Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

11 files changed, 2910 insertions, 0 deletions

diff --git a/third_party/rust/pin-project-internal/.cargo-checksum.json b/third_party/rust/pin-project-internal/.cargo-checksum.json
new file mode 100644
index 0000000000..f79ba56439
--- /dev/null
+++ b/third_party/rust/pin-project-internal/.cargo-checksum.json
@@ -0,0 +1 @@
+{"files":{"Cargo.toml":"211aa0caf26529737530a9979eefc1a3acea84a4d7ce1943efb935ca0de3cf02","LICENSE-APACHE":"0d542e0c8804e39aa7f37eb00da5a762149dc682d7829451287e11b938e94594","LICENSE-MIT":"23f18e03dc49df91622fe2a76176497404e46ced8a715d9d2b67a7446571cca3","src/lib.rs":"19e5ab2e30ce5ca53e877826e4eadf7cb7311e72b568573be38ecc8c39556896","src/pin_project/args.rs":"14a11ef2e85c4f4cf00e29d3527d622500b87bdd90c60e7b0223278b1f0989ca","src/pin_project/attribute.rs":"3e392493e875f0c935525579ba9bd888d8e00b57b3d6594b7fde040c31790784","src/pin_project/derive.rs":"5e8b1dc2fbcec3a0f724fc1806116784c0fec46507a9b1ce73c34580ac4372b5","src/pin_project/mod.rs":"83e6fc982a8c136811332512abc7d368e5d09b94f245de5d19490f835e85943a","src/pinned_drop.rs":"1d4cffdd4176a16c440a2a3a5039dfcf14ff42ef9e2aa7069134dfac8ba69658","src/utils.rs":"6dc65cccfbd9c8f706dbc7003458c583d57db026d2860a965c4f12222ebb3720"},"package":"39407670928234ebc5e6e580247dd567ad73a3578460c5990f9503df207e8f07"}
\ No newline at end of file
diff --git a/third_party/rust/pin-project-internal/Cargo.toml b/third_party/rust/pin-project-internal/Cargo.toml
new file mode 100644
index 0000000000..822357e479
--- /dev/null
+++ b/third_party/rust/pin-project-internal/Cargo.toml
@@ -0,0 +1,51 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2018"
+rust-version = "1.56"
+name = "pin-project-internal"
+version = "1.1.0"
+description = """
+Implementation detail of the `pin-project` crate.
+"""
+keywords = [
+    "pin",
+    "macros",
+    "attribute",
+]
+categories = [
+    "no-std",
+    "rust-patterns",
+]
+license = "Apache-2.0 OR MIT"
+repository = "https://github.com/taiki-e/pin-project"
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+
+[lib]
+proc-macro = true
+
+[dependencies.proc-macro2]
+version = "1"
+
+[dependencies.quote]
+version = "1"
+
+[dependencies.syn]
+version = "2.0.1"
+features = [
+    "full",
+    "visit-mut",
+]
+
+[dev-dependencies]
diff --git a/third_party/rust/pin-project-internal/LICENSE-APACHE b/third_party/rust/pin-project-internal/LICENSE-APACHE
new file mode 100644
index 0000000000..f433b1a53f
--- /dev/null
+++ b/third_party/rust/pin-project-internal/LICENSE-APACHE
@@ -0,0 +1,177 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
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+   END OF TERMS AND CONDITIONS
diff --git a/third_party/rust/pin-project-internal/LICENSE-MIT b/third_party/rust/pin-project-internal/LICENSE-MIT
new file mode 100644
index 0000000000..31aa79387f
--- /dev/null
+++ b/third_party/rust/pin-project-internal/LICENSE-MIT
@@ -0,0 +1,23 @@
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software
+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/third_party/rust/pin-project-internal/src/lib.rs b/third_party/rust/pin-project-internal/src/lib.rs
new file mode 100644
index 0000000000..3eb33238ad
--- /dev/null
+++ b/third_party/rust/pin-project-internal/src/lib.rs
@@ -0,0 +1,583 @@
+//! 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()
+}
diff --git a/third_party/rust/pin-project-internal/src/pin_project/args.rs b/third_party/rust/pin-project-internal/src/pin_project/args.rs
new file mode 100644
index 0000000000..d242ae71c7
--- /dev/null
+++ b/third_party/rust/pin-project-internal/src/pin_project/args.rs
