rust/kernel/init/macros.rs

   1 // SPDX-License-Identifier: Apache-2.0 OR MIT
   2
   3 //! This module provides the macros that actually implement the proc-macros `pin_data` and
   4 //! `pinned_drop`. It also contains `__init_internal` the implementation of the `{try_}{pin_}init!`
   5 //! macros.
   6 //!
   7 //! These macros should never be called directly, since they expect their input to be
   8 //! in a certain format which is internal. If used incorrectly, these macros can lead to UB even in
   9 //! safe code! Use the public facing macros instead.
  10 //!
  11 //! This architecture has been chosen because the kernel does not yet have access to `syn` which
  12 //! would make matters a lot easier for implementing these as proc-macros.
  13 //!
  14 //! # Macro expansion example
  15 //!
  16 //! This section is intended for readers trying to understand the macros in this module and the
  17 //! `pin_init!` macros from `init.rs`.
  18 //!
  19 //! We will look at the following example:
  20 //!
  21 //! ```rust,ignore
  22 //! # use kernel::init::*;
  23 //! # use core::pin::Pin;
  24 //! #[pin_data]
  25 //! #[repr(C)]
  26 //! struct Bar<T> {
  27 //!     #[pin]
  28 //!     t: T,
  29 //!     pub x: usize,
  30 //! }
  31 //!
  32 //! impl<T> Bar<T> {
  33 //!     fn new(t: T) -> impl PinInit<Self> {
  34 //!         pin_init!(Self { t, x: 0 })
  35 //!     }
  36 //! }
  37 //!
  38 //! #[pin_data(PinnedDrop)]
  39 //! struct Foo {
  40 //!     a: usize,
  41 //!     #[pin]
  42 //!     b: Bar<u32>,
  43 //! }
  44 //!
  45 //! #[pinned_drop]
  46 //! impl PinnedDrop for Foo {
  47 //!     fn drop(self: Pin<&mut Self>) {
  48 //!         pr_info!("{self:p} is getting dropped.");
  49 //!     }
  50 //! }
  51 //!
  52 //! let a = 42;
  53 //! let initializer = pin_init!(Foo {
  54 //!     a,
  55 //!     b <- Bar::new(36),
  56 //! });
  57 //! ```
  58 //!
  59 //! This example includes the most common and important features of the pin-init API.
  60 //!
  61 //! Below you can find individual section about the different macro invocations. Here are some
  62 //! general things we need to take into account when designing macros:
  63 //! - use global paths, similarly to file paths, these start with the separator: `::core::panic!()`
  64 //!   this ensures that the correct item is used, since users could define their own `mod core {}`
  65 //!   and then their own `panic!` inside to execute arbitrary code inside of our macro.
  66 //! - macro `unsafe` hygiene: we need to ensure that we do not expand arbitrary, user-supplied
  67 //!   expressions inside of an `unsafe` block in the macro, because this would allow users to do
  68 //!   `unsafe` operations without an associated `unsafe` block.
  69 //!
  70 //! ## `#[pin_data]` on `Bar`
  71 //!
  72 //! This macro is used to specify which fields are structurally pinned and which fields are not. It
  73 //! is placed on the struct definition and allows `#[pin]` to be placed on the fields.
  74 //!
  75 //! Here is the definition of `Bar` from our example:
  76 //!
  77 //! ```rust,ignore
  78 //! # use kernel::init::*;
  79 //! #[pin_data]
  80 //! #[repr(C)]
  81 //! struct Bar<T> {
  82 //!     #[pin]
  83 //!     t: T,
  84 //!     pub x: usize,
  85 //! }
  86 //! ```
  87 //!
  88 //! This expands to the following code:
  89 //!
  90 //! ```rust,ignore
  91 //! // Firstly the normal definition of the struct, attributes are preserved:
  92 //! #[repr(C)]
  93 //! struct Bar<T> {
  94 //!     t: T,
  95 //!     pub x: usize,
  96 //! }
  97 //! // Then an anonymous constant is defined, this is because we do not want any code to access the
  98 //! // types that we define inside:
  99 //! const _: () = {
 100 //!     // We define the pin-data carrying struct, it is a ZST and needs to have the same generics,
 101 //!     // since we need to implement access functions for each field and thus need to know its
 102 //!     // type.
 103 //!     struct __ThePinData<T> {
 104 //!         __phantom: ::core::marker::PhantomData<fn(Bar<T>) -> Bar<T>>,
 105 //!     }
 106 //!     // We implement `Copy` for the pin-data struct, since all functions it defines will take
 107 //!     // `self` by value.
 108 //!     impl<T> ::core::clone::Clone for __ThePinData<T> {
 109 //!         fn clone(&self) -> Self {
 110 //!             *self
 111 //!         }
 112 //!     }
 113 //!     impl<T> ::core::marker::Copy for __ThePinData<T> {}
 114 //!     // For every field of `Bar`, the pin-data struct will define a function with the same name
 115 //!     // and accessor (`pub` or `pub(crate)` etc.). This function will take a pointer to the
 116 //!     // field (`slot`) and a `PinInit` or `Init` depending on the projection kind of the field
 117 //!     // (if pinning is structural for the field, then `PinInit` otherwise `Init`).
 118 //!     #[allow(dead_code)]
 119 //!     impl<T> __ThePinData<T> {
 120 //!         unsafe fn t<E>(
 121 //!             self,
 122 //!             slot: *mut T,
 123 //!             // Since `t` is `#[pin]`, this is `PinInit`.
 124 //!             init: impl ::kernel::init::PinInit<T, E>,
 125 //!         ) -> ::core::result::Result<(), E> {
 126 //!             unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
 127 //!         }
 128 //!         pub unsafe fn x<E>(
 129 //!             self,
 130 //!             slot: *mut usize,
 131 //!             // Since `x` is not `#[pin]`, this is `Init`.
 132 //!             init: impl ::kernel::init::Init<usize, E>,
 133 //!         ) -> ::core::result::Result<(), E> {
 134 //!             unsafe { ::kernel::init::Init::__init(init, slot) }
 135 //!         }
 136 //!     }
 137 //!     // Implement the internal `HasPinData` trait that associates `Bar` with the pin-data struct
 138 //!     // that we constructed above.
 139 //!     unsafe impl<T> ::kernel::init::__internal::HasPinData for Bar<T> {
 140 //!         type PinData = __ThePinData<T>;
 141 //!         unsafe fn __pin_data() -> Self::PinData {
 142 //!             __ThePinData {
 143 //!                 __phantom: ::core::marker::PhantomData,
 144 //!             }
 145 //!         }
 146 //!     }
 147 //!     // Implement the internal `PinData` trait that marks the pin-data struct as a pin-data
 148 //!     // struct. This is important to ensure that no user can implement a rouge `__pin_data`
 149 //!     // function without using `unsafe`.
 150 //!     unsafe impl<T> ::kernel::init::__internal::PinData for __ThePinData<T> {
 151 //!         type Datee = Bar<T>;
 152 //!     }
 153 //!     // Now we only want to implement `Unpin` for `Bar` when every structurally pinned field is
 154 //!     // `Unpin`. In other words, whether `Bar` is `Unpin` only depends on structurally pinned
 155 //!     // fields (those marked with `#[pin]`). These fields will be listed in this struct, in our
 156 //!     // case no such fields exist, hence this is almost empty. The two phantomdata fields exist
 157 //!     // for two reasons:
 158 //!     // - `__phantom`: every generic must be used, since we cannot really know which generics
 159 //!     //   are used, we declere all and then use everything here once.
