Convert ast::def_id into a struct.

src/libsyntax/ast.rs

@@ -93,7 +93,10 @@ type node_id = int;
 
 #[auto_encode]
 #[auto_decode]
-type def_id = {crate: crate_num, node: node_id};
+struct def_id {
+    crate: crate_num,
+    node: node_id,
+}
 
 impl def_id : cmp::Eq {
     pure fn eq(&self, other: &def_id) -> bool {

src/libsyntax/ast_util.rs

@@ -54,7 +54,9 @@ pure fn path_name_i(idents: &[ident], intr: @token::ident_interner) -> ~str {
 
 pure fn path_to_ident(p: @path) -> ident { vec::last(p.idents) }
 
-pure fn local_def(id: node_id) -> def_id { {crate: local_crate, node: id} }
+pure fn local_def(id: node_id) -> def_id {
+    ast::def_id { crate: local_crate, node: id }
+}
 
 pure fn is_local(did: ast::def_id) -> bool { did.crate == local_crate }