@@ -0,0 +1,253 @@
+use proc_macro2::{Span, TokenStream};
+use quote::quote;
+use syn::{
+    parse::{Parse, ParseStream},
+    spanned::Spanned,
+    Attribute, Error, Ident, Result, Token,
+};
+
+use super::PIN;
+use crate::utils::{ParseBufferExt, SliceExt};
+
+pub(super) fn parse_args(attrs: &[Attribute]) -> Result<Args> {
+    // `(__private(<args>))` -> `<args>`
+    struct Input(Option<TokenStream>);
+
+    impl Parse for Input {
+        fn parse(input: ParseStream<'_>) -> Result<Self> {
+            Ok(Self((|| {
+                let private = input.parse::<Ident>().ok()?;
+                if private == "__private" {
+                    input.parenthesized().ok()?.parse::<TokenStream>().ok()
+                } else {
+                    None
+                }
+            })()))
+        }
+    }
+
+    if let Some(attr) = attrs.find("pin_project") {
+        bail!(attr, "duplicate #[pin_project] attribute");
+    }
+
+    let mut attrs = attrs.iter().filter(|attr| attr.path().is_ident(PIN));
+
+    let prev = if let Some(attr) = attrs.next() {
+        (attr, syn::parse2::<Input>(attr.meta.require_list()?.tokens.clone())?.0)
+    } else {
+        // This only fails if another macro removes `#[pin]`.
+        bail!(TokenStream::new(), "#[pin_project] attribute has been removed");
+    };
+
+    if let Some(attr) = attrs.next() {
+        let (prev_attr, prev_res) = &prev;
+        // As the `#[pin]` attribute generated by `#[pin_project]`
+        // has the same span as `#[pin_project]`, it is possible
+        // that a useless error message will be generated.
+        // So, use the span of `prev_attr` if it is not a valid attribute.
+        let res = syn::parse2::<Input>(attr.meta.require_list()?.tokens.clone())?.0;
+        let span = match (prev_res, res) {
+            (Some(_), _) => attr,
+            (None, _) => prev_attr,
+        };
+        bail!(span, "duplicate #[pin] attribute");
+    }
+    // This `unwrap` only fails if another macro removes `#[pin]` and inserts own `#[pin]`.
+    syn::parse2(prev.1.unwrap())
+}
+
+pub(super) struct Args {
+    /// `PinnedDrop` argument.
+    pub(super) pinned_drop: Option<Span>,
+    /// `UnsafeUnpin` or `!Unpin` argument.
+    pub(super) unpin_impl: UnpinImpl,
+    /// `project = <ident>` argument.
+    pub(super) project: Option<Ident>,
+    /// `project_ref = <ident>` argument.
+    pub(super) project_ref: Option<Ident>,
+    /// `project_replace [= <ident>]` argument.
+    pub(super) project_replace: ProjReplace,
+}
+
+impl Parse for Args {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        mod kw {
+            syn::custom_keyword!(Unpin);
+        }
+
+        /// Parses `= <value>` in `<name> = <value>` and returns value and span of name-value pair.
+        fn parse_value(
+            input: ParseStream<'_>,
+            name: &Ident,
+            has_prev: bool,
+        ) -> Result<(Ident, TokenStream)> {
+            if input.is_empty() {
+                bail!(name, "expected `{0} = <identifier>`, found `{0}`", name);
+            }
+            let eq_token: Token![=] = input.parse()?;
+            if input.is_empty() {
+                let span = quote!(#name #eq_token);
+                bail!(span, "expected `{0} = <identifier>`, found `{0} =`", name);
+            }
+            let value: Ident = input.parse()?;
+            let span = quote!(#name #value);
+            if has_prev {
+                bail!(span, "duplicate `{}` argument", name);
+            }
+            Ok((value, span))
+        }
+
+        let mut pinned_drop