international/mule.el (make-translation-table-from-alist): Accept nil or zero-length vector for FROM and TO.

2 files changed, 29 insertions, 15 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 193e0c0ebf2..48c73bb4196 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2014-12-29  K. Handa  <handa@gnu.org>
+
+        * international/mule.el (make-translation-table-from-alist):
+        Accept nil or zero-length vector for FROM and TO.
+
 2014-12-28  Ivan Shmakov  <ivan@siamics.net>
 
         * net/shr.el (shr-tag-table): Fix handling of tbody/header/footer
diff --git a/lisp/international/mule.el b/lisp/international/mule.el
index 4f8d50c8c84..fd527b1059e 100644
--- a/lisp/international/mule.el
+++ b/lisp/international/mule.el
@@ -2317,7 +2317,13 @@ ALIST is an alist, each element has the form (FROM . TO).
 FROM and TO are a character or a vector of characters.
 If FROM is a character, that character is translated to TO.
 If FROM is a vector of characters, that sequence is translated to TO.
-The first extra-slot of the value is a translation table for reverse mapping."
+The first extra-slot of the value is a translation table for reverse mapping.
+
+FROM and TO may be nil.  If TO is nil, the translation from FROM
+to nothing is defined in the translation table and that element
+is ignored in the reverse map.  If FROM is nil, the translation
+from TO to nothing is defined in the reverse map only.  A vector
+of length zero has the same meaning as specifying nil."
   (let ((tables (vector (make-char-table 'translation-table)
                         (make-char-table 'translation-table)))
         table max-lookup from to idx val)
@@ -2330,20 +2336,23 @@ The first extra-slot of the value is a translation table for reverse mapping."
           (setq from (cdr elt) to (car elt)))
         (if (characterp from)
             (setq idx from)
-          (setq idx (aref from 0)
-                max-lookup (max max-lookup (length from))))
-        (setq val (aref table idx))
-        (if val
-            (progn
-              (or (consp val)
-                  (setq val (list (cons (vector idx) val))))
-              (if (characterp from)
-                  (setq from (vector from)))
-              (setq val (nconc val (list (cons from to)))))
-          (if (characterp from)
-              (setq val to)
-            (setq val (list (cons from to)))))
-        (aset table idx val))
+          (if (= (length from) 0)
+              (setq idx nil)
+            (setq idx (aref from 0)
+                  max-lookup (max max-lookup (length from)))))
+        (when idx
+          (setq val (aref table idx))
+          (if val
+              (progn
+                (or (consp val)
+                    (setq val (list (cons (vector idx) val))))
+                (if (characterp from)
+                    (setq from (vector from)))
+                (setq val (nconc val (list (cons from to)))))
+            (if (characterp from)
+                (setq val to)
+              (setq val (list (cons from to)))))
+          (aset table idx val)))
       (set-char-table-extra-slot table 1 max-lookup))
     (set-char-table-extra-slot (aref tables 0) 0 (aref tables 1))
     (aref tables 0)))