// SPDX-License-Identifier: Apache-2.0 OR MIT
//! This module provides the macros that actually implement the proc-macros `pin_data` and
//! `pinned_drop`. It also contains `__init_internal` the implementation of the `{try_}{pin_}init!`
//! macros.
//!
//! These macros should never be called directly, since they expect their input to be
//! in a certain format which is internal. If used incorrectly, these macros can lead to UB even in
//! safe code! Use the public facing macros instead.
//!
//! This architecture has been chosen because the kernel does not yet have access to `syn` which
//! would make matters a lot easier for implementing these as proc-macros.
//!
//! # Macro expansion example
//!
//! This section is intended for readers trying to understand the macros in this module and the
//! `pin_init!` macros from `init.rs`.
//!
//! We will look at the following example:
//!
//! ```rust,ignore
//! # use kernel::init::*;
//! # use core::pin::Pin;
//! #[pin_data]
//! #[repr(C)]
//! struct Bar<T> {
//! #[pin]
//! t: T,
//! pub x: usize,
//! }
//!
//! impl<T> Bar<T> {
//! fn new(t: T) -> impl PinInit<Self> {
//! pin_init!(Self { t, x: 0 })
//! }
//! }
//!
//! #[pin_data(PinnedDrop)]
//! struct Foo {
//! a: usize,
//! #[pin]
//! b: Bar<u32>,
//! }
//!
//! #[pinned_drop]
//! impl PinnedDrop for Foo {
//! fn drop(self: Pin<&mut Self>) {
//! pr_info!("{self:p} is getting dropped.");
//! }
//! }
//!
//! let a = 42;
//! let initializer = pin_init!(Foo {
//! a,
//! b <- Bar::new(36),
//! });
//! ```
//!
//! This example includes the most common and important features of the pin-init API.
//!
//! Below you can find individual section about the different macro invocations. Here are some
//! general things we need to take into account when designing macros:
//! - use global paths, similarly to file paths, these start with the separator: `::core::panic!()`
//! this ensures that the correct item is used, since users could define their own `mod core {}`
//! and then their own `panic!` inside to execute arbitrary code inside of our macro.
//! - macro `unsafe` hygiene: we need to ensure that we do not expand arbitrary, user-supplied
//! expressions inside of an `unsafe` block in the macro, because this would allow users to do
//! `unsafe` operations without an associated `unsafe` block.
//!
//! ## `#[pin_data]` on `Bar`
//!
//! This macro is used to specify which fields are structurally pinned and which fields are not. It
//! is placed on the struct definition and allows `#[pin]` to be placed on the fields.
//!
//! Here is the definition of `Bar` from our example:
//!
//! ```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,ignore
//! // Firstly the normal definition of the struct, attributes are preserved:
//! #[repr(C)]
//! struct Bar<T> {
//! t: T,
//! pub x: usize,
//! }
//! // Then an anonymous constant is defined, this is because we do not want any code to access the
//! // types that we define inside:
//! const _: () = {
//! // We define the pin-data carrying struct, it is a ZST and needs to have the same generics,
//! // since we need to implement access functions for each field and thus need to know its
//! // type.
//! struct __ThePinData<T> {
//! __phantom: ::core::marker::PhantomData<fn(Bar<T>) -> Bar<T>>,
//! }
//! // We implement `Copy` for the pin-data struct, since all functions it defines will take
//! // `self` by value.
//! impl<T> ::core::clone::Clone for __ThePinData<T> {
//! fn clone(&self) -> Self {
//! *self
//! }
//! }
//! impl<T> ::core::marker::Copy for __ThePinData<T> {}
//! // For every field of `Bar`, the pin-data struct will define a function with the same name
//! // and accessor (`pub` or `pub(crate)` etc.). This function will take a pointer to the
//! // field (`slot`) and a `PinInit` or `Init` depending on the projection kind of the field
//! // (if pinning is structural for the field, then `PinInit` otherwise `Init`).
//! #[allow(dead_code)]
//! impl<T> __ThePinData<T> {
//! unsafe fn t<E>(
//! self,
//! slot: *mut T,
//! // Since `t` is `#[pin]`, this is `PinInit`.
//! init: impl ::kernel::init::PinInit<T, E>,
//! ) -> ::core::result::Result<(), E> {
//! 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 above.
//! unsafe impl<T> ::kernel::init::__internal::HasPinData for Bar<T> {
//! type PinData = __ThePinData<T>;
//! unsafe fn __pin_data() -> Self::PinData {
//! __ThePinData {
//! __phantom: ::core::marker::PhantomData,
//! }
//! }
//! }
//! // Implement the internal `PinData` trait that marks the pin-data struct as a pin-data
//! // struct. This is important to ensure that no user can implement a rouge `__pin_data`
//! // function without using `unsafe`.
//! unsafe impl<T> ::kernel::init::__internal::PinData for __ThePinData<T> {
//! type Datee = Bar<T>;
//! }
//! // Now we only want to implement `Unpin` for `Bar` when every structurally pinned field is
//! // `Unpin`. In other words, whether `Bar` is `Unpin` only depends on structurally pinned
//! // fields (those marked with `#[pin]`). These fields will be listed in this struct, in our
//! // case no such fields exist, hence this is almost empty. The two phantomdata fields exist
//! // for two reasons:
//! // - `__phantom`: every generic must be used, since we cannot really know which generics
//! // are used, we declere all and then use everything here once.
