Commit dd601050 authored by Eli Zaretskii's avatar Eli Zaretskii
Browse files

Allow to search for characters whose bidi directionality was overridden.

 src/bidi.c (bidi_find_first_overridden): New function.
 src/xdisp.c (Fbidi_find_overridden_directionality): New function.
 (syms_of_xdisp): Defsubr it.
 src/dispextern.h (bidi_find_first_overridden): Add prototype.

 doc/lispref/display.texi (Bidirectional Display): Document

 etc/NEWS: Mention 'bidi-find-overridden-directionality'.
parent a92789b1
2014-12-02 Eli Zaretskii <>
* display.texi (Bidirectional Display): Document
2014-11-29 Paul Eggert <>
Lessen focus on ChangeLog files, as opposed to change log entries.
......@@ -6800,3 +6800,57 @@ affect all Emacs frames and windows.
appropriate mirrored character in the reordered text. Lisp programs
can affect the mirrored display by changing this property. Again, any
such changes affect all of Emacs display.
@cindex overriding bidirectional properties
@cindex directional overrides
@cindex LRO
@cindex RLO
The bidirectional properties of characters can be overridden by
inserting into the text special directional control characters,
(@acronym{RLO}). Any characters between a @acronym{RLO} and the
following newline or POP DIRECTIONAL FORMATTING (@acronym{PDF})
control character, whichever comes first, will be displayed as if they
were strong right-to-left characters, i.e.@: they will be reversed on
display. Similarly, any characters between @acronym{LRO} and
@acronym{PDF} or newline will display as if they were strong
left-to-right, and will @emph{not} be reversed even if they are strong
right-to-left characters.
@cindex phishing using directional overrides
@cindex malicious use of directional overrides
These overrides are useful when you want to make some text
unaffected by the reordering algorithm, and instead directly control
the display order. But they can also be used for malicious purposes,
known as @dfn{phishing}. Specifically, a URL on a Web page or a link
in an email message can be manipulated to make its visual appearance
unrecognizable, or similar to some popular benign location, while the
real location, interpreted by a browser in the logical order, is very
Emacs provides a primitive that applications can use to detect
instances of text whose bidirectional properties were overridden so as
to make a left-to-right character display as if it were a
right-to-left character, or vise versa.
@defun bidi-find-overridden-directionality from to &optional object
This function looks at the text of the specified @var{object} between
positions @var{from} (inclusive) and @var{to} (exclusive), and returns
the first position where it finds a strong left-to-right character
whose directional properties were forced to display the character as
right-to-left, or for a strong right-to-left character that was forced
to display as left-to-right. If it finds no such characters in the
specified region of text, it returns @code{nil}.
The optional argument @var{object} specifies which text to search, and
defaults to the current buffer. If @var{object} is non-@code{nil}, it
can be some other buffer, or it can be a string or a window. If it is
a string, the function searches that string. If it is a window, the
function searches the buffer displayed in that window. If a buffer
whose text you want to examine is displayed in some window, we
recommend to specify it by that window, rather than pass the buffer to
the function. This is because telling the function about the window
allows it to correctly account for window-specific overlays, which
might change the result of the function if some text in the buffer is
covered by overlays.
@end defun
2014-12-02 Eli Zaretskii <>
* NEWS: Mention 'bidi-find-overridden-directionality'.
2014-11-29 Paul Eggert <>
Lessen focus on ChangeLog files, as opposed to change log entries.
......@@ -98,6 +98,13 @@ environment. For the time being this is implemented for modern POSIX
systems and for MS-Windows, for other systems they fall back to their
counterparts `string-lessp' and `string-equal'.
** The new function `bidi-find-overridden-directionality' allows to
find characters whose directionality was, perhaps maliciously,
overridden by directional override control characters. Lisp programs
can use this to detect potential phishing of URLs and other links that
exploits bidirectional display reordering.
*** The ls-lisp package uses `string-collate-lessp' to sort file names.
If you want the old, locale-independent sorting, customize the new
option `ls-lisp-use-string-collate' to a nil value.
2014-12-02 Eli Zaretskii <>
* bidi.c (bidi_find_first_overridden): New function.
* xdisp.c (Fbidi_find_overridden_directionality): New function.
(syms_of_xdisp): Defsubr it.
* dispextern.h (bidi_find_first_overridden): Add prototype.
2014-12-02 Jan Djärv <>
* nsimage.m (initFromSkipXBM:width:height:flip:length:): Set bmRep
......@@ -3376,6 +3376,33 @@ bidi_move_to_visually_next (struct bidi_it *bidi_it)
/* Utility function for looking for strong directional characters
whose bidi type was overridden by a directional override. */
bidi_find_first_overridden (struct bidi_it *bidi_it)
ptrdiff_t found_pos = ZV;
/* Need to call bidi_resolve_weak, not bidi_resolve_explicit,
because the directional overrides are applied by the
former. */
bidi_type_t type = bidi_resolve_weak (bidi_it);
