| //! Implementation detail of the `pin-project` crate. - **do not use directly** |
| |
| #![doc(test( |
| no_crate_inject, |
| attr( |
| deny(warnings, rust_2018_idioms, single_use_lifetimes), |
| allow(dead_code, unused_variables) |
| ) |
| ))] |
| #![forbid(unsafe_code)] |
| #![warn(rust_2018_idioms, single_use_lifetimes, unreachable_pub)] |
| #![warn(clippy::pedantic)] |
| #![allow( |
| clippy::needless_doctest_main, |
| clippy::similar_names, |
| clippy::single_match_else, |
| clippy::too_many_lines |
| )] |
| |
| // older compilers require explicit `extern crate`. |
| #[allow(unused_extern_crates)] |
| extern crate proc_macro; |
| |
| #[macro_use] |
| mod utils; |
| |
| mod pin_project; |
| mod pinned_drop; |
| |
| use proc_macro::TokenStream; |
| |
| /// An attribute that creates projection types covering all the fields of |
| /// struct or enum. |
| /// |
| /// This attribute creates projection types according to the following rules: |
| /// |
| /// - For the fields that use `#[pin]` attribute, create the pinned reference to |
| /// the field. |
| /// - For the other fields, create a normal reference to the field. |
| /// |
| /// And the following methods are implemented on the original type: |
| /// |
| /// ```rust |
| /// # use std::pin::Pin; |
| /// # type Projection<'a> = &'a (); |
| /// # type ProjectionRef<'a> = &'a (); |
| /// # trait Dox { |
| /// fn project(self: Pin<&mut Self>) -> Projection<'_>; |
| /// fn project_ref(self: Pin<&Self>) -> ProjectionRef<'_>; |
| /// # } |
| /// ``` |
| /// |
| /// By passing an argument with the same name as the method to the attribute, |
| /// you can name the projection type returned from the method. This allows you |
| /// to use pattern matching on the projected types. |
| /// |
| /// ```rust |
| /// # use pin_project::pin_project; |
| /// # use std::pin::Pin; |
| /// #[pin_project(project = EnumProj)] |
| /// enum Enum<T> { |
| /// Variant(#[pin] T), |
| /// } |
| /// |
| /// impl<T> Enum<T> { |
| /// fn method(self: Pin<&mut Self>) { |
| /// let this: EnumProj<'_, T> = self.project(); |
| /// match this { |
| /// EnumProj::Variant(x) => { |
| /// let _: Pin<&mut T> = x; |
| /// } |
| /// } |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// Note that the projection types returned by `project` and `project_ref` have |
| /// an additional lifetime at the beginning of generics. |
| /// |
| /// ```text |
| /// let this: EnumProj<'_, T> = self.project(); |
| /// ^^ |
| /// ``` |
| /// |
| /// The visibility of the projected types and projection methods is based on the |
| /// original type. However, if the visibility of the original type is `pub`, the |
| /// visibility of the projected types and the projection methods is downgraded |
| /// to `pub(crate)`. |
| /// |
| /// # Safety |
| /// |
| /// This attribute is completely safe. In the absence of other `unsafe` code |
| /// *that you write*, it is impossible to cause [undefined |
| /// behavior][undefined-behavior] with this attribute. |
| /// |
| /// This is accomplished by enforcing the four requirements for pin projection |
| /// stated in [the Rust documentation][pin-projection]: |
| /// |
| /// 1. The struct must only be [`Unpin`] if all the structural fields are |
| /// [`Unpin`]. |
| /// |
| /// To enforce this, this attribute will automatically generate an [`Unpin`] |
| /// implementation for you, which will require that all structurally pinned |
| /// fields be [`Unpin`]. |
| /// |
| /// If you attempt to provide an [`Unpin`] impl, the blanket impl will then |
| /// apply to your type, causing a compile-time error due to the conflict with |
| /// the second impl. |
| /// |
| /// If you wish to provide a manual [`Unpin`] impl, you can do so via the |
| /// [`UnsafeUnpin`][unsafe-unpin] argument. |
| /// |
| /// 2. The destructor of the struct must not move structural fields out of its |
| /// argument. |
| /// |
| /// To enforce this, this attribute will generate code like this: |
| /// |
| /// ```rust |
| /// struct MyStruct {} |