 160 //!     // - `__phantom_pin`: uses the `'__pin` lifetime and ensures that this struct is invariant
 161 //!     //   over it. The lifetime is needed to work around the limitation that trait bounds must
 162 //!     //   not be trivial, e.g. the user has a `#[pin] PhantomPinned` field -- this is
 163 //!     //   unconditionally `!Unpin` and results in an error. The lifetime tricks the compiler
 164 //!     //   into accepting these bounds regardless.
 165 //!     #[allow(dead_code)]
 166 //!     struct __Unpin<'__pin, T> {
 167 //!         __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
 168 //!         __phantom: ::core::marker::PhantomData<fn(Bar<T>) -> Bar<T>>,
 169 //!         // Our only `#[pin]` field is `t`.
 170 //!         t: T,
 171 //!     }
 172 //!     #[doc(hidden)]
 173 //!     impl<'__pin, T> ::core::marker::Unpin for Bar<T>
 174 //!     where
 175 //!         __Unpin<'__pin, T>: ::core::marker::Unpin,
 176 //!     {}
 177 //!     // Now we need to ensure that `Bar` does not implement `Drop`, since that would give users
 178 //!     // access to `&mut self` inside of `drop` even if the struct was pinned. This could lead to
 179 //!     // UB with only safe code, so we disallow this by giving a trait implementation error using
 180 //!     // a direct impl and a blanket implementation.
 181 //!     trait MustNotImplDrop {}
 182 //!     // Normally `Drop` bounds do not have the correct semantics, but for this purpose they do
 183 //!     // (normally people want to know if a type has any kind of drop glue at all, here we want
 184 //!     // to know if it has any kind of custom drop glue, which is exactly what this bound does).
 185 //!     #[allow(drop_bounds)]
 186 //!     impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
 187 //!     impl<T> MustNotImplDrop for Bar<T> {}
 188 //!     // Here comes a convenience check, if one implemented `PinnedDrop`, but forgot to add it to
 189 //!     // `#[pin_data]`, then this will error with the same mechanic as above, this is not needed
 190 //!     // for safety, but a good sanity check, since no normal code calls `PinnedDrop::drop`.
 191 //!     #[allow(non_camel_case_types)]
 192 //!     trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
 193 //!     impl<
 194 //!         T: ::kernel::init::PinnedDrop,
 195 //!     > UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
 196 //!     impl<T> UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for Bar<T> {}
 197 //! };
 198 //! ```
 199 //!
 200 //! ## `pin_init!` in `impl Bar`
 201 //!
 202 //! This macro creates an pin-initializer for the given struct. It requires that the struct is
 203 //! annotated by `#[pin_data]`.
 204 //!
 205 //! Here is the impl on `Bar` defining the new function:
 206 //!
 207 //! ```rust,ignore
 208 //! impl<T> Bar<T> {
 209 //!     fn new(t: T) -> impl PinInit<Self> {
 210 //!         pin_init!(Self { t, x: 0 })
 211 //!     }
 212 //! }
 213 //! ```
 214 //!
 215 //! This expands to the following code:
 216 //!
 217 //! ```rust,ignore
 218 //! impl<T> Bar<T> {
 219 //!     fn new(t: T) -> impl PinInit<Self> {
 220 //!         {
 221 //!             // We do not want to allow arbitrary returns, so we declare this type as the `Ok`
 222 //!             // return type and shadow it later when we insert the arbitrary user code. That way
 223 //!             // there will be no possibility of returning without `unsafe`.
 224 //!             struct __InitOk;
 225 //!             // Get the data about fields from the supplied type.
 226 //!             // - the function is unsafe, hence the unsafe block
 227 //!             // - we `use` the `HasPinData` trait in the block, it is only available in that
 228 //!             //   scope.
 229 //!             let data = unsafe {
 230 //!                 use ::kernel::init::__internal::HasPinData;
 231 //!                 Self::__pin_data()
 232 //!             };
 233 //!             // Ensure that `data` really is of type `PinData` and help with type inference:
 234 //!             let init = ::kernel::init::__internal::PinData::make_closure::<
 235 //!                 _,
 236 //!                 __InitOk,
 237 //!                 ::core::convert::Infallible,
 238 //!             >(data, move |slot| {
 239 //!                 {
 240 //!                     // Shadow the structure so it cannot be used to return early. If a user
 241 //!                     // tries to write `return Ok(__InitOk)`, then they get a type error,
 242 //!                     // since that will refer to this struct instead of the one defined
 243 //!                     // above.
 244 //!                     struct __InitOk;
 245 //!                     // This is the expansion of `t,`, which is syntactic sugar for `t: t,`.
 246 //!                     {
 247 //!                         unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).t), t) };
 248 //!                     }
 249 //!                     // Since initialization could fail later (not in this case, since the
 250 //!                     // error type is `Infallible`) we will need to drop this field if there
 251 //!                     // is an error later. This `DropGuard` will drop the field when it gets
 252 //!                     // dropped and has not yet been forgotten.
 253 //!                     let t = unsafe {
 254 //!                         ::pinned_init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).t))
 255 //!                     };
 256 //!                     // Expansion of `x: 0,`:
 257 //!                     // Since this can be an arbitrary expression we cannot place it inside
 258 //!                     // of the `unsafe` block, so we bind it here.
 259 //!                     {
 260 //!                         let x = 0;
 261 //!                         unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).x), x) };
 262 //!                     }
 263 //!                     // We again create a `DropGuard`.
 264 //!                     let x = unsafe {
 265 //!                         ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).x))
 266 //!                     };
 267 //!                     // Since initialization has successfully completed, we can now forget
 268 //!                     // the guards. This is not `mem::forget`, since we only have
 269 //!                     // `&DropGuard`.
 270 //!                     ::core::mem::forget(x);
 271 //!                     ::core::mem::forget(t);
 272 //!                     // Here we use the type checker to ensure that every field has been
 273 //!                     // initialized exactly once, since this is `if false` it will never get
 274 //!                     // executed, but still type-checked.
 275 //!                     // Additionally we abuse `slot` to automatically infer the correct type
 276 //!                     // for the struct. This is also another check that every field is
 277 //!                     // accessible from this scope.
 278 //!                     #[allow(unreachable_code, clippy::diverging_sub_expression)]
 279 //!                     let _ = || {
 280 //!                         unsafe {
 281 //!                             ::core::ptr::write(
 282 //!                                 slot,
 283 //!                                 Self {
 284 //!                                     // We only care about typecheck finding every field
 285 //!                                     // here, the expression does not matter, just conjure
 286 //!                                     // one using `panic!()`:
 287 //!                                     t: ::core::panic!(),
 288 //!                                     x: ::core::panic!(),
 289 //!                                 },
 290 //!                             );
 291 //!                         };
 292 //!                     };
 293 //!                 }
 294 //!                 // We leave the scope above and gain access to the previously shadowed
 295 //!                 // `__InitOk` that we need to return.
 296 //!                 Ok(__InitOk)
 297 //!             });
 298 //!             // Change the return type from `__InitOk` to `()`.
 299 //!             let init = move |
 300 //!                 slot,
 301 //!             | -> ::core::result::Result<(), ::core::convert::Infallible> {
 302 //!                 init(slot).map(|__InitOk| ())
 303 //!             };
 304 //!             // Construct the initializer.
