TrustedRandomAccess specialisation for Cloned.

This verifies that TrustedRandomAccess has no side effects when the
iterator item implements Copy. This also implements TrustedLen and
TrustedRandomAccess for str::Bytes.

src/libcore/iter/mod.rs

@@ -488,7 +488,7 @@ impl<'a, I, T: 'a> FusedIterator for Cloned<I>
 {}
 
 #[doc(hidden)]
-unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
+default unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
     where I: TrustedRandomAccess<Item=&'a T>, T: Clone
 {
     unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
@@ -499,6 +499,18 @@ unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
     fn may_have_side_effect() -> bool { true }
 }
 
+#[doc(hidden)]
+unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
+    where I: TrustedRandomAccess<Item=&'a T>, T: Copy
+{
+    unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
+        *self.it.get_unchecked(i)
+    }
+
+    #[inline]
+    fn may_have_side_effect() -> bool { false }
+}
+
 #[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<'a, I, T: 'a> TrustedLen for Cloned<I>
     where I: TrustedLen<Item=&'a T>,

src/libcore/str/mod.rs

@@ -20,7 +20,8 @@ use self::pattern::{Searcher, ReverseSearcher, DoubleEndedSearcher};
 use char;
 use convert::TryFrom;
 use fmt;
-use iter::{Map, Cloned, FusedIterator};
+use iter::{Map, Cloned, FusedIterator, TrustedLen};
+use iter_private::TrustedRandomAccess;
 use slice::{self, SliceIndex};
 use mem;
 
@@ -818,6 +819,17 @@ impl<'a> ExactSizeIterator for Bytes<'a> {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a> FusedIterator for Bytes<'a> {}
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<'a> TrustedLen for Bytes<'a> {}
+
+#[doc(hidden)]
+unsafe impl<'a> TrustedRandomAccess for Bytes<'a> {
+    unsafe fn get_unchecked(&mut self, i: usize) -> u8 {
+        self.0.get_unchecked(i)
+    }
+    fn may_have_side_effect() -> bool { false }
+}
+
 /// This macro generates a Clone impl for string pattern API
 /// wrapper types of the form X<'a, P>
 macro_rules! derive_pattern_clone {