backport #8185, #as_json isolates options when encoding a hash.

activesupport/CHANGELOG.md

@@ -1,5 +1,10 @@
 ## Rails 3.2.10 (unreleased)
 
+*   `#as_json` isolates options when encoding a hash. [Backport #8185]
+    Fix #8182
+
+    *Yves Senn*
+
 *   Handle the possible Permission Denied errors atomic.rb might trigger due to
     its chown and chmod calls. [Backport #8027]
 

activesupport/lib/active_support/json/encoding.rb

@@ -61,7 +61,7 @@ def options_for(value)
             # hashes and arrays need to get encoder in the options, so that they can detect circular references
             options.merge(:encoder => self)
           else
-            options
+            options.dup
           end
         end
 

activesupport/test/json/encoding_test.rb

@@ -22,6 +22,15 @@ def as_json(options)
     end
   end
 
+  class CustomWithOptions
+    attr_accessor :foo, :bar
+
+    def as_json(options={})
+      options[:only] = %w(foo bar)
+      super(options)
+    end
+  end
+
   TrueTests     = [[ true,  %(true)  ]]
   FalseTests    = [[ false, %(false) ]]
   NilTests      = [[ nil,   %(null)  ]]
@@ -239,6 +248,15 @@ def test_enumerable_should_pass_encoding_options_to_children_in_to_json
     assert_equal(%([{"address":{"city":"London"}},{"address":{"city":"Paris"}}]), json)
   end
 
+  def test_to_json_should_not_keep_options_around
+    f = CustomWithOptions.new
+    f.foo = "hello"
+    f.bar = "world"
+
+    hash = {"foo" => f, "other_hash" => {"foo" => "other_foo", "test" => "other_test"}}
+    assert_equal(%({"foo":{"foo":"hello","bar":"world"},"other_hash":{"foo":"other_foo","test":"other_test"}}), hash.to_json)
+  end
+
   def test_struct_encoding
     Struct.new('UserNameAndEmail', :name, :email)
     Struct.new('UserNameAndDate', :name, :date)