[WIP] Unify AST Visitors with a macro like MIR Visitors

compiler/rustc_ast/src/lib.rs

@@ -15,6 +15,7 @@
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
+#![feature(macro_metavar_expr)]
 #![feature(negative_impls)]
 #![feature(never_type)]
 #![feature(rustdoc_internals)]
@@ -37,14 +38,13 @@ pub mod attr;
 pub mod entry;
 pub mod expand;
 pub mod format;
-pub mod mut_visit;
 pub mod node_id;
 pub mod ptr;
 pub mod token;
 pub mod tokenstream;
-pub mod visit;
-
+pub mod visitors;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+pub use visitors::{mut_visit, visit};
 
 pub use self::ast::*;
 pub use self::ast_traits::{AstDeref, AstNodeWrapper, HasAttrs, HasNodeId, HasTokens};