move the check for singleton class allocation to ClassNodes

Author: Nicolas Laurent

src/main/java/org/truffleruby/core/klass/ClassNodes.java

@@ -271,10 +271,17 @@ public abstract static class AllocateInstanceNode extends CoreMethodArrayArgumen
 
         @Child private DispatchNode allocateNode = DispatchNode.create();
 
-        @Specialization
-        protected Object newInstance(VirtualFrame frame, RubyClass rubyClass) {
+        @Specialization(guards = "!rubyClass.isSingleton")
+        protected Object newInstance(RubyClass rubyClass) {
             return allocateNode.call(rubyClass, "__allocate__");
         }
+
+        @Specialization(guards = "rubyClass.isSingleton")
+        protected RubyClass newSingletonInstance(RubyClass rubyClass) {
+            throw new RaiseException(
+                    getContext(),
+                    getContext().getCoreExceptions().typeErrorCantCreateInstanceOfSingletonClass(this));
+        }
     }
 
     @CoreMethod(names = "new", needsBlock = true, rest = true)
@@ -289,16 +296,23 @@ public static NewNode create() {
 
         public abstract Object execute(VirtualFrame frame, Object rubyClass, Object[] args, Object block);
 
-        @Specialization
+        @Specialization(guards = "!rubyClass.isSingleton")
         protected Object newInstance(VirtualFrame frame, RubyClass rubyClass, Object[] args, NotProvided block) {
             return doNewInstance(frame, rubyClass, args, null);
         }
 
-        @Specialization
+        @Specialization(guards = "!rubyClass.isSingleton")
         protected Object newInstance(VirtualFrame frame, RubyClass rubyClass, Object[] args, RubyProc block) {
             return doNewInstance(frame, rubyClass, args, block);
         }
 
+        @Specialization(guards = "rubyClass.isSingleton")
+        protected RubyClass newSingletonInstance(RubyClass rubyClass, Object[] args, Object maybeBlock) {
+            throw new RaiseException(
+                    getContext(),
+                    getContext().getCoreExceptions().typeErrorCantCreateInstanceOfSingletonClass(this));
+        }
+
         @Override
         public Object inlineExecute(VirtualFrame frame, Object self, Object[] args, Object proc) {
             return execute(frame, self, args, proc);
@@ -409,6 +423,5 @@ protected RubyClass allocate(RubyClass classClass) {
                     getEncapsulatingSourceSection(),
                     classClass);
         }
-
     }
 }