From c6dd07d66fa469d963d3771e001d45c462f413e3 Mon Sep 17 00:00:00 2001
From: Jean Boussier <jean.boussier@gmail.com>
Date: Fri, 20 Jun 2025 11:23:10 +0100
Subject: [PATCH] Allocate singleton classes as namespaceable if their parent
 are

---
 class.c | 52 ++++++++++++++++++++++++++++++++++------------------
 1 file changed, 34 insertions(+), 18 deletions(-)

diff --git a/class.c b/class.c
index e29478d9ee..dd0e79bfa9 100644
--- a/class.c
+++ b/class.c
@@ -644,14 +644,18 @@ class_switch_superclass(VALUE super, VALUE klass)
  * @note this function is not Class#allocate.
  */
 static VALUE
-class_alloc(enum ruby_value_type type, VALUE klass)
+class_alloc0(enum ruby_value_type type, VALUE klass, bool namespaceable)
 {
     rb_ns_subclasses_t *ns_subclasses;
     rb_subclass_anchor_t *anchor;
     const rb_namespace_t *ns = rb_definition_namespace();
 
-    size_t alloc_size = sizeof(struct RClass_and_rb_classext_t);
     if (!ruby_namespace_init_done) {
+        namespaceable = true;
+    }
+
+    size_t alloc_size = sizeof(struct RClass_and_rb_classext_t);
+    if (namespaceable) {
         alloc_size = sizeof(struct RClass_namespaceable);
     }
 
@@ -672,7 +676,7 @@ class_alloc(enum ruby_value_type type, VALUE klass)
 
     VALUE flags = type;
     if (RGENGC_WB_PROTECTED_CLASS) flags |= FL_WB_PROTECTED;
-    if (!ruby_namespace_init_done) flags |= RCLASS_NAMESPACEABLE;
+    if (namespaceable) flags |= RCLASS_NAMESPACEABLE;
 
     NEWOBJ_OF(obj, struct RClass, klass, flags, alloc_size, 0);
 
@@ -688,7 +692,7 @@ class_alloc(enum ruby_value_type type, VALUE klass)
     RCLASS_PRIME_NS((VALUE)obj) = ns;
     // Classes/Modules defined in user namespaces are
     // writable directly because it exists only in a namespace.
-    RCLASS_SET_PRIME_CLASSEXT_WRITABLE((VALUE)obj, ruby_namespace_init_done || NAMESPACE_USER_P(ns));
+    RCLASS_SET_PRIME_CLASSEXT_WRITABLE((VALUE)obj, !namespaceable || NAMESPACE_USER_P(ns));
 
     RCLASS_SET_ORIGIN((VALUE)obj, (VALUE)obj);
     RCLASS_SET_REFINED_CLASS((VALUE)obj, Qnil);
@@ -698,6 +702,12 @@ class_alloc(enum ruby_value_type type, VALUE klass)
     return (VALUE)obj;
 }
 
+static VALUE
+class_alloc(enum ruby_value_type type, VALUE klass)
+{
+    return class_alloc0(type, klass, false);
+}
+
 static VALUE
 class_associate_super(VALUE klass, VALUE super, bool init)
 {
@@ -733,6 +743,23 @@ class_clear_method_table(VALUE c)
     RCLASS_WRITE_M_TBL_EVEN_WHEN_PROMOTED(c, rb_id_table_create(0));
 }
 
+static VALUE
+class_boot_namespaceable(VALUE super, bool namespaceable)
+{
+    VALUE klass = class_alloc0(T_CLASS, rb_cClass, namespaceable);
+
+    // initialize method table prior to class_associate_super()
+    // because class_associate_super() may cause GC and promote klass
+    class_initialize_method_table(klass);
+
+    class_associate_super(klass, super, true);
+    if (super && !UNDEF_P(super)) {
+        rb_class_set_initialized(klass);
+    }
+
+    return (VALUE)klass;
+}
+
 /**
  * A utility function that wraps class_alloc.
  *
@@ -745,18 +772,7 @@ class_clear_method_table(VALUE c)
 VALUE
 rb_class_boot(VALUE super)
 {
-    VALUE klass = class_alloc(T_CLASS, rb_cClass);
-
-    // initialize method table prior to class_associate_super()
-    // because class_associate_super() may cause GC and promote klass
-    class_initialize_method_table(klass);
-
-    class_associate_super(klass, super, true);
-    if (super && !UNDEF_P(super)) {
-        rb_class_set_initialized(klass);
-    }
-
-    return (VALUE)klass;
+    return class_boot_namespaceable(super, false);
 }
 
 static VALUE *
@@ -1254,7 +1270,7 @@ static inline VALUE
 make_metaclass(VALUE klass)
 {
     VALUE super;
-    VALUE metaclass = rb_class_boot(Qundef);
+    VALUE metaclass = class_boot_namespaceable(Qundef, FL_TEST_RAW(klass, RCLASS_NAMESPACEABLE));
 
     FL_SET(metaclass, FL_SINGLETON);
     rb_singleton_class_attached(metaclass, klass);
@@ -1290,7 +1306,7 @@ static inline VALUE
 make_singleton_class(VALUE obj)
 {
     VALUE orig_class = METACLASS_OF(obj);
-    VALUE klass = rb_class_boot(orig_class);
+    VALUE klass = class_boot_namespaceable(orig_class, FL_TEST_RAW(orig_class, RCLASS_NAMESPACEABLE));
 
     FL_SET(klass, FL_SINGLETON);
     RBASIC_SET_CLASS(obj, klass);