Commit f1827846 authored by Eli Zaretskii's avatar Eli Zaretskii

Implement copying of a buffer portion while preserving visual order.

 See http://lists.gnu.org/archive/html/emacs-devel/2014-11/msg02203.html
 and http://lists.gnu.org/archive/html/emacs-devel/2014-12/msg00063.html
 for the rationale.

 lisp/simple.el (bidi-directional-controls-chars)
 (bidi-directional-non-controls-chars): New variables.
 (squeeze-bidi-context-1, squeeze-bidi-context)
 (line-substring-with-bidi-context)
 (buffer-substring-with-bidi-context): New functions.

 doc/lispref/display.texi (Bidirectional Display): Document
 'buffer-substring-with-bidi-context'.
 doc/lispref/text.texi (Buffer Contents): Mention
 'buffer-substring-with-bidi-context' with a cross-reference.

 etc/NEWS: Mention 'buffer-substring-with-bidi-context'.
parent 2bef807c
2014-12-04 Eli Zaretskii <eliz@gnu.org>
* display.texi (Bidirectional Display): Document
'buffer-substring-with-bidi-context'.
* text.texi (Buffer Contents): Mention
'buffer-substring-with-bidi-context' with a cross-reference.
2014-12-02 Eli Zaretskii <eliz@gnu.org>
* display.texi (Bidirectional Display): Document
......
......@@ -6854,3 +6854,27 @@ 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
@cindex copying bidirectional text, preserve visual order
@cindex visual order, preserve when copying bidirectional text
When text that includes mixed right-to-left and left-to-right
characters and bidirectional controls is copied into a different
location, it can change its visual appearance, and also can affect the
visual appearance of the surrounding text at destination. This is
because reordering of bidirectional text specified by the
@acronym{UBA} has non-trivial context-dependent effects both on the
copied text and on the text at copy destination that will surround it.
Sometimes, a Lisp program may need to preserve the exact visual
appearance of the copied text at destination, and of the text that
surrounds the copy. Lisp programs can use the following function to
achieve that effect.
@defun buffer-substring-with-bidi-context start end &optional no-properties
This function works similar to @code{buffer-substring} (@pxref{Buffer
Contents}), but it prepends and appends to the copied text bidi
directional control characters necessary to preserve the visual
appearance of the text when it is inserted at another place. Optional
argument @var{no-properties}, if non-@code{nil}, means remove the text
properties from the copy of the text.
@end defun
......@@ -219,6 +219,12 @@ This function returns the contents of the entire accessible portion of
the current buffer, as a string.
@end defun
If you need to make sure the resulting string, when copied to a
different location, will not change its visual appearance due to
reordering of bidirectional text, use the
@code{buffer-substring-with-bidi-context} function
(@pxref{Bidirectional Display, buffer-substring-with-bidi-context}).
@defun filter-buffer-substring start end &optional delete
This function filters the buffer text between @var{start} and @var{end}
using a function specified by the variable
......
2014-12-04 Eli Zaretskii <eliz@gnu.org>
* NEWS: Mention 'buffer-substring-with-bidi-context'.
2014-12-02 Eli Zaretskii <eliz@gnu.org>
* NEWS: Mention 'bidi-find-overridden-directionality'.
......
......@@ -105,6 +105,13 @@ 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 new function `buffer-substring-with-bidi-context' allows to
copy a portion of a buffer into a different location while preserving
the visual appearance both of the copied text and the text at
destination, even when the copied text includes mixed bidirectional
text and directional control characters.
*** 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.
......
2014-12-04 Eli Zaretskii <eliz@gnu.org>
Implement copying of a buffer portion while preserving visual order.
* simple.el (bidi-directional-controls-chars)
(bidi-directional-non-controls-chars): New variables.
(squeeze-bidi-context-1, squeeze-bidi-context)
(line-substring-with-bidi-context)
(buffer-substring-with-bidi-context): New functions.
* files.el (file-tree-walk): Doc fix.
2014-12-04 Rupert Swarbrick <ruperts@broadcom.com> (tiny change)
......
......@@ -4126,6 +4126,144 @@ The argument is used for internal purposes; do not supply one."
(setq this-command 'kill-region)
(message "If the next command is a kill, it will append"))
(setq last-command 'kill-region)))
(defvar bidi-directional-controls-chars "\x202a-\x202e\x2066-\x2069"
"Character set that matches bidirectional formatting control characters.")
(defvar bidi-directional-non-controls-chars "^\x202a-\x202e\x2066-\x2069"
"Character set that matches any character except bidirectional controls.")
(defun squeeze-bidi-context-1 (from to category replacement)
"A subroutine of `squeeze-bidi-context'.
FROM and TO should be markers, CATEGORY and REPLACEMENT should be strings."
