move lib/go/gremlin to ent/dialect (#1192)

Summary:
Pull Request resolved: https://github.com/facebookexternal/fbc/pull/1192

Pull Request resolved: https://github.com/facebookincubator/ent/pull/11

Reviewed By: alexsn

Differential Revision: D16377224

fbshipit-source-id: 07ca7436eb9b64fbe2299568560b91466b2417ba

dialect/gremlin/encoding/graphson/struct.go

@@ -0,0 +1,37 @@
+package graphson
+
+import (
+	"github.com/json-iterator/go"
+)
+
+// DecoratorOfStructField decorates a struct field value encoder.
+func (encodeExtension) DecoratorOfStructField(enc jsoniter.ValEncoder, tag string) jsoniter.ValEncoder {
+	typ, _ := parseTag(tag)
+	if typ == "" {
+		return nil
+	}
+
+	encoder, ok := enc.(typeEncoder)
+	if !ok {
+		encoder = typeEncoder{ValEncoder: enc}
+	}
+	encoder.Type = Type(typ)
+
+	return encoder
+}
+
+// DecoratorOfStructField decorates a struct field value decoder.
+func (decodeExtension) DecoratorOfStructField(dec jsoniter.ValDecoder, tag string) jsoniter.ValDecoder {
+	typ, _ := parseTag(tag)
+	if typ == "" {
+		return nil
+	}
+
+	decoder, ok := dec.(typeDecoder)
+	if !ok {
+		decoder = typeDecoder{ValDecoder: dec}
+	}
+	decoder.typeChecker = Type(typ)
+
+	return decoder
+}