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.

Author: kennytm

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
@@ -503,15 +503,15 @@ 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
     }
 }
 
 #[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())) }
     }
 }

src/liballoc/rc.rs

@@ -1145,15 +1145,15 @@ 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)
     }
 }
 
 #[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());

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()
     }
 }

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())
     }
 }

src/libcore/array.rs

@@ -139,7 +139,7 @@ macro_rules! array_impls {
             }
 
             #[stable(feature = "try_from", since = "1.34.0")]
-            impl<'a, T> TryFrom<&'a [T]> for [T; $N] where T: Copy {
+            impl<T> TryFrom<&[T]> for [T; $N] where T: Copy {
                 type Error = TryFromSliceError;
 
                 fn try_from(slice: &[T]) -> Result<[T; $N], TryFromSliceError> {

src/libcore/cmp.rs

@@ -1030,26 +1030,26 @@ mod impls {
     // & pointers
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<'a, 'b, A: ?Sized, B: ?Sized> PartialEq<&'b B> for &'a A where A: PartialEq<B> {
+    impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &A where A: PartialEq<B> {
         #[inline]
-        fn eq(&self, other: & &'b B) -> bool { PartialEq::eq(*self, *other) }
+        fn eq(&self, other: & &B) -> bool { PartialEq::eq(*self, *other) }
         #[inline]
-        fn ne(&self, other: & &'b B) -> bool { PartialEq::ne(*self, *other) }
+        fn ne(&self, other: & &B) -> bool { PartialEq::ne(*self, *other) }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<'a, 'b, A: ?Sized, B: ?Sized> PartialOrd<&'b B> for &'a A where A: PartialOrd<B> {
+    impl<A: ?Sized, B: ?Sized> PartialOrd<&B> for &A where A: PartialOrd<B> {
         #[inline]
-        fn partial_cmp(&self, other: &&'b B) -> Option<Ordering> {
+        fn partial_cmp(&self, other: &&B) -> Option<Ordering> {
             PartialOrd::partial_cmp(*self, *other)
         }
         #[inline]
-        fn lt(&self, other: & &'b B) -> bool { PartialOrd::lt(*self, *other) }
+        fn lt(&self, other: & &B) -> bool { PartialOrd::lt(*self, *other) }
         #[inline]
-        fn le(&self, other: & &'b B) -> bool { PartialOrd::le(*self, *other) }
+        fn le(&self, other: & &B) -> bool { PartialOrd::le(*self, *other) }
         #[inline]
-        fn ge(&self, other: & &'b B) -> bool { PartialOrd::ge(*self, *other) }
+        fn ge(&self, other: & &B) -> bool { PartialOrd::ge(*self, *other) }
         #[inline]
-        fn gt(&self, other: & &'b B) -> bool { PartialOrd::gt(*self, *other) }
+        fn gt(&self, other: & &B) -> bool { PartialOrd::gt(*self, *other) }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
     impl<A: ?Sized> Ord for &A where A: Ord {
@@ -1062,26 +1062,26 @@ mod impls {
     // &mut pointers
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    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) }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<'a, 'b, A: ?Sized, B: ?Sized> PartialOrd<&'b mut B> for &'a mut A where A: PartialOrd<B> {
+    impl<A: ?Sized, B: ?Sized> PartialOrd<&mut B> for &mut A where A: PartialOrd<B> {
         #[inline]
-        fn partial_cmp(&self, other: &&'b mut B) -> Option<Ordering> {
+        fn partial_cmp(&self, other: &&mut B) -> Option<Ordering> {
             PartialOrd::partial_cmp(*self, *other)
         }
         #[inline]
-        fn lt(&self, other: &&'b mut B) -> bool { PartialOrd::lt(*self, *other) }
+        fn lt(&self, other: &&mut B) -> bool { PartialOrd::lt(*self, *other) }
         #[inline]
-        fn le(&self, other: &&'b mut B) -> bool { PartialOrd::le(*self, *other) }
+        fn le(&self, other: &&mut B) -> bool { PartialOrd::le(*self, *other) }
         #[inline]
-        fn ge(&self, other: &&'b mut B) -> bool { PartialOrd::ge(*self, *other) }
+        fn ge(&self, other: &&mut B) -> bool { PartialOrd::ge(*self, *other) }
         #[inline]
-        fn gt(&self, other: &&'b mut B) -> bool { PartialOrd::gt(*self, *other) }
+        fn gt(&self, other: &&mut B) -> bool { PartialOrd::gt(*self, *other) }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
     impl<A: ?Sized> Ord for &mut A where A: Ord {
@@ -1092,18 +1092,18 @@ mod impls {
     impl<A: ?Sized> Eq for &mut A where A: Eq {}
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<'a, 'b, A: ?Sized, B: ?Sized> PartialEq<&'b mut B> for &'a A where A: PartialEq<B> {
+    impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &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) }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<'a, 'b, A: ?Sized, B: ?Sized> PartialEq<&'b B> for &'a mut A where A: PartialEq<B> {
+    impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &mut A where A: PartialEq<B> {
         #[inline]
-        fn eq(&self, other: &&'b B) -> bool { PartialEq::eq(*self, *other) }
+        fn eq(&self, other: &&B) -> bool { PartialEq::eq(*self, *other) }
         #[inline]
-        fn ne(&self, other: &&'b B) -> bool { PartialEq::ne(*self, *other) }
+        fn ne(&self, other: &&B) -> bool { PartialEq::ne(*self, *other) }
     }
 }

