rust: init: update macro expansion example in docs

Also improve the explaining comments.

Signed-off-by: Benno Lossin <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Reviewed-by: Martin Rodriguez Reboredo <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Miguel Ojeda <[email protected]>

Author: BennoLossin

rust/kernel/init/macros.rs

@@ -16,8 +16,9 @@
 //!
 //! We will look at the following example:
 //!
-//! ```rust
+//! ```rust,ignore
 //! # use kernel::init::*;
+//! # use core::pin::Pin;
 //! #[pin_data]
 //! #[repr(C)]
 //! struct Bar<T> {
@@ -71,19 +72,20 @@
 //!
 //! Here is the definition of `Bar` from our example:
 //!
-//! ```rust
+//! ```rust,ignore
 //! # use kernel::init::*;
 //! #[pin_data]
 //! #[repr(C)]
 //! struct Bar<T> {
+//!     #[pin]
 //!     t: T,
 //!     pub x: usize,
 //! }
 //! ```
 //!
 //! This expands to the following code:
 //!
-//! ```rust
+//! ```rust,ignore
 //! // Firstly the normal definition of the struct, attributes are preserved:
 //! #[repr(C)]
 //! struct Bar<T> {
@@ -116,20 +118,22 @@
 //!         unsafe fn t<E>(
 //!             self,
 //!             slot: *mut T,
-//!             init: impl ::kernel::init::Init<T, E>,
+//!             // Since `t` is `#[pin]`, this is `PinInit`.
+//!             init: impl ::kernel::init::PinInit<T, E>,
 //!         ) -> ::core::result::Result<(), E> {
-//!             unsafe { ::kernel::init::Init::__init(init, slot) }
+//!             unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
 //!         }
 //!         pub unsafe fn x<E>(
 //!             self,
 //!             slot: *mut usize,
+//!             // Since `x` is not `#[pin]`, this is `Init`.
 //!             init: impl ::kernel::init::Init<usize, E>,
 //!         ) -> ::core::result::Result<(), E> {
 //!             unsafe { ::kernel::init::Init::__init(init, slot) }
 //!         }
 //!     }
 //!     // Implement the internal `HasPinData` trait that associates `Bar` with the pin-data struct
-//!     // that we constructed beforehand.
+//!     // that we constructed above.
 //!     unsafe impl<T> ::kernel::init::__internal::HasPinData for Bar<T> {
 //!         type PinData = __ThePinData<T>;
 //!         unsafe fn __pin_data() -> Self::PinData {
@@ -160,6 +164,8 @@
 //!     struct __Unpin<'__pin, T> {
 //!         __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
 //!         __phantom: ::core::marker::PhantomData<fn(Bar<T>) -> Bar<T>>,
+//!         // Our only `#[pin]` field is `t`.
+//!         t: T,
 //!     }
 //!     #[doc(hidden)]
 //!     impl<'__pin, T>
@@ -193,7 +199,7 @@
 //!
 //! Here is the impl on `Bar` defining the new function:
 //!
-//! ```rust
+//! ```rust,ignore
 //! impl<T> Bar<T> {
 //!     fn new(t: T) -> impl PinInit<Self> {
 //!         pin_init!(Self { t, x: 0 })
@@ -203,7 +209,7 @@
 //!
 //! This expands to the following code:
 //!
-//! ```rust
+//! ```rust,ignore
 //! impl<T> Bar<T> {
 //!     fn new(t: T) -> impl PinInit<Self> {
 //!         {
@@ -232,25 +238,31 @@
 //!                     // that will refer to this struct instead of the one defined above.
 //!                     struct __InitOk;
 //!                     // This is the expansion of `t,`, which is syntactic sugar for `t: t,`.
-//!                     unsafe { ::core::ptr::write(&raw mut (*slot).t, t) };
+//!                     unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).t), t) };
 //!                     // Since initialization could fail later (not in this case, since the error
-//!                     // type is `Infallible`) we will need to drop this field if it fails. This
-//!                     // `DropGuard` will drop the field when it gets dropped and has not yet
-//!                     // been forgotten. We make a reference to it, so users cannot `mem::forget`
-//!                     // it from the initializer, since the name is the same as the field.
+//!                     // type is `Infallible`) we will need to drop this field if there is an
+//!                     // error later. This `DropGuard` will drop the field when it gets dropped
+//!                     // and has not yet been forgotten. We make a reference to it, so users
+//!                     // cannot `mem::forget` it from the initializer, since the name is the same
+//!                     // as the field (including hygiene).
 //!                     let t = &unsafe {
-//!                         ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).t)
+//!                         ::kernel::init::__internal::DropGuard::new(
+//!                             ::core::addr_of_mut!((*slot).t),
+//!                         )
 //!                     };
 //!                     // Expansion of `x: 0,`:
 //!                     // Since this can be an arbitrary expression we cannot place it inside of
 //!                     // the `unsafe` block, so we bind it here.
 //!                     let x = 0;
-//!                     unsafe { ::core::ptr::write(&raw mut (*slot).x, x) };
+//!                     unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).x), x) };
+//!                     // We again create a `DropGuard`.
 //!                     let x = &unsafe {
-//!                         ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).x)
+//!                         ::kernel::init::__internal::DropGuard::new(
+//!                             ::core::addr_of_mut!((*slot).x),
+//!                         )
 //!                     };
 //!
-//!                     // Here we use the type checker to ensuer that every field has been
