`#as_json` isolates options when encoding a hash. Closes #8182

Setting options in a custom `#as_json` method had side effects.
Modifications of the `options` hash leaked outside and influenced
the conversion of other objects contained in the hash.

1 files changed, 18 insertions, 0 deletions

diff --git a/activesupport/test/json/encoding_test.rb b/activesupport/test/json/encoding_test.rb
index 7ed71f9abc..5bb2a45c87 100644
--- a/activesupport/test/json/encoding_test.rb
+++ b/activesupport/test/json/encoding_test.rb
@@ -22,6 +22,15 @@ class TestJSONEncoding < ActiveSupport::TestCase
     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)  ]]
@@ -248,6 +257,15 @@ class TestJSONEncoding < ActiveSupport::TestCase
     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)