From 99213dc2df2d3b76e0139956cb6257378961c821 Mon Sep 17 00:00:00 2001
From: Vasiliy Ermolovich <younash@gmail.com>
Date: Mon, 2 Apr 2018 18:22:19 +0300
Subject: [PATCH] Fix Kernel#singleton_method with Module#Prepend.

---
 proc.c                   |  6 +++---
 test/ruby/test_method.rb | 10 ++++++++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/proc.c b/proc.c
index 7134f68..551a135 100644
--- a/proc.c
+++ b/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);
diff --git a/test/ruby/test_method.rb b/test/ruby/test_method.rb
index 0ef913f..67c24a8 100644
--- a/test/ruby/test_method.rb
+++ b/test/ruby/test_method.rb
@@ -782,6 +782,16 @@ def o.bar; :bar; end
     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)
-- 
2.1.1