merges r20866 and r20891 from trunk into ruby_1_9_1.

* error.c (exc_equal): duck typing equal to make it transitive.
  [ruby-dev:34880]

git-svn-id: http://svn.ruby-lang.org/repos/ruby/branches/ruby_1_9_1@20947 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 11 insertions, 4 deletions

diff --git a/error.c b/error.c
index c28a855ea..90a7d417e 100644
--- a/error.c
+++ b/error.c
@@ -554,15 +554,22 @@ exc_set_backtrace(VALUE exc, VALUE bt)
 static VALUE
 exc_equal(VALUE exc, VALUE obj)
 {
+    VALUE mesg, backtrace;
     ID id_mesg;
 
     if (exc == obj) return Qtrue;
-    if (rb_obj_class(exc) != rb_obj_class(obj))
-	return Qfalse;
     CONST_ID(id_mesg, "mesg");
-    if (!rb_equal(rb_attr_get(exc, id_mesg), rb_attr_get(obj, id_mesg)))
+    if (rb_obj_class(exc) != rb_obj_class(obj)) {
+	mesg = rb_funcall(obj, rb_intern("message"), 0, 0);
+	backtrace = rb_funcall(obj, rb_intern("backtrace"), 0, 0);
+    }
+    else {
+	mesg = rb_attr_get(obj, id_mesg);
+	backtrace = exc_backtrace(obj);
+    }
+    if (!rb_equal(rb_attr_get(exc, id_mesg), mesg))
 	return Qfalse;
-    if (!rb_equal(exc_backtrace(exc), exc_backtrace(obj)))
+    if (!rb_equal(exc_backtrace(exc), backtrace))
 	return Qfalse;
     return Qtrue;
 }