+//!                     // Here we use the type checker to ensure that every field has been
 //!                     // initialized exactly once, since this is `if false` it will never get
 //!                     // executed, but still type-checked.
 //!                     // Additionally we abuse `slot` to automatically infer the correct type for
@@ -272,15 +284,15 @@
 //!                         };
 //!                     }
 //!                     // Since initialization has successfully completed, we can now forget the
-//!                     // guards.
+//!                     // guards. This is not `mem::forget`, since we only have `&DropGuard`.
 //!                     unsafe { ::kernel::init::__internal::DropGuard::forget(t) };
 //!                     unsafe { ::kernel::init::__internal::DropGuard::forget(x) };
 //!                 }
 //!                 // We leave the scope above and gain access to the previously shadowed
 //!                 // `__InitOk` that we need to return.
 //!                 Ok(__InitOk)
 //!             });
-//!             // Change the return type of the closure.
+//!             // Change the return type from `__InitOk` to `()`.
 //!             let init = move |slot| -> ::core::result::Result<(), ::core::convert::Infallible> {
 //!                 init(slot).map(|__InitOk| ())
 //!             };
@@ -299,7 +311,7 @@
 //! Since we already took a look at `#[pin_data]` on `Bar`, this section will only explain the
 //! differences/new things in the expansion of the `Foo` definition:
 //!
-//! ```rust
+//! ```rust,ignore
 //! #[pin_data(PinnedDrop)]
 //! struct Foo {
 //!     a: usize,
@@ -310,7 +322,7 @@
 //!
 //! This expands to the following code:
 //!
-//! ```rust
+//! ```rust,ignore
 //! struct Foo {
 //!     a: usize,
 //!     b: Bar<u32>,
@@ -330,8 +342,6 @@
 //!         unsafe fn b<E>(
 //!             self,
 //!             slot: *mut Bar<u32>,
-//!             // Note that this is `PinInit` instead of `Init`, this is because `b` is
-//!             // structurally pinned, as marked by the `#[pin]` attribute.
 //!             init: impl ::kernel::init::PinInit<Bar<u32>, E>,
 //!         ) -> ::core::result::Result<(), E> {
 //!             unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
@@ -359,14 +369,13 @@
 //!     struct __Unpin<'__pin> {
 //!         __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
 //!         __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
-//!         // Since this field is `#[pin]`, it is listed here.
 //!         b: Bar<u32>,
 //!     }
 //!     #[doc(hidden)]
 //!     impl<'__pin> ::core::marker::Unpin for Foo where __Unpin<'__pin>: ::core::marker::Unpin {}
 //!     // Since we specified `PinnedDrop` as the argument to `#[pin_data]`, we expect `Foo` to
 //!     // implement `PinnedDrop`. Thus we do not need to prevent `Drop` implementations like
-//!     // before, instead we implement it here and delegate to `PinnedDrop`.
+//!     // before, instead we implement `Drop` here and delegate to `PinnedDrop`.
 //!     impl ::core::ops::Drop for Foo {
 //!         fn drop(&mut self) {
 //!             // Since we are getting dropped, no one else has a reference to `self` and thus we
@@ -388,7 +397,7 @@
 //!
 //! Here is the `PinnedDrop` impl for `Foo`:
 //!
-//! ```rust
+//! ```rust,ignore
 //! #[pinned_drop]
 //! impl PinnedDrop for Foo {
 //!     fn drop(self: Pin<&mut Self>) {
@@ -399,7 +408,7 @@
 //!
 //! This expands to the following code:
 //!
-//! ```rust
+//! ```rust,ignore
 //! // `unsafe`, full path and the token parameter are added, everything else stays the same.
 //! unsafe impl ::kernel::init::PinnedDrop for Foo {
 //!     fn drop(self: Pin<&mut Self>, _: ::kernel::init::__internal::OnlyCallFromDrop) {
@@ -410,10 +419,10 @@
 //!
 //! ## `pin_init!` on `Foo`
 //!
-//! Since we already took a look at `pin_init!` on `Bar`, this section will only explain the
-//! differences/new things in the expansion of `pin_init!` on `Foo`:
+//! Since we already took a look at `pin_init!` on `Bar`, this section will only show the expansion
+//! of `pin_init!` on `Foo`:
 //!
-//! ```rust
+//! ```rust,ignore
 //! let a = 42;
 //! let initializer = pin_init!(Foo {
 //!     a,
@@ -423,7 +432,7 @@
 //!
 //! This expands to the following code:
 //!
-//! ```rust
+//! ```rust,ignore
 //! let a = 42;
 //! let initializer = {
 //!     struct __InitOk;
@@ -438,13 +447,15 @@
 //!     >(data, move |slot| {
 //!         {
 //!             struct __InitOk;
-//!             unsafe { ::core::ptr::write(&raw mut (*slot).a, a) };
-//!             let a = &unsafe { ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).a) };
+//!             unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).a), a) };
+//!             let a = &unsafe {
+//!                 ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).a))
+//!             };
 //!             let b = Bar::new(36);
-//!             // Here we use `data` to access the correct field and require that `b` is of type
-//!             // `PinInit<Bar<u32>, Infallible>`.
-//!             unsafe { data.b(&raw mut (*slot).b, b)? };
-//!             let b = &unsafe { ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).b) };
+//!             unsafe { data.b(::core::addr_of_mut!((*slot).b), b)? };
+//!             let b = &unsafe {
+//!                 ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).b))
+//!             };
 //!
 //!             #[allow(unreachable_code, clippy::diverging_sub_expression)]
 //!             if false {