Use more impl header lifetime elision

There are two big categories of changes in here

- Removing lifetimes from common traits that can essentially never user a lifetime from an input (particularly `Drop` & `Debug`)
- Forwarding impls that are only possible because the lifetime doesn't matter (like `impl<R: Read + ?Sized> Read for &mut R`)

I omitted things that seemed like they could be more controversial, like the handful of iterators that have a `Item: 'static` despite the iterator having a lifetime or the `PartialEq` implementations where the flipped one cannot elide the lifetime.

src/liballoc/borrow.rs

@@ -182,8 +182,8 @@ pub enum Cow<'a, B: ?Sized + 'a>
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, B: ?Sized + ToOwned> Clone for Cow<'a, B> {
-    fn clone(&self) -> Cow<'a, B> {
+impl<B: ?Sized + ToOwned> Clone for Cow<'_, B> {
+    fn clone(&self) -> Self {
         match *self {
             Borrowed(b) => Borrowed(b),
             Owned(ref o) => {
@@ -193,7 +193,7 @@ impl<'a, B: ?Sized + ToOwned> Clone for Cow<'a, B> {
         }
     }
 
-    fn clone_from(&mut self, source: &Cow<'a, B>) {
+    fn clone_from(&mut self, source: &Self) {
         if let Owned(ref mut dest) = *self {
             if let Owned(ref o) = *source {
                 o.borrow().clone_into(dest);
@@ -296,11 +296,11 @@ impl<B: ?Sized + ToOwned> Deref for Cow<'_, B> {
 impl<B: ?Sized> Eq for Cow<'_, B> where B: Eq + ToOwned {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, B: ?Sized> Ord for Cow<'a, B>
+impl<B: ?Sized> Ord for Cow<'_, B>
     where B: Ord + ToOwned
 {
     #[inline]
-    fn cmp(&self, other: &Cow<'a, B>) -> Ordering {
+    fn cmp(&self, other: &Self) -> Ordering {
         Ord::cmp(&**self, &**other)
     }
 }
@@ -353,18 +353,18 @@ impl<B: ?Sized> fmt::Display for Cow<'_, B>
 }
 
 #[stable(feature = "default", since = "1.11.0")]
-impl<'a, B: ?Sized> Default for Cow<'a, B>
+impl<B: ?Sized> Default for Cow<'_, B>
     where B: ToOwned,
           <B as ToOwned>::Owned: Default
 {
     /// Creates an owned Cow<'a, B> with the default value for the contained owned value.
-    fn default() -> Cow<'a, B> {
+    fn default() -> Self {
         Owned(<B as ToOwned>::Owned::default())
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, B: ?Sized> Hash for Cow<'a, B>
+impl<B: ?Sized> Hash for Cow<'_, B>
     where B: Hash + ToOwned
 {
     #[inline]

src/liballoc/collections/binary_heap.rs

@@ -947,8 +947,8 @@ impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
 
 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T> Clone for Iter<'a, T> {
-    fn clone(&self) -> Iter<'a, T> {
+impl<T> Clone for Iter<'_, T> {
+    fn clone(&self) -> Self {
         Iter { iter: self.iter.clone() }
     }
 }

src/liballoc/collections/btree/map.rs

@@ -1218,8 +1218,8 @@ impl<K, V> ExactSizeIterator for Iter<'_, K, V> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, K, V> Clone for Iter<'a, K, V> {
-    fn clone(&self) -> Iter<'a, K, V> {
+impl<K, V> Clone for Iter<'_, K, V> {
+    fn clone(&self) -> Self {
         Iter {
             range: self.range.clone(),
             length: self.length,
@@ -1441,8 +1441,8 @@ impl<K, V> ExactSizeIterator for Keys<'_, K, V> {
 impl<K, V> FusedIterator for Keys<'_, K, V> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, K, V> Clone for Keys<'a, K, V> {
-    fn clone(&self) -> Keys<'a, K, V> {
+impl<K, V> Clone for Keys<'_, K, V> {
+    fn clone(&self) -> Self {
         Keys { inner: self.inner.clone() }
     }
 }
@@ -1478,8 +1478,8 @@ impl<K, V> ExactSizeIterator for Values<'_, K, V> {
 impl<K, V> FusedIterator for Values<'_, K, V> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, K, V> Clone for Values<'a, K, V> {
-    fn clone(&self) -> Values<'a, K, V> {
+impl<K, V> Clone for Values<'_, K, V> {
+    fn clone(&self) -> Self {
         Values { inner: self.inner.clone() }
     }
 }
@@ -1606,8 +1606,8 @@ impl<'a, K, V> Range<'a, K, V> {
 impl<K, V> FusedIterator for Range<'_, K, V> {}
 
