Fix lookup on HashWithIndifferentAccess for array values.

Author: zetter

activesupport/lib/active_support/hash_with_indifferent_access.rb

@@ -164,7 +164,8 @@ def convert_value(value)
         if value.is_a? Hash
           value.nested_under_indifferent_access
         elsif value.is_a?(Array)
-          value.dup.replace(value.map { |e| convert_value(e) })
+          value = value.dup if value.frozen?
+          value.replace(value.map { |e| convert_value(e) })
         else
           value
         end

activesupport/test/core_ext/hash_ext_test.rb

@@ -457,6 +457,13 @@ def test_indifferent_to_hash
     assert_equal '1234', roundtrip.default
   end
 
+  def test_lookup_returns_the_same_object_that_is_stored_in_hash_indifferent_access
+    hash = HashWithIndifferentAccess.new {|h, k| h[k] = []}
+    hash[:a] << 1
+
+    assert_equal [1], hash[:a]
+  end
+
   def test_indifferent_hash_with_array_of_hashes
     hash = { "urls" => { "url" => [ { "address" => "1" }, { "address" => "2" } ] }}.with_indifferent_access
     assert_equal "1", hash[:urls][:url].first[:address]