[PATCH] Threading with In-reply-to

[Peter Bloomfield <PeterBloomfield MindSpring com>]

When a message contains an "In-reply-to" header but no "References", 
Balsa seems not to use the former for threading. JWZ threading mostly 
compensates by checking the subject, but simple threading fails. The 
attached patch makes sure that the parent message-id from the 
"In-reply-to" header appears as the last reference. It improves 
threading, at least for me and at least for one mailbox, and doesn't 
seem to break anything else.

Comments?

Peter
Index: libbalsa/message.c
===================================================================
RCS file: /cvs/gnome/balsa/libbalsa/message.c,v
retrieving revision 1.91
diff -u -r1.91 message.c
--- libbalsa/message.c	2002/06/13 08:44:45	1.91
+++ libbalsa/message.c	2002/07/15 12:37:53
@@ -1289,32 +1289,30 @@
         }
 
     /* more! */
-    /* FIXME: message->references_for_threading is just the reverse of
-     * message->references; is there any reason to clutter up the
-     * message structure with it, and allocate memory for another set of
-     * g_strdup's? */
+    
+    if (!message->references_for_threading) {
+        GList *tmp = g_list_copy(message->references);
+
+        if (message->in_reply_to) {
+            /* some mailers provide in_reply_to but no references, and
+             * some apparently provide both but with the references in
+             * the wrong order; we'll just make sure it's the first item
+             * of this list (which will be the last after reversing it,
+             * below) */
+            GList *foo =
+                g_list_find_custom(tmp, message->in_reply_to,
+                                   (GCompareFunc) strcmp);
+                
+            if (foo) {
+                tmp = g_list_remove_link(tmp, foo);
+                g_list_free_1(foo);
+            }
 
-    if (!message->references_for_threading) 
-        message->references_for_threading = 
-            g_list_reverse(g_list_copy(message->references));
-#if 0
-    /* According to  RFC 1036 (section 2.2.5), MessageIDs in References header
-     * must be in the oldest first order; the direct parent should be last. 
-     * It seems, however, some MUAs ignore this rule.
-     * For example, one of them adds the direct parent to the head of
-     * the References header.
-     */
-    if (message->in_reply_to != NULL &&
-        message->references_for_threading != NULL &&
-        1 < g_list_length(message->references_for_threading) &&
-        strcmp(message->in_reply_to,
-               (g_list_first(message->references_for_threading))->data) ==
-        0) {
-        GList *foo = message->references_for_threading;
-        message->references_for_threading = g_list_remove(foo, foo->data);
+            tmp = g_list_prepend(tmp, message->in_reply_to);
+        }
+
+        message->references_for_threading = g_list_reverse(tmp);
     }
-#endif
-    
 }
 
 /* libbalsa_message_title: