Change #[privatize] into #[derive(DenyPublicFields)]

components/deny_public_fields/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "deny_public_fields"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+path = "lib.rs"
+proc-macro = true
+
+[dependencies]
+syn = "0.10"
+synstructure = "0.4"

components/deny_public_fields/lib.rs

@@ -0,0 +1,26 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+extern crate proc_macro;
+extern crate syn;
+extern crate synstructure;
+
+#[proc_macro_derive(DenyPublicFields)]
+pub fn expand_token_stream(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    expand_string(&input.to_string()).parse().unwrap()
+}
+
+fn expand_string(input: &str) -> String {
+    let type_ = syn::parse_macro_input(input).unwrap();
+
+    let style = synstructure::BindStyle::Ref.into();
+    synstructure::each_field(&type_, &style, |binding| {
+        if binding.field.vis != syn::Visibility::Inherited {
+            panic!("Field {} should not be public", binding.ident);
+        }
+        "".to_owned()
+    });
+
+    "".to_owned()
+}