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

4 files changed, 23 insertions, 23 deletions

diff --git a/src/libstd/sync/mpsc/select.rs b/src/libstd/sync/mpsc/select.rs
index 8f6f9818d5c..8591b55dc58 100644
--- a/src/libstd/sync/mpsc/select.rs
+++ b/src/libstd/sync/mpsc/select.rs
@@ -321,7 +321,7 @@ impl Drop for Select {
     }
 }
 
-impl<'rx, T: Send> Drop for Handle<'rx, T> {
+impl<T: Send> Drop for Handle<'_, T> {
     fn drop(&mut self) {
         unsafe { self.remove() }
     }
@@ -347,7 +347,7 @@ impl fmt::Debug for Select {
     }
 }
 
-impl<'rx, T:Send+'rx> fmt::Debug for Handle<'rx, T> {
+impl<T: Send> fmt::Debug for Handle<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("Handle").finish()
     }
diff --git a/src/libstd/sync/mutex.rs b/src/libstd/sync/mutex.rs
index 340dca7ce73..954867911a0 100644
--- a/src/libstd/sync/mutex.rs
+++ b/src/libstd/sync/mutex.rs
@@ -150,9 +150,9 @@ pub struct MutexGuard<'a, T: ?Sized + 'a> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T: ?Sized> !Send for MutexGuard<'a, T> { }
+impl<T: ?Sized> !Send for MutexGuard<'_, T> { }
 #[stable(feature = "mutexguard", since = "1.19.0")]
-unsafe impl<'a, T: ?Sized + Sync> Sync for MutexGuard<'a, T> { }
+unsafe impl<T: ?Sized + Sync> Sync for MutexGuard<'_, T> { }
 
 impl<T> Mutex<T> {
     /// Creates a new mutex in an unlocked state ready for use.
@@ -421,7 +421,7 @@ impl<'mutex, T: ?Sized> MutexGuard<'mutex, T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'mutex, T: ?Sized> Deref for MutexGuard<'mutex, T> {
+impl<T: ?Sized> Deref for MutexGuard<'_, T> {
     type Target = T;
 
     fn deref(&self) -> &T {
@@ -430,14 +430,14 @@ impl<'mutex, T: ?Sized> Deref for MutexGuard<'mutex, T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'mutex, T: ?Sized> DerefMut for MutexGuard<'mutex, T> {
+impl<T: ?Sized> DerefMut for MutexGuard<'_, T> {
     fn deref_mut(&mut self) -> &mut T {
         unsafe { &mut *self.__lock.data.get() }
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T: ?Sized> Drop for MutexGuard<'a, T> {
+impl<T: ?Sized> Drop for MutexGuard<'_, T> {
     #[inline]
     fn drop(&mut self) {
         unsafe {
@@ -448,14 +448,14 @@ impl<'a, T: ?Sized> Drop for MutexGuard<'a, T> {
 }
 
 #[stable(feature = "std_debug", since = "1.16.0")]
-impl<'a, T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'a, T> {
+impl<T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Debug::fmt(&**self, f)
     }
 }
 
 #[stable(feature = "std_guard_impls", since = "1.20.0")]
-impl<'a, T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'a, T> {
+impl<T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         (**self).fmt(f)
     }
diff --git a/src/libstd/sync/once.rs b/src/libstd/sync/once.rs
index 656389789d7..e207d0170d7 100644
--- a/src/libstd/sync/once.rs
+++ b/src/libstd/sync/once.rs
@@ -436,7 +436,7 @@ impl fmt::Debug for Once {
     }
 }
 
-impl<'a> Drop for Finish<'a> {
+impl Drop for Finish<'_> {
     fn drop(&mut self) {
         // Swap out our state with however we finished. We should only ever see
         // an old state which was RUNNING.
diff --git a/src/libstd/sync/rwlock.rs b/src/libstd/sync/rwlock.rs
index 730362e2ac8..7f3cb4f72c7 100644
--- a/src/libstd/sync/rwlock.rs
+++ b/src/libstd/sync/rwlock.rs
@@ -91,10 +91,10 @@ pub struct RwLockReadGuard<'a, T: ?Sized + 'a> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T: ?Sized> !Send for RwLockReadGuard<'a, T> {}
+impl<T: ?Sized> !Send for RwLockReadGuard<'_, T> {}
 
