Merge pull request #197 from eregon/fix-detection-json-gem

Fix detection for the json_gem adapter

lib/multi_json.rb

@@ -47,7 +47,7 @@ def default_adapter
  return :oj if defined?(::Oj)
  return :yajl if defined?(::Yajl)
  return :jr_jackson if defined?(::JrJackson)
- return :json_gem if defined?(::JSON::JSON_LOADED)
+ return :json_gem if defined?(::JSON::Ext::Parser)
  return :gson if defined?(::Gson)
 
  REQUIREMENT_MAP.each do |adapter, library|

spec/multi_json_spec.rb

@@ -30,6 +30,24 @@
  end
  end
 
+ context 'when JSON pure is already loaded' do
+ it 'default_adapter tries to require each adapter in turn and does not assume :json_gem is already loaded' do
+ require 'json/pure'
+ expect(JSON::JSON_LOADED).to be_truthy
+
+ undefine_constants :Oj, :Yajl, :Gson, :JrJackson do
+ # simulate that the json_gem is not loaded
+ ext = defined?(JSON::Ext::Parser) ? JSON::Ext.send(:remove_const, :Parser) : nil
+ begin
+ expect(MultiJson).to receive(:require)
+ MultiJson.default_adapter
+ ensure
+ JSON::Ext::Parser = ext if ext
+ end
+ end
+ end
+ end
+
  context 'caching' do
  before { MultiJson.use adapter }
  let(:adapter) { MultiJson::Adapters::JsonGem }