Fix Kernel#singleton_method with Module#Prepend

* proc.c (rb_obj_singleton_method): search the method entry from
  the origin class, for fix prepended modules.  [Bug #14658]

From: Vasiliy Ermolovich <younash@gmail.com>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63067 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

proc.c

@@ -1771,11 +1771,11 @@ VALUE
 rb_obj_singleton_method(VALUE obj, VALUE vid)
 {
     const rb_method_entry_t *me;
-    VALUE klass;
+    VALUE klass = RCLASS_ORIGIN(rb_singleton_class_get(obj));
     ID id = rb_check_id(&vid);
 
     if (!id) {
-	if (!NIL_P(klass = rb_singleton_class_get(obj)) &&
+	if (!NIL_P(klass) &&
 	    respond_to_missing_p(klass, obj, vid, FALSE)) {
 	    id = rb_intern_str(vid);
 	    return mnew_missing(klass, obj, id, rb_cMethod);
@@ -1784,7 +1784,7 @@ rb_obj_singleton_method(VALUE obj, VALUE vid)
 	rb_name_err_raise("undefined singleton method `%1$s' for `%2$s'",
 			  obj, vid);
     }
-    if (NIL_P(klass = rb_singleton_class_get(obj)) ||
+    if (NIL_P(klass) ||
 	UNDEFINED_METHOD_ENTRY_P(me = rb_method_entry_at(klass, id)) ||
 	UNDEFINED_REFINED_METHOD_P(me->def)) {
 	vid = ID2SYM(id);

test/ruby/test_method.rb

@@ -782,6 +782,16 @@ class TestMethod < Test::Unit::TestCase
     assert_equal(:bar, m.call, feature8391)
   end
 
+  def test_singleton_method_prepend
+    bug14658 = '[Bug #14658]'
+    c1 = Class.new
+    o = c1.new
+    def o.bar; :bar; end
+    class << o; prepend Module.new; end
+    m = assert_nothing_raised(NameError, bug14658) {o.singleton_method(:bar)}
+    assert_equal(:bar, m.call, bug14658)
+  end
+
   Feature9783 = '[ruby-core:62212] [Feature #9783]'
 
   def assert_curry_three_args(m)