src/libcore/internal_macros.rs

@@ -37,21 +37,21 @@ macro_rules! forward_ref_binop {
         }
 
         #[$attr]
-        impl<'a> $imp<&'a $u> for $t {
+        impl $imp<&$u> for $t {
             type Output = <$t as $imp<$u>>::Output;
 
             #[inline]
-            fn $method(self, other: &'a $u) -> <$t as $imp<$u>>::Output {
+            fn $method(self, other: &$u) -> <$t as $imp<$u>>::Output {
                 $imp::$method(self, *other)
             }
         }
 
         #[$attr]
-        impl<'a, 'b> $imp<&'a $u> for &'b $t {
+        impl $imp<&$u> for &$t {
             type Output = <$t as $imp<$u>>::Output;
 
             #[inline]
-            fn $method(self, other: &'a $u) -> <$t as $imp<$u>>::Output {
+            fn $method(self, other: &$u) -> <$t as $imp<$u>>::Output {
                 $imp::$method(*self, *other)
             }
         }
@@ -67,9 +67,9 @@ macro_rules! forward_ref_op_assign {
     };
     (impl $imp:ident, $method:ident for $t:ty, $u:ty, #[$attr:meta]) => {
         #[$attr]
-        impl<'a> $imp<&'a $u> for $t {
+        impl $imp<&$u> for $t {
             #[inline]
-            fn $method(&mut self, other: &'a $u) {
+            fn $method(&mut self, other: &$u) {
                 $imp::$method(self, *other);
             }
         }

src/libcore/ptr.rs

@@ -2837,15 +2837,15 @@ impl<T: ?Sized> fmt::Pointer for Unique<T> {
 }
 
 #[unstable(feature = "ptr_internals", issue = "0")]
-impl<'a, T: ?Sized> From<&'a mut T> for Unique<T> {
-    fn from(reference: &'a mut T) -> Self {
+impl<T: ?Sized> From<&mut T> for Unique<T> {
+    fn from(reference: &mut T) -> Self {
         unsafe { Unique { pointer: reference as *mut T, _marker: PhantomData } }
     }
 }
 
 #[unstable(feature = "ptr_internals", issue = "0")]
-impl<'a, T: ?Sized> From<&'a T> for Unique<T> {
-    fn from(reference: &'a T) -> Self {
+impl<T: ?Sized> From<&T> for Unique<T> {
+    fn from(reference: &T) -> Self {
         unsafe { Unique { pointer: reference as *const T, _marker: PhantomData } }
     }
 }
@@ -3049,17 +3049,17 @@ impl<T: ?Sized> From<Unique<T>> for NonNull<T> {
 }
 
