From 7a3748266b3790de241b0dce90e0ebbe581850f4 Mon Sep 17 00:00:00 2001
From: Charles Oliver Nutter <headius@headius.com>
Date: Thu, 11 Dec 2025 17:36:30 -0600
Subject: [PATCH] Disallow anonymous Data from being dumped

This feature leaked out without much discussion, but there's many
reasons why it should not be supported:

* Each instance of an anonymous Data in the stream will cause a new
  Data subtype to be defined.
* Multiple objects of the same anonymous Data cannot be round-
  tripped, since they will no longer be of the same type after
  loading.

As with Marshal's behavior for anonymous classes and structs, Psych
should reject such objects rather than attempt to fake a Data class
that appears to fit the original structure.
---
 lib/psych/visitors/yaml_tree.rb       | 1 +
 test/psych/test_object_references.rb  | 4 +++-
 test/psych/visitors/test_yaml_tree.rb | 7 ++++---
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/lib/psych/visitors/yaml_tree.rb b/lib/psych/visitors/yaml_tree.rb
index b6c86f4c..632dc141 100644
--- a/lib/psych/visitors/yaml_tree.rb
+++ b/lib/psych/visitors/yaml_tree.rb
@@ -163,6 +163,7 @@ def visit_Object o
       alias :visit_Delegator :visit_Object
 
       def visit_Data o
+        raise TypeError, "can't dump anonymous Data: #{o}" unless o.class.name
         ivars = o.instance_variables
         if ivars.empty?
           tag = ['!ruby/data', o.class.name].compact.join(':')
diff --git a/test/psych/test_object_references.rb b/test/psych/test_object_references.rb
index 0498d54e..be245cc6 100644
--- a/test/psych/test_object_references.rb
+++ b/test/psych/test_object_references.rb
@@ -31,9 +31,11 @@ def test_struct_has_references
       assert_reference_trip Struct.new(:foo).new(1)
     end
 
+    D = Data.define(:foo) unless RUBY_VERSION < "3.2"
+
     def test_data_has_references
       omit "Data requires ruby >= 3.2" if RUBY_VERSION < "3.2"
-      assert_reference_trip Data.define(:foo).new(1)
+      assert_reference_trip D.new(1)
     end
 
     def assert_reference_trip obj
diff --git a/test/psych/visitors/test_yaml_tree.rb b/test/psych/visitors/test_yaml_tree.rb
index bd3919f8..d99dc050 100644
--- a/test/psych/visitors/test_yaml_tree.rb
+++ b/test/psych/visitors/test_yaml_tree.rb
@@ -83,13 +83,14 @@ def test_data
       def test_data_anon
         omit "Data requires ruby >= 3.2" if RUBY_VERSION < "3.2"
         d = Data.define(:foo).new('bar')
-        obj =  Psych.unsafe_load(Psych.dump(d))
-        assert_equal d.foo, obj.foo
+        assert_raise(TypeError) { Psych.dump(d) }
       end
 
+      D2 = Data.define(:method) unless RUBY_VERSION < "3.2"
+
       def test_data_override_method
         omit "Data requires ruby >= 3.2" if RUBY_VERSION < "3.2"
-        d = Data.define(:method).new('override')
+        d = D2.new('override')
         obj =  Psych.unsafe_load(Psych.dump(d))
         assert_equal d.method, obj.method
       end