Decode AttrId via mk_attr_id

src/librustc_metadata/decoder.rs

@@ -980,14 +980,7 @@ impl<'a, 'tcx> CrateMetadata {
     }
 
     fn get_attributes(&self, item: &Entry<'tcx>, sess: &Session) -> Vec<ast::Attribute> {
-        item.attributes
-            .decode((self, sess))
-            .map(|mut attr| {
-                // Need new unique IDs: old thread-local IDs won't map to new threads.
-                attr.id = attr::mk_attr_id();
-                attr
-            })
-            .collect()
+        item.attributes.decode((self, sess)).collect()
     }
 
     // Translate a DefId from the current compilation environment to a DefId

src/libsyntax/ast.rs

@@ -2104,9 +2104,7 @@ pub enum AttrStyle {
     Inner,
 }
 
-#[derive(
-    Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, PartialOrd, Ord, Copy,
-)]
+#[derive(Clone, PartialEq, Eq, Hash, Debug, PartialOrd, Ord, Copy)]
 pub struct AttrId(pub usize);
 
 impl Idx for AttrId {
@@ -2118,6 +2116,18 @@ impl Idx for AttrId {
     }
 }
 
+impl rustc_serialize::Encodable for AttrId {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_unit()
+    }
+}
+
+impl rustc_serialize::Decodable for AttrId {
+    fn decode<D: Decoder>(d: &mut D) -> Result<AttrId, D::Error> {
+        d.read_nil().map(|_| crate::attr::mk_attr_id())
+    }
+}
+
 /// Metadata associated with an item.
 /// Doc-comments are promoted to attributes that have `is_sugared_doc = true`.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]