generator.c: fix infinite recursion

* ext/json/generator/generator.c (generate_json): get rid of
  unnecessary recursive calls which can cause infinite recursion.
  T_STRING may not have rb_cString.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49562 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 10 insertions, 0 deletions

diff --git a/test/json/test_json_generate.rb b/test/json/test_json_generate.rb
index 8db0b7890b..1834290944 100755
--- a/test/json/test_json_generate.rb
+++ b/test/json/test_json_generate.rb
@@ -334,4 +334,14 @@ EOT
       assert_equal true, JSON.generate(["\xea"])
     end
   end
+
+  def test_string_subclass
+    s = Class.new(String) do
+      def to_s; self; end
+      undef to_json
+    end
+    assert_nothing_raised(SystemStackError) do
+      assert_equal '[""]', JSON.generate([s.new])
+    end
+  end
 end