//! // - `__phantom_pin`: uses the `'__pin` lifetime and ensures that this struct is invariant
//! // over it. The lifetime is needed to work around the limitation that trait bounds must
//! // not be trivial, e.g. the user has a `#[pin] PhantomPinned` field -- this is
//! // unconditionally `!Unpin` and results in an error. The lifetime tricks the compiler
//! // into accepting these bounds regardless.
//! #[allow(dead_code)]
//! 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> ::core::marker::Unpin for Bar<T>
//! where
//! __Unpin<'__pin, T>: ::core::marker::Unpin,
//! {}
//! // Now we need to ensure that `Bar` does not implement `Drop`, since that would give users
//! // access to `&mut self` inside of `drop` even if the struct was pinned. This could lead to
//! // UB with only safe code, so we disallow this by giving a trait implementation error using
//! // a direct impl and a blanket implementation.
//! trait MustNotImplDrop {}
//! // Normally `Drop` bounds do not have the correct semantics, but for this purpose they do
//! // (normally people want to know if a type has any kind of drop glue at all, here we want
//! // to know if it has any kind of custom drop glue, which is exactly what this bound does).
//! #[allow(drop_bounds)]
//! impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
//! impl<T> MustNotImplDrop for Bar<T> {}
//! // Here comes a convenience check, if one implemented `PinnedDrop`, but forgot to add it to
//! // `#[pin_data]`, then this will error with the same mechanic as above, this is not needed
//! // for safety, but a good sanity check, since no normal code calls `PinnedDrop::drop`.
//! #[allow(non_camel_case_types)]
//! trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
//! impl<
//! T: ::kernel::init::PinnedDrop,
//! > UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
//! impl<T> UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for Bar<T> {}
//! };
//! ```
//!
//! ## `pin_init!` in `impl Bar`
//!
//! This macro creates an pin-initializer for the given struct. It requires that the struct is
//! annotated by `#[pin_data]`.
//!
//! Here is the impl on `Bar` defining the new function:
//!
//! ```rust,ignore
//! impl<T> Bar<T> {
//! fn new(t: T) -> impl PinInit<Self> {
//! pin_init!(Self { t, x: 0 })
//! }
//! }
//! ```
//!
//! This expands to the following code:
//!
//! ```rust,ignore
//! impl<T> Bar<T> {
//! fn new(t: T) -> impl PinInit<Self> {
//! {
//! // We do not want to allow arbitrary returns, so we declare this type as the `Ok`
//! // return type and shadow it later when we insert the arbitrary user code. That way
//! // there will be no possibility of returning without `unsafe`.
//! struct __InitOk;
//! // Get the data about fields from the supplied type.
//! // - the function is unsafe, hence the unsafe block
//! // - we `use` the `HasPinData` trait in the block, it is only available in that
//! // scope.
//! let data = unsafe {
//! use ::kernel::init::__internal::HasPinData;
//! Self::__pin_data()
//! };
//! // Ensure that `data` really is of type `PinData` and help with type inference:
//! let init = ::kernel::init::__internal::PinData::make_closure::<
//! _,
//! __InitOk,
//! ::core::convert::Infallible,
//! >(data, move |slot| {
//! {
//! // Shadow the structure so it cannot be used to return early. If a user
//! // tries to write `return Ok(__InitOk)`, then they get a type error,
//! // since 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(::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 there
//! // is an error later. This `DropGuard` will drop the field when it gets
//! // dropped and has not yet been forgotten.
//! let __t_guard = unsafe {
//! ::pinned_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(::core::addr_of_mut!((*slot).x), x) };
//! }
//! // We again create a `DropGuard`.
//! let __x_guard = unsafe {
//! ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).x))
//! };
//! // Since initialization has successfully completed, we can now forget
//! // the guards. This is not `mem::forget`, since we only have
//! // `&DropGuard`.
//! ::core::mem::forget(__x_guard);
//! ::core::mem::forget(__t_guard);
//! // 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 the struct. This is also another check that every field is
//! // accessible from this scope.
//! #[allow(unreachable_code, clippy::diverging_sub_expression)]
//! let _ = || {
//! unsafe {
//! ::core::ptr::write(
//! slot,
//! Self {
//! // We only care about typecheck finding every field
//! // here, the expression does not matter, just conjure
//! // one using `panic!()`:
//! t: ::core::panic!(),
//! x: ::core::panic!(),
//! },
//! );
//! };
//! };
//! }
//! // We leave the scope above and gain access to the previously shadowed
//! // `__InitOk` that we need to return.
//! Ok(__InitOk)
//! });
//! // Change the return type from `__InitOk` to `()`.
//! let init = move |
//! slot,
//! | -> ::core::result::Result<(), ::core::convert::Infallible> {
//! init(slot).map(|__InitOk| ())
//! };
//! // Construct the initializer.
//! let init = unsafe {
//! ::kernel::init::pin_init_from_closure::<
//! _,
//! ::core::convert::Infallible,
//! >(init)
//! };
//! init
//! }
//! }
//! }
//! ```
//!
//! ## `#[pin_data]` on `Foo`
//!
//! 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,ignore
//! #[pin_data(PinnedDrop)]
//! struct Foo {
//! a: usize,
//! #[pin]
//! b: Bar<u32>,
//! }
//! ```
//!
//! This expands to the following code:
//!
