compiler: fold by value

compiler/rustc_data_structures/src/lib.rs

@@ -27,6 +27,7 @@
 #![feature(extend_one)]
 #![feature(const_panic)]
 #![feature(min_const_generics)]
+#![feature(new_uninit)]
 #![feature(once_cell)]
 #![feature(maybe_uninit_uninit_array)]
 #![allow(rustc::default_hash_types)]
@@ -70,6 +71,7 @@ pub mod box_region;
 pub mod captures;
 pub mod const_cstr;
 pub mod flock;
+pub mod functor;
 pub mod fx;
 pub mod graph;
 pub mod jobserver;