merges r20866 and r20968 from trunk into ruby_1_9_1.

* error.c (exc_equal): duck typing equal to make it transitive.
  [ruby-dev:34880]
--
* error.c (exc_equal): == method should not raise Exception.
  [ruby-dev:37519]

* sample/test.rb: fix test

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_1@21025 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 22 insertions, 4 deletions

diff --git a/error.c b/error.c
index c28a855ea7..b6ab8c4959 100644
--- a/error.c
+++ b/error.c
@@ -554,15 +554,33 @@ 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)) {
+	ID id_message, id_backtrace;
+	CONST_ID(id_message, "message");
+	CONST_ID(id_backtrace, "backtrace");
+
+	if (rb_respond_to(obj, id_message) && rb_respond_to(obj, id_backtrace)) {
+	    mesg = rb_funcall(obj, id_message, 0, 0);
+	    backtrace = rb_funcall(obj, id_backtrace, 0, 0);
+	}
+	else {
+	    return Qfalse;
+	}
+    }
+    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;
 }