Fixed AST::Node#updated to always return a copy. (#25)

Previously it relied on a call chain #initialize -> #freeze that returns `self`.
However, overriding constructor in a custom subclass and returning something else breaks `updated`.

lib/ast/node.rb

@@ -140,7 +140,9 @@ def updated(type=nil, children=nil, properties=nil)
           properties.nil?
         self
       else
-        original_dup.send :initialize, new_type, new_children, new_properties
+        copy = original_dup
+        copy.send :initialize, new_type, new_children, new_properties
+        copy
       end
     end
 

test/test_ast.rb

@@ -7,9 +7,17 @@ class MetaNode < AST::Node
     attr_reader :meta
   end
 
+  class SubclassNode < AST::Node
+    def initialize(*)
+      super
+      nil
+    end
+  end
+
   before do
     @node = AST::Node.new(:node, [ 0, 1 ])
     @metanode = MetaNode.new(:node, [ 0, 1 ], :meta => 'value')
+    @subclass_node = SubclassNode.new(:node, [ 0, 1 ])
   end
 
   it 'should have accessors for type and children' do
@@ -55,6 +63,12 @@ class MetaNode < AST::Node
     updated.meta.should.equal 'other_value'
   end
 
+  it 'returns updated node for subclasses that override constructor' do
+    updated = @subclass_node.updated(nil, [2])
+    updated.type.should.equal :node
+    updated.children.should.equal [2]
+  end
+
   it 'should format to_sexp correctly' do
     AST::Node.new(:a, [ :sym, [ 1, 2 ] ]).to_sexp.should.equal '(a :sym [1, 2])'
     AST::Node.new(:a, [ :sym, @node ]).to_sexp.should.equal "(a :sym\n  (node 0 1))"