//! ```rust,ignore
//! struct Foo {
//! a: usize,
//! b: Bar<u32>,
//! }
//! const _: () = {
//! struct __ThePinData {
//! __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
//! }
//! impl ::core::clone::Clone for __ThePinData {
//! fn clone(&self) -> Self {
//! *self
//! }
//! }
//! impl ::core::marker::Copy for __ThePinData {}
//! #[allow(dead_code)]
//! impl __ThePinData {
//! unsafe fn b<E>(
//! self,
//! slot: *mut Bar<u32>,
//! init: impl ::kernel::init::PinInit<Bar<u32>, E>,
//! ) -> ::core::result::Result<(), E> {
//! unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
//! }
//! unsafe fn a<E>(
//! self,
//! slot: *mut usize,
//! init: impl ::kernel::init::Init<usize, E>,
//! ) -> ::core::result::Result<(), E> {
//! unsafe { ::kernel::init::Init::__init(init, slot) }
//! }
//! }
//! unsafe impl ::kernel::init::__internal::HasPinData for Foo {
//! type PinData = __ThePinData;
//! unsafe fn __pin_data() -> Self::PinData {
//! __ThePinData {
//! __phantom: ::core::marker::PhantomData,
//! }
//! }
//! }
//! unsafe impl ::kernel::init::__internal::PinData for __ThePinData {
//! type Datee = Foo;
//! }
//! #[allow(dead_code)]
//! struct __Unpin<'__pin> {
//! __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
//! __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
//! 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 `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
//! // can assume that we never move.
//! let pinned = unsafe { ::core::pin::Pin::new_unchecked(self) };
//! // Create the unsafe token that proves that we are inside of a destructor, this
//! // type is only allowed to be created in a destructor.
//! let token = unsafe { ::kernel::init::__internal::OnlyCallFromDrop::new() };
//! ::kernel::init::PinnedDrop::drop(pinned, token);
//! }
//! }
//! };
//! ```
//!
//! ## `#[pinned_drop]` on `impl PinnedDrop for Foo`
//!
//! This macro is used to implement the `PinnedDrop` trait, since that trait is `unsafe` and has an
//! extra parameter that should not be used at all. The macro hides that parameter.
//!
//! Here is the `PinnedDrop` impl for `Foo`:
//!
//! ```rust,ignore
//! #[pinned_drop]
//! impl PinnedDrop for Foo {
//! fn drop(self: Pin<&mut Self>) {
//! pr_info!("{self:p} is getting dropped.");
//! }
//! }
//! ```
//!
//! This expands to the following code:
//!
//! ```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) {
//! pr_info!("{self:p} is getting dropped.");
//! }
//! }
//! ```
//!
//! ## `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,ignore
//! let a = 42;
//! let initializer = pin_init!(Foo {
//! a,
//! b <- Bar::new(36),
//! });
//! ```
//!
//! This expands to the following code:
//!
//! ```rust,ignore
//! let a = 42;
//! let initializer = {
//! struct __InitOk;
//! let data = unsafe {
//! use ::kernel::init::__internal::HasPinData;
//! Foo::__pin_data()
//! };
//! let init = ::kernel::init::__internal::PinData::make_closure::<
//! _,
//! __InitOk,
//! ::core::convert::Infallible,
//! >(data, move |slot| {
//! {
//! struct __InitOk;
//! {
//! unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).a), a) };
//! }
//! let __a_guard = unsafe {
//! ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).a))
//! };
//! let init = Bar::new(36);
//! unsafe { data.b(::core::addr_of_mut!((*slot).b), b)? };
//! let __b_guard = unsafe {
//! ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).b))
//! };
//! ::core::mem::forget(__b_guard);
//! ::core::mem::forget(__a_guard);
//! #[allow(unreachable_code, clippy::diverging_sub_expression)]
//! let _ = || {
//! unsafe {
//! ::core::ptr::write(
//! slot,
//! Foo {
//! a: ::core::panic!(),
//! b: ::core::panic!(),
//! },
//! );
//! };
//! };
//! }
//! Ok(__InitOk)
//! });
//! let init = move |
//! slot,
//! | -> ::core::result::Result<(), ::core::convert::Infallible> {
//! init(slot).map(|__InitOk| ())
//! };
//! let init = unsafe {
//! ::kernel::init::pin_init_from_closure::<_, ::core::convert::Infallible>(init)
//! };
//! init
//! };
//! ```
/// Creates a `unsafe impl<...> PinnedDrop for $type` block.
///
/// See [`PinnedDrop`] for more information.
#[doc(hidden)]
#[macro_export]
macro_rules! __pinned_drop {
(
@impl_sig($($impl_sig:tt)*),
@impl_body(
$(#[$($attr:tt)*])*
fn drop($($sig:tt)*) {
$($inner:tt)*
}
),
) => {
unsafe $($impl_sig)* {
// Inherit all attributes and the type/ident tokens for the signature.
$(#[$($attr)*])*
fn drop($($sig)*, _: $crate::init::__internal::OnlyCallFromDrop) {
$($inner)*
}
}
}
}
/// This macro first parses the struct definition such that it separates pinned and not pinned
/// fields. Afterwards it declares the struct and implement the `PinData` trait safely.
#[doc(hidden)]
#[macro_export]
macro_rules! __pin_data {
// Proc-macro entry point, this is supplied by the proc-macro pre-parsing.
(parse_input:
@args($($pinned_drop:ident)?),
@sig(
$(#[$($struct_attr:tt)*])*
$vis:vis struct $name:ident
$(where $($whr:tt)*)?