 #[stable(feature = "btree_range", since = "1.17.0")]
-impl<'a, K, V> Clone for Range<'a, K, V> {
-    fn clone(&self) -> Range<'a, K, V> {
+impl<K, V> Clone for Range<'_, K, V> {
+    fn clone(&self) -> Self {
         Range {
             front: self.front,
             back: self.back,

src/liballoc/collections/btree/set.rs

@@ -907,8 +907,8 @@ impl<T: Debug> Debug for BTreeSet<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T> Clone for Iter<'a, T> {
-    fn clone(&self) -> Iter<'a, T> {
+impl<T> Clone for Iter<'_, T> {
+    fn clone(&self) -> Self {
         Iter { iter: self.iter.clone() }
     }
 }
@@ -963,8 +963,8 @@ impl<T> ExactSizeIterator for IntoIter<T> {
 impl<T> FusedIterator for IntoIter<T> {}
 
 #[stable(feature = "btree_range", since = "1.17.0")]
-impl<'a, T> Clone for Range<'a, T> {
-    fn clone(&self) -> Range<'a, T> {
+impl<T> Clone for Range<'_, T> {
+    fn clone(&self) -> Self {
         Range { iter: self.iter.clone() }
     }
 }
@@ -998,8 +998,8 @@ fn cmp_opt<T: Ord>(x: Option<&T>, y: Option<&T>, short: Ordering, long: Ordering
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T> Clone for Difference<'a, T> {
-    fn clone(&self) -> Difference<'a, T> {
+impl<T> Clone for Difference<'_, T> {
+    fn clone(&self) -> Self {
         Difference {
             a: self.a.clone(),
             b: self.b.clone(),
@@ -1036,8 +1036,8 @@ impl<'a, T: Ord> Iterator for Difference<'a, T> {
 impl<T: Ord> FusedIterator for Difference<'_, T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T> Clone for SymmetricDifference<'a, T> {
-    fn clone(&self) -> SymmetricDifference<'a, T> {
+impl<T> Clone for SymmetricDifference<'_, T> {
+    fn clone(&self) -> Self {
         SymmetricDifference {
             a: self.a.clone(),
             b: self.b.clone(),
@@ -1070,8 +1070,8 @@ impl<'a, T: Ord> Iterator for SymmetricDifference<'a, T> {
 impl<T: Ord> FusedIterator for SymmetricDifference<'_, T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T> Clone for Intersection<'a, T> {
-    fn clone(&self) -> Intersection<'a, T> {
+impl<T> Clone for Intersection<'_, T> {
+    fn clone(&self) -> Self {
         Intersection {
             a: self.a.clone(),
             b: self.b.clone(),
@@ -1108,8 +1108,8 @@ impl<'a, T: Ord> Iterator for Intersection<'a, T> {
 impl<T: Ord> FusedIterator for Intersection<'_, T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T> Clone for Union<'a, T> {
-    fn clone(&self) -> Union<'a, T> {
+impl<T> Clone for Union<'_, T> {
+    fn clone(&self) -> Self {
         Union {
             a: self.a.clone(),
             b: self.b.clone(),

src/liballoc/collections/linked_list.rs

@@ -1200,16 +1200,16 @@ unsafe impl<T: Send> Send for LinkedList<T> {}
 unsafe impl<T: Sync> Sync for LinkedList<T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<'a, T: Sync> Send for Iter<'a, T> {}
+unsafe impl<T: Sync> Send for Iter<'_, T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<'a, T: Sync> Sync for Iter<'a, T> {}
+unsafe impl<T: Sync> Sync for Iter<'_, T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<'a, T: Send> Send for IterMut<'a, T> {}
+unsafe impl<T: Send> Send for IterMut<'_, T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<'a, T: Sync> Sync for IterMut<'a, T> {}
+unsafe impl<T: Sync> Sync for IterMut<'_, T> {}
 
