Lisp_Object
get_it_property (struct it *it, Lisp_Object prop)
{
- Lisp_Object position, object = it->object;
+ Lisp_Object position, object;
- if (STRINGP (object))
- position = make_fixnum (IT_STRING_CHARPOS (*it));
- else if (BUFFERP (object))
+ if (STRINGP (it->string))
+ {
+ position = make_fixnum (IT_STRING_CHARPOS (*it));
+ object = it->string;
+ }
+ else if (BUFFERP (it->object))
{
position = make_fixnum (IT_CHARPOS (*it));
object = it->window;
@@ -24825,15 +24866,21 @@ get_it_property (struct it *it, Lisp_Object prop)
current IT->OBJECT and the underlying buffer text. */
static Lisp_Object
-get_line_prefix_it_property (struct it *it, Lisp_Object prop)
+get_line_prefix_it_property (struct it *it, Lisp_Object prop,
+ int *from_buffer)
{
Lisp_Object prefix = get_it_property (it, prop);
+ *from_buffer = false;
+
/* If we are looking at a display or overlay string, check also the
underlying buffer text. */
- if (NILP (prefix) && it->sp > 0 && STRINGP (it->object))
- return Fget_char_property (make_fixnum (IT_CHARPOS (*it)), prop,
- it->w->contents);
+ if (NILP (prefix) && it->sp > 0 && STRINGP (it->string))
+ {
+ *from_buffer = true;
+ return Fget_char_property (make_fixnum (IT_CHARPOS (*it)), prop,
+ it->w->contents);
+ }
return prefix;
}
@@ -24844,21 +24891,22 @@ handle_line_prefix (struct it *it)
{
Lisp_Object prefix;
bool wrap_prop = false;
+ int from_buffer;
if (it->continuation_lines_width > 0)
{
- prefix = get_line_prefix_it_property (it, Qwrap_prefix);
+ prefix = get_line_prefix_it_property (it, Qwrap_prefix, &from_buffer);
if (NILP (prefix))
prefix = Vwrap_prefix;
wrap_prop = true;
}
else
{
- prefix = get_line_prefix_it_property (it, Qline_prefix);
+ prefix = get_line_prefix_it_property (it, Qline_prefix, &from_buffer);
if (NILP (prefix))
prefix = Vline_prefix;
}
- if (! NILP (prefix) && push_prefix_prop (it, prefix))
+ if (! NILP (prefix) && push_prefix_prop (it, prefix, from_buffer))
{
/* If the prefix is wider than the window, and we try to wrap
it, it would acquire its own wrap prefix, and so on till the
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1994-97 Ian Jackson.