From ed6fbb79e19bf401db0e85447fee955fd10a25c7 Mon Sep 17 00:00:00 2001
From: Peter Zhu <peter@peterzhu.ca>
Date: Mon, 16 Jan 2023 09:32:37 -0500
Subject: [PATCH] Fix crash when defining ivars on special constants

[Bug #19339]
---
 test/ruby/test_variable.rb | 6 ++++++
 vm_insnhelper.c            | 5 +++++
 2 files changed, 11 insertions(+)

diff --git a/test/ruby/test_variable.rb b/test/ruby/test_variable.rb
index f8a7c68fd3..9acba39f40 100644
--- a/test/ruby/test_variable.rb
+++ b/test/ruby/test_variable.rb
@@ -261,6 +261,12 @@ class TestVariable < Test::Unit::TestCase
         v.instance_variable_set(:@foo, :bar)
       end
 
+      assert_raise_with_message(FrozenError, msg, "[Bug #19339]") do
+        v.instance_eval do
+          @a = 1
+        end
+      end
+
       assert_nil EnvUtil.suppress_warning {v.instance_variable_get(:@foo)}
       assert_not_send([v, :instance_variable_defined?, :@foo])
 
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 9c2947523c..29753f1800 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -1562,6 +1562,11 @@ vm_getinstancevariable(const rb_iseq_t *iseq, VALUE obj, ID id, IVC ic)
 static inline void
 vm_setinstancevariable(const rb_iseq_t *iseq, VALUE obj, ID id, VALUE val, IVC ic)
 {
+    if (RB_SPECIAL_CONST_P(obj)) {
+        rb_error_frozen_object(obj);
+        return;
+    }
+
     shape_id_t dest_shape_id;
     attr_index_t index;
     vm_ic_atomic_shape_and_index(ic, &dest_shape_id, &index);