From b929af430c39df6597d2f3f53b82c38b1d76217b Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@ruby-lang.org>
Date: Fri, 24 Sep 2021 01:30:00 +0900
Subject: [PATCH] Use the flag for uninitialized module [Bug #18185]

Make `Module#ancestors` not to include `BasicObject`.
---
 class.c                  | 15 +++++++++------
 test/ruby/test_module.rb |  3 +++
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/class.c b/class.c
index 8e37f8a93e..ca8bdc2e79 100644
--- a/class.c
+++ b/class.c
@@ -351,19 +351,22 @@ copy_tables(VALUE clone, VALUE orig)
 
 static bool ensure_origin(VALUE klass);
 
+/**
+ * If this flag is set, that module is allocated but not initialized yet.
+ */
+enum {RMODULE_ALLOCATED_BUT_NOT_INITIALIZED = RUBY_FL_USER5};
+
 static inline bool
 RMODULE_UNINITIALIZED(VALUE module)
 {
-    return RCLASS_SUPER(module) == rb_cBasicObject;
+    return FL_TEST_RAW(module, RMODULE_ALLOCATED_BUT_NOT_INITIALIZED);
 }
 
 void
 rb_module_set_initialized(VALUE mod)
 {
-    if (RMODULE_UNINITIALIZED(mod)) {
-        RB_OBJ_WRITE(mod, &RCLASS(mod)->super, 0);
-        /* no more re-initialization */
-    }
+    FL_UNSET_RAW(mod, RMODULE_ALLOCATED_BUT_NOT_INITIALIZED);
+    /* no more re-initialization */
 }
 
 void
@@ -817,7 +820,7 @@ rb_module_s_alloc(VALUE klass)
 {
     VALUE mod = class_alloc(T_MODULE, klass);
     RCLASS_M_TBL_INIT(mod);
-    RB_OBJ_WRITE(mod, &RCLASS(mod)->super, rb_cBasicObject);
+    FL_SET(mod, RMODULE_ALLOCATED_BUT_NOT_INITIALIZED);
     return mod;
 }
 
diff --git a/test/ruby/test_module.rb b/test/ruby/test_module.rb
index 429fab897e..be23b84c46 100644
--- a/test/ruby/test_module.rb
+++ b/test/ruby/test_module.rb
@@ -449,7 +449,9 @@ class TestModule < Test::Unit::TestCase
   class Bug18185 < Module
     module InstanceMethods
     end
+    attr_reader :ancestor_list
     def initialize
+      @ancestor_list = ancestors
       include InstanceMethods
     end
     class Foo
@@ -470,6 +472,7 @@ class TestModule < Test::Unit::TestCase
     assert_equal(1, anc.count(BasicObject), ->{anc.inspect})
     b = c.new(key: 1)
     assert_equal(1, b.key)
+    assert_not_include(mod.ancestor_list, BasicObject)
   end
 
   def test_dup