 305 //!             let init = unsafe {
 306 //!                 ::kernel::init::pin_init_from_closure::<
 307 //!                     _,
 308 //!                     ::core::convert::Infallible,
 309 //!                 >(init)
 310 //!             };
 311 //!             init
 312 //!         }
 313 //!     }
 314 //! }
 315 //! ```
 316 //!
 317 //! ## `#[pin_data]` on `Foo`
 318 //!
 319 //! Since we already took a look at `#[pin_data]` on `Bar`, this section will only explain the
 320 //! differences/new things in the expansion of the `Foo` definition:
 321 //!
 322 //! ```rust,ignore
 323 //! #[pin_data(PinnedDrop)]
 324 //! struct Foo {
 325 //!     a: usize,
 326 //!     #[pin]
 327 //!     b: Bar<u32>,
 328 //! }
 329 //! ```
 330 //!
 331 //! This expands to the following code:
 332 //!
 333 //! ```rust,ignore
 334 //! struct Foo {
 335 //!     a: usize,
 336 //!     b: Bar<u32>,
 337 //! }
 338 //! const _: () = {
 339 //!     struct __ThePinData {
 340 //!         __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
 341 //!     }
 342 //!     impl ::core::clone::Clone for __ThePinData {
 343 //!         fn clone(&self) -> Self {
 344 //!             *self
 345 //!         }
 346 //!     }
 347 //!     impl ::core::marker::Copy for __ThePinData {}
 348 //!     #[allow(dead_code)]
 349 //!     impl __ThePinData {
 350 //!         unsafe fn b<E>(
 351 //!             self,
 352 //!             slot: *mut Bar<u32>,
 353 //!             init: impl ::kernel::init::PinInit<Bar<u32>, E>,
 354 //!         ) -> ::core::result::Result<(), E> {
 355 //!             unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
 356 //!         }
 357 //!         unsafe fn a<E>(
 358 //!             self,
 359 //!             slot: *mut usize,
 360 //!             init: impl ::kernel::init::Init<usize, E>,
 361 //!         ) -> ::core::result::Result<(), E> {
 362 //!             unsafe { ::kernel::init::Init::__init(init, slot) }
 363 //!         }
 364 //!     }
 365 //!     unsafe impl ::kernel::init::__internal::HasPinData for Foo {
 366 //!         type PinData = __ThePinData;
 367 //!         unsafe fn __pin_data() -> Self::PinData {
 368 //!             __ThePinData {
 369 //!                 __phantom: ::core::marker::PhantomData,
 370 //!             }
 371 //!         }
 372 //!     }
 373 //!     unsafe impl ::kernel::init::__internal::PinData for __ThePinData {
 374 //!         type Datee = Foo;
 375 //!     }
 376 //!     #[allow(dead_code)]
 377 //!     struct __Unpin<'__pin> {
 378 //!         __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
 379 //!         __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
 380 //!         b: Bar<u32>,
 381 //!     }
 382 //!     #[doc(hidden)]
 383 //!     impl<'__pin> ::core::marker::Unpin for Foo
 384 //!     where
 385 //!         __Unpin<'__pin>: ::core::marker::Unpin,
 386 //!     {}
 387 //!     // Since we specified `PinnedDrop` as the argument to `#[pin_data]`, we expect `Foo` to
 388 //!     // implement `PinnedDrop`. Thus we do not need to prevent `Drop` implementations like
 389 //!     // before, instead we implement `Drop` here and delegate to `PinnedDrop`.
 390 //!     impl ::core::ops::Drop for Foo {
 391 //!         fn drop(&mut self) {
 392 //!             // Since we are getting dropped, no one else has a reference to `self` and thus we
 393 //!             // can assume that we never move.
 394 //!             let pinned = unsafe { ::core::pin::Pin::new_unchecked(self) };
 395 //!             // Create the unsafe token that proves that we are inside of a destructor, this
 396 //!             // type is only allowed to be created in a destructor.
 397 //!             let token = unsafe { ::kernel::init::__internal::OnlyCallFromDrop::new() };
 398 //!             ::kernel::init::PinnedDrop::drop(pinned, token);
 399 //!         }
 400 //!     }
 401 //! };
 402 //! ```
 403 //!
 404 //! ## `#[pinned_drop]` on `impl PinnedDrop for Foo`
 405 //!
 406 //! This macro is used to implement the `PinnedDrop` trait, since that trait is `unsafe` and has an
 407 //! extra parameter that should not be used at all. The macro hides that parameter.
 408 //!
 409 //! Here is the `PinnedDrop` impl for `Foo`:
 410 //!
 411 //! ```rust,ignore
 412 //! #[pinned_drop]
 413 //! impl PinnedDrop for Foo {
 414 //!     fn drop(self: Pin<&mut Self>) {
 415 //!         pr_info!("{self:p} is getting dropped.");
 416 //!     }
 417 //! }
 418 //! ```
 419 //!
 420 //! This expands to the following code:
 421 //!
 422 //! ```rust,ignore
 423 //! // `unsafe`, full path and the token parameter are added, everything else stays the same.
 424 //! unsafe impl ::kernel::init::PinnedDrop for Foo {
 425 //!     fn drop(self: Pin<&mut Self>, _: ::kernel::init::__internal::OnlyCallFromDrop) {
 426 //!         pr_info!("{self:p} is getting dropped.");
 427 //!     }
 428 //! }
 429 //! ```
 430 //!
 431 //! ## `pin_init!` on `Foo`
 432 //!
 433 //! Since we already took a look at `pin_init!` on `Bar`, this section will only show the expansion
 434 //! of `pin_init!` on `Foo`:
 435 //!
 436 //! ```rust,ignore
 437 //! let a = 42;
 438 //! let initializer = pin_init!(Foo {
 439 //!     a,
 440 //!     b <- Bar::new(36),
 441 //! });
 442 //! ```
 443 //!
 444 //! This expands to the following code:
 445 //!
 446 //! ```rust,ignore
 447 //! let a = 42;
 448 //! let initializer = {
 449 //!     struct __InitOk;
 450 //!     let data = unsafe {
 451 //!         use ::kernel::init::__internal::HasPinData;
 452 //!         Foo::__pin_data()
 453 //!     };
 454 //!     let init = ::kernel::init::__internal::PinData::make_closure::<
 455 //!         _,
 456 //!         __InitOk,
 457 //!         ::core::convert::Infallible,
 458 //!     >(data, move |slot| {
 459 //!         {
 460 //!             struct __InitOk;
 461 //!             {
 462 //!                 unsafe { ::core::ptr::write(::core::addr_of_mut!((*slot).a), a) };
 463 //!             }
 464 //!             let a = unsafe {
 465 //!                 ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).a))
 466 //!             };
 467 //!             let init = Bar::new(36);
 468 //!             unsafe { data.b(::core::addr_of_mut!((*slot).b), b)? };
 469 //!             let b = unsafe {
 470 //!                 ::kernel::init::__internal::DropGuard::new(::core::addr_of_mut!((*slot).b))
 471 //!             };
 472 //!             ::core::mem::forget(b);
 473 //!             ::core::mem::forget(a);
 474 //!             #[allow(unreachable_code, clippy::diverging_sub_expression)]
 475 //!             let _ = || {
 476 //!                 unsafe {
 477 //!                     ::core::ptr::write(
 478 //!                         slot,
 479 //!                         Foo {
 480 //!                             a: ::core::panic!(),
 481 //!                             b: ::core::panic!(),
 482 //!                         },
 483 //!                     );
 484 //!                 };
 485 //!             };
 486 //!         }
 487 //!         Ok(__InitOk)
 488 //!     });
 489 //!     let init = move |
 490 //!         slot,
 491 //!     | -> ::core::result::Result<(), ::core::convert::Infallible> {
 492 //!         init(slot).map(|__InitOk| ())
 493 //!     };
 494 //!     let init = unsafe {
 495 //!         ::kernel::init::pin_init_from_closure::<_, ::core::convert::Infallible>(init)
 496 //!     };
 497 //!     init
 498 //! };
 499 //! ```
 500
 501 /// Creates a `unsafe impl<...> PinnedDrop for $type` block.
