Rollup merge of #58553 - scottmcm:more-ihle, r=Centril

Use more impl header lifetime elision

Inspired by seeing explicit lifetimes on these two:

- https://doc.rust-lang.org/nightly/std/slice/struct.Iter.html#impl-FusedIterator
- https://doc.rust-lang.org/nightly/std/primitive.u32.html#impl-Not

And a follow-up to https://github.com/rust-lang/rust/pull/54687, that started using IHLE in libcore.

Most of the changes in here fall into two big categories:

- Removing lifetimes from common traits that can essentially never user a lifetime from an input (particularly `Drop`, `Debug`, and `Clone`)

- 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](https://internals.rust-lang.org/t/impl-type-parameter-aliases/9403/2?u=scottmcm).

I also removed two lifetimes that turned out to be completely unused; see https://github.com/rust-lang/rust/issues/41960#issuecomment-464557423

7 files changed, 38 insertions, 38 deletions

diff --git a/src/liballoc/borrow.rs b/src/liballoc/borrow.rs
index 40c71f12cd8..74c80a08b12 100644
--- a/src/liballoc/borrow.rs
+++ b/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]
diff --git a/src/liballoc/collections/binary_heap.rs b/src/liballoc/collections/binary_heap.rs
index 3b94379b58f..ccd4e9dbc04 100644
--- a/src/liballoc/collections/binary_heap.rs
+++ b/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() }
     }
 }
diff --git a/src/liballoc/collections/btree/map.rs b/src/liballoc/collections/btree/map.rs
index 5ec5064b735..250927138b3 100644
--- a/src/liballoc/collections/btree/map.rs
+++ b/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,
diff --git a/src/liballoc/collections/btree/set.rs b/src/liballoc/collections/btree/set.rs
index 870e3e47692..2be6455ad59 100644
--- a/src/liballoc/collections/btree/set.rs
+++ b/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(),
diff --git a/src/liballoc/collections/linked_list.rs b/src/liballoc/collections/linked_list.rs
index afd8078cdd7..c2ee2e63156 100644
--- a/src/liballoc/collections/linked_list.rs
+++ b/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 {
diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs
index b6fdaa89992..f778c4cbfde 100644
--- a/src/liballoc/collections/vec_deque.rs
+++ b/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")
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index 57723e4d212..a351d482fed 100644
--- a/src/liballoc/vec.rs
+++ b/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())