Add support for Data objects with ivars

This sets the ivars _before_ calling initialize, which feels wrong.  But
Data doesn't give us any mechanism for setting the members other than 1)
initialize, or 2) drop down into the C API.  Since initialize freezes
the object, we need to set the ivars before that.  I think this is a
reasonable compromise—if users need better handling, they can implement
their own `encode_with` and `init_with`.  But it will lead to unhappy
surprises for some users.

Alternatively, we could use the C API, similarly to Marshal.  Psych _is_
already using the C API for path2class and build_exception.  This would
be the least surprising behavior for users, I think.

2 files changed, 87 insertions, 0 deletions

diff --git a/test/psych/test_data.rb b/test/psych/test_data.rb
new file mode 100644
index 0000000000..a67a037b9e
--- /dev/null
+++ b/test/psych/test_data.rb
@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+class PsychDataWithIvar < Data.define(:foo)
+  attr_reader :bar
+  def initialize(**)
+    @bar = 'hello'
+    super
+  end
+end unless RUBY_VERSION < "3.2"
+
+module Psych
+  class TestData < TestCase
+    class SelfReferentialData < Data.define(:foo)
+      attr_accessor :ref
+      def initialize(foo:)
+        @ref = self
+        super
+      end
+    end unless RUBY_VERSION < "3.2"
+
+    def setup
+      omit "Data requires ruby >= 3.2" if RUBY_VERSION < "3.2"
+    end
+
+    # TODO: move to another test?
+    def test_dump_data
+      assert_equal <<~eoyml, Psych.dump(PsychDataWithIvar["bar"])
+        --- !ruby/data-with-ivars:PsychDataWithIvar
+        members:
+          foo: bar
+        ivars:
+          "@bar": hello
+      eoyml
+    end
+
+    def test_self_referential_data
+      circular = SelfReferentialData.new("foo")
+
+      loaded = Psych.unsafe_load(Psych.dump(circular))
+      assert_instance_of(SelfReferentialData, loaded.ref)
+
+      assert_equal(circular, loaded)
+      assert_same(loaded, loaded.ref)
+    end
+
+    def test_roundtrip
+      thing = PsychDataWithIvar.new("bar")
+      data = Psych.unsafe_load(Psych.dump(thing))
+
+      assert_equal "hello", data.bar
+      assert_equal "bar",   data.foo
+    end
+
+    def test_load
+      obj = Psych.unsafe_load(<<~eoyml)
+        --- !ruby/data-with-ivars:PsychDataWithIvar
+        members:
+          foo: bar
+        ivars:
+          "@bar": hello
+      eoyml
+
+      assert_equal "hello", obj.bar
+      assert_equal "bar",   obj.foo
+    end
+  end
+end
+
diff --git a/test/psych/test_serialize_subclasses.rb b/test/psych/test_serialize_subclasses.rb
index 344c79b3ef..640c331337 100644
--- a/test/psych/test_serialize_subclasses.rb
+++ b/test/psych/test_serialize_subclasses.rb
@@ -35,5 +35,23 @@ module Psych
       so = StructSubclass.new('foo', [1,2,3])
       assert_equal so, Psych.unsafe_load(Psych.dump(so))
     end
+
+    class DataSubclass < Data.define(:foo)
+      def initialize(foo:)
+        @bar = "hello #{foo}"
+        super(foo: foo)
+      end
+
+      def == other
+        super(other) && @bar == other.instance_eval{ @bar }
+      end
+    end unless RUBY_VERSION < "3.2"
+
+    def test_data_subclass
+      omit "Data requires ruby >= 3.2" if RUBY_VERSION < "3.2"
+      so = DataSubclass.new('foo')
+      assert_equal so, Psych.unsafe_load(Psych.dump(so))
+    end
+
   end
 end