BasicObject.dup should be TypeError: can't copy the root class

Author: eregon

spec/ruby/core/class/dup_spec.rb

@@ -61,4 +61,7 @@ def self.message
     CoreClassSpecs::RecordCopy.name.should == "CoreClassSpecs::RecordCopy"
   end
 
+  it "raises TypeError if called on BasicObject" do
+    -> { BasicObject.dup }.should raise_error(TypeError, "can't copy the root class")
+  end
 end

src/main/java/org/truffleruby/core/kernel/KernelNodes.java

@@ -518,7 +518,12 @@ protected RubyDynamicObject copyRubyDynamicObject(RubyDynamicObject self,
 
         @Specialization
         protected RubyDynamicObject copyRubyClass(RubyClass self,
-                @Cached @Exclusive CopyInstanceVariablesNode copyInstanceVariablesNode) {
+                @Cached @Exclusive CopyInstanceVariablesNode copyInstanceVariablesNode,
+                @Cached InlinedBranchProfile rootClassProfile) {
+            if (self == coreLibrary().basicObjectClass) {
+                rootClassProfile.enter(this);
+                throw new RaiseException(getContext(), coreExceptions().typeError("can't copy the root class", this));
+            }
             var newClass = new RubyClass(coreLibrary().classClass, getLanguage(), getEncapsulatingSourceSection(),
                     null, null, false, null, self.superclass);
             copyInstanceVariablesNode.execute(newClass, self);