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

5 files changed, 19 insertions, 19 deletions

diff --git a/src/libstd/io/buffered.rs b/src/libstd/io/buffered.rs
index 0615cd59db4..0c1d155a916 100644
--- a/src/libstd/io/buffered.rs
+++ b/src/libstd/io/buffered.rs
@@ -1174,7 +1174,7 @@ mod tests {
         // Issue #32085
         struct FailFlushWriter<'a>(&'a mut Vec<u8>);
 
-        impl<'a> Write for FailFlushWriter<'a> {
+        impl Write for FailFlushWriter<'_> {
             fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
                 self.0.extend_from_slice(buf);
                 Ok(buf.len())
diff --git a/src/libstd/io/cursor.rs b/src/libstd/io/cursor.rs
index b205f788838..758d8568672 100644
--- a/src/libstd/io/cursor.rs
+++ b/src/libstd/io/cursor.rs
@@ -279,7 +279,7 @@ fn vec_write(pos_mut: &mut u64, vec: &mut Vec<u8>, buf: &[u8]) -> io::Result<usi
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> Write for Cursor<&'a mut [u8]> {
+impl Write for Cursor<&mut [u8]> {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         slice_write(&mut self.pos, self.inner, buf)
@@ -288,7 +288,7 @@ impl<'a> Write for Cursor<&'a mut [u8]> {
 }
 
 #[stable(feature = "cursor_mut_vec", since = "1.25.0")]
-impl<'a> Write for Cursor<&'a mut Vec<u8>> {
+impl Write for Cursor<&mut Vec<u8>> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         vec_write(&mut self.pos, self.inner, buf)
     }
diff --git a/src/libstd/io/impls.rs b/src/libstd/io/impls.rs
index ec75a87aec3..2577b284714 100644
--- a/src/libstd/io/impls.rs
+++ b/src/libstd/io/impls.rs
@@ -7,7 +7,7 @@ use mem;
 // Forwarding implementations
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, R: Read + ?Sized> Read for &'a mut R {
+impl<R: Read + ?Sized> Read for &mut R {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         (**self).read(buf)
@@ -34,7 +34,7 @@ impl<'a, R: Read + ?Sized> Read for &'a mut R {
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, W: Write + ?Sized> Write for &'a mut W {
+impl<W: Write + ?Sized> Write for &mut W {
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> { (**self).write(buf) }
 
@@ -52,12 +52,12 @@ impl<'a, W: Write + ?Sized> Write for &'a mut W {
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, S: Seek + ?Sized> Seek for &'a mut S {
+impl<S: Seek + ?Sized> Seek for &mut S {
     #[inline]
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> { (**self).seek(pos) }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, B: BufRead + ?Sized> BufRead for &'a mut B {
+impl<B: BufRead + ?Sized> BufRead for &mut B {
     #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> { (**self).fill_buf() }
 
@@ -152,7 +152,7 @@ impl<B: BufRead + ?Sized> BufRead for Box<B> {
 /// Note that reading updates the slice to point to the yet unread part.
 /// The slice will be empty when EOF is reached.
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> Read for &'a [u8] {
+impl Read for &[u8] {
     #[inline]
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         let amt = cmp::min(buf.len(), self.len());
@@ -207,7 +207,7 @@ impl<'a> Read for &'a [u8] {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> BufRead for &'a [u8] {
+impl BufRead for &[u8] {
     #[inline]
     fn fill_buf(&mut self) -> io::Result<&[u8]> { Ok(*self) }
 
@@ -221,7 +221,7 @@ impl<'a> BufRead for &'a [u8] {
 /// Note that writing updates the slice to point to the yet unwritten part.
 /// The slice will be empty when it has been completely overwritten.
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> Write for &'a mut [u8] {
+impl Write for &mut [u8] {
     #[inline]
     fn write(&mut self, data: &[u8]) -> io::Result<usize> {
         let amt = cmp::min(data.len(), self.len());
diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index c0570ae60a1..b634ea43e34 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -299,7 +299,7 @@ const DEFAULT_BUF_SIZE: usize = ::sys_common::io::DEFAULT_BUF_SIZE;
 
 struct Guard<'a> { buf: &'a mut Vec<u8>, len: usize }
 
-impl<'a> Drop for Guard<'a> {
+impl Drop for Guard<'_> {
     fn drop(&mut self) {
         unsafe { self.buf.set_len(self.len); }
     }
@@ -1114,7 +1114,7 @@ pub trait Write {
             error: Result<()>,
         }
 
-        impl<'a, T: Write + ?Sized> fmt::Write for Adaptor<'a, T> {
+        impl<T: Write + ?Sized> fmt::Write for Adaptor<'_, T> {
             fn write_str(&mut self, s: &str) -> fmt::Result {
                 match self.inner.write_all(s.as_bytes()) {
                     Ok(()) => Ok(()),
diff --git a/src/libstd/io/stdio.rs b/src/libstd/io/stdio.rs
index 4068c0f9c7d..0324568e6fb 100644
--- a/src/libstd/io/stdio.rs
+++ b/src/libstd/io/stdio.rs
@@ -312,7 +312,7 @@ impl Read for Stdin {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> Read for StdinLock<'a> {
+impl Read for StdinLock<'_> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         self.inner.read(buf)
     }
@@ -323,13 +323,13 @@ impl<'a> Read for StdinLock<'a> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> BufRead for StdinLock<'a> {
+impl BufRead for StdinLock<'_> {
     fn fill_buf(&mut self) -> io::Result<&[u8]> { self.inner.fill_buf() }
     fn consume(&mut self, n: usize) { self.inner.consume(n) }
 }
 
 #[stable(feature = "std_debug", since = "1.16.0")]
-impl<'a> fmt::Debug for StdinLock<'a> {
+impl fmt::Debug for StdinLock<'_> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("StdinLock { .. }")
     }
@@ -485,7 +485,7 @@ impl Write for Stdout {
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> Write for StdoutLock<'a> {
+impl Write for StdoutLock<'_> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         self.inner.borrow_mut().write(buf)
     }
@@ -495,7 +495,7 @@ impl<'a> Write for StdoutLock<'a> {
 }
 
 #[stable(feature = "std_debug", since = "1.16.0")]
-impl<'a> fmt::Debug for StdoutLock<'a> {
+impl fmt::Debug for StdoutLock<'_> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("StdoutLock { .. }")
     }
@@ -638,7 +638,7 @@ impl Write for Stderr {
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> Write for StderrLock<'a> {
+impl Write for StderrLock<'_> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         self.inner.borrow_mut().write(buf)
     }
@@ -648,7 +648,7 @@ impl<'a> Write for StderrLock<'a> {
 }
 
 #[stable(feature = "std_debug", since = "1.16.0")]
-impl<'a> fmt::Debug for StderrLock<'a> {
+impl fmt::Debug for StderrLock<'_> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("StderrLock { .. }")
     }