In nightly Clippy (i.e. Rust 1.83.0), the `needless_lifetimes` lint has
been extended [1] to suggest eliding `impl` lifetimes, e.g.

    error: the following explicit lifetimes could be elided: 'a
    --> rust/kernel/list.rs:647:6
        |
    647 | impl<'a, T: ?Sized + ListItem<ID>, const ID: u64> FusedIterator for Iter<'a, T, ID> {}
        |      ^^                                                                  ^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes
        = note: `-D clippy::needless-lifetimes` implied by `-D warnings`
        = help: to override `-D warnings` add `#[allow(clippy::needless_lifetimes)]`
    help: elide the lifetimes
        |
    647 - impl<'a, T: ?Sized + ListItem<ID>, const ID: u64> FusedIterator for Iter<'a, T, ID> {}
    647 + impl<T: ?Sized + ListItem<ID>, const ID: u64> FusedIterator for Iter<'_, T, ID> {}

Thus clean them.

Link: https://github.com/rust-lang/rust-clippy/pull/13286 [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
Do we want this in general, or just in some cases? There is an issue about this
where we may want to leave some feedback:

    https://github.com/rust-lang/rust-clippy/issues/13514

 rust/kernel/list.rs   |  2 +-
 rust/kernel/rbtree.rs | 14 +++++++-------
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/rust/kernel/list.rs b/rust/kernel/list.rs
index 5b4aec29eb67..cbccd932fa43 100644
--- a/rust/kernel/list.rs
+++ b/rust/kernel/list.rs
@@ -644,7 +644,7 @@ pub fn remove(self) -> ListArc<T, ID> {
     }
 }

-impl<'a, T: ?Sized + ListItem<ID>, const ID: u64> FusedIterator for Iter<'a, T, ID> {}
+impl<T: ?Sized + ListItem<ID>, const ID: u64> FusedIterator for Iter<'_, T, ID> {}

 impl<'a, T: ?Sized + ListItem<ID>, const ID: u64> IntoIterator for &'a List<T, ID> {
     type IntoIter = Iter<'a, T, ID>;
diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
index 25eb36fd1cdc..232a5eefa6f9 100644
--- a/rust/kernel/rbtree.rs
+++ b/rust/kernel/rbtree.rs
@@ -729,13 +729,13 @@ pub struct Cursor<'a, K, V> {
 // SAFETY: The [`Cursor`] has exclusive access to both `K` and `V`, so it is sufficient to require them to be `Send`.
 // The cursor only gives out immutable references to the keys, but since it has excusive access to those same
 // keys, `Send` is sufficient. `Sync` would be okay, but it is more restrictive to the user.
-unsafe impl<'a, K: Send, V: Send> Send for Cursor<'a, K, V> {}
+unsafe impl<K: Send, V: Send> Send for Cursor<'_, K, V> {}

 // SAFETY: The [`Cursor`] gives out immutable references to K and mutable references to V,
 // so it has the same thread safety requirements as mutable references.
-unsafe impl<'a, K: Sync, V: Sync> Sync for Cursor<'a, K, V> {}
+unsafe impl<K: Sync, V: Sync> Sync for Cursor<'_, K, V> {}

-impl<'a, K, V> Cursor<'a, K, V> {
+impl<K, V> Cursor<'_, K, V> {
     /// The current node
     pub fn current(&self) -> (&K, &V) {
         // SAFETY:
@@ -948,11 +948,11 @@ pub struct Iter<'a, K, V> {

 // SAFETY: The [`Iter`] gives out immutable references to K and V, so it has the same
 // thread safety requirements as immutable references.
-unsafe impl<'a, K: Sync, V: Sync> Send for Iter<'a, K, V> {}
+unsafe impl<K: Sync, V: Sync> Send for Iter<'_, K, V> {}

 // SAFETY: The [`Iter`] gives out immutable references to K and V, so it has the same
 // thread safety requirements as immutable references.
-unsafe impl<'a, K: Sync, V: Sync> Sync for Iter<'a, K, V> {}
+unsafe impl<K: Sync, V: Sync> Sync for Iter<'_, K, V> {}

 impl<'a, K, V> Iterator for Iter<'a, K, V> {
     type Item = (&'a K, &'a V);
@@ -983,11 +983,11 @@ pub struct IterMut<'a, K, V> {
 // SAFETY: The [`IterMut`] has exclusive access to both `K` and `V`, so it is sufficient to require them to be `Send`.
 // The iterator only gives out immutable references to the keys, but since the iterator has excusive access to those same
 // keys, `Send` is sufficient. `Sync` would be okay, but it is more restrictive to the user.
-unsafe impl<'a, K: Send, V: Send> Send for IterMut<'a, K, V> {}
+unsafe impl<K: Send, V: Send> Send for IterMut<'_, K, V> {}

 // SAFETY: The [`IterMut`] gives out immutable references to K and mutable references to V, so it has the same
 // thread safety requirements as mutable references.
-unsafe impl<'a, K: Sync, V: Sync> Sync for IterMut<'a, K, V> {}
+unsafe impl<K: Sync, V: Sync> Sync for IterMut<'_, K, V> {}

 impl<'a, K, V> Iterator for IterMut<'a, K, V> {
     type Item = (&'a K, &'a mut V);

base-commit: 8cf0b93919e13d1e8d4466eb4080a4c4d9d66d7b
--
2.47.0

On Sun, Oct 13, 2024 at 1:13 AM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> In nightly Clippy (i.e. Rust 1.83.0), the `needless_lifetimes` lint has
> been extended [1] to suggest eliding `impl` lifetimes, e.g.
>
>     error: the following explicit lifetimes could be elided: 'a
>     --> rust/kernel/list.rs:647:6
>         |
>     647 | impl<'a, T: ?Sized + ListItem<ID>, const ID: u64> FusedIterator for Iter<'a, T, ID> {}
>         |      ^^                                                                  ^^
>         |
>         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes
>         = note: `-D clippy::needless-lifetimes` implied by `-D warnings`
>         = help: to override `-D warnings` add `#[allow(clippy::needless_lifetimes)]`
>     help: elide the lifetimes
>         |
>     647 - impl<'a, T: ?Sized + ListItem<ID>, const ID: u64> FusedIterator for Iter<'a, T, ID> {}
>     647 + impl<T: ?Sized + ListItem<ID>, const ID: u64> FusedIterator for Iter<'_, T, ID> {}
>
> Thus clean them.
>
> Link: https://github.com/rust-lang/rust-clippy/pull/13286 [1]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
> Do we want this in general, or just in some cases? There is an issue about this
> where we may want to leave some feedback:
>
>     https://github.com/rust-lang/rust-clippy/issues/13514

If this lint lands for real, then this change LGTM:

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

However, I don't think the lint is useful. I would rather that we are
able to allow this lint.

Alice