Inhibit null-string composition component (Bug#6988).

2 files changed, 12 insertions, 3 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index ad25d537f2b..2ee709f62b2 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2012-02-01  Kenichi Handa  <handa@m17n.org>
+
+        * composite.el (compose-region, compose-string): Signal error for
+        a null string component (Bug#6988).
+
 2012-01-31  Chong Yidong  <cyd@gnu.org>
 
         * frame.el (set-frame-font): New arg ALL-FRAMES.
diff --git a/lisp/composite.el b/lisp/composite.el
index 72317ac470e..739ec8bbcbd 100644
--- a/lisp/composite.el
+++ b/lisp/composite.el
@@ -211,7 +211,7 @@ or a vector or list of integers and rules.
 If it is a character, it is an alternate character to display instead
 of the text in the region.
 
-If it is a string, the elements are alternate characters.  In
+If it is a string, the elements are one or more alternate characters.  In
 this case, TAB element has a special meaning.  If the first
 character is TAB, the glyphs are displayed with left padding space
 so that no pixel overlaps with the previous column.  If the last
@@ -234,7 +234,9 @@ text in the composition."
   (let ((modified-p (buffer-modified-p))
         (inhibit-read-only t))
     (if (or (vectorp components) (listp components))
-        (setq components (encode-composition-components components)))
+        (setq components (encode-composition-components components))
+      (if (= (length components) 0)
+          (error "Invalid composition component: %s" components)))
     (compose-region-internal start end components modification-func)
     (restore-buffer-modified-p modified-p)))
 
@@ -267,7 +269,9 @@ Optional 5th argument MODIFICATION-FUNC is a function to call to
 adjust the composition when it gets invalid because of a change of
 text in the composition."
   (if (or (vectorp components) (listp components))
-      (setq components (encode-composition-components components)))
+      (setq components (encode-composition-components components))
+    (if (= (length components) 0)
+        (error "Invalid composition component: %s" components)))
   (or start (setq start 0))
   (or end (setq end (length string)))
   (compose-string-internal string start end components modification-func)