(let ((pt (copy-marker from))
(limit (copy-marker to))
(old-pt 0)
lim1)
(setq lim1 limit)
(goto-char pt)
(while (< pt limit)
(if (> pt old-pt)
(move-marker lim1
(save-excursion
;; L and R categories include embedding and
;; override controls, but we don't want to
;; replace them, because that might change
;; the visual order. Likewise with PDF and
;; isolate controls.
(+ pt (skip-chars-forward
bidi-directional-non-controls-chars
limit)))))
;; Replace any run of non-RTL characters by a single LRM.
(if (null (re-search-forward category lim1 t))
;; No more characters of CATEGORY, we are done.
(setq pt limit)
(replace-match replacement nil t)
(move-marker pt (point)))
(setq old-pt pt)
;; Skip directional controls, if any.
(move-marker
pt (+ pt (skip-chars-forward bidi-directional-controls-chars limit))))))
(defun squeeze-bidi-context (from to)
"Replace characters between FROM and TO while keeping bidi context.
This function replaces the region of text with as few characters
as possible, while preserving the effect that region will have on
bidirectional display before and after the region."
(let ((start (set-marker (make-marker)
(if (> from 0) from (+ (point-max) from))))
(end (set-marker (make-marker) to))
;; This is for when they copy text with read-only text
;; properties.
(inhibit-read-only t))
(if (null (marker-position end))
(setq end (point-max-marker)))
;; Replace each run of non-RTL characters with a single LRM.
(squeeze-bidi-context-1 start end "\\CR+" "\x200e")
;; Replace each run of non-LTR characters with a single RLM. Note
;; that the \cR category includes both the Arabic Letter (AL) and
;; R characters; here we ignore the distinction between them,
;; because that distinction only affects Arabic Number (AN)
;; characters, which are weak and don't affect the reordering.
(squeeze-bidi-context-1 start end "\\CL+" "\x200f")))
(defun line-substring-with-bidi-context (start end &optional no-properties)
"Return buffer text between START and END with its bidi context.
START and END are assumed to belong to the same physical line
of buffer text. This function prepends and appends to the text
between START and END bidi control characters that preserve the
visual order of that text when it is inserted at some other place."
(if (or (< start (point-min))
(> end (point-max)))
(signal 'args-out-of-range (list (current-buffer) start end)))
(let ((buf (current-buffer))
substr para-dir from to)
(save-excursion
(goto-char start)
(setq para-dir (current-bidi-paragraph-direction))
(setq from (line-beginning-position)
to (line-end-position))
(goto-char from)
;; If we don't have any mixed directional characters in the
;; entire line, we can just copy the substring without adding
;; any context.
(if (or (looking-at-p "\\CR*$")
(looking-at-p "\\CL*$"))
(setq substr (if no-properties
(buffer-substring-no-properties start end)
(buffer-substring start end)))
(setq substr
(with-temp-buffer
(if no-properties
(insert-buffer-substring-no-properties buf from to)
(insert-buffer-substring buf from to))
(squeeze-bidi-context 1 (1+ (- start from)))
(squeeze-bidi-context (- end to) nil)
(buffer-substring 1 (point-max)))))
;; Wrap the string in LRI/RLI..PDI pair to achieve 2 effects:
;; (1) force the string to have the same base embedding
;; direction as the paragraph direction at the source, no matter
;; what is the paragraph direction at destination; and (2) avoid
;; affecting the visual order of the surrounding text at
;; destination if there are characters of different
;; directionality there.
(concat (if (eq para-dir 'left-to-right) "\x2066" "\x2067")
substr "\x2069"))))
(defun buffer-substring-with-bidi-context (start end &optional no-properties)
"Return portion of current buffer between START and END with bidi context.
This function works similar to `buffer-substring', but it prepends and
appends to the text bidi directional control characters necessary to
preserve the visual appearance of the text if it is inserted at another
place. This is useful when the buffer substring includes bidirectional
text and control characters that cause non-trivial reordering on display.
If copied verbatim, such text can have a very different visual appearance,
and can also change the visual appearance of the surrounding text at the
destination of the copy.
Optional argument NO-PROPERTIES, if non-nil, means copy the text without
the text properties."
(let (line-end substr)
(if (or (< start (point-min))
(> end (point-max)))
(signal 'args-out-of-range (list (current-buffer) start end)))
(save-excursion
(goto-char start)
(setq line-end (min end (line-end-position)))
(while (< start end)
(setq substr
(concat substr
(if substr "\n" "")
(line-substring-with-bidi-context start line-end
no-properties)))
(forward-line 1)
(setq start (point))
(setq line-end (min end (line-end-position))))
substr)))
;; Yanking.
......
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