Fix behavior of trying to parse non-string objects

Author: YuheiNakasaka

lib/json/common.rb

@@ -16,7 +16,7 @@ class << self
     #   ruby = [0, 1, nil]
     #   JSON[ruby] # => '[0,1,null]'
     def [](object, opts = {})
-      if object.respond_to? :to_str
+      if object.respond_to?(:to_str) && object.to_str.is_a?(String)
         JSON.parse(object.to_str, opts)
       else
         JSON.generate(object, opts)
@@ -683,7 +683,7 @@ def jj(*objs)
   # The _opts_ argument is passed through to generate/parse respectively. See
   # generate and parse for their documentation.
   def JSON(object, *args)
-    if object.respond_to? :to_str
+    if object.respond_to?(:to_str) && object.to_str.is_a?(String)
       JSON.parse(object.to_str, args.first)
     else
       JSON.generate(object, args.first)

tests/json_common_interface_test.rb

@@ -6,6 +6,13 @@
 class JSONCommonInterfaceTest < Test::Unit::TestCase
   include JSON
 
+  module MethodMissing
+    def method_missing(name, *args); end
+    def respond_to_missing?(name, include_private)
+      true
+    end
+  end
+
   def setup
     @hash = {
       'a' => 2,
@@ -17,12 +24,26 @@ def setup
       'h' => 1000.0,
       'i' => 0.001
     }
+
+    @hash_with_method_missing = {
+      'a' => 2,
+      'b' => 3.141,
+      'c' => 'c',
+      'd' => [ 1, "b", 3.14 ],
+      'e' => { 'foo' => 'bar' },
+      'g' => "\"\0\037",
+      'h' => 1000.0,
+      'i' => 0.001
+    }
+    @hash_with_method_missing.extend MethodMissing
+
     @json = '{"a":2,"b":3.141,"c":"c","d":[1,"b",3.14],"e":{"foo":"bar"},'\
       '"g":"\\"\\u0000\\u001f","h":1000.0,"i":0.001}'
   end
 
   def test_index
     assert_equal @json, JSON[@hash]
+    assert_equal @json, JSON[@hash_with_method_missing]
     assert_equal @hash, JSON[@json]
   end
 
@@ -121,6 +142,7 @@ def test_dump_should_modify_defaults
 
   def test_JSON
     assert_equal @json, JSON(@hash)
+    assert_equal @json, JSON(@hash_with_method_missing)
     assert_equal @hash, JSON(@json)
   end