Fix json generation for symbols on TruffleRuby

Author: rwstauner

lib/json/truffle_ruby/generator.rb

@@ -48,7 +48,7 @@ module Generator
       SCRIPT_SAFE_ESCAPE_PATTERN = /[\/"\\\x0-\x1f\u2028-\u2029]/
 
       def self.native_type?(value) # :nodoc:
-        (false == value || true == value || nil == value || String === value || Array === value || Hash === value || Integer === value || Float === value || Fragment === value)
+        (false == value || true == value || nil == value || String === value || Symbol === value || Array === value || Hash === value || Integer === value || Float === value || Fragment === value)
       end
 
       def self.native_key?(key) # :nodoc:

test/json/json_coder_test.rb

@@ -19,6 +19,11 @@ def test_json_coder_with_proc_with_unsupported_value
     assert_raise(JSON::GeneratorError) { coder.dump([Object.new]) }
   end
 
+  def test_json_coder_with_proc_returning_symbol
+    coder = JSON::Coder.new { _1 }
+    assert_equal %({"sym":"sym"}), coder.dump({ sym: :sym })
+  end
+
   def test_json_coder_hash_key
     obj = Object.new
     coder = JSON::Coder.new do |obj, is_key|

test/json/json_generator_test.rb

@@ -82,6 +82,8 @@ def test_dump_strict
     assert_equal '"hello"', dump(:hello, strict: true)
     assert_equal '"hello"', :hello.to_json(strict: true)
     assert_equal '"World"', "World".to_json(strict: true)
+    assert_equal '["hello"]', dump([:hello], strict: true)
+    assert_equal '{"hello":"world"}', dump({ hello: :world }, strict: true)
   end
 
   def test_not_frozen