From 632ab19c4ddfdd7bf73adf0215e488382f02bb1a Mon Sep 17 00:00:00 2001
From: nobu <nobu@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Thu, 14 Feb 2013 02:08:31 +0000
Subject: [PATCH] class.c: cyclic prepend

* class.c (include_modules_at): detect cyclic prepend with original
  method table.  [ruby-core:52205] [Bug #7841]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39236 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 ChangeLog                |  5 +++++
 class.c                  |  7 ++++---
 test/ruby/test_module.rb | 10 ++++++++++
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 1f8afcf7ff..e81d653e1d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Feb 14 11:08:15 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* class.c (include_modules_at): detect cyclic prepend with original
+	  method table.  [ruby-core:52205] [Bug #7841]
+
 Thu Feb 14 10:30:41 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* vm_method.c: call method_removed hook on called class, not on
diff --git a/class.c b/class.c
index 36e7b76caf..c1903f9076 100644
--- a/class.c
+++ b/class.c
@@ -681,7 +681,7 @@ rb_include_class_new(VALUE module, VALUE super)
     return (VALUE)klass;
 }
 
-static int include_modules_at(VALUE klass, VALUE c, VALUE module);
+static int include_modules_at(const VALUE klass, VALUE c, VALUE module);
 
 void
 rb_include_module(VALUE klass, VALUE module)
@@ -713,17 +713,18 @@ add_refined_method_entry_i(st_data_t key, st_data_t value, st_data_t data)
 }
 
 static int
-include_modules_at(VALUE klass, VALUE c, VALUE module)
+include_modules_at(const VALUE klass, VALUE c, VALUE module)
 {
     VALUE p;
     int changed = 0;
+    const st_table *const klass_m_tbl = RCLASS_M_TBL(RCLASS_ORIGIN(klass));
 
     while (module) {
 	int superclass_seen = FALSE;
 
 	if (RCLASS_ORIGIN(module) != module)
 	    goto skip;
-	if (RCLASS_M_TBL(klass) && RCLASS_M_TBL(klass) == RCLASS_M_TBL(module))
+	if (klass_m_tbl && klass_m_tbl == RCLASS_M_TBL(module))
 	    return -1;
 	/* ignore if the module included already in superclasses */
 	for (p = RCLASS_SUPER(klass); p; p = RCLASS_SUPER(p)) {
diff --git a/test/ruby/test_module.rb b/test/ruby/test_module.rb
index 6fbf3af2e3..6b9ac4416b 100644
--- a/test/ruby/test_module.rb
+++ b/test/ruby/test_module.rb
@@ -1465,6 +1465,16 @@ class TestModule < Test::Unit::TestCase
     assert_equal([:m1], Class.new(Class.new{def m2;end}){ prepend Module.new; def m1; end }.instance_methods(false), bug6660)
   end
 
+  def test_cyclic_prepend
+    bug7841 = '[ruby-core:52205] [Bug #7841]'
+    m1 = Module.new
+    m2 = Module.new
+    m1.instance_eval { prepend(m2) }
+    assert_raise(ArgumentError, bug7841) do
+      m2.instance_eval { prepend(m1) }
+    end
+  end
+
   def test_class_variables
     m = Module.new
     m.class_variable_set(:@@foo, 1)