From ccdf75c1c208212a703e025d1043f959199249d7 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Wed, 31 May 2023 08:31:13 +0900
Subject: [PATCH] error.c: a new function `mrb_check_frozen_value()`

---
 include/mruby.h |  2 +-
 src/class.c     | 13 ++++++++-----
 src/error.c     | 16 +++++++++++++++-
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/include/mruby.h b/include/mruby.h
index 12be6faf8..3ecea7029 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -1434,7 +1434,7 @@ MRB_INLINE void mrb_check_frozen(mrb_state *mrb, void *o)
 {
   if (mrb_frozen_p((struct RBasic*)o)) mrb_frozen_error(mrb, o);
 }
-
+MRB_API void mrb_check_frozen_value(mrb_state *mrb, mrb_value v);
 MRB_API void mrb_define_alias(mrb_state *mrb, struct RClass *c, const char *a, const char *b);
 MRB_API void mrb_define_alias_id(mrb_state *mrb, struct RClass *c, mrb_sym a, mrb_sym b);
 MRB_API const char *mrb_class_name(mrb_state *mrb, struct RClass* klass);
diff --git a/src/class.c b/src/class.c
index 326f16e40..e30102e10 100644
--- a/src/class.c
+++ b/src/class.c
@@ -756,7 +756,13 @@ mrb_define_method_raw(mrb_state *mrb, struct RClass *c, mrb_sym mid, mrb_method_
 
   MRB_CLASS_ORIGIN(c);
   h = c->mt;
-  mrb_check_frozen(mrb, c);
+  if (c->tt == MRB_TT_SCLASS && mrb_frozen_p(c)) {
+    mrb_value v = mrb_iv_get(mrb, mrb_obj_value(c), MRB_SYM(__attached__));
+    mrb_check_frozen_value(mrb, v);
+  }
+  else {
+    mrb_check_frozen(mrb, c);
+  }
   if (!h) h = c->mt = mt_new(mrb);
   if (MRB_METHOD_PROC_P(m)) {
     struct RProc *p = MRB_METHOD_PROC(m);
@@ -1011,10 +1017,7 @@ get_args_v(mrb_state *mrb, mrb_args_format format, void** ptr, va_list *ap)
       if (i < argc) {
         pickarg = &argv[i++];
         if (needmodify && !mrb_nil_p(*pickarg)) {
-          if (mrb_immediate_p(*pickarg)) {
-            mrb_raisef(mrb, E_FROZEN_ERROR, "can't modify frozen %t", *pickarg);
-          }
-          mrb_check_frozen(mrb, mrb_obj_ptr(*pickarg));
+          mrb_check_frozen_value(mrb, *pickarg);
         }
       }
       else {
diff --git a/src/error.c b/src/error.c
index 0b20ec541..7a2a30530 100644
--- a/src/error.c
+++ b/src/error.c
@@ -518,10 +518,24 @@ mrb_no_method_error(mrb_state *mrb, mrb_sym id, mrb_value args, char const* fmt,
   mrb_exc_raise(mrb, exc);
 }
 
+static mrb_noreturn void
+frozen_error(mrb_state *mrb, mrb_value v)
+{
+  mrb_raisef(mrb, E_FROZEN_ERROR, "can't modify frozen %t", v);
+}
+
 MRB_API mrb_noreturn void
 mrb_frozen_error(mrb_state *mrb, void *frozen_obj)
 {
-  mrb_raisef(mrb, E_FROZEN_ERROR, "can't modify frozen %t", mrb_obj_value(frozen_obj));
+  frozen_error(mrb, mrb_obj_value(frozen_obj));
+}
+
+MRB_API void
+mrb_check_frozen_value(mrb_state *mrb, mrb_value v)
+{
+  if (mrb_immediate_p(v) || mrb_frozen_p(mrb_basic_ptr(v))) {
+    frozen_error(mrb, v);
+  }
 }
 
 MRB_API mrb_noreturn void