compiler: support System.Json.* syscalls

pkg/compiler/syscall.go

@@ -10,6 +10,10 @@ var syscalls = map[string]map[string]string{
 		"Next":   "System.Enumerator.Next",
 		"Value":  "System.Enumerator.Value",
 	},
+	"json": {
+		"Serialize":   "System.Json.Serialize",
+		"Deserialize": "System.Json.Deserialize",
+	},
 	"storage": {
 		"ConvertContextToReadOnly": "System.Storage.AsReadOnly",
 		"Delete":                   "System.Storage.Delete",

pkg/interop/json/json.go

@@ -0,0 +1,28 @@
+/*
+Package json provides various JSON serialization/deserialization routines.
+*/
+package json
+
+// ToJSON serializes value to json. It uses `System.Json.Serialize` syscall.
+// Serialization format is the following:
+// []byte -> base64 string
+// bool -> json boolean
+// nil -> Null
+// string -> base64 encoded sequence of underlying bytes
+// (u)int* -> integer, only value in -2^53..2^53 are allowed
+// []interface{} -> json array
+// map[type1]type2 -> json object with string keys marshaled as strings (not base64).
+func ToJSON(item interface{}) []byte {
+	return nil
+}
+
+// FromJSON deserializes value from json. It uses `System.Json.Deserialize` syscall.
+// It performs deserialization as follows:
+// strings -> []byte (string) from base64
+// integers -> (u)int* types
+// null -> interface{}(nil)
+// arrays -> []interface{}
+// maps -> map[string]interface{}
+func FromJSON(data []byte) interface{} {
+	return nil
+}