[ruby/psych] Handle Ruby 3.5 new Set class

Since `Set` no longer is a regular object class holding a Hash
it needs to be specially handled.

https://github.com/ruby/psych/commit/c2d185d27c

ext/psych/lib/psych/core_ext.rb

@@ -17,3 +17,17 @@ end
 if defined?(::IRB)
   require_relative 'y'
 end
+
+
+# TODO: how best to check for builtin Set?
+if defined?(::Set) && Object.const_source_location(:Set) == ["ruby", 0]
+  class Set
+    def encode_with(coder)
+      coder["hash"] = to_h
+    end
+
+    def init_with(coder)
+      replace(coder["hash"].keys)
+    end
+  end
+end

test/psych/test_psych_set.rb

@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+module Psych
+  class TestPsychSet < TestCase
+    def setup
+      super
+      @set = Psych::Set.new
+      @set['foo'] = 'bar'
+      @set['bar'] = 'baz'
+    end
+
+    def test_dump
+      assert_match(/!set/, Psych.dump(@set))
+    end
+
+    def test_roundtrip
+      assert_cycle(@set)
+    end
+
+    ###
+    # FIXME: Syck should also support !!set as shorthand
+    def test_load_from_yaml
+      loaded = Psych.unsafe_load(<<-eoyml)
+--- !set
+foo: bar
+bar: baz
+      eoyml
+      assert_equal(@set, loaded)
+    end
+
+    def test_loaded_class
+      assert_instance_of(Psych::Set, Psych.unsafe_load(Psych.dump(@set)))
+    end
+
+    def test_set_shorthand
+      loaded = Psych.unsafe_load(<<-eoyml)
+--- !!set
+foo: bar
+bar: baz
+      eoyml
+      assert_instance_of(Psych::Set, loaded)
+    end
+
+    def test_set_self_reference
+      @set['self'] = @set
+      assert_cycle(@set)
+    end
+
+    def test_stringify_names
+      @set[:symbol] = :value
+
+      assert_match(/^:symbol: :value/, Psych.dump(@set))
+      assert_match(/^symbol: :value/, Psych.dump(@set, stringify_names: true))
+    end
+  end
+end

test/psych/test_set.rb

@@ -1,57 +1,36 @@
+# encoding: UTF-8
 # frozen_string_literal: true
 require_relative 'helper'
+require 'set' unless defined?(Set)
 
 module Psych
   class TestSet < TestCase
     def setup
-      super
+      @set = ::Set.new([1, 2, 3])
-      @set = Psych::Set.new
-      @set['foo'] = 'bar'
-      @set['bar'] = 'baz'
     end
 
     def test_dump
-      assert_match(/!set/, Psych.dump(@set))
+      assert_equal <<~YAML, Psych.dump(@set)
+        --- !ruby/object:Set
+        hash:
+          1: true
+          2: true
+          3: true
+      YAML
+    end
+
+    def test_load
+      assert_equal @set, Psych.load(<<~YAML, permitted_classes: [::Set])
+        --- !ruby/object:Set
+        hash:
+          1: true
+          2: true
+          3: true
+      YAML
     end
 
     def test_roundtrip
-      assert_cycle(@set)
+      assert_equal @set, Psych.load(Psych.dump(@set), permitted_classes: [::Set])
-    end
-
-    ###
-    # FIXME: Syck should also support !!set as shorthand
-    def test_load_from_yaml
-      loaded = Psych.unsafe_load(<<-eoyml)
---- !set
-foo: bar
-bar: baz
-      eoyml
-      assert_equal(@set, loaded)
-    end
-
-    def test_loaded_class
-      assert_instance_of(Psych::Set, Psych.unsafe_load(Psych.dump(@set)))
-    end
-
-    def test_set_shorthand
-      loaded = Psych.unsafe_load(<<-eoyml)
---- !!set
-foo: bar
-bar: baz
-      eoyml
-      assert_instance_of(Psych::Set, loaded)
-    end
-
-    def test_set_self_reference
-      @set['self'] = @set
-      assert_cycle(@set)
-    end
-
-    def test_stringify_names
-      @set[:symbol] = :value
-
-      assert_match(/^:symbol: :value/, Psych.dump(@set))
-      assert_match(/^symbol: :value/, Psych.dump(@set, stringify_names: true))
     end
   end
 end