| /// trait MyStructMustNotImplDrop {} |
| /// # #[allow(unknown_lints, drop_bounds)] |
| /// impl<T: Drop> MyStructMustNotImplDrop for T {} |
| /// impl MyStructMustNotImplDrop for MyStruct {} |
| /// ``` |
| /// |
| /// If you attempt to provide an [`Drop`] impl, the blanket impl will then |
| /// apply to your type, causing a compile-time error due to the conflict with |
| /// the second impl. |
| /// |
| /// If you wish to provide a custom [`Drop`] impl, you can annotate an impl |
| /// with [`#[pinned_drop]`][pinned-drop]. This impl takes a pinned version of |
| /// your struct - that is, [`Pin`]`<&mut MyStruct>` where `MyStruct` is the |
| /// type of your struct. |
| /// |
| /// You can call `.project()` on this type as usual, along with any other |
| /// methods you have defined. Because your code is never provided with |
| /// a `&mut MyStruct`, it is impossible to move out of pin-projectable |
| /// fields in safe code in your destructor. |
| /// |
| /// 3. You must make sure that you uphold the [`Drop` |
| /// guarantee][drop-guarantee]: once your struct is pinned, the memory that |
| /// contains the content is not overwritten or deallocated without calling |
| /// the content's destructors. |
| /// |
| /// Safe code doesn't need to worry about this - the only way to violate |
| /// this requirement is to manually deallocate memory (which is `unsafe`), |
| /// or to overwrite a field with something else. |
| /// Because your custom destructor takes [`Pin`]`<&mut MyStruct>`, it's |
| /// impossible to obtain a mutable reference to a pin-projected field in safe |
| /// code. |
| /// |
| /// 4. You must not offer any other operations that could lead to data being |
| /// moved out of the structural fields when your type is pinned. |
| /// |
| /// As with requirement 3, it is impossible for safe code to violate this. |
| /// This crate ensures that safe code can never obtain a mutable reference to |
| /// `#[pin]` fields, which prevents you from ever moving out of them in safe |
| /// code. |
| /// |
| /// Pin projections are also incompatible with [`#[repr(packed)]`][repr-packed] |
| /// types. Attempting to use this attribute on a `#[repr(packed)]` type results |
| /// in a compile-time error. |
| /// |
| /// # Examples |
| /// |
| /// `#[pin_project]` can be used on structs and enums. |
| /// |
| /// ```rust |
| /// use std::pin::Pin; |
| /// |
| /// use pin_project::pin_project; |
| /// |
| /// #[pin_project] |
| /// struct Struct<T, U> { |
| /// #[pin] |
| /// pinned: T, |
| /// unpinned: U, |
| /// } |
| /// |
| /// impl<T, U> Struct<T, U> { |
| /// fn method(self: Pin<&mut Self>) { |
| /// let this = self.project(); |
| /// let _: Pin<&mut T> = this.pinned; |
| /// let _: &mut U = this.unpinned; |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// ```rust |
| /// use std::pin::Pin; |
| /// |
| /// use pin_project::pin_project; |
| /// |
| /// #[pin_project] |
| /// struct TupleStruct<T, U>(#[pin] T, U); |
| /// |
| /// impl<T, U> TupleStruct<T, U> { |
| /// fn method(self: Pin<&mut Self>) { |
| /// let this = self.project(); |
| /// let _: Pin<&mut T> = this.0; |
| /// let _: &mut U = this.1; |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// To use `#[pin_project]` on enums, you need to name the projection type |
| /// returned from the method. |
| /// |
| /// ```rust |
| /// use std::pin::Pin; |
| /// |
| /// use pin_project::pin_project; |
| /// |
| /// #[pin_project(project = EnumProj)] |
| /// enum Enum<T, U> { |
| /// Tuple(#[pin] T), |
| /// Struct { field: U }, |
| /// Unit, |
| /// } |
| /// |
| /// impl<T, U> Enum<T, U> { |
| /// fn method(self: Pin<&mut Self>) { |
| /// match self.project() { |
| /// EnumProj::Tuple(x) => { |
| /// let _: Pin<&mut T> = x; |
| /// } |
| /// EnumProj::Struct { field } => { |
| /// let _: &mut U = field; |
| /// } |
| /// EnumProj::Unit => {} |
| /// } |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// When `#[pin_project]` is used on enums, only named projection types and |