 #[stable(feature = "nonnull", since = "1.25.0")]
-impl<'a, T: ?Sized> From<&'a mut T> for NonNull<T> {
+impl<T: ?Sized> From<&mut T> for NonNull<T> {
     #[inline]
-    fn from(reference: &'a mut T) -> Self {
+    fn from(reference: &mut T) -> Self {
         unsafe { NonNull { pointer: reference as *mut T } }
     }
 }
 
 #[stable(feature = "nonnull", since = "1.25.0")]
-impl<'a, T: ?Sized> From<&'a T> for NonNull<T> {
+impl<T: ?Sized> From<&T> for NonNull<T> {
     #[inline]
-    fn from(reference: &'a T) -> Self {
+    fn from(reference: &T) -> Self {
         unsafe { NonNull { pointer: reference as *const T } }
     }
 }

src/libstd/collections/hash/set.rs

@@ -850,7 +850,7 @@ impl<T, S> Default for HashSet<T, S>
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, 'b, T, S> BitOr<&'b HashSet<T, S>> for &'a HashSet<T, S>
+impl<T, S> BitOr<&HashSet<T, S>> for &HashSet<T, S>
     where T: Eq + Hash + Clone,
           S: BuildHasher + Default
 {
@@ -882,7 +882,7 @@ impl<'a, 'b, T, S> BitOr<&'b HashSet<T, S>> for &'a HashSet<T, S>
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, 'b, T, S> BitAnd<&'b HashSet<T, S>> for &'a HashSet<T, S>
+impl<T, S> BitAnd<&HashSet<T, S>> for &HashSet<T, S>
     where T: Eq + Hash + Clone,
           S: BuildHasher + Default
 {
@@ -914,7 +914,7 @@ impl<'a, 'b, T, S> BitAnd<&'b HashSet<T, S>> for &'a HashSet<T, S>
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, 'b, T, S> BitXor<&'b HashSet<T, S>> for &'a HashSet<T, S>
+impl<T, S> BitXor<&HashSet<T, S>> for &HashSet<T, S>
     where T: Eq + Hash + Clone,
           S: BuildHasher + Default
 {
@@ -946,7 +946,7 @@ impl<'a, 'b, T, S> BitXor<&'b HashSet<T, S>> for &'a HashSet<T, S>
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, 'b, T, S> Sub<&'b HashSet<T, S>> for &'a HashSet<T, S>
+impl<T, S> Sub<&HashSet<T, S>> for &HashSet<T, S>
     where T: Eq + Hash + Clone,
           S: BuildHasher + Default
 {

src/libstd/error.rs

@@ -337,7 +337,7 @@ impl From<String> for Box<dyn Error> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, 'b> From<&'b str> for Box<dyn Error + Send + Sync + 'a> {
+impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> {
     /// Converts a [`str`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
     ///
     /// # Examples
@@ -351,13 +351,13 @@ impl<'a, 'b> From<&'b str> for Box<dyn Error + Send + Sync + 'a> {
     /// assert!(
     ///     mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
     /// ```
-    fn from(err: &'b str) -> Box<dyn Error + Send + Sync + 'a> {
+    fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a> {
         From::from(String::from(err))
     }
 }
 
 #[stable(feature = "string_box_error", since = "1.6.0")]
-impl<'a> From<&'a str> for Box<dyn Error> {
+impl From<&str> for Box<dyn Error> {
     /// Converts a [`str`] into a box of dyn [`Error`].
     ///
     /// # Examples
@@ -370,7 +370,7 @@ impl<'a> From<&'a str> for Box<dyn Error> {
     /// let a_boxed_error = Box::<Error>::from(a_str_error);
     /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
     /// ```
-    fn from(err: &'a str) -> Box<dyn Error> {
+    fn from(err: &str) -> Box<dyn Error> {
         From::from(String::from(err))
     }
 }