 502 ///
 503 /// See [`PinnedDrop`] for more information.
 504 #[doc(hidden)]
 505 #[macro_export]
 506 macro_rules! __pinned_drop {
 507     (
 508         @impl_sig($($impl_sig:tt)*),
 509         @impl_body(
 510             $(#[$($attr:tt)*])*
 511             fn drop($($sig:tt)*) {
 512                 $($inner:tt)*
 513             }
 514         ),
 515     ) => {
 516         unsafe $($impl_sig)* {
 517             // Inherit all attributes and the type/ident tokens for the signature.
 518             $(#[$($attr)*])*
 519             fn drop($($sig)*, _: $crate::init::__internal::OnlyCallFromDrop) {
 520                 $($inner)*
 521             }
 522         }
 523     }
 524 }
 525
 526 /// This macro first parses the struct definition such that it separates pinned and not pinned
 527 /// fields. Afterwards it declares the struct and implement the `PinData` trait safely.
 528 #[doc(hidden)]
 529 #[macro_export]
 530 macro_rules! __pin_data {
 531     // Proc-macro entry point, this is supplied by the proc-macro pre-parsing.
 532     (parse_input:
 533         @args($($pinned_drop:ident)?),
 534         @sig(
 535             $(#[$($struct_attr:tt)*])*
 536             $vis:vis struct $name:ident
 537             $(where $($whr:tt)*)?
 538         ),
 539         @impl_generics($($impl_generics:tt)*),
 540         @ty_generics($($ty_generics:tt)*),
 541         @body({ $($fields:tt)* }),
 542     ) => {
 543         // We now use token munching to iterate through all of the fields. While doing this we
 544         // identify fields marked with `#[pin]`, these fields are the 'pinned fields'. The user
 545         // wants these to be structurally pinned. The rest of the fields are the
 546         // 'not pinned fields'. Additionally we collect all fields, since we need them in the right
 547         // order to declare the struct.
 548         //
 549         // In this call we also put some explaining comments for the parameters.
 550         $crate::__pin_data!(find_pinned_fields:
 551             // Attributes on the struct itself, these will just be propagated to be put onto the
 552             // struct definition.
 553             @struct_attrs($(#[$($struct_attr)*])*),
 554             // The visibility of the struct.
 555             @vis($vis),
 556             // The name of the struct.
 557             @name($name),
 558             // The 'impl generics', the generics that will need to be specified on the struct inside
 559             // of an `impl<$ty_generics>` block.
 560             @impl_generics($($impl_generics)*),
 561             // The 'ty generics', the generics that will need to be specified on the impl blocks.
 562             @ty_generics($($ty_generics)*),
 563             // The where clause of any impl block and the declaration.
 564             @where($($($whr)*)?),
 565             // The remaining fields tokens that need to be processed.
 566             // We add a `,` at the end to ensure correct parsing.
 567             @fields_munch($($fields)* ,),
 568             // The pinned fields.
 569             @pinned(),
 570             // The not pinned fields.
 571             @not_pinned(),
 572             // All fields.
 573             @fields(),
 574             // The accumulator containing all attributes already parsed.
 575             @accum(),
 576             // Contains `yes` or `` to indicate if `#[pin]` was found on the current field.
 577             @is_pinned(),
 578             // The proc-macro argument, this should be `PinnedDrop` or ``.
 579             @pinned_drop($($pinned_drop)?),
 580         );
 581     };
 582     (find_pinned_fields:
 583         @struct_attrs($($struct_attrs:tt)*),
 584         @vis($vis:vis),
 585         @name($name:ident),
 586         @impl_generics($($impl_generics:tt)*),
 587         @ty_generics($($ty_generics:tt)*),
 588         @where($($whr:tt)*),
 589         // We found a PhantomPinned field, this should generally be pinned!
 590         @fields_munch($field:ident : $($($(::)?core::)?marker::)?PhantomPinned, $($rest:tt)*),
 591         @pinned($($pinned:tt)*),
 592         @not_pinned($($not_pinned:tt)*),
 593         @fields($($fields:tt)*),
 594         @accum($($accum:tt)*),
 595         // This field is not pinned.
 596         @is_pinned(),
 597         @pinned_drop($($pinned_drop:ident)?),
 598     ) => {
 599         ::core::compile_error!(concat!(
 600             "The field `",
 601             stringify!($field),
 602             "` of type `PhantomPinned` only has an effect, if it has the `#[pin]` attribute.",
 603         ));
 604         $crate::__pin_data!(find_pinned_fields:
 605             @struct_attrs($($struct_attrs)*),
 606             @vis($vis),
 607             @name($name),
 608             @impl_generics($($impl_generics)*),
 609             @ty_generics($($ty_generics)*),
 610             @where($($whr)*),
 611             @fields_munch($($rest)*),
 612             @pinned($($pinned)* $($accum)* $field: ::core::marker::PhantomPinned,),
 613             @not_pinned($($not_pinned)*),
 614             @fields($($fields)* $($accum)* $field: ::core::marker::PhantomPinned,),
 615             @accum(),
 616             @is_pinned(),
 617             @pinned_drop($($pinned_drop)?),
 618         );
 619     };
 620     (find_pinned_fields:
 621         @struct_attrs($($struct_attrs:tt)*),
 622         @vis($vis:vis),
 623         @name($name:ident),
 624         @impl_generics($($impl_generics:tt)*),
 625         @ty_generics($($ty_generics:tt)*),
 626         @where($($whr:tt)*),
 627         // We reached the field declaration.
 628         @fields_munch($field:ident : $type:ty, $($rest:tt)*),
 629         @pinned($($pinned:tt)*),
 630         @not_pinned($($not_pinned:tt)*),
 631         @fields($($fields:tt)*),
 632         @accum($($accum:tt)*),
 633         // This field is pinned.
 634         @is_pinned(yes),
 635         @pinned_drop($($pinned_drop:ident)?),
 636     ) => {
 637         $crate::__pin_data!(find_pinned_fields:
 638             @struct_attrs($($struct_attrs)*),
 639             @vis($vis),
 640             @name($name),
 641             @impl_generics($($impl_generics)*),
 642             @ty_generics($($ty_generics)*),
 643             @where($($whr)*),
 644             @fields_munch($($rest)*),
 645             @pinned($($pinned)* $($accum)* $field: $type,),
 646             @not_pinned($($not_pinned)*),
 647             @fields($($fields)* $($accum)* $field: $type,),
 648             @accum(),
 649             @is_pinned(),
 650             @pinned_drop($($pinned_drop)?),
 651         );
 652     };
 653     (find_pinned_fields:
 654         @struct_attrs($($struct_attrs:tt)*),
 655         @vis($vis:vis),
 656         @name($name:ident),
 657         @impl_generics($($impl_generics:tt)*),
 658         @ty_generics($($ty_generics:tt)*),
 659         @where($($whr:tt)*),
 660         // We reached the field declaration.
