Enable rustc_pass_by_value for Span

compiler/rustc_span/src/lib.rs

@@ -22,6 +22,7 @@
 #![feature(negative_impls)]
 #![feature(nll)]
 #![feature(min_specialization)]
+#![feature(rustc_attrs)]
 #![allow(rustc::potential_query_instability)]
 
 #[macro_use]

compiler/rustc_span/src/span_encoding.rs

@@ -61,8 +61,7 @@ use rustc_data_structures::fx::FxIndexSet;
 /// using the callback `SPAN_TRACK` to access the query engine.
 ///
 #[derive(Clone, Copy, Eq, PartialEq, Hash)]
-// FIXME: Enable this in the bootstrap bump, but separate commit.
-// #[rustc_pass_by_value]
+#[rustc_pass_by_value]
 pub struct Span {
     base_or_index: u32,
     len_or_tag: u16,