 #[stable(feature = "rwlock_guard_sync", since = "1.23.0")]
-unsafe impl<'a, T: ?Sized + Sync> Sync for RwLockReadGuard<'a, T> {}
+unsafe impl<T: ?Sized + Sync> Sync for RwLockReadGuard<'_, T> {}
 
 /// RAII structure used to release the exclusive write access of a lock when
 /// dropped.
@@ -113,10 +113,10 @@ pub struct RwLockWriteGuard<'a, T: ?Sized + 'a> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T: ?Sized> !Send for RwLockWriteGuard<'a, T> {}
+impl<T: ?Sized> !Send for RwLockWriteGuard<'_, T> {}
 
 #[stable(feature = "rwlock_guard_sync", since = "1.23.0")]
-unsafe impl<'a, T: ?Sized + Sync> Sync for RwLockWriteGuard<'a, T> {}
+unsafe impl<T: ?Sized + Sync> Sync for RwLockWriteGuard<'_, T> {}
 
 impl<T> RwLock<T> {
     /// Creates a new instance of an `RwLock<T>` which is unlocked.
@@ -480,7 +480,7 @@ impl<'rwlock, T: ?Sized> RwLockWriteGuard<'rwlock, T> {
 }
 
 #[stable(feature = "std_debug", since = "1.16.0")]
-impl<'a, T: fmt::Debug> fmt::Debug for RwLockReadGuard<'a, T> {
+impl<T: fmt::Debug> fmt::Debug for RwLockReadGuard<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("RwLockReadGuard")
             .field("lock", &self.__lock)
@@ -489,14 +489,14 @@ impl<'a, T: fmt::Debug> fmt::Debug for RwLockReadGuard<'a, T> {
 }
 
 #[stable(feature = "std_guard_impls", since = "1.20.0")]
-impl<'a, T: ?Sized + fmt::Display> fmt::Display for RwLockReadGuard<'a, T> {
+impl<T: ?Sized + fmt::Display> fmt::Display for RwLockReadGuard<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         (**self).fmt(f)
     }
 }
 
 #[stable(feature = "std_debug", since = "1.16.0")]
-impl<'a, T: fmt::Debug> fmt::Debug for RwLockWriteGuard<'a, T> {
+impl<T: fmt::Debug> fmt::Debug for RwLockWriteGuard<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("RwLockWriteGuard")
             .field("lock", &self.__lock)
@@ -505,14 +505,14 @@ impl<'a, T: fmt::Debug> fmt::Debug for RwLockWriteGuard<'a, T> {
 }
 
 #[stable(feature = "std_guard_impls", since = "1.20.0")]
-impl<'a, T: ?Sized + fmt::Display> fmt::Display for RwLockWriteGuard<'a, T> {
+impl<T: ?Sized + fmt::Display> fmt::Display for RwLockWriteGuard<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         (**self).fmt(f)
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'rwlock, T: ?Sized> Deref for RwLockReadGuard<'rwlock, T> {
+impl<T: ?Sized> Deref for RwLockReadGuard<'_, T> {
     type Target = T;
 
     fn deref(&self) -> &T {
@@ -521,7 +521,7 @@ impl<'rwlock, T: ?Sized> Deref for RwLockReadGuard<'rwlock, T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'rwlock, T: ?Sized> Deref for RwLockWriteGuard<'rwlock, T> {
+impl<T: ?Sized> Deref for RwLockWriteGuard<'_, T> {
     type Target = T;
 
     fn deref(&self) -> &T {
@@ -530,21 +530,21 @@ impl<'rwlock, T: ?Sized> Deref for RwLockWriteGuard<'rwlock, T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'rwlock, T: ?Sized> DerefMut for RwLockWriteGuard<'rwlock, T> {
+impl<T: ?Sized> DerefMut for RwLockWriteGuard<'_, T> {
     fn deref_mut(&mut self) -> &mut T {
         unsafe { &mut *self.__lock.data.get() }
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T: ?Sized> Drop for RwLockReadGuard<'a, T> {
+impl<T: ?Sized> Drop for RwLockReadGuard<'_, T> {
     fn drop(&mut self) {
         unsafe { self.__lock.inner.read_unlock(); }
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T: ?Sized> Drop for RwLockWriteGuard<'a, T> {
+impl<T: ?Sized> Drop for RwLockWriteGuard<'_, T> {
     fn drop(&mut self) {
         self.__lock.poison.done(&self.__poison);
         unsafe { self.__lock.inner.write_unlock(); }