 661         @fields_munch($field:ident : $type:ty, $($rest:tt)*),
 662         @pinned($($pinned:tt)*),
 663         @not_pinned($($not_pinned:tt)*),
 664         @fields($($fields:tt)*),
 665         @accum($($accum:tt)*),
 666         // This field is not pinned.
 667         @is_pinned(),
 668         @pinned_drop($($pinned_drop:ident)?),
 669     ) => {
 670         $crate::__pin_data!(find_pinned_fields:
 671             @struct_attrs($($struct_attrs)*),
 672             @vis($vis),
 673             @name($name),
 674             @impl_generics($($impl_generics)*),
 675             @ty_generics($($ty_generics)*),
 676             @where($($whr)*),
 677             @fields_munch($($rest)*),
 678             @pinned($($pinned)*),
 679             @not_pinned($($not_pinned)* $($accum)* $field: $type,),
 680             @fields($($fields)* $($accum)* $field: $type,),
 681             @accum(),
 682             @is_pinned(),
 683             @pinned_drop($($pinned_drop)?),
 684         );
 685     };
 686     (find_pinned_fields:
 687         @struct_attrs($($struct_attrs:tt)*),
 688         @vis($vis:vis),
 689         @name($name:ident),
 690         @impl_generics($($impl_generics:tt)*),
 691         @ty_generics($($ty_generics:tt)*),
 692         @where($($whr:tt)*),
 693         // We found the `#[pin]` attr.
 694         @fields_munch(#[pin] $($rest:tt)*),
 695         @pinned($($pinned:tt)*),
 696         @not_pinned($($not_pinned:tt)*),
 697         @fields($($fields:tt)*),
 698         @accum($($accum:tt)*),
 699         @is_pinned($($is_pinned:ident)?),
 700         @pinned_drop($($pinned_drop:ident)?),
 701     ) => {
 702         $crate::__pin_data!(find_pinned_fields:
 703             @struct_attrs($($struct_attrs)*),
 704             @vis($vis),
 705             @name($name),
 706             @impl_generics($($impl_generics)*),
 707             @ty_generics($($ty_generics)*),
 708             @where($($whr)*),
 709             @fields_munch($($rest)*),
 710             // We do not include `#[pin]` in the list of attributes, since it is not actually an
 711             // attribute that is defined somewhere.
 712             @pinned($($pinned)*),
 713             @not_pinned($($not_pinned)*),
 714             @fields($($fields)*),
 715             @accum($($accum)*),
 716             // Set this to `yes`.
 717             @is_pinned(yes),
 718             @pinned_drop($($pinned_drop)?),
 719         );
 720     };
 721     (find_pinned_fields:
 722         @struct_attrs($($struct_attrs:tt)*),
 723         @vis($vis:vis),
 724         @name($name:ident),
 725         @impl_generics($($impl_generics:tt)*),
 726         @ty_generics($($ty_generics:tt)*),
 727         @where($($whr:tt)*),
 728         // We reached the field declaration with visibility, for simplicity we only munch the
 729         // visibility and put it into `$accum`.
 730         @fields_munch($fvis:vis $field:ident $($rest:tt)*),
 731         @pinned($($pinned:tt)*),
 732         @not_pinned($($not_pinned:tt)*),
 733         @fields($($fields:tt)*),
 734         @accum($($accum:tt)*),
 735         @is_pinned($($is_pinned:ident)?),
 736         @pinned_drop($($pinned_drop:ident)?),
 737     ) => {
 738         $crate::__pin_data!(find_pinned_fields:
 739             @struct_attrs($($struct_attrs)*),
 740             @vis($vis),
 741             @name($name),
 742             @impl_generics($($impl_generics)*),
 743             @ty_generics($($ty_generics)*),
 744             @where($($whr)*),
 745             @fields_munch($field $($rest)*),
 746             @pinned($($pinned)*),
 747             @not_pinned($($not_pinned)*),
 748             @fields($($fields)*),
 749             @accum($($accum)* $fvis),
 750             @is_pinned($($is_pinned)?),
 751             @pinned_drop($($pinned_drop)?),
 752         );
 753     };
 754     (find_pinned_fields:
 755         @struct_attrs($($struct_attrs:tt)*),
 756         @vis($vis:vis),
 757         @name($name:ident),
 758         @impl_generics($($impl_generics:tt)*),
 759         @ty_generics($($ty_generics:tt)*),
 760         @where($($whr:tt)*),
 761         // Some other attribute, just put it into `$accum`.
 762         @fields_munch(#[$($attr:tt)*] $($rest:tt)*),
 763         @pinned($($pinned:tt)*),
 764         @not_pinned($($not_pinned:tt)*),
 765         @fields($($fields:tt)*),
 766         @accum($($accum:tt)*),
 767         @is_pinned($($is_pinned:ident)?),
 768         @pinned_drop($($pinned_drop:ident)?),
 769     ) => {
 770         $crate::__pin_data!(find_pinned_fields:
 771             @struct_attrs($($struct_attrs)*),
 772             @vis($vis),
 773             @name($name),
 774             @impl_generics($($impl_generics)*),
 775             @ty_generics($($ty_generics)*),
 776             @where($($whr)*),
 777             @fields_munch($($rest)*),
 778             @pinned($($pinned)*),
 779             @not_pinned($($not_pinned)*),
 780             @fields($($fields)*),
 781             @accum($($accum)* #[$($attr)*]),
 782             @is_pinned($($is_pinned)?),
 783             @pinned_drop($($pinned_drop)?),
 784         );
 785     };
 786     (find_pinned_fields:
 787         @struct_attrs($($struct_attrs:tt)*),
 788         @vis($vis:vis),
 789         @name($name:ident),
 790         @impl_generics($($impl_generics:tt)*),
 791         @ty_generics($($ty_generics:tt)*),
 792         @where($($whr:tt)*),
 793         // We reached the end of the fields, plus an optional additional comma, since we added one
 794         // before and the user is also allowed to put a trailing comma.
 795         @fields_munch($(,)?),
 796         @pinned($($pinned:tt)*),
 797         @not_pinned($($not_pinned:tt)*),
 798         @fields($($fields:tt)*),
 799         @accum(),
 800         @is_pinned(),
 801         @pinned_drop($($pinned_drop:ident)?),
 802     ) => {
 803         // Declare the struct with all fields in the correct order.
 804         $($struct_attrs)*
 805         $vis struct $name <$($impl_generics)*>
 806         where $($whr)*
 807         {
 808             $($fields)*
 809         }
 810
 811         // We put the rest into this const item, because it then will not be accessible to anything
 812         // outside.
 813         const _: () = {
 814             // We declare this struct which will host all of the projection function for our type.
 815             // it will be invariant over all generic parameters which are inherited from the
 816             // struct.
 817             $vis struct __ThePinData<$($impl_generics)*>
 818             where $($whr)*
 819             {
 820                 __phantom: ::core::marker::PhantomData<
 821                     fn($name<$($ty_generics)*>) -> $name<$($ty_generics)*>
 822                 >,
 823             }
 824
 825             impl<$($impl_generics)*> ::core::clone::Clone for __ThePinData<$($ty_generics)*>
 826             where $($whr)*
 827             {
 828                 fn clone(&self) -> Self { *self }
 829             }
 830
 831             impl<$($impl_generics)*> ::core::marker::Copy for __ThePinData<$($ty_generics)*>
 832             where $($whr)*
 833             {}
 834
 835             // Make all projection functions.