 #[cfg(test)]
 mod tests {

src/liballoc/collections/vec_deque.rs

@@ -2132,8 +2132,8 @@ impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
 
 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T> Clone for Iter<'a, T> {
-    fn clone(&self) -> Iter<'a, T> {
+impl<T> Clone for Iter<'_, T> {
+    fn clone(&self) -> Self {
         Iter {
             ring: self.ring,
             tail: self.tail,
@@ -2225,7 +2225,7 @@ pub struct IterMut<'a, T: 'a> {
 }
 
 #[stable(feature = "collection_debug", since = "1.17.0")]
-impl<'a, T: fmt::Debug> fmt::Debug for IterMut<'_, T> {
+impl<T: fmt::Debug> fmt::Debug for IterMut<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let (front, back) = RingSlices::ring_slices(&*self.ring, self.head, self.tail);
         f.debug_tuple("IterMut")

src/liballoc/vec.rs

@@ -2455,7 +2455,7 @@ pub struct Drain<'a, T: 'a> {
 }
 
 #[stable(feature = "collection_debug", since = "1.17.0")]
-impl<'a, T: 'a + fmt::Debug> fmt::Debug for Drain<'a, T> {
+impl<T: fmt::Debug> fmt::Debug for Drain<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_tuple("Drain")
          .field(&self.iter.as_slice())

src/libcore/future/future.rs

@@ -100,7 +100,7 @@ pub trait Future {
     fn poll(self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<Self::Output>;
 }
 
-impl<'a, F: ?Sized + Future + Unpin> Future for &'a mut F {
+impl<F: ?Sized + Future + Unpin> Future for &mut F {
     type Output = F::Output;
 
     fn poll(mut self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<Self::Output> {

src/libcore/internal_macros.rs

@@ -7,7 +7,7 @@ macro_rules! forward_ref_unop {
     };
     (impl $imp:ident, $method:ident for $t:ty, #[$attr:meta]) => {
         #[$attr]
-        impl<'a> $imp for &'a $t {
+        impl $imp for &$t {
             type Output = <$t as $imp>::Output;
 
             #[inline]

src/libcore/option.rs

@@ -874,7 +874,7 @@ impl<T> Option<T> {
     }
 }
 
-impl<'a, T: Copy> Option<&'a T> {
+impl<T: Copy> Option<&T> {
     /// Maps an `Option<&T>` to an `Option<T>` by copying the contents of the
     /// option.
     ///
@@ -895,7 +895,7 @@ impl<'a, T: Copy> Option<&'a T> {
     }
 }
 
-impl<'a, T: Copy> Option<&'a mut T> {
+impl<T: Copy> Option<&mut T> {
     /// Maps an `Option<&mut T>` to an `Option<T>` by copying the contents of the
     /// option.
     ///
@@ -916,7 +916,7 @@ impl<'a, T: Copy> Option<&'a mut T> {
     }
 }
 
-impl<'a, T: Clone> Option<&'a T> {
+impl<T: Clone> Option<&T> {
     /// Maps an `Option<&T>` to an `Option<T>` by cloning the contents of the
     /// option.
     ///
@@ -935,7 +935,7 @@ impl<'a, T: Clone> Option<&'a T> {
     }
 }
 
-impl<'a, T: Clone> Option<&'a mut T> {
+impl<T: Clone> Option<&mut T> {
     /// Maps an `Option<&mut T>` to an `Option<T>` by cloning the contents of the
     /// option.
     ///

src/libcore/slice/mod.rs

@@ -2899,7 +2899,7 @@ macro_rules! iterator {
         }
 
         #[stable(feature = "rust1", since = "1.0.0")]
-        impl<'a, T> ExactSizeIterator for $name<'a, T> {
+        impl<T> ExactSizeIterator for $name<'_, T> {
             #[inline(always)]
             fn len(&self) -> usize {
                 len!(self)
@@ -3094,10 +3094,10 @@ macro_rules! iterator {
         }
 
         #[stable(feature = "fused", since = "1.26.0")]
-        impl<'a, T> FusedIterator for $name<'a, T> {}
+        impl<T> FusedIterator for $name<'_, T> {}
 
         #[unstable(feature = "trusted_len", issue = "37572")]
-        unsafe impl<'a, T> TrustedLen for $name<'a, T> {}
+        unsafe impl<T> TrustedLen for $name<'_, T> {}
     }
 }
 
