impl TrustedRandomAccess for vec::IntoIter

3 files changed, 28 insertions, 3 deletions

diff --git a/library/alloc/src/vec.rs b/library/alloc/src/vec.rs
index 9327cf16c15..27f2440ddc0 100644
--- a/library/alloc/src/vec.rs
+++ b/library/alloc/src/vec.rs
@@ -58,7 +58,9 @@ use core::cmp::{self, Ordering};
 use core::fmt;
 use core::hash::{Hash, Hasher};
 use core::intrinsics::{arith_offset, assume};
-use core::iter::{FromIterator, FusedIterator, InPlaceIterable, SourceIter, TrustedLen};
+use core::iter::{
+    FromIterator, FusedIterator, InPlaceIterable, SourceIter, TrustedLen, TrustedRandomAccess,
+};
 use core::marker::PhantomData;
 use core::mem::{self, ManuallyDrop, MaybeUninit};
 use core::ops::Bound::{Excluded, Included, Unbounded};
@@ -2936,6 +2938,25 @@ impl<T> FusedIterator for IntoIter<T> {}
 #[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<T> TrustedLen for IntoIter<T> {}
 
+#[doc(hidden)]
+#[unstable(issue = "0", feature = "std_internals")]
+// T: Copy as approximation for !Drop since get_unchecked does not advance self.ptr
+// and thus we can't implement drop-handling
+unsafe impl<T> TrustedRandomAccess for IntoIter<T>
+where
+    T: Copy,
+{
+    unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
+        unsafe {
+            if mem::size_of::<T>() == 0 { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
+        }
+    }
+
+    fn may_have_side_effect() -> bool {
+        false
+    }
+}
+
 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
 impl<T: Clone> Clone for IntoIter<T> {
     fn clone(&self) -> IntoIter<T> {
diff --git a/library/core/src/iter/adapters/mod.rs b/library/core/src/iter/adapters/mod.rs
index 0ad279c5533..12fdd3f49c3 100644
--- a/library/core/src/iter/adapters/mod.rs
+++ b/library/core/src/iter/adapters/mod.rs
@@ -18,7 +18,8 @@ pub use self::chain::Chain;
 pub use self::flatten::{FlatMap, Flatten};
 pub use self::fuse::Fuse;
 use self::zip::try_get_unchecked;
-pub(crate) use self::zip::TrustedRandomAccess;
+#[unstable(feature = "trusted_random_access", issue = "none")]
+pub use self::zip::TrustedRandomAccess;
 pub use self::zip::Zip;
 
 /// This trait provides transitive access to source-stages in an interator-adapter pipeline
@@ -480,6 +481,7 @@ where
 unsafe impl<I> TrustedRandomAccess for Cloned<I>
 where
     I: TrustedRandomAccess,
+
 {
     #[inline]
     fn may_have_side_effect() -> bool {
diff --git a/library/core/src/iter/mod.rs b/library/core/src/iter/mod.rs
index f35994560c5..922ffd1e0b5 100644
--- a/library/core/src/iter/mod.rs
+++ b/library/core/src/iter/mod.rs
@@ -357,6 +357,8 @@ pub use self::adapters::MapWhile;
 pub use self::adapters::SourceIter;
 #[stable(feature = "iterator_step_by", since = "1.28.0")]
 pub use self::adapters::StepBy;
+#[unstable(feature = "trusted_random_access", issue = "none")]
+pub use self::adapters::TrustedRandomAccess;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::adapters::{Chain, Cycle, Enumerate, Filter, FilterMap, Map, Rev, Zip};
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -364,7 +366,7 @@ pub use self::adapters::{FlatMap, Peekable, Scan, Skip, SkipWhile, Take, TakeWhi
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::adapters::{Fuse, Inspect};
 
-pub(crate) use self::adapters::{process_results, TrustedRandomAccess};
+pub(crate) use self::adapters::process_results;
 
 mod adapters;
 mod range;