if ((type == STRONG_R && bidi_it->orig_type == STRONG_L)
|| (type == STRONG_L
&& (bidi_it->orig_type == STRONG_R
|| bidi_it->orig_type == STRONG_AL)))
found_pos = bidi_it->charpos;
} while (found_pos == ZV
&& bidi_it->charpos < ZV
&& bidi_it->ch != BIDI_EOB
&& bidi_it->ch != '\n');
return found_pos;
/* This is meant to be called from within the debugger, whenever you
wish to examine the cache contents. */
void bidi_dump_cached_states (void) EXTERNALLY_VISIBLE;
......@@ -3173,6 +3173,7 @@ extern void bidi_push_it (struct bidi_it *);
extern void bidi_pop_it (struct bidi_it *);
extern void *bidi_shelve_cache (void);
extern void bidi_unshelve_cache (void *, bool);
extern ptrdiff_t bidi_find_first_overridden (struct bidi_it *);
/* Defined in xdisp.c */
......@@ -21032,6 +21032,143 @@ See also `bidi-paragraph-direction'. */)
DEFUN ("bidi-find-overridden-directionality",
Sbidi_find_overridden_directionality, 2, 3, 0,
doc: /* Return position between FROM and TO where directionality was overridden.
This function returns the first character position in the specified
region of OBJECT where there is a character whose `bidi-class' property
is `L', but which was forced to display as `R' by a directional
override, and likewise with characters whose `bidi-class' is `R'
or `AL' that were forced to display as `L'.
If no such character is found, the function returns nil.
OBJECT is a Lisp string or buffer to search for overridden
directionality, and defaults to the current buffer if nil or omitted.
OBJECT can also be a window, in which case the function will search
the buffer displayed in that window. Passing the window instead of
a buffer is preferable when the buffer is displayed in some window,
because this function will then be able to correctly account for
window-specific overlays, which can affect the results.
Strong directional characters `L', `R', and `AL' can have their
intrinsic directionality overridden by directional override
control characters RLO \(u+202e) and LRO \(u+202d). See the
function `get-char-code-property' for a way to inquire about
the `bidi-class' property of a character. */)
(Lisp_Object from, Lisp_Object to, Lisp_Object object)
struct buffer *buf = current_buffer;
struct buffer *old = buf;
struct window *w = NULL;
bool frame_window_p = FRAME_WINDOW_P (SELECTED_FRAME ());
struct bidi_it itb;
ptrdiff_t from_pos, to_pos, from_bpos;
void *itb_data;
if (!NILP (object))
if (BUFFERP (object))
buf = XBUFFER (object);
else if (WINDOWP (object))
w = decode_live_window (object);
buf = XBUFFER (w->contents);
frame_window_p = FRAME_WINDOW_P (XFRAME (w->frame));
CHECK_STRING (object);
if (STRINGP (object))
/* Characters in unibyte strings are always treated by bidi.c as
strong LTR. */
if (!STRING_MULTIBYTE (object)
/* When we are loading loadup.el, the character property
tables needed for bidi iteration are not yet
available. */
|| !NILP (Vpurify_flag))
return Qnil;
validate_subarray (object, from, to, SCHARS (object), &from_pos, &to_pos);
if (from_pos >= SCHARS (object))
return Qnil;
/* Set up the bidi iterator. */
itb_data = bidi_shelve_cache ();
itb.paragraph_dir = NEUTRAL_DIR;
itb.string.lstring = object;
itb.string.s = NULL;
itb.string.schars = SCHARS (object);
itb.string.bufpos = 0;
itb.string.from_disp_str = 0;
itb.string.unibyte = 0;
itb.w = w;
bidi_init_it (0, 0, frame_window_p, &itb);
/* Nothing this fancy can happen in unibyte buffers, or in a
buffer that disabled reordering, or if FROM is at EOB. */
if (NILP (BVAR (buf, bidi_display_reordering))
|| NILP (BVAR (buf, enable_multibyte_characters))
/* When we are loading loadup.el, the character property
tables needed for bidi iteration are not yet
available. */
|| !NILP (Vpurify_flag))
return Qnil;
set_buffer_temp (buf);
validate_region (&from, &to);
from_pos = XINT (from);
to_pos = XINT (to);
if (from_pos >= ZV)
return Qnil;
/* Set up the bidi iterator. */
itb_data = bidi_shelve_cache ();
from_bpos = CHAR_TO_BYTE (from_pos);
if (from_pos == BEGV)
itb.charpos = BEGV;
itb.bytepos = BEGV_BYTE;
else if (FETCH_CHAR (from_bpos - 1) == '\n')
itb.charpos = from_pos;
itb.bytepos = from_bpos;
itb.charpos = find_newline_no_quit (from_pos, CHAR_TO_BYTE (from_pos),
-1, &itb.bytepos);
itb.paragraph_dir = NEUTRAL_DIR;
itb.string.s = NULL;
itb.string.lstring = Qnil;
itb.string.bufpos = 0;
itb.string.from_disp_str = 0;
itb.string.unibyte = 0;
itb.w = w;
bidi_init_it (itb.charpos, itb.bytepos, frame_window_p, &itb);
ptrdiff_t found;
do {
/* For the purposes of this function, the actual base direction of
the paragraph doesn't matter, so just set it to L2R. */
bidi_paragraph_init (L2R, &itb, 0);
while ((found = bidi_find_first_overridden (&itb)) < from_pos)
} while (found == ZV && == '\n' && itb.charpos < to_pos);
bidi_unshelve_cache (itb_data, 0);
set_buffer_temp (old);
return (from_pos <= found && found < to_pos) ? make_number (found) : Qnil;
DEFUN ("move-point-visually", Fmove_point_visually,
Smove_point_visually, 1, 1, 0,
doc: /* Move point in the visual order in the specified DIRECTION.
......@@ -30461,6 +30598,7 @@ syms_of_xdisp (void)
defsubr (&Scurrent_bidi_paragraph_direction);
defsubr (&Swindow_text_pixel_size);
defsubr (&Smove_point_visually);
defsubr (&Sbidi_find_overridden_directionality);
DEFSYM (Qmenu_bar_update_hook, "menu-bar-update-hook");
DEFSYM (Qoverriding_terminal_local_map, "overriding-terminal-local-map");
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