 836             $crate::__pin_data!(make_pin_data:
 837                 @pin_data(__ThePinData),
 838                 @impl_generics($($impl_generics)*),
 839                 @ty_generics($($ty_generics)*),
 840                 @where($($whr)*),
 841                 @pinned($($pinned)*),
 842                 @not_pinned($($not_pinned)*),
 843             );
 844
 845             // SAFETY: We have added the correct projection functions above to `__ThePinData` and
 846             // we also use the least restrictive generics possible.
 847             unsafe impl<$($impl_generics)*>
 848                 $crate::init::__internal::HasPinData for $name<$($ty_generics)*>
 849             where $($whr)*
 850             {
 851                 type PinData = __ThePinData<$($ty_generics)*>;
 852
 853                 unsafe fn __pin_data() -> Self::PinData {
 854                     __ThePinData { __phantom: ::core::marker::PhantomData }
 855                 }
 856             }
 857
 858             unsafe impl<$($impl_generics)*>
 859                 $crate::init::__internal::PinData for __ThePinData<$($ty_generics)*>
 860             where $($whr)*
 861             {
 862                 type Datee = $name<$($ty_generics)*>;
 863             }
 864
 865             // This struct will be used for the unpin analysis. Since only structurally pinned
 866             // fields are relevant whether the struct should implement `Unpin`.
 867             #[allow(dead_code)]
 868             struct __Unpin <'__pin, $($impl_generics)*>
 869             where $($whr)*
 870             {
 871                 __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
 872                 __phantom: ::core::marker::PhantomData<
 873                     fn($name<$($ty_generics)*>) -> $name<$($ty_generics)*>
 874                 >,
 875                 // Only the pinned fields.
 876                 $($pinned)*
 877             }
 878
 879             #[doc(hidden)]
 880             impl<'__pin, $($impl_generics)*> ::core::marker::Unpin for $name<$($ty_generics)*>
 881             where
 882                 __Unpin<'__pin, $($ty_generics)*>: ::core::marker::Unpin,
 883                 $($whr)*
 884             {}
 885
 886             // We need to disallow normal `Drop` implementation, the exact behavior depends on
 887             // whether `PinnedDrop` was specified as the parameter.
 888             $crate::__pin_data!(drop_prevention:
 889                 @name($name),
 890                 @impl_generics($($impl_generics)*),
 891                 @ty_generics($($ty_generics)*),
 892                 @where($($whr)*),
 893                 @pinned_drop($($pinned_drop)?),
 894             );
 895         };
 896     };
 897     // When no `PinnedDrop` was specified, then we have to prevent implementing drop.
 898     (drop_prevention:
 899         @name($name:ident),
 900         @impl_generics($($impl_generics:tt)*),
 901         @ty_generics($($ty_generics:tt)*),
 902         @where($($whr:tt)*),
 903         @pinned_drop(),
 904     ) => {
 905         // We prevent this by creating a trait that will be implemented for all types implementing
 906         // `Drop`. Additionally we will implement this trait for the struct leading to a conflict,
 907         // if it also implements `Drop`
 908         trait MustNotImplDrop {}
 909         #[allow(drop_bounds)]
 910         impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
 911         impl<$($impl_generics)*> MustNotImplDrop for $name<$($ty_generics)*>
 912         where $($whr)* {}
 913         // We also take care to prevent users from writing a useless `PinnedDrop` implementation.
 914         // They might implement `PinnedDrop` correctly for the struct, but forget to give
 915         // `PinnedDrop` as the parameter to `#[pin_data]`.
 916         #[allow(non_camel_case_types)]
 917         trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
 918         impl<T: $crate::init::PinnedDrop>
 919             UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
 920         impl<$($impl_generics)*>
 921             UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for $name<$($ty_generics)*>
 922         where $($whr)* {}
 923     };
 924     // When `PinnedDrop` was specified we just implement `Drop` and delegate.
 925     (drop_prevention:
 926         @name($name:ident),
 927         @impl_generics($($impl_generics:tt)*),
 928         @ty_generics($($ty_generics:tt)*),
 929         @where($($whr:tt)*),
 930         @pinned_drop(PinnedDrop),
 931     ) => {
 932         impl<$($impl_generics)*> ::core::ops::Drop for $name<$($ty_generics)*>
 933         where $($whr)*
 934         {
 935             fn drop(&mut self) {
 936                 // SAFETY: Since this is a destructor, `self` will not move after this function
 937                 // terminates, since it is inaccessible.
 938                 let pinned = unsafe { ::core::pin::Pin::new_unchecked(self) };
 939                 // SAFETY: Since this is a drop function, we can create this token to call the
 940                 // pinned destructor of this type.
 941                 let token = unsafe { $crate::init::__internal::OnlyCallFromDrop::new() };
 942                 $crate::init::PinnedDrop::drop(pinned, token);
 943             }
 944         }
 945     };
 946     // If some other parameter was specified, we emit a readable error.
 947     (drop_prevention:
 948         @name($name:ident),
 949         @impl_generics($($impl_generics:tt)*),
 950         @ty_generics($($ty_generics:tt)*),
 951         @where($($whr:tt)*),
 952         @pinned_drop($($rest:tt)*),
 953     ) => {
 954         compile_error!(
 955             "Wrong parameters to `#[pin_data]`, expected nothing or `PinnedDrop`, got '{}'.",
 956             stringify!($($rest)*),
 957         );
 958     };
 959     (make_pin_data:
 960         @pin_data($pin_data:ident),
 961         @impl_generics($($impl_generics:tt)*),
 962         @ty_generics($($ty_generics:tt)*),
 963         @where($($whr:tt)*),
 964         @pinned($($(#[$($p_attr:tt)*])* $pvis:vis $p_field:ident : $p_type:ty),* $(,)?),
 965         @not_pinned($($(#[$($attr:tt)*])* $fvis:vis $field:ident : $type:ty),* $(,)?),
 966     ) => {
 967         // For every field, we create a projection function according to its projection type. If a
 968         // field is structurally pinned, then it must be initialized via `PinInit`, if it is not
 969         // structurally pinned, then it can be initialized via `Init`.
 970         //
 971         // The functions are `unsafe` to prevent accidentally calling them.
 972         #[allow(dead_code)]
 973         impl<$($impl_generics)*> $pin_data<$($ty_generics)*>
 974         where $($whr)*
 975         {
 976             $(
 977                 $(#[$($p_attr)*])*
 978                 $pvis unsafe fn $p_field<E>(
 979                     self,
 980                     slot: *mut $p_type,
 981                     init: impl $crate::init::PinInit<$p_type, E>,
 982                 ) -> ::core::result::Result<(), E> {
 983                     unsafe { $crate::init::PinInit::__pinned_init(init, slot) }
 984                 }
 985             )*
 986             $(
 987                 $(#[$($attr)*])*
 988                 $fvis unsafe fn $field<E>(
 989                     self,
 990                     slot: *mut $type,
 991                     init: impl $crate::init::Init<$type, E>,
 992                 ) -> ::core::result::Result<(), E> {
 993                     unsafe { $crate::init::Init::__init(init, slot) }
 994                 }
 995             )*
 996         }
 997     };
 998 }
 999
1000 /// The internal init macro. Do not call manually!
1001 ///
1002 /// This is called by the `{try_}{pin_}init!` macros with various inputs.
1003 ///
1004 /// This macro has multiple internal call configurations, these are always the very first ident:
1005 /// - nothing: this is the base case and called by the `{try_}{pin_}init!` macros.
1006 /// - `with_update_parsed`: when the `..Zeroable::zeroed()` syntax has been handled.
1007 /// - `init_slot`: recursively creates the code that initializes all fields in `slot`.
