Fix behavior of string-mark-left-to-right.

* lisp/subr.el (string-mark-left-to-right): Search the entire string
for RTL script, not just the terminating character.  Doc fix.

2 files changed, 26 insertions, 10 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index bde9d54cfa2..b9cf5367bf0 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2011-08-12  Chong Yidong  <cyd@stupidchicken.com>
+
+        * subr.el (string-mark-left-to-right): Search the entire string
+        for RTL script, not just the terminating character.  Doc fix.
+
 2011-08-12  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * progmodes/js.el (js-syntax-propertize, js-syntax-propertize-regexp):
diff --git a/lisp/subr.el b/lisp/subr.el
index a897da1d9ba..a4251b6fee6 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -3540,18 +3540,29 @@ to case differences."
                          str2 0 (length str1) ignore-case)))
 
 (defun string-mark-left-to-right (str)
-  "Return a string that can be safely embedded in left-to-right text.
-If STR ends in right-to-left (RTL) script, return a string
-consisting of STR followed by an invisible left-to-right
-mark (LRM) character.  Otherwise, return STR."
+  "Return a string that can be safely inserted in left-to-right text.
+If STR contains right-to-left (RTL) script, return a string
+consisting of STR followed by a terminating invisible
+left-to-right mark (LRM) character.
+
+The LRM character marks the end of an RTL segment, and resets the
+display direction of any subsequent text to left-to-right.
+\(Otherwise, some of that text might be displayed as part of the
+RTL segment, based on the bidirectional display algorithm.)
+
+If STR contains no RTL characters, return STR."
   (unless (stringp str)
     (signal 'wrong-type-argument (list 'stringp str)))
-  (if (and (> (length str) 0)
-           (eq (get-char-code-property (aref str (1- (length str)))
-                                       'bidi-class)
-               'R))
-      (concat str (propertize (string ?\x200e) 'invisible t))
-    str))
+  (let ((len (length str))
+        (n 0)
+        rtl-found)
+    (while (and (not rtl-found) (< n len))
+      (setq rtl-found (memq (get-char-code-property
+                             (aref str n) 'bidi-class) '(R AL RLO))
+            n (1+ n)))
+    (if rtl-found
+        (concat str (propertize (string ?\x200e) 'invisible t))
+      str)))
 
 ;;;; invisibility specs