Add internal plugin for creating Reflectable implementations

components/plugins/reflector.rs

@@ -0,0 +1,50 @@
+/* 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/. */
+
+use syntax::ext::base::ExtCtxt;
+use syntax::codemap::Span;
+use syntax::ptr::P;
+use syntax::ast::{Item, MetaItem};
+use syntax::ast;
+use utils::match_ty_unwrap;
+
+
+pub fn expand_reflector(cx: &mut ExtCtxt, span: Span, _: &MetaItem, item: &Item, push: |P<Item>|) {
+
+    if let ast::ItemStruct(ref def, _) = item.node {
+        let struct_name = item.ident;
+        match def.fields.iter().find(|f| match_ty_unwrap(&*f.node.ty, &["dom", "bindings", "utils", "Reflector"]).is_some()) {
+            // If it has a field that is a Reflector, use that
+            Some(f) => {
+                let field_name = f.node.ident();
+                let impl_item = quote_item!(cx,
+                    impl ::dom::bindings::utils::Reflectable for $struct_name {
+                        fn reflector<'a>(&'a self) -> &'a ::dom::bindings::utils::Reflector {
+                            &self.$field_name
+                        }
+                    }
+                );
+                impl_item.map(|it| push(it))
+            },
+            // Or just call it on the first field (supertype).
+            // TODO: Write a lint to ensure that this first field is indeed a #[dom_struct],
+            // and the only such field in the struct definition (including reflectors)
+            // Unfortunately we can't do it here itself because a def_map (from middle) is not available
+            // at expansion time
+            None => {
+                let field_name = def.fields[0].node.ident();
+                let impl_item = quote_item!(cx,
+                    impl ::dom::bindings::utils::Reflectable for $struct_name {
+                        fn reflector<'a>(&'a self) -> &'a ::dom::bindings::utils::Reflector {
+                            self.$field_name.reflector()
+                        }
+                    }
+                );
+                impl_item.map(|it| push(it))
+            }
+        };
+    } else {
+        cx.span_bug(span, "#[dom_struct] seems to have been applied to a non-struct");
+    }
+}