),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@body({ $($fields:tt)* }),
) => {
// We now use token munching to iterate through all of the fields. While doing this we
// identify fields marked with `#[pin]`, these fields are the 'pinned fields'. The user
// wants these to be structurally pinned. The rest of the fields are the
// 'not pinned fields'. Additionally we collect all fields, since we need them in the right
// order to declare the struct.
//
// In this call we also put some explaining comments for the parameters.
$crate::__pin_data!(find_pinned_fields:
// Attributes on the struct itself, these will just be propagated to be put onto the
// struct definition.
@struct_attrs($(#[$($struct_attr)*])*),
// The visibility of the struct.
@vis($vis),
// The name of the struct.
@name($name),
// The 'impl generics', the generics that will need to be specified on the struct inside
// of an `impl<$ty_generics>` block.
@impl_generics($($impl_generics)*),
// The 'ty generics', the generics that will need to be specified on the impl blocks.
@ty_generics($($ty_generics)*),
// The 'decl generics', the generics that need to be specified on the struct
// definition.
@decl_generics($($decl_generics)*),
// The where clause of any impl block and the declaration.
@where($($($whr)*)?),
// The remaining fields tokens that need to be processed.
// We add a `,` at the end to ensure correct parsing.
@fields_munch($($fields)* ,),
// The pinned fields.
@pinned(),
// The not pinned fields.
@not_pinned(),
// All fields.
@fields(),
// The accumulator containing all attributes already parsed.
@accum(),
// Contains `yes` or `` to indicate if `#[pin]` was found on the current field.
@is_pinned(),
// The proc-macro argument, this should be `PinnedDrop` or ``.
@pinned_drop($($pinned_drop)?),
);
};
(find_pinned_fields:
@struct_attrs($($struct_attrs:tt)*),
@vis($vis:vis),
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We found a PhantomPinned field, this should generally be pinned!
@fields_munch($field:ident : $($($(::)?core::)?marker::)?PhantomPinned, $($rest:tt)*),
@pinned($($pinned:tt)*),
@not_pinned($($not_pinned:tt)*),
@fields($($fields:tt)*),
@accum($($accum:tt)*),
// This field is not pinned.
@is_pinned(),
@pinned_drop($($pinned_drop:ident)?),
) => {
::core::compile_error!(concat!(
"The field `",
stringify!($field),
"` of type `PhantomPinned` only has an effect, if it has the `#[pin]` attribute.",
));
$crate::__pin_data!(find_pinned_fields:
@struct_attrs($($struct_attrs)*),
@vis($vis),
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($($rest)*),
@pinned($($pinned)* $($accum)* $field: ::core::marker::PhantomPinned,),
@not_pinned($($not_pinned)*),
@fields($($fields)* $($accum)* $field: ::core::marker::PhantomPinned,),
@accum(),
@is_pinned(),
@pinned_drop($($pinned_drop)?),
);
};
(find_pinned_fields:
@struct_attrs($($struct_attrs:tt)*),
@vis($vis:vis),
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We reached the field declaration.
@fields_munch($field:ident : $type:ty, $($rest:tt)*),
@pinned($($pinned:tt)*),
@not_pinned($($not_pinned:tt)*),
@fields($($fields:tt)*),
@accum($($accum:tt)*),
// This field is pinned.
@is_pinned(yes),
@pinned_drop($($pinned_drop:ident)?),
) => {
$crate::__pin_data!(find_pinned_fields:
@struct_attrs($($struct_attrs)*),
@vis($vis),
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($($rest)*),
@pinned($($pinned)* $($accum)* $field: $type,),
@not_pinned($($not_pinned)*),
@fields($($fields)* $($accum)* $field: $type,),
@accum(),
@is_pinned(),
@pinned_drop($($pinned_drop)?),
);
};
(find_pinned_fields:
@struct_attrs($($struct_attrs:tt)*),
@vis($vis:vis),
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We reached the field declaration.
@fields_munch($field:ident : $type:ty, $($rest:tt)*),
@pinned($($pinned:tt)*),
@not_pinned($($not_pinned:tt)*),
@fields($($fields:tt)*),
@accum($($accum:tt)*),
// This field is not pinned.
@is_pinned(),
@pinned_drop($($pinned_drop:ident)?),
) => {
$crate::__pin_data!(find_pinned_fields:
@struct_attrs($($struct_attrs)*),
@vis($vis),
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($($rest)*),
@pinned($($pinned)*),
@not_pinned($($not_pinned)* $($accum)* $field: $type,),
@fields($($fields)* $($accum)* $field: $type,),
@accum(),
@is_pinned(),
@pinned_drop($($pinned_drop)?),
);
};
(find_pinned_fields:
@struct_attrs($($struct_attrs:tt)*),
@vis($vis:vis),
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We found the `#[pin]` attr.
@fields_munch(#[pin] $($rest:tt)*),
@pinned($($pinned:tt)*),
@not_pinned($($not_pinned:tt)*),
@fields($($fields:tt)*),
@accum($($accum:tt)*),
@is_pinned($($is_pinned:ident)?),
@pinned_drop($($pinned_drop:ident)?),
) => {
$crate::__pin_data!(find_pinned_fields:
@struct_attrs($($struct_attrs)*),
@vis($vis),
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($($rest)*),
// We do not include `#[pin]` in the list of attributes, since it is not actually an
// attribute that is defined somewhere.