| /// methods are generated because there is no way to access variants of |
| /// projected types without naming it. |
| /// For example, in the above example, only the `project` method is generated, |
| /// and the `project_ref` method is not generated. |
| /// (When `#[pin_project]` is used on structs, both methods are always generated.) |
| /// |
| /// ```rust,compile_fail,E0599 |
| /// # use pin_project::pin_project; |
| /// # use std::pin::Pin; |
| /// # |
| /// # #[pin_project(project = EnumProj)] |
| /// # enum Enum<T, U> { |
| /// # Tuple(#[pin] T), |
| /// # Struct { field: U }, |
| /// # Unit, |
| /// # } |
| /// # |
| /// impl<T, U> Enum<T, U> { |
| /// fn call_project_ref(self: Pin<&Self>) { |
| /// let _this = self.project_ref(); |
| /// //~^ ERROR no method named `project_ref` found for struct `Pin<&Enum<T, U>>` in the current scope |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// If you want to call `.project()` multiple times or later use the |
| /// original [`Pin`] type, it needs to use [`.as_mut()`][`Pin::as_mut`] to avoid |
| /// consuming the [`Pin`]. |
| /// |
| /// ```rust |
| /// use std::pin::Pin; |
| /// |
| /// use pin_project::pin_project; |
| /// |
| /// #[pin_project] |
| /// struct Struct<T> { |
| /// #[pin] |
| /// field: T, |
| /// } |
| /// |
| /// impl<T> Struct<T> { |
| /// fn call_project_twice(mut self: Pin<&mut Self>) { |
| /// // `project` consumes `self`, so reborrow the `Pin<&mut Self>` via `as_mut`. |
| /// self.as_mut().project(); |
| /// self.as_mut().project(); |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// # `!Unpin` |
| /// |
| /// If you want to ensure that [`Unpin`] is not implemented, use the `!Unpin` |
| /// argument to `#[pin_project]`. |
| /// |
| /// ```rust |
| /// use pin_project::pin_project; |
| /// |
| /// #[pin_project(!Unpin)] |
| /// struct Struct<T> { |
| /// field: T, |
| /// } |
| /// ``` |
| /// |
| /// This is equivalent to using `#[pin]` attribute for the [`PhantomPinned`] |
| /// field. |
| /// |
| /// ```rust |
| /// use std::marker::PhantomPinned; |
| /// |
| /// use pin_project::pin_project; |
| /// |
| /// #[pin_project] |
| /// struct Struct<T> { |
| /// field: T, |
| /// #[pin] // <------ This `#[pin]` is required to make `Struct` to `!Unpin`. |
| /// _pin: PhantomPinned, |
| /// } |
| /// ``` |
| /// |
| /// Note that using [`PhantomPinned`] without `#[pin]` attribute has no effect. |
| /// |
| /// # `UnsafeUnpin` |
| /// |
| /// If you want to implement [`Unpin`] manually, you must use the `UnsafeUnpin` |
| /// argument to `#[pin_project]`. |
| /// |
| /// ```rust |
| /// use pin_project::{pin_project, UnsafeUnpin}; |
| /// |
| /// #[pin_project(UnsafeUnpin)] |
| /// struct Struct<T, U> { |
| /// #[pin] |
| /// pinned: T, |
| /// unpinned: U, |
| /// } |
| /// |
| /// unsafe impl<T: Unpin, U> UnsafeUnpin for Struct<T, U> {} |
| /// ``` |
| /// |
| /// Note the usage of the unsafe [`UnsafeUnpin`] trait, instead of the usual |
| /// [`Unpin`] trait. [`UnsafeUnpin`] behaves exactly like [`Unpin`], except that |
| /// is unsafe to implement. This unsafety comes from the fact that pin |
| /// projections are being used. If you implement [`UnsafeUnpin`], you must |
| /// ensure that it is only implemented when all pin-projected fields implement |
| /// [`Unpin`]. |
| /// |
| /// See [`UnsafeUnpin`] trait for more details. |
| /// |
| /// # `#[pinned_drop]` |
| /// |
| /// In order to correctly implement pin projections, a type's [`Drop`] impl must |
| /// not move out of any structurally pinned fields. Unfortunately, |
| /// [`Drop::drop`] takes `&mut Self`, not [`Pin`]`<&mut Self>`. |
| /// |
| /// To ensure that this requirement is upheld, the `#[pin_project]` attribute |
| /// will provide a [`Drop`] impl for you. This [`Drop`] impl will delegate to |
| /// an impl block annotated with `#[pinned_drop]` if you use the `PinnedDrop` |
| /// argument to `#[pin_project]`. |
| /// |
| /// This impl block acts just like a normal [`Drop`] impl, |
| /// except for the following two: |
| /// |