1008 /// - `make_initializer`: recursively create the struct initializer that guarantees that every
1009 ///   field has been initialized exactly once.
1010 #[doc(hidden)]
1011 #[macro_export]
1012 macro_rules! __init_internal {
1013     (
1014         @this($($this:ident)?),
1015         @typ($t:path),
1016         @fields($($fields:tt)*),
1017         @error($err:ty),
1018         // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
1019         // case.
1020         @data($data:ident, $($use_data:ident)?),
1021         // `HasPinData` or `HasInitData`.
1022         @has_data($has_data:ident, $get_data:ident),
1023         // `pin_init_from_closure` or `init_from_closure`.
1024         @construct_closure($construct_closure:ident),
1025         @munch_fields(),
1026     ) => {
1027         $crate::__init_internal!(with_update_parsed:
1028             @this($($this)?),
1029             @typ($t),
1030             @fields($($fields)*),
1031             @error($err),
1032             @data($data, $($use_data)?),
1033             @has_data($has_data, $get_data),
1034             @construct_closure($construct_closure),
1035             @zeroed(), // Nothing means default behavior.
1036         )
1037     };
1038     (
1039         @this($($this:ident)?),
1040         @typ($t:path),
1041         @fields($($fields:tt)*),
1042         @error($err:ty),
1043         // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
1044         // case.
1045         @data($data:ident, $($use_data:ident)?),
1046         // `HasPinData` or `HasInitData`.
1047         @has_data($has_data:ident, $get_data:ident),
1048         // `pin_init_from_closure` or `init_from_closure`.
1049         @construct_closure($construct_closure:ident),
1050         @munch_fields(..Zeroable::zeroed()),
1051     ) => {
1052         $crate::__init_internal!(with_update_parsed:
1053             @this($($this)?),
1054             @typ($t),
1055             @fields($($fields)*),
1056             @error($err),
1057             @data($data, $($use_data)?),
1058             @has_data($has_data, $get_data),
1059             @construct_closure($construct_closure),
1060             @zeroed(()), // `()` means zero all fields not mentioned.
1061         )
1062     };
1063     (
1064         @this($($this:ident)?),
1065         @typ($t:path),
1066         @fields($($fields:tt)*),
1067         @error($err:ty),
1068         // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
1069         // case.
1070         @data($data:ident, $($use_data:ident)?),
1071         // `HasPinData` or `HasInitData`.
1072         @has_data($has_data:ident, $get_data:ident),
1073         // `pin_init_from_closure` or `init_from_closure`.
1074         @construct_closure($construct_closure:ident),
1075         @munch_fields($ignore:tt $($rest:tt)*),
1076     ) => {
1077         $crate::__init_internal!(
1078             @this($($this)?),
1079             @typ($t),
1080             @fields($($fields)*),
1081             @error($err),
1082             @data($data, $($use_data)?),
1083             @has_data($has_data, $get_data),
1084             @construct_closure($construct_closure),
1085             @munch_fields($($rest)*),
1086         )
1087     };
1088     (with_update_parsed:
1089         @this($($this:ident)?),
1090         @typ($t:path),
1091         @fields($($fields:tt)*),
1092         @error($err:ty),
1093         // Either `PinData` or `InitData`, `$use_data` should only be present in the `PinData`
1094         // case.
1095         @data($data:ident, $($use_data:ident)?),
1096         // `HasPinData` or `HasInitData`.
1097         @has_data($has_data:ident, $get_data:ident),
1098         // `pin_init_from_closure` or `init_from_closure`.
1099         @construct_closure($construct_closure:ident),
1100         @zeroed($($init_zeroed:expr)?),
1101     ) => {{
1102         // We do not want to allow arbitrary returns, so we declare this type as the `Ok` return
1103         // type and shadow it later when we insert the arbitrary user code. That way there will be
1104         // no possibility of returning without `unsafe`.
1105         struct __InitOk;
1106         // Get the data about fields from the supplied type.
1107         let data = unsafe {
1108             use $crate::init::__internal::$has_data;
1109             // Here we abuse `paste!` to retokenize `$t`. Declarative macros have some internal
1110             // information that is associated to already parsed fragments, so a path fragment
1111             // cannot be used in this position. Doing the retokenization results in valid rust
1112             // code.
1113             ::kernel::macros::paste!($t::$get_data())
1114         };
1115         // Ensure that `data` really is of type `$data` and help with type inference:
1116         let init = $crate::init::__internal::$data::make_closure::<_, __InitOk, $err>(
1117             data,
1118             move |slot| {
1119                 {
1120                     // Shadow the structure so it cannot be used to return early.
1121                     struct __InitOk;
1122                     // If `$init_zeroed` is present we should zero the slot now and not emit an
1123                     // error when fields are missing (since they will be zeroed). We also have to
1124                     // check that the type actually implements `Zeroable`.
1125                     $({
1126                         fn assert_zeroable<T: $crate::init::Zeroable>(_: *mut T) {}
1127                         // Ensure that the struct is indeed `Zeroable`.
1128                         assert_zeroable(slot);
1129                         // SAFETY: The type implements `Zeroable` by the check above.
1130                         unsafe { ::core::ptr::write_bytes(slot, 0, 1) };
1131                         $init_zeroed // This will be `()` if set.
1132                     })?
1133                     // Create the `this` so it can be referenced by the user inside of the
1134                     // expressions creating the individual fields.
1135                     $(let $this = unsafe { ::core::ptr::NonNull::new_unchecked(slot) };)?
1136                     // Initialize every field.
1137                     $crate::__init_internal!(init_slot($($use_data)?):
1138                         @data(data),
1139                         @slot(slot),
1140                         @guards(),
1141                         @munch_fields($($fields)*,),
1142                     );
1143                     // We use unreachable code to ensure that all fields have been mentioned exactly
1144                     // once, this struct initializer will still be type-checked and complain with a
1145                     // very natural error message if a field is forgotten/mentioned more than once.
1146                     #[allow(unreachable_code, clippy::diverging_sub_expression)]
1147                     let _ = || {
1148                         $crate::__init_internal!(make_initializer:
1149                             @slot(slot),
1150                             @type_name($t),
1151                             @munch_fields($($fields)*,),
1152                             @acc(),
1153                         );
1154                     };
1155                 }
1156                 Ok(__InitOk)
1157             }
1158         );
1159         let init = move |slot| -> ::core::result::Result<(), $err> {
1160             init(slot).map(|__InitOk| ())
1161         };
1162         let init = unsafe { $crate::init::$construct_closure::<_, $err>(init) };
1163         init
1164     }};
1165     (init_slot($($use_data:ident)?):
1166         @data($data:ident),
1167         @slot($slot:ident),
1168         @guards($($guards:ident,)*),
1169         @munch_fields($(..Zeroable::zeroed())? $(,)?),
1170     ) => {
1171         // Endpoint of munching, no fields are left. If execution reaches this point, all fields
1172         // have been initialized. Therefore we can now dismiss the guards by forgetting them.
1173         $(::core::mem::forget($guards);)*
1174     };
1175     (init_slot($use_data:ident): // `use_data` is present, so we use the `data` to init fields.
1176         @data($data:ident),
1177         @slot($slot:ident),
1178         @guards($($guards:ident,)*),
1179         // In-place initialization syntax.
1180         @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
1181     ) => {
1182         let init = $val;
1183         // Call the initializer.
1184         //
1185         // SAFETY: `slot` is valid, because we are inside of an initializer closure, we
1186         // return when an error/panic occurs.
