rust: pin-init: add `std` and `alloc` support from the user-space version

To synchronize the kernel's version of pin-init with the user-space
version, introduce support for `std` and `alloc`. While the kernel uses
neither, the user-space version has to support both. Thus include the
required `#[cfg]`s and additional code.

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Fiona Behrens <me@kloenk.dev>
Tested-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250308110339.2997091-17-benno.lossin@proton.me
[ Undo the temporary `--extern force:alloc` since now we have contents
  for `alloc` here. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 35 insertions, 6 deletions

diff --git a/rust/pin-init/src/lib.rs b/rust/pin-init/src/lib.rs
index 41bfb35c7a2c..58b77a158c34 100644
--- a/rust/pin-init/src/lib.rs
+++ b/rust/pin-init/src/lib.rs
@@ -204,8 +204,16 @@
 //! [structurally pinned fields]:
 //!     https://doc.rust-lang.org/std/pin/index.html#pinning-is-structural-for-field
 //! [stack]: crate::stack_pin_init
-//! [`Arc<T>`]: https://rust.docs.kernel.org/kernel/sync/struct.Arc.html
-//! [`Box<T>`]: https://rust.docs.kernel.org/kernel/alloc/kbox/struct.Box.html
+#![cfg_attr(
+    kernel,
+    doc = "[`Arc<T>`]: https://rust.docs.kernel.org/kernel/sync/struct.Arc.html"
+)]
+#![cfg_attr(
+    kernel,
+    doc = "[`Box<T>`]: https://rust.docs.kernel.org/kernel/alloc/kbox/struct.Box.html"
+)]
+#![cfg_attr(not(kernel), doc = "[`Arc<T>`]: alloc::alloc::sync::Arc")]
+#![cfg_attr(not(kernel), doc = "[`Box<T>`]: alloc::alloc::boxed::Box")]
 //! [`impl PinInit<Foo>`]: PinInit
 //! [`impl PinInit<T, E>`]: PinInit
 //! [`impl Init<T, E>`]: Init
@@ -239,6 +247,11 @@ pub mod __internal;
 #[doc(hidden)]
 pub mod macros;
 
+#[cfg(any(feature = "std", feature = "alloc"))]
+mod alloc;
+#[cfg(any(feature = "std", feature = "alloc"))]
+pub use alloc::InPlaceInit;
+
 /// Used to specify the pinning information of the fields of a struct.
 ///
 /// This is somewhat similar in purpose as
@@ -914,8 +927,16 @@ macro_rules! assert_pinned {
 ///     - `slot` is not partially initialized.
 /// - while constructing the `T` at `slot` it upholds the pinning invariants of `T`.
 ///
-/// [`Arc<T>`]: https://rust.docs.kernel.org/kernel/sync/struct.Arc.html
-/// [`Box<T>`]: https://rust.docs.kernel.org/kernel/alloc/kbox/struct.Box.html
+#[cfg_attr(
+    kernel,
+    doc = "[`Arc<T>`]: https://rust.docs.kernel.org/kernel/sync/struct.Arc.html"
+)]
+#[cfg_attr(
+    kernel,
+    doc = "[`Box<T>`]: https://rust.docs.kernel.org/kernel/alloc/kbox/struct.Box.html"
+)]
+#[cfg_attr(not(kernel), doc = "[`Arc<T>`]: alloc::alloc::sync::Arc")]
+#[cfg_attr(not(kernel), doc = "[`Box<T>`]: alloc::alloc::boxed::Box")]
 #[must_use = "An initializer must be used in order to create its value."]
 pub unsafe trait PinInit<T: ?Sized, E = Infallible>: Sized {
     /// Initializes `slot`.
@@ -1005,8 +1026,16 @@ where
 /// Contrary to its supertype [`PinInit<T, E>`] the caller is allowed to
 /// move the pointee after initialization.
 ///
-/// [`Arc<T>`]: https://rust.docs.kernel.org/kernel/sync/struct.Arc.html
-/// [`Box<T>`]: https://rust.docs.kernel.org/kernel/alloc/kbox/struct.Box.html
+#[cfg_attr(
+    kernel,
+    doc = "[`Arc<T>`]: https://rust.docs.kernel.org/kernel/sync/struct.Arc.html"
+)]
+#[cfg_attr(
+    kernel,
+    doc = "[`Box<T>`]: https://rust.docs.kernel.org/kernel/alloc/kbox/struct.Box.html"
+)]
+#[cfg_attr(not(kernel), doc = "[`Arc<T>`]: alloc::alloc::sync::Arc")]
+#[cfg_attr(not(kernel), doc = "[`Box<T>`]: alloc::alloc::boxed::Box")]
 #[must_use = "An initializer must be used in order to create its value."]
 pub unsafe trait Init<T: ?Sized, E = Infallible>: PinInit<T, E> {
     /// Initializes `slot`.