| /// - `drop` method takes [`Pin`]`<&mut Self>` |
| /// - Name of the trait is `PinnedDrop`. |
| /// |
| /// ```rust |
| /// # use std::pin::Pin; |
| /// pub trait PinnedDrop { |
| /// fn drop(self: Pin<&mut Self>); |
| /// } |
| /// ``` |
| /// |
| /// `#[pin_project]` implements the actual [`Drop`] trait via `PinnedDrop` you |
| /// implemented. To drop a type that implements `PinnedDrop`, use the [`drop`] |
| /// function just like dropping a type that directly implements [`Drop`]. |
| /// |
| /// In particular, it will never be called more than once, just like |
| /// [`Drop::drop`]. |
| /// |
| /// For example: |
| /// |
| /// ```rust |
| /// use std::{fmt::Debug, pin::Pin}; |
| /// |
| /// use pin_project::{pin_project, pinned_drop}; |
| /// |
| /// #[pin_project(PinnedDrop)] |
| /// struct PrintOnDrop<T: Debug, U: Debug> { |
| /// #[pin] |
| /// pinned_field: T, |
| /// unpin_field: U, |
| /// } |
| /// |
| /// #[pinned_drop] |
| /// impl<T: Debug, U: Debug> PinnedDrop for PrintOnDrop<T, U> { |
| /// fn drop(self: Pin<&mut Self>) { |
| /// println!("Dropping pinned field: {:?}", self.pinned_field); |
| /// println!("Dropping unpin field: {:?}", self.unpin_field); |
| /// } |
| /// } |
| /// |
| /// fn main() { |
| /// let _x = PrintOnDrop { pinned_field: true, unpin_field: 40 }; |
| /// } |
| /// ``` |
| /// |
| /// See also [`#[pinned_drop]`][macro@pinned_drop] attribute. |
| /// |
| /// # `project_replace` method |
| /// |
| /// In addition to the `project` and `project_ref` methods which are always |
| /// provided when you use the `#[pin_project]` attribute, there is a third |
| /// method, `project_replace` which can be useful in some situations. It is |
| /// equivalent to [`Pin::set`], except that the unpinned fields are moved and |
| /// returned, instead of being dropped in-place. |
| /// |
| /// ```rust |
| /// # use std::pin::Pin; |
| /// # type ProjectionOwned = (); |
| /// # trait Dox { |
| /// fn project_replace(self: Pin<&mut Self>, other: Self) -> ProjectionOwned; |
| /// # } |
| /// ``` |
| /// |
| /// The `ProjectionOwned` type is identical to the `Self` type, except that |
| /// all pinned fields have been replaced by equivalent [`PhantomData`] types. |
| /// |
| /// This method is opt-in, because it is only supported for [`Sized`] types, and |
| /// because it is incompatible with the [`#[pinned_drop]`][pinned-drop] |
| /// attribute described above. It can be enabled by using |
| /// `#[pin_project(project_replace)]`. |
| /// |
| /// For example: |
| /// |
| /// ```rust |
| /// use std::{marker::PhantomData, pin::Pin}; |
| /// |
| /// use pin_project::pin_project; |
| /// |
| /// #[pin_project(project_replace)] |
| /// struct Struct<T, U> { |
| /// #[pin] |
| /// pinned_field: T, |
| /// unpinned_field: U, |
| /// } |
| /// |
| /// impl<T, U> Struct<T, U> { |
| /// fn method(self: Pin<&mut Self>, other: Self) { |
| /// let this = self.project_replace(other); |
| /// let _: U = this.unpinned_field; |
| /// let _: PhantomData<T> = this.pinned_field; |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// By passing the value to the `project_replace` argument, you can name the |
| /// returned type of the `project_replace` method. This is necessary whenever |
| /// destructuring the return type of the `project_replace` method, and work in exactly |
| /// the same way as the `project` and `project_ref` arguments. |
| /// |
| /// ```rust |
| /// use pin_project::pin_project; |
| /// |
| /// #[pin_project(project_replace = EnumProjOwn)] |
| /// enum Enum<T, U> { |
| /// A { |
| /// #[pin] |
| /// pinned_field: T, |
| /// unpinned_field: U, |
| /// }, |
| /// B, |
| /// } |
| /// |
| /// let mut x = Box::pin(Enum::A { pinned_field: 42, unpinned_field: "hello" }); |
| /// |
| /// match x.as_mut().project_replace(Enum::B) { |
| /// EnumProjOwn::A { unpinned_field, .. } => assert_eq!(unpinned_field, "hello"), |
| /// EnumProjOwn::B => unreachable!(), |
| /// } |
| /// ``` |
| /// |
| /// [`PhantomData`]: core::marker::PhantomData |