@pinned($($pinned)*),
@not_pinned($($not_pinned)*),
@fields($($fields)*),
@accum($($accum)*),
// Set this to `yes`.
@is_pinned(yes),
@pinned_drop($($pinned_drop)?),
);
};
(find_pinned_fields:
@struct_attrs($($struct_attrs:tt)*),
@vis($vis:vis),
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We reached the field declaration with visibility, for simplicity we only munch the
// visibility and put it into `$accum`.
@fields_munch($fvis:vis $field:ident $($rest:tt)*),
@pinned($($pinned:tt)*),
@not_pinned($($not_pinned:tt)*),
@fields($($fields:tt)*),
@accum($($accum:tt)*),
@is_pinned($($is_pinned:ident)?),
@pinned_drop($($pinned_drop:ident)?),
) => {
$crate::__pin_data!(find_pinned_fields:
@struct_attrs($($struct_attrs)*),
@vis($vis),
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($field $($rest)*),
@pinned($($pinned)*),
@not_pinned($($not_pinned)*),
@fields($($fields)*),
@accum($($accum)* $fvis),
@is_pinned($($is_pinned)?),
@pinned_drop($($pinned_drop)?),
);
};
(find_pinned_fields:
@struct_attrs($($struct_attrs:tt)*),
@vis($vis:vis),
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// Some other attribute, just put it into `$accum`.
@fields_munch(#[$($attr:tt)*] $($rest:tt)*),
@pinned($($pinned:tt)*),
@not_pinned($($not_pinned:tt)*),
@fields($($fields:tt)*),
@accum($($accum:tt)*),
@is_pinned($($is_pinned:ident)?),
@pinned_drop($($pinned_drop:ident)?),
) => {
$crate::__pin_data!(find_pinned_fields:
@struct_attrs($($struct_attrs)*),
@vis($vis),
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@decl_generics($($decl_generics)*),
@where($($whr)*),
@fields_munch($($rest)*),
@pinned($($pinned)*),
@not_pinned($($not_pinned)*),
@fields($($fields)*),
@accum($($accum)* #[$($attr)*]),
@is_pinned($($is_pinned)?),
@pinned_drop($($pinned_drop)?),
);
};
(find_pinned_fields:
@struct_attrs($($struct_attrs:tt)*),
@vis($vis:vis),
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@decl_generics($($decl_generics:tt)*),
@where($($whr:tt)*),
// We reached the end of the fields, plus an optional additional comma, since we added one
// before and the user is also allowed to put a trailing comma.
@fields_munch($(,)?),
@pinned($($pinned:tt)*),
@not_pinned($($not_pinned:tt)*),
@fields($($fields:tt)*),
@accum(),
@is_pinned(),
@pinned_drop($($pinned_drop:ident)?),
) => {
// Declare the struct with all fields in the correct order.
$($struct_attrs)*
$vis struct $name <$($decl_generics)*>
where $($whr)*
{
$($fields)*
}
// We put the rest into this const item, because it then will not be accessible to anything
// outside.
const _: () = {
// We declare this struct which will host all of the projection function for our type.
// it will be invariant over all generic parameters which are inherited from the
// struct.
$vis struct __ThePinData<$($impl_generics)*>
where $($whr)*
{
__phantom: ::core::marker::PhantomData<
fn($name<$($ty_generics)*>) -> $name<$($ty_generics)*>
>,
}
impl<$($impl_generics)*> ::core::clone::Clone for __ThePinData<$($ty_generics)*>
where $($whr)*
{
fn clone(&self) -> Self { *self }
}
impl<$($impl_generics)*> ::core::marker::Copy for __ThePinData<$($ty_generics)*>
where $($whr)*
{}
// Make all projection functions.
$crate::__pin_data!(make_pin_data:
@pin_data(__ThePinData),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@where($($whr)*),
@pinned($($pinned)*),
@not_pinned($($not_pinned)*),
);
// SAFETY: We have added the correct projection functions above to `__ThePinData` and
// we also use the least restrictive generics possible.
unsafe impl<$($impl_generics)*>
$crate::init::__internal::HasPinData for $name<$($ty_generics)*>
where $($whr)*
{
type PinData = __ThePinData<$($ty_generics)*>;
unsafe fn __pin_data() -> Self::PinData {
__ThePinData { __phantom: ::core::marker::PhantomData }
}
}
unsafe impl<$($impl_generics)*>
$crate::init::__internal::PinData for __ThePinData<$($ty_generics)*>
where $($whr)*
{
type Datee = $name<$($ty_generics)*>;
}
// This struct will be used for the unpin analysis. Since only structurally pinned
// fields are relevant whether the struct should implement `Unpin`.
#[allow(dead_code)]
struct __Unpin <'__pin, $($impl_generics)*>
where $($whr)*
{
__phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
__phantom: ::core::marker::PhantomData<
fn($name<$($ty_generics)*>) -> $name<$($ty_generics)*>
>,
// Only the pinned fields.
$($pinned)*
}
#[doc(hidden)]
impl<'__pin, $($impl_generics)*> ::core::marker::Unpin for $name<$($ty_generics)*>
where
__Unpin<'__pin, $($ty_generics)*>: ::core::marker::Unpin,
$($whr)*
{}
// We need to disallow normal `Drop` implementation, the exact behavior depends on
// whether `PinnedDrop` was specified as the parameter.
