Fix Struct subclasses explicitly inherited and don't provide #members method

Author: andrykonchin

CHANGELOG.md

@@ -12,6 +12,7 @@ Compatibility:
 * Support String patterns in `StringScanner#{exist?,scan_until,skip_until,check_until,search_full}` methods (@andrykonchin).
 * Implement `ObjectSpace::WeakKeyMap` (#3681, @andrykonchin).
 * Fix `String#slice` called with negative offset (@andrykonchin).
+* Fix explicitly inherited `Struct` subclasses and don't provide `#members` method (#3802, @andrykonchin).
 
 Performance:
 

spec/ruby/core/struct/fixtures/classes.rb

@@ -29,4 +29,6 @@ def initialize(*)
       super
     end
   end
+
+  class StructSubclass < Struct; end
 end

spec/ruby/core/struct/keyword_init_spec.rb

@@ -1,4 +1,5 @@
 require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
 
 ruby_version_is "3.1" do
   # See https://bugs.ruby-lang.org/issues/18008
@@ -36,5 +37,11 @@
       struct = Struct.new(:arg, keyword_init: {})
       struct.keyword_init?.should be_true
     end
+
+    context "class inheriting Struct" do
+      it "isn't available in a subclass" do
+        StructClasses::StructSubclass.should_not.respond_to?(:keyword_init?)
+      end
+    end
   end
 end

spec/ruby/core/struct/members_spec.rb

@@ -11,3 +11,15 @@
 
   it_behaves_like :struct_accessor, :members
 end
+
+describe "StructClass#members" do
+  it "returns an array of attribute names" do
+    StructClasses::Car.members.should == [:make, :model, :year]
+  end
+
+  context "class inheriting Struct" do
+    it "isn't available in a subclass" do
+      StructClasses::StructSubclass.should_not.respond_to?(:members)
+    end
+  end
+end

src/main/ruby/truffleruby/core/struct.rb

@@ -81,6 +81,10 @@ def self.keyword_init?
         return nil if Primitive.nil?(self::KEYWORD_INIT)
         Primitive.as_boolean(self::KEYWORD_INIT)
       end
+
+      def self.members
+        self::STRUCT_ATTRS.dup
+      end
     end
 
     const_set klass_name, klass if klass_name
@@ -318,10 +322,6 @@ def self.length
     self::STRUCT_ATTRS.size
   end
 
-  def self.members
-    self::STRUCT_ATTRS.dup
-  end
-
   def members
     Primitive.class(self).members
   end