[PATCH v2 09/33] rust: remove `RUSTC_HAS_SLICE_AS_FLATTENED` and simplify code

[Miguel Ojeda <ojeda@kernel.org>]

With the Rust version bump in place, the `RUSTC_HAS_SLICE_AS_FLATTENED`
Kconfig (automatic) option is always true.

Thus remove the option and simplify the code.

In particular, this includes removing the `slice` module which contained
the temporary slice helpers, i.e. the `AsFlattened` extension trait and
its `impl`s.

Reviewed-by: Tamir Duberstein <tamird@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 init/Kconfig           |  3 ---
 rust/kernel/lib.rs     |  1 -
 rust/kernel/prelude.rs |  3 ---
 rust/kernel/slice.rs   | 49 ------------------------------------------
 4 files changed, 56 deletions(-)
 delete mode 100644 rust/kernel/slice.rs

diff --git a/init/Kconfig b/init/Kconfig
index b8a1ab0d49d4..c38f49228157 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -178,9 +178,6 @@ config LD_CAN_USE_KEEP_IN_OVERLAY
 	# https://github.com/llvm/llvm-project/pull/130661
 	def_bool LD_IS_BFD || LLD_VERSION >= 210000
 
-config RUSTC_HAS_SLICE_AS_FLATTENED
-	def_bool RUSTC_VERSION >= 108000
-
 config RUSTC_HAS_COERCE_POINTEE
 	def_bool RUSTC_VERSION >= 108400
 
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 138d846f798d..621cae75030c 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -140,7 +140,6 @@
 pub mod security;
 pub mod seq_file;
 pub mod sizes;
-pub mod slice;
 #[cfg(CONFIG_SOC_BUS)]
 pub mod soc;
 #[doc(hidden)]
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index e9d37f307f2a..44edf72a4a24 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -107,6 +107,3 @@
 // `super::std_vendor` is hidden, which makes the macro inline for some reason.
 #[doc(no_inline)]
 pub use super::dbg;
-
-#[cfg(not(CONFIG_RUSTC_HAS_SLICE_AS_FLATTENED))]
-pub use super::slice::AsFlattened;
diff --git a/rust/kernel/slice.rs b/rust/kernel/slice.rs
deleted file mode 100644
index ca2cde135061..000000000000
--- a/rust/kernel/slice.rs
+++ /dev/null
@@ -1,49 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-
-//! Additional (and temporary) slice helpers.
-
-/// Extension trait providing a portable version of [`as_flattened`] and
-/// [`as_flattened_mut`].
-///
-/// In Rust 1.80, the previously unstable `slice::flatten` family of methods
-/// have been stabilized and renamed from `flatten` to `as_flattened`.
-///
-/// This creates an issue for as long as the MSRV is < 1.80, as the same functionality is provided
-/// by different methods depending on the compiler version.
-///
-/// This extension trait solves this by abstracting `as_flatten` and calling the correct method
-/// depending on the Rust version.
-///
-/// This trait can be removed once the MSRV passes 1.80.
-///
-/// [`as_flattened`]: https://doc.rust-lang.org/std/primitive.slice.html#method.as_flattened
-/// [`as_flattened_mut`]: https://doc.rust-lang.org/std/primitive.slice.html#method.as_flattened_mut
-#[cfg(not(CONFIG_RUSTC_HAS_SLICE_AS_FLATTENED))]
-pub trait AsFlattened<T> {
-    /// Takes a `&[[T; N]]` and flattens it to a `&[T]`.
-    ///
-    /// This is an portable layer on top of [`as_flattened`]; see its documentation for details.
-    ///
-    /// [`as_flattened`]: https://doc.rust-lang.org/std/primitive.slice.html#method.as_flattened
-    fn as_flattened(&self) -> &[T];
-
-    /// Takes a `&mut [[T; N]]` and flattens it to a `&mut [T]`.
-    ///
-    /// This is an portable layer on top of [`as_flattened_mut`]; see its documentation for details.
-    ///
-    /// [`as_flattened_mut`]: https://doc.rust-lang.org/std/primitive.slice.html#method.as_flattened_mut
-    fn as_flattened_mut(&mut self) -> &mut [T];
-}
-
-#[cfg(not(CONFIG_RUSTC_HAS_SLICE_AS_FLATTENED))]
-impl<T, const N: usize> AsFlattened<T> for [[T; N]] {
-    #[allow(clippy::incompatible_msrv)]
-    fn as_flattened(&self) -> &[T] {
-        self.flatten()
-    }
-
-    #[allow(clippy::incompatible_msrv)]
-    fn as_flattened_mut(&mut self) -> &mut [T] {
-        self.flatten_mut()
-    }
-}
-- 
2.53.0