$crate::__pin_data!(drop_prevention:
@name($name),
@impl_generics($($impl_generics)*),
@ty_generics($($ty_generics)*),
@where($($whr)*),
@pinned_drop($($pinned_drop)?),
);
};
};
// When no `PinnedDrop` was specified, then we have to prevent implementing drop.
(drop_prevention:
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@where($($whr:tt)*),
@pinned_drop(),
) => {
// We prevent this by creating a trait that will be implemented for all types implementing
// `Drop`. Additionally we will implement this trait for the struct leading to a conflict,
// if it also implements `Drop`
trait MustNotImplDrop {}
#[allow(drop_bounds)]
impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
impl<$($impl_generics)*> MustNotImplDrop for $name<$($ty_generics)*>
where $($whr)* {}
// We also take care to prevent users from writing a useless `PinnedDrop` implementation.
// They might implement `PinnedDrop` correctly for the struct, but forget to give
// `PinnedDrop` as the parameter to `#[pin_data]`.
#[allow(non_camel_case_types)]
trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
impl<T: $crate::init::PinnedDrop>
UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
impl<$($impl_generics)*>
UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for $name<$($ty_generics)*>
where $($whr)* {}
};
// When `PinnedDrop` was specified we just implement `Drop` and delegate.
(drop_prevention:
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@where($($whr:tt)*),
@pinned_drop(PinnedDrop),
) => {
impl<$($impl_generics)*> ::core::ops::Drop for $name<$($ty_generics)*>
where $($whr)*
{
fn drop(&mut self) {
// SAFETY: Since this is a destructor, `self` will not move after this function
// terminates, since it is inaccessible.
let pinned = unsafe { ::core::pin::Pin::new_unchecked(self) };
// SAFETY: Since this is a drop function, we can create this token to call the
// pinned destructor of this type.
let token = unsafe { $crate::init::__internal::OnlyCallFromDrop::new() };
$crate::init::PinnedDrop::drop(pinned, token);
}
}
};
// If some other parameter was specified, we emit a readable error.
(drop_prevention:
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@where($($whr:tt)*),
@pinned_drop($($rest:tt)*),
) => {
compile_error!(
"Wrong parameters to `#[pin_data]`, expected nothing or `PinnedDrop`, got '{}'.",
stringify!($($rest)*),
);
};
(make_pin_data:
@pin_data($pin_data:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@where($($whr:tt)*),
@pinned($($(#[$($p_attr:tt)*])* $pvis:vis $p_field:ident : $p_type:ty),* $(,)?),
@not_pinned($($(#[$($attr:tt)*])* $fvis:vis $field:ident : $type:ty),* $(,)?),
) => {
// For every field, we create a projection function according to its projection type. If a
// field is structurally pinned, then it must be initialized via `PinInit`, if it is not
// structurally pinned, then it can be initialized via `Init`.
//
// The functions are `unsafe` to prevent accidentally calling them.
#[allow(dead_code)]
impl<$($impl_generics)*> $pin_data<$($ty_generics)*>
where $($whr)*
{
$(
$(#[$($p_attr)*])*
$pvis unsafe fn $p_field<E>(
self,
slot: *mut $p_type,
init: impl $crate::init::PinInit<$p_type, E>,
) -> ::core::result::Result<(), E> {
unsafe { $crate::init::PinInit::__pinned_init(init, slot) }
}
)*
$(
$(#[$($attr)*])*
$fvis unsafe fn $field<E>(
self,
slot: *mut $type,
init: impl $crate::init::Init<$type, E>,
) -> ::core::result::Result<(), E> {
unsafe { $crate::init::Init::__init(init, slot) }
}
)*
}
};
}
/// The internal init macro. Do not call manually!
///
/// This is called by the `{try_}{pin_}init!` macros with various inputs.
///
/// This macro has multiple internal call configurations, these are always the very first ident:
/// - nothing: this is the base case and called by the `{try_}{pin_}init!` macros.
/// - `with_update_parsed`: when the `..Zeroable::zeroed()` syntax has been handled.
/// - `init_slot`: recursively creates the code that initializes all fields in `slot`.
/// - `make_initializer`: recursively create the struct initializer that guarantees that every
/// field has been initialized exactly once.
#[doc(hidden)]
#[macro_export]
macro_rules! __init_internal {
(
@this($($this:ident)?),
@typ($t:path),
@fields($($fields:tt)*),
@error($err:ty),
// Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
// case.
@data($data:ident, $($use_data:ident)?),
// `HasPinData` or `HasInitData`.
@has_data($has_data:ident, $get_data:ident),
// `pin_init_from_closure` or `init_from_closure`.
@construct_closure($construct_closure:ident),
@munch_fields(),
) => {
$crate::__init_internal!(with_update_parsed:
@this($($this)?),
@typ($t),
@fields($($fields)*),
@error($err),
@data($data, $($use_data)?),
@has_data($has_data, $get_data),
@construct_closure($construct_closure),
@zeroed(), // Nothing means default behavior.
)
};
(
@this($($this:ident)?),
@typ($t:path),
@fields($($fields:tt)*),
@error($err:ty),
// Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
// case.
@data($data:ident, $($use_data:ident)?),
// `HasPinData` or `HasInitData`.
@has_data($has_data:ident, $get_data:ident),
// `pin_init_from_closure` or `init_from_closure`.
