(find-safe-coding-system): New function.

1 files changed, 32 insertions, 0 deletions

diff --git a/lisp/international/mule-util.el b/lisp/international/mule-util.el
index 3fd3a57b68b..c6316358dac 100644
--- a/lisp/international/mule-util.el
+++ b/lisp/international/mule-util.el
@@ -287,6 +287,38 @@ or one is an alias of the other."
              (or (eq eol-type-1 eol-type-2)
                  (and (vectorp eol-type-1) (vectorp eol-type-2)))))))
 
+;;;###autoload
+(defun find-safe-coding-system (from to)
+  "Return a list of proper coding systems to encode a text between FROM and TO.
+All coding systems in the list can safely encode any multibyte characters
+in the region.
+
+If the region contains no multibyte charcters, the returned list
+contains a single element `undecided'.
+
+Kludgy feature: if FROM is a string, then that string is the target
+for finding proper coding systems, and TO is ignored."
+  (let ((found (if (stringp from)
+                   (find-charset-string from)
+                 (find-charset-region from to)))
+        (l coding-system-list)
+        codings coding safe)
+    (if (and (= (length found) 1)
+             (eq 'ascii (car found)))
+        '(undecided)
+      (while l
+        (setq coding (car l) l (cdr l))
+        (if (and (eq coding (coding-system-base coding))
+                 (setq safe (coding-system-get coding 'safe-charsets))
+                 (or (eq safe t)
+                     (catch 'tag
+                       (mapcar (function (lambda (x)
+                                           (if (not (memq x safe))
+                                               (throw 'tag nil))))
+                               found))))
+            (setq codings (cons coding codings))))
+      codings)))
+
 
 ;;; Composite charcater manipulations.