| /// [`PhantomPinned`]: core::marker::PhantomPinned |
| /// [`Pin::as_mut`]: core::pin::Pin::as_mut |
| /// [`Pin::set`]: core::pin::Pin::set |
| /// [`Pin`]: core::pin::Pin |
| /// [`UnsafeUnpin`]: https://docs.rs/pin-project/1/pin_project/trait.UnsafeUnpin.html |
| /// [drop-guarantee]: core::pin#drop-guarantee |
| /// [pin-projection]: core::pin#projections-and-structural-pinning |
| /// [pinned-drop]: macro@pin_project#pinned_drop |
| /// [repr-packed]: https://doc.rust-lang.org/nomicon/other-reprs.html#reprpacked |
| /// [undefined-behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html |
| /// [unsafe-unpin]: macro@pin_project#unsafeunpin |
| #[proc_macro_attribute] |
| pub fn pin_project(args: TokenStream, input: TokenStream) -> TokenStream { |
| pin_project::attribute(&args.into(), input.into()).into() |
| } |
| |
| /// An attribute used for custom implementations of [`Drop`]. |
| /// |
| /// This attribute is used in conjunction with the `PinnedDrop` argument to |
| /// the [`#[pin_project]`][macro@pin_project] attribute. |
| /// |
| /// The impl block annotated with this attribute acts just like a normal |
| /// [`Drop`] impl, except for the following two: |
| /// |
| /// - `drop` method takes [`Pin`]`<&mut Self>` |
| /// - Name of the trait is `PinnedDrop`. |
| /// |
| /// ```rust |
| /// # use std::pin::Pin; |
| /// pub trait PinnedDrop { |
| /// fn drop(self: Pin<&mut Self>); |
| /// } |
| /// ``` |
| /// |
| /// `#[pin_project]` implements the actual [`Drop`] trait via `PinnedDrop` you |
| /// implemented. To drop a type that implements `PinnedDrop`, use the [`drop`] |
| /// function just like dropping a type that directly implements [`Drop`]. |
| /// |
| /// In particular, it will never be called more than once, just like |
| /// [`Drop::drop`]. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// use std::pin::Pin; |
| /// |
| /// use pin_project::{pin_project, pinned_drop}; |
| /// |
| /// #[pin_project(PinnedDrop)] |
| /// struct PrintOnDrop { |
| /// #[pin] |
| /// field: u8, |
| /// } |
| /// |
| /// #[pinned_drop] |
| /// impl PinnedDrop for PrintOnDrop { |
| /// fn drop(self: Pin<&mut Self>) { |
| /// println!("Dropping: {}", self.field); |
| /// } |
| /// } |
| /// |
| /// fn main() { |
| /// let _x = PrintOnDrop { field: 50 }; |
| /// } |
| /// ``` |
| /// |
| /// See also ["pinned-drop" section of `#[pin_project]` attribute][pinned-drop]. |
| /// |
| /// # Why `#[pinned_drop]` attribute is needed? |
| /// |
| /// Implementing `PinnedDrop::drop` is safe, but calling it is not safe. |
| /// This is because destructors can be called multiple times in safe code and |
| /// [double dropping is unsound][rust-lang/rust#62360]. |
| /// |
| /// Ideally, it would be desirable to be able to forbid manual calls in |
| /// the same way as [`Drop::drop`], but the library cannot do it. So, by using |
| /// macros and replacing them with private traits like the following, |
| /// this crate prevent users from calling `PinnedDrop::drop` in safe code. |
| /// |
| /// ```rust |
| /// # use std::pin::Pin; |
| /// pub trait PinnedDrop { |
| /// unsafe fn drop(self: Pin<&mut Self>); |
| /// } |
| /// ``` |
| /// |
| /// This allows implementing [`Drop`] safely using `#[pinned_drop]`. |
| /// Also by using the [`drop`] function just like dropping a type that directly |
| /// implements [`Drop`], can drop safely a type that implements `PinnedDrop`. |
| /// |
| /// [rust-lang/rust#62360]: https://github.com/rust-lang/rust/pull/62360 |
| /// [`Pin`]: core::pin::Pin |
| /// [pinned-drop]: macro@pin_project#pinned_drop |
| #[proc_macro_attribute] |
| pub fn pinned_drop(args: TokenStream, input: TokenStream) -> TokenStream { |
| let input = syn::parse_macro_input!(input); |
| pinned_drop::attribute(&args.into(), input).into() |
| } |
| |
| // Not public API. |
| #[doc(hidden)] |
| #[proc_macro_derive(__PinProjectInternalDerive, attributes(pin))] |
| pub fn __pin_project_internal_derive(input: TokenStream) -> TokenStream { |
| pin_project::derive(input.into()).into() |
| } |