@@ -4361,8 +4361,8 @@ pub struct RChunks<'a, T:'a> {
 
 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
 #[stable(feature = "rchunks", since = "1.31.0")]
-impl<'a, T> Clone for RChunks<'a, T> {
-    fn clone(&self) -> RChunks<'a, T> {
+impl<T> Clone for RChunks<'_, T> {
+    fn clone(&self) -> Self {
         RChunks {
             v: self.v,
             chunk_size: self.chunk_size,
@@ -4451,13 +4451,13 @@ impl<'a, T> DoubleEndedIterator for RChunks<'a, T> {
 }
 
 #[stable(feature = "rchunks", since = "1.31.0")]
-impl<'a, T> ExactSizeIterator for RChunks<'a, T> {}
+impl<T> ExactSizeIterator for RChunks<'_, T> {}
 
 #[unstable(feature = "trusted_len", issue = "37572")]
-unsafe impl<'a, T> TrustedLen for RChunks<'a, T> {}
+unsafe impl<T> TrustedLen for RChunks<'_, T> {}
 
 #[stable(feature = "rchunks", since = "1.31.0")]
-impl<'a, T> FusedIterator for RChunks<'a, T> {}
+impl<T> FusedIterator for RChunks<'_, T> {}
 
 #[doc(hidden)]
 #[stable(feature = "rchunks", since = "1.31.0")]
@@ -4576,13 +4576,13 @@ impl<'a, T> DoubleEndedIterator for RChunksMut<'a, T> {
 }
 
 #[stable(feature = "rchunks", since = "1.31.0")]
-impl<'a, T> ExactSizeIterator for RChunksMut<'a, T> {}
+impl<T> ExactSizeIterator for RChunksMut<'_, T> {}
 
 #[unstable(feature = "trusted_len", issue = "37572")]
-unsafe impl<'a, T> TrustedLen for RChunksMut<'a, T> {}
+unsafe impl<T> TrustedLen for RChunksMut<'_, T> {}
 
 #[stable(feature = "rchunks", since = "1.31.0")]
-impl<'a, T> FusedIterator for RChunksMut<'a, T> {}
+impl<T> FusedIterator for RChunksMut<'_, T> {}
 
 #[doc(hidden)]
 #[stable(feature = "rchunks", since = "1.31.0")]
@@ -4707,10 +4707,10 @@ impl<'a, T> ExactSizeIterator for RChunksExact<'a, T> {
 }
 
 #[unstable(feature = "trusted_len", issue = "37572")]
-unsafe impl<'a, T> TrustedLen for RChunksExact<'a, T> {}
+unsafe impl<T> TrustedLen for RChunksExact<'_, T> {}
 
 #[stable(feature = "rchunks", since = "1.31.0")]
-impl<'a, T> FusedIterator for RChunksExact<'a, T> {}
+impl<T> FusedIterator for RChunksExact<'_, T> {}
 
 #[doc(hidden)]
 #[stable(feature = "rchunks", since = "1.31.0")]
@@ -4818,17 +4818,17 @@ impl<'a, T> DoubleEndedIterator for RChunksExactMut<'a, T> {
 }
 
 #[stable(feature = "rchunks", since = "1.31.0")]
-impl<'a, T> ExactSizeIterator for RChunksExactMut<'a, T> {
+impl<T> ExactSizeIterator for RChunksExactMut<'_, T> {
     fn is_empty(&self) -> bool {
         self.v.is_empty()
     }
 }
 
 #[unstable(feature = "trusted_len", issue = "37572")]
-unsafe impl<'a, T> TrustedLen for RChunksExactMut<'a, T> {}
+unsafe impl<T> TrustedLen for RChunksExactMut<'_, T> {}
 
 #[stable(feature = "rchunks", since = "1.31.0")]
-impl<'a, T> FusedIterator for RChunksExactMut<'a, T> {}
+impl<T> FusedIterator for RChunksExactMut<'_, T> {}
 
 #[doc(hidden)]
 #[stable(feature = "rchunks", since = "1.31.0")]

src/libcore/str/mod.rs

@@ -820,7 +820,7 @@ impl FusedIterator for Bytes<'_> {}
 unsafe impl TrustedLen for Bytes<'_> {}
 
 #[doc(hidden)]
-unsafe impl<'a> TrustedRandomAccess for Bytes<'a> {
+unsafe impl TrustedRandomAccess for Bytes<'_> {
     unsafe fn get_unchecked(&mut self, i: usize) -> u8 {
         self.0.get_unchecked(i)
     }