[dependencies]
arrayvec = { version = "0.7", default-features = false }
-rustc_serialize = { path = "../rustc_serialize" }
-rustc_macros = { path = "../rustc_macros" }
+rustc_serialize = { path = "../rustc_serialize", optional = true }
+rustc_macros = { path = "../rustc_macros", optional = true }
smallvec = "1.8.1"
+
+[features]
+default = ["nightly"]
+nightly = ["rustc_serialize", "rustc_macros"]