@construct_closure($construct_closure:ident),
@munch_fields(..Zeroable::zeroed()),
) => {
$crate::__init_internal!(with_update_parsed:
@this($($this)?),
@typ($t),
@fields($($fields)*),
@error($err),
@data($data, $($use_data)?),
@has_data($has_data, $get_data),
@construct_closure($construct_closure),
@zeroed(()), // `()` means zero all fields not mentioned.
)
};
(
@this($($this:ident)?),
@typ($t:path),
@fields($($fields:tt)*),
@error($err:ty),
// Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
// case.
@data($data:ident, $($use_data:ident)?),
// `HasPinData` or `HasInitData`.
@has_data($has_data:ident, $get_data:ident),
// `pin_init_from_closure` or `init_from_closure`.
@construct_closure($construct_closure:ident),
@munch_fields($ignore:tt $($rest:tt)*),
) => {
$crate::__init_internal!(
@this($($this)?),
@typ($t),
@fields($($fields)*),
@error($err),
@data($data, $($use_data)?),
@has_data($has_data, $get_data),
@construct_closure($construct_closure),
@munch_fields($($rest)*),
)
};
(with_update_parsed:
@this($($this:ident)?),
@typ($t:path),
@fields($($fields:tt)*),
@error($err:ty),
// Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
// case.
@data($data:ident, $($use_data:ident)?),
// `HasPinData` or `HasInitData`.
@has_data($has_data:ident, $get_data:ident),
// `pin_init_from_closure` or `init_from_closure`.
@construct_closure($construct_closure:ident),
@zeroed($($init_zeroed:expr)?),
) => {{
// We do not want to allow arbitrary returns, so we declare this type as the `Ok` return
// type and shadow it later when we insert the arbitrary user code. That way there will be
// no possibility of returning without `unsafe`.
struct __InitOk;
// Get the data about fields from the supplied type.
let data = unsafe {
use $crate::init::__internal::$has_data;
// Here we abuse `paste!` to retokenize `$t`. Declarative macros have some internal
// information that is associated to already parsed fragments, so a path fragment
// cannot be used in this position. Doing the retokenization results in valid rust
// code.
::kernel::macros::paste!($t::$get_data())
};
// Ensure that `data` really is of type `$data` and help with type inference:
let init = $crate::init::__internal::$data::make_closure::<_, __InitOk, $err>(
data,
move |slot| {
{
// Shadow the structure so it cannot be used to return early.
struct __InitOk;
// If `$init_zeroed` is present we should zero the slot now and not emit an
// error when fields are missing (since they will be zeroed). We also have to
// check that the type actually implements `Zeroable`.
$({
fn assert_zeroable<T: $crate::init::Zeroable>(_: *mut T) {}
// Ensure that the struct is indeed `Zeroable`.
assert_zeroable(slot);
// SAFETY: The type implements `Zeroable` by the check above.
unsafe { ::core::ptr::write_bytes(slot, 0, 1) };
$init_zeroed // This will be `()` if set.
})?
// Create the `this` so it can be referenced by the user inside of the
// expressions creating the individual fields.
$(let $this = unsafe { ::core::ptr::NonNull::new_unchecked(slot) };)?
// Initialize every field.
$crate::__init_internal!(init_slot($($use_data)?):
@data(data),
@slot(slot),
@guards(),
@munch_fields($($fields)*,),
);
// We use unreachable code to ensure that all fields have been mentioned exactly
// once, this struct initializer will still be type-checked and complain with a
// very natural error message if a field is forgotten/mentioned more than once.
#[allow(unreachable_code, clippy::diverging_sub_expression)]
let _ = || {
$crate::__init_internal!(make_initializer:
@slot(slot),
@type_name($t),
@munch_fields($($fields)*,),
@acc(),
);
};
}
Ok(__InitOk)
}
);
let init = move |slot| -> ::core::result::Result<(), $err> {
init(slot).map(|__InitOk| ())
};
let init = unsafe { $crate::init::$construct_closure::<_, $err>(init) };
init
}};
(init_slot($($use_data:ident)?):
@data($data:ident),
@slot($slot:ident),
@guards($($guards:ident,)*),
@munch_fields($(..Zeroable::zeroed())? $(,)?),
) => {
// Endpoint of munching, no fields are left. If execution reaches this point, all fields
// have been initialized. Therefore we can now dismiss the guards by forgetting them.
$(::core::mem::forget($guards);)*
};
(init_slot($use_data:ident): // `use_data` is present, so we use the `data` to init fields.
@data($data:ident),
@slot($slot:ident),
@guards($($guards:ident,)*),
// In-place initialization syntax.
@munch_fields($field:ident <- $val:expr, $($rest:tt)*),
) => {
let init = $val;
// Call the initializer.
//
// SAFETY: `slot` is valid, because we are inside of an initializer closure, we
// return when an error/panic occurs.
// We also use the `data` to require the correct trait (`Init` or `PinInit`) for `$field`.
unsafe { $data.$field(::core::ptr::addr_of_mut!((*$slot).$field), init)? };
// Create the drop guard:
//
// We rely on macro hygiene to make it impossible for users to access this local variable.
// We use `paste!` to create new hygiene for `$field`.
::kernel::macros::paste! {
// SAFETY: We forget the guard later when initialization has succeeded.
let [< __ $field _guard >] = unsafe {
$crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
};
$crate::__init_internal!(init_slot($use_data):
@data($data),
@slot($slot),
@guards([< __ $field _guard >], $($guards,)*),
@munch_fields($($rest)*),
);
}
};
(init_slot(): // No `use_data`, so we use `Init::__init` directly.