1187         // We also use the `data` to require the correct trait (`Init` or `PinInit`) for `$field`.
1188         unsafe { $data.$field(::core::ptr::addr_of_mut!((*$slot).$field), init)? };
1189         // Create the drop guard:
1190         //
1191         // We rely on macro hygiene to make it impossible for users to access this local variable.
1192         // We use `paste!` to create new hygiene for `$field`.
1193         ::kernel::macros::paste! {
1194             // SAFETY: We forget the guard later when initialization has succeeded.
1195             let [<$field>] = unsafe {
1196                 $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
1197             };
1198
1199             $crate::__init_internal!(init_slot($use_data):
1200                 @data($data),
1201                 @slot($slot),
1202                 @guards([<$field>], $($guards,)*),
1203                 @munch_fields($($rest)*),
1204             );
1205         }
1206     };
1207     (init_slot(): // No `use_data`, so we use `Init::__init` directly.
1208         @data($data:ident),
1209         @slot($slot:ident),
1210         @guards($($guards:ident,)*),
1211         // In-place initialization syntax.
1212         @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
1213     ) => {
1214         let init = $val;
1215         // Call the initializer.
1216         //
1217         // SAFETY: `slot` is valid, because we are inside of an initializer closure, we
1218         // return when an error/panic occurs.
1219         unsafe { $crate::init::Init::__init(init, ::core::ptr::addr_of_mut!((*$slot).$field))? };
1220         // Create the drop guard:
1221         //
1222         // We rely on macro hygiene to make it impossible for users to access this local variable.
1223         // We use `paste!` to create new hygiene for `$field`.
1224         ::kernel::macros::paste! {
1225             // SAFETY: We forget the guard later when initialization has succeeded.
1226             let [<$field>] = unsafe {
1227                 $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
1228             };
1229
1230             $crate::__init_internal!(init_slot():
1231                 @data($data),
1232                 @slot($slot),
1233                 @guards([<$field>], $($guards,)*),
1234                 @munch_fields($($rest)*),
1235             );
1236         }
1237     };
1238     (init_slot($($use_data:ident)?):
1239         @data($data:ident),
1240         @slot($slot:ident),
1241         @guards($($guards:ident,)*),
1242         // Init by-value.
1243         @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
1244     ) => {
1245         {
1246             $(let $field = $val;)?
1247             // Initialize the field.
1248             //
1249             // SAFETY: The memory at `slot` is uninitialized.
1250             unsafe { ::core::ptr::write(::core::ptr::addr_of_mut!((*$slot).$field), $field) };
1251         }
1252         // Create the drop guard:
1253         //
1254         // We rely on macro hygiene to make it impossible for users to access this local variable.
1255         // We use `paste!` to create new hygiene for `$field`.
1256         ::kernel::macros::paste! {
1257             // SAFETY: We forget the guard later when initialization has succeeded.
1258             let [<$field>] = unsafe {
1259                 $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
1260             };
1261
1262             $crate::__init_internal!(init_slot($($use_data)?):
1263                 @data($data),
1264                 @slot($slot),
1265                 @guards([<$field>], $($guards,)*),
1266                 @munch_fields($($rest)*),
1267             );
1268         }
1269     };
1270     (make_initializer:
1271         @slot($slot:ident),
1272         @type_name($t:path),
1273         @munch_fields(..Zeroable::zeroed() $(,)?),
1274         @acc($($acc:tt)*),
1275     ) => {
1276         // Endpoint, nothing more to munch, create the initializer. Since the users specified
1277         // `..Zeroable::zeroed()`, the slot will already have been zeroed and all field that have
1278         // not been overwritten are thus zero and initialized. We still check that all fields are
1279         // actually accessible by using the struct update syntax ourselves.
1280         // We are inside of a closure that is never executed and thus we can abuse `slot` to
1281         // get the correct type inference here:
1282         #[allow(unused_assignments)]
1283         unsafe {
1284             let mut zeroed = ::core::mem::zeroed();
1285             // We have to use type inference here to make zeroed have the correct type. This does
1286             // not get executed, so it has no effect.
1287             ::core::ptr::write($slot, zeroed);
1288             zeroed = ::core::mem::zeroed();
1289             // Here we abuse `paste!` to retokenize `$t`. Declarative macros have some internal
1290             // information that is associated to already parsed fragments, so a path fragment
1291             // cannot be used in this position. Doing the retokenization results in valid rust
1292             // code.
1293             ::kernel::macros::paste!(
1294                 ::core::ptr::write($slot, $t {
1295                     $($acc)*
1296                     ..zeroed
1297                 });
1298             );
1299         }
1300     };
1301     (make_initializer:
1302         @slot($slot:ident),
1303         @type_name($t:path),
1304         @munch_fields($(,)?),
1305         @acc($($acc:tt)*),
1306     ) => {
1307         // Endpoint, nothing more to munch, create the initializer.
1308         // Since we are in the closure that is never called, this will never get executed.
1309         // We abuse `slot` to get the correct type inference here:
1310         unsafe {
1311             // Here we abuse `paste!` to retokenize `$t`. Declarative macros have some internal
1312             // information that is associated to already parsed fragments, so a path fragment
1313             // cannot be used in this position. Doing the retokenization results in valid rust
1314             // code.
1315             ::kernel::macros::paste!(
1316                 ::core::ptr::write($slot, $t {
1317                     $($acc)*
1318                 });
1319             );
1320         }
1321     };
1322     (make_initializer:
1323         @slot($slot:ident),
1324         @type_name($t:path),
1325         @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
1326         @acc($($acc:tt)*),
1327     ) => {
1328         $crate::__init_internal!(make_initializer:
1329             @slot($slot),
1330             @type_name($t),
1331             @munch_fields($($rest)*),
1332             @acc($($acc)* $field: ::core::panic!(),),
1333         );
1334     };
1335     (make_initializer:
1336         @slot($slot:ident),
1337         @type_name($t:path),
1338         @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
1339         @acc($($acc:tt)*),
1340     ) => {
1341         $crate::__init_internal!(make_initializer:
1342             @slot($slot),
1343             @type_name($t),
1344             @munch_fields($($rest)*),
1345             @acc($($acc)* $field: ::core::panic!(),),
1346         );
1347     };
1348 }
1349
1350 #[doc(hidden)]
1351 #[macro_export]
1352 macro_rules! __derive_zeroable {
1353     (parse_input:
1354         @sig(
1355             $(#[$($struct_attr:tt)*])*
1356             $vis:vis struct $name:ident
1357             $(where $($whr:tt)*)?
1358         ),
1359         @impl_generics($($impl_generics:tt)*),
1360         @ty_generics($($ty_generics:tt)*),
1361         @body({
1362             $(
1363                 $(#[$($field_attr:tt)*])*
1364                 $field:ident : $field_ty:ty
1365             ),* $(,)?
1366         }),
1367     ) => {
1368         // SAFETY: Every field type implements `Zeroable` and padding bytes may be zero.
1369         #[automatically_derived]
1370         unsafe impl<$($impl_generics)*> $crate::init::Zeroable for $name<$($ty_generics)*>
1371         where
1372             $($($whr)*)?
1373         {}
1374         const _: () = {
1375             fn assert_zeroable<T: ?::core::marker::Sized + $crate::init::Zeroable>() {}
1376             fn ensure_zeroable<$($impl_generics)*>()
1377                 where $($($whr)*)?
1378             {
1379                 $(assert_zeroable::<$field_ty>();)*
1380             }
1381         };
1382     };
1383 }