From a79c59472df38297c246b27713c277f2edaefa7a Mon Sep 17 00:00:00 2001
From: Jeremy Evans <code@jeremyevans.net>
Date: Wed, 5 Jan 2022 16:12:31 -0800
Subject: [PATCH] Allow include before calling Module#initialize

This is to allow Module subclasses that include modules before
calling super in the subclass's initialize.

Remove rb_module_check_initializable from Module#initialize.
Module#initialize only calls module_exec if a block is passed,
it doesn't have other issues that would cause problems if
called multiple times or with an already initialized module.

Move initialization of super to Module#allocate, though I'm not
sure it is required there.  However, it's needed to be removed
from Module#initialize for this to work.

Fixes [Bug #18292]
---
 class.c                  |  1 +
 object.c                 |  1 -
 test/ruby/test_module.rb | 10 ++++++++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/class.c b/class.c
index 1281a243ab..5ece9e34e8 100644
--- a/class.c
+++ b/class.c
@@ -912,6 +912,7 @@ rb_module_s_alloc(VALUE klass)
     VALUE mod = class_alloc(T_MODULE, klass);
     RCLASS_M_TBL_INIT(mod);
     FL_SET(mod, RMODULE_ALLOCATED_BUT_NOT_INITIALIZED);
+    RB_OBJ_WRITE(mod, &RCLASS(mod)->super, 0);
     return mod;
 }
 
diff --git a/object.c b/object.c
index 2c9cbe7403..9243df5587 100644
--- a/object.c
+++ b/object.c
@@ -1689,7 +1689,6 @@ static VALUE rb_mod_initialize_exec(VALUE module);
 static VALUE
 rb_mod_initialize(VALUE module)
 {
-    rb_module_check_initializable(module);
     return rb_mod_initialize_exec(module);
 }
 
diff --git a/test/ruby/test_module.rb b/test/ruby/test_module.rb
index e1524a5d81..b84a090fce 100644
--- a/test/ruby/test_module.rb
+++ b/test/ruby/test_module.rb
@@ -519,6 +519,16 @@ class TestModule < Test::Unit::TestCase
     assert_raise(ArgumentError) { Module.new { include } }
   end
 
+  def test_include_before_initialize
+    m = Class.new(Module) do
+      def initialize(...)
+        include Enumerable
+        super
+      end
+    end.new
+    assert_equal(true, m < Enumerable)
+  end
+
   def test_prepend_self
     m = Module.new
     assert_equal([m], m.ancestors)