@data($data:ident),
@slot($slot:ident),
@guards($($guards:ident,)*),
// In-place initialization syntax.
@munch_fields($field:ident <- $val:expr, $($rest:tt)*),
) => {
let init = $val;
// Call the initializer.
//
// SAFETY: `slot` is valid, because we are inside of an initializer closure, we
// return when an error/panic occurs.
unsafe { $crate::init::Init::__init(init, ::core::ptr::addr_of_mut!((*$slot).$field))? };
// Create the drop guard:
//
// We rely on macro hygiene to make it impossible for users to access this local variable.
// We use `paste!` to create new hygiene for `$field`.
::kernel::macros::paste! {
// SAFETY: We forget the guard later when initialization has succeeded.
let [< __ $field _guard >] = unsafe {
$crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
};
$crate::__init_internal!(init_slot():
@data($data),
@slot($slot),
@guards([< __ $field _guard >], $($guards,)*),
@munch_fields($($rest)*),
);
}
};
(init_slot($($use_data:ident)?):
@data($data:ident),
@slot($slot:ident),
@guards($($guards:ident,)*),
// Init by-value.
@munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
) => {
{
$(let $field = $val;)?
// Initialize the field.
//
// SAFETY: The memory at `slot` is uninitialized.
unsafe { ::core::ptr::write(::core::ptr::addr_of_mut!((*$slot).$field), $field) };
}
// Create the drop guard:
//
// We rely on macro hygiene to make it impossible for users to access this local variable.
// We use `paste!` to create new hygiene for `$field`.
::kernel::macros::paste! {
// SAFETY: We forget the guard later when initialization has succeeded.
let [< __ $field _guard >] = unsafe {
$crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
};
$crate::__init_internal!(init_slot($($use_data)?):
@data($data),
@slot($slot),
@guards([< __ $field _guard >], $($guards,)*),
@munch_fields($($rest)*),
);
}
};
(make_initializer:
@slot($slot:ident),
@type_name($t:path),
@munch_fields(..Zeroable::zeroed() $(,)?),
@acc($($acc:tt)*),
) => {
// Endpoint, nothing more to munch, create the initializer. Since the users specified
// `..Zeroable::zeroed()`, the slot will already have been zeroed and all field that have
// not been overwritten are thus zero and initialized. We still check that all fields are
// actually accessible by using the struct update syntax ourselves.
// We are inside of a closure that is never executed and thus we can abuse `slot` to
// get the correct type inference here:
#[allow(unused_assignments)]
unsafe {
let mut zeroed = ::core::mem::zeroed();
// We have to use type inference here to make zeroed have the correct type. This does
// not get executed, so it has no effect.
::core::ptr::write($slot, zeroed);
zeroed = ::core::mem::zeroed();
// Here we abuse `paste!` to retokenize `$t`. Declarative macros have some internal
// information that is associated to already parsed fragments, so a path fragment
// cannot be used in this position. Doing the retokenization results in valid rust
// code.
::kernel::macros::paste!(
::core::ptr::write($slot, $t {
$($acc)*
..zeroed
});
);
}
};
(make_initializer:
@slot($slot:ident),
@type_name($t:path),
@munch_fields($(,)?),
@acc($($acc:tt)*),
) => {
// Endpoint, nothing more to munch, create the initializer.
// Since we are in the closure that is never called, this will never get executed.
// We abuse `slot` to get the correct type inference here:
unsafe {
// Here we abuse `paste!` to retokenize `$t`. Declarative macros have some internal
// information that is associated to already parsed fragments, so a path fragment
// cannot be used in this position. Doing the retokenization results in valid rust
// code.
::kernel::macros::paste!(
::core::ptr::write($slot, $t {
$($acc)*
});
);
}
};
(make_initializer:
@slot($slot:ident),
@type_name($t:path),
@munch_fields($field:ident <- $val:expr, $($rest:tt)*),
@acc($($acc:tt)*),
) => {
$crate::__init_internal!(make_initializer:
@slot($slot),
@type_name($t),
@munch_fields($($rest)*),
@acc($($acc)* $field: ::core::panic!(),),
);
};
(make_initializer:
@slot($slot:ident),
@type_name($t:path),
@munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
@acc($($acc:tt)*),
) => {
$crate::__init_internal!(make_initializer:
@slot($slot),
@type_name($t),
@munch_fields($($rest)*),
@acc($($acc)* $field: ::core::panic!(),),
);
};
}
#[doc(hidden)]
#[macro_export]
macro_rules! __derive_zeroable {
(parse_input:
@sig(
$(#[$($struct_attr:tt)*])*
$vis:vis struct $name:ident
$(where $($whr:tt)*)?
),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@body({
$(
$(#[$($field_attr:tt)*])*
$field:ident : $field_ty:ty
),* $(,)?
}),
) => {
// SAFETY: Every field type implements `Zeroable` and padding bytes may be zero.
#[automatically_derived]
unsafe impl<$($impl_generics)*> $crate::init::Zeroable for $name<$($ty_generics)*>
where
$($($whr)*)?
{}
const _: () = {
fn assert_zeroable<T: ?::core::marker::Sized + $crate::init::Zeroable>() {}
fn ensure_zeroable<$($impl_generics)*>()
where $($($whr)*)?
{
$(assert_zeroable::<$field_ty>();)*
}
};
};
}
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