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

2 files changed, 4 insertions, 4 deletions

diff --git a/src/libstd/ffi/c_str.rs b/src/libstd/ffi/c_str.rs
index caf490a0277..0ef72242827 100644
--- a/src/libstd/ffi/c_str.rs
+++ b/src/libstd/ffi/c_str.rs
@@ -659,8 +659,8 @@ impl fmt::Debug for CStr {
 }
 
 #[stable(feature = "cstr_default", since = "1.10.0")]
-impl<'a> Default for &'a CStr {
-    fn default() -> &'a CStr {
+impl Default for &CStr {
+    fn default() -> Self {
         const SLICE: &[c_char] = &[0];
         unsafe { CStr::from_ptr(SLICE.as_ptr()) }
     }
diff --git a/src/libstd/ffi/os_str.rs b/src/libstd/ffi/os_str.rs
index 7dbf15cdc90..81433832ffc 100644
--- a/src/libstd/ffi/os_str.rs
+++ b/src/libstd/ffi/os_str.rs
@@ -778,10 +778,10 @@ impl Default for Box<OsStr> {
 }
 
 #[stable(feature = "osstring_default", since = "1.9.0")]
-impl<'a> Default for &'a OsStr {
+impl Default for &OsStr {
     /// Creates an empty `OsStr`.
     #[inline]
-    fn default() -> &'a OsStr {
+    fn default() -> Self {
         OsStr::new("")
     }
 }