Better detection of potentially malicious bidi text

* src/bidi.c (bidi_find_first_overridden): Extend to detect more
subtle effects of directional formatting controls, to include
embeddings and isolates.
* src/xdisp.c (Fbidi_find_overridden_directionality): Accept an
additional argument BASE-DIR to specify the base direction of the
paragraphs.

* lisp/international/mule-cmds.el (confusingly-reordered): New
face.
(reorder-starters, reorder-enders): New variables.
(highlight-confusing-reorderings): New command to detect and
highlight suspiciously reordered text.

* test/src/xdisp-tests.el
(xdisp-tests--find-directional-overrides): New test.

* etc/NEWS: Announce the new and improved features.
* etc/tutorials/TUTORIAL.he: Fix embeddings with incorrect
directions.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/src/xdisp-tests.el b/test/src/xdisp-tests.el
index 4e7d2ad8ab2..a385ded8e1d 100644
--- a/test/src/xdisp-tests.el
+++ b/test/src/xdisp-tests.el
@@ -99,4 +99,19 @@
            (width-in-chars (/ (car size) char-width)))
       (should (equal width-in-chars 3)))))
 
+(ert-deftest xdisp-tests--find-directional-overrides ()
+  (with-temp-buffer
+    (insert "\
+int main() {
+  bool isAdmin = false;
+  /*‮ }⁦if (isAdmin)⁩ ⁦ begin admins only */
+  printf(\"You are an admin.\\n\");
+  /* end admins only ‮ { ⁦*/
+  return 0;
+}")
+    (goto-char (point-min))
+    (should (eq (bidi-find-overridden-directionality (point-min) (point-max)
+                                                     nil)
+                46))))
+
 ;;; xdisp-tests.el ends here