Simplify proc_macro code using Bound::cloned().

Author: m-ou-se

library/proc_macro/src/lib.rs

@@ -31,6 +31,7 @@
 #![feature(restricted_std)]
 #![feature(rustc_attrs)]
 #![feature(min_specialization)]
+#![feature(bound_cloned)]
 #![recursion_limit = "256"]
 
 #[unstable(feature = "proc_macro_internals", issue = "27812")]
@@ -43,7 +44,7 @@ mod diagnostic;
 pub use diagnostic::{Diagnostic, Level, MultiSpan};
 
 use std::cmp::Ordering;
-use std::ops::{Bound, RangeBounds};
+use std::ops::RangeBounds;
 use std::path::PathBuf;
 use std::str::FromStr;
 use std::{error, fmt, iter, mem};
@@ -1162,16 +1163,7 @@ impl Literal {
     // was 'c' or whether it was '\u{63}'.
     #[unstable(feature = "proc_macro_span", issue = "54725")]
     pub fn subspan<R: RangeBounds<usize>>(&self, range: R) -> Option<Span> {
-        // HACK(eddyb) something akin to `Option::cloned`, but for `Bound<&T>`.
-        fn cloned_bound<T: Clone>(bound: Bound<&T>) -> Bound<T> {
-            match bound {
-                Bound::Included(x) => Bound::Included(x.clone()),
-                Bound::Excluded(x) => Bound::Excluded(x.clone()),
-                Bound::Unbounded => Bound::Unbounded,
-            }
-        }
-
-        self.0.subspan(cloned_bound(range.start_bound()), cloned_bound(range.end_bound())).map(Span)
+        self.0.subspan(range.start_bound().cloned(), range.end_bound().cloned()).map(Span)
     }
 }