Rollup merge of #59056 - scottmcm:even-fewer-lifetimes, r=sfackler

Use lifetime contravariance to elide more lifetimes in core+alloc+std

Sample:
```diff
-    impl<'a, 'b, A: ?Sized, B: ?Sized> PartialEq<&'b mut B> for &'a mut A where A: PartialEq<B> {
+    impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &mut A where A: PartialEq<B> {
         #[inline]
-        fn eq(&self, other: &&'b mut B) -> bool { PartialEq::eq(*self, *other) }
+        fn eq(&self, other: &&mut B) -> bool { PartialEq::eq(*self, *other) }
         #[inline]
-        fn ne(&self, other: &&'b mut B) -> bool { PartialEq::ne(*self, *other) }
+        fn ne(&self, other: &&mut B) -> bool { PartialEq::ne(*self, *other) }
     }
```

[I didn't know this worked](https://internals.rust-lang.org/t/why-can-you-use-different-unconstrained-lifetimes-to-implement-traits/9544/2?u=scottmcm) until recently, but since defining methods contravariantly in their lifetimes this way has worked back to Rust 1.0, we might as well take advantage of combining it with IHLE.

4 files changed, 16 insertions, 16 deletions

diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index 74325a69e15..9bce142b483 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -489,7 +489,7 @@ impl<T: ?Sized> From<Box<T>> for Pin<Box<T>> {
 }
 
 #[stable(feature = "box_from_slice", since = "1.17.0")]
-impl<'a, T: Copy> From<&'a [T]> for Box<[T]> {
+impl<T: Copy> From<&[T]> for Box<[T]> {
     /// Converts a `&[T]` into a `Box<[T]>`
     ///
     /// This conversion allocates on the heap
@@ -503,7 +503,7 @@ impl<'a, T: Copy> From<&'a [T]> for Box<[T]> {
     ///
     /// println!("{:?}", boxed_slice);
     /// ```
-    fn from(slice: &'a [T]) -> Box<[T]> {
+    fn from(slice: &[T]) -> Box<[T]> {
         let mut boxed = unsafe { RawVec::with_capacity(slice.len()).into_box() };
         boxed.copy_from_slice(slice);
         boxed
@@ -511,7 +511,7 @@ impl<'a, T: Copy> From<&'a [T]> for Box<[T]> {
 }
 
 #[stable(feature = "box_from_slice", since = "1.17.0")]
-impl<'a> From<&'a str> for Box<str> {
+impl From<&str> for Box<str> {
     /// Converts a `&str` into a `Box<str>`
     ///
     /// This conversion allocates on the heap
@@ -523,7 +523,7 @@ impl<'a> From<&'a str> for Box<str> {
     /// println!("{}", boxed);
     /// ```
     #[inline]
-    fn from(s: &'a str) -> Box<str> {
+    fn from(s: &str) -> Box<str> {
         unsafe { from_boxed_utf8_unchecked(Box::from(s.as_bytes())) }
     }
 }
diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index 12f75d84211..68eecd97ea1 100644
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -1145,7 +1145,7 @@ impl<T> From<T> for Rc<T> {
 }
 
 #[stable(feature = "shared_from_slice", since = "1.21.0")]
-impl<'a, T: Clone> From<&'a [T]> for Rc<[T]> {
+impl<T: Clone> From<&[T]> for Rc<[T]> {
     #[inline]
     fn from(v: &[T]) -> Rc<[T]> {
         <Self as RcFromSlice<T>>::from_slice(v)
@@ -1153,7 +1153,7 @@ impl<'a, T: Clone> From<&'a [T]> for Rc<[T]> {
 }
 
 #[stable(feature = "shared_from_slice", since = "1.21.0")]
-impl<'a> From<&'a str> for Rc<str> {
+impl From<&str> for Rc<str> {
     #[inline]
     fn from(v: &str) -> Rc<str> {
         let rc = Rc::<[u8]>::from(v.as_bytes());
diff --git a/src/liballoc/string.rs b/src/liballoc/string.rs
index b714df5d36b..a3e2098695f 100644
--- a/src/liballoc/string.rs
+++ b/src/liballoc/string.rs
@@ -2172,9 +2172,9 @@ impl AsRef<[u8]> for String {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> From<&'a str> for String {
+impl From<&str> for String {
     #[inline]
-    fn from(s: &'a str) -> String {
+    fn from(s: &str) -> String {
         s.to_owned()
     }
 }
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index adcd3d84f48..cd62c3e0524 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -2182,25 +2182,25 @@ impl<T> AsMut<[T]> for Vec<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, T: Clone> From<&'a [T]> for Vec<T> {
+impl<T: Clone> From<&[T]> for Vec<T> {
     #[cfg(not(test))]
-    fn from(s: &'a [T]) -> Vec<T> {
+    fn from(s: &[T]) -> Vec<T> {
         s.to_vec()
     }
     #[cfg(test)]
-    fn from(s: &'a [T]) -> Vec<T> {
+    fn from(s: &[T]) -> Vec<T> {
         crate::slice::to_vec(s)
     }
 }
 
 #[stable(feature = "vec_from_mut", since = "1.19.0")]
-impl<'a, T: Clone> From<&'a mut [T]> for Vec<T> {
+impl<T: Clone> From<&mut [T]> for Vec<T> {
     #[cfg(not(test))]
-    fn from(s: &'a mut [T]) -> Vec<T> {
+    fn from(s: &mut [T]) -> Vec<T> {
         s.to_vec()
     }
     #[cfg(test)]
-    fn from(s: &'a mut [T]) -> Vec<T> {
+    fn from(s: &mut [T]) -> Vec<T> {
         crate::slice::to_vec(s)
     }
 }
@@ -2231,8 +2231,8 @@ impl<T> From<Vec<T>> for Box<[T]> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> From<&'a str> for Vec<u8> {
-    fn from(s: &'a str) -> Vec<u8> {
+impl From<&str> for Vec<u8> {
+    fn from(s: &str) -> Vec<u8> {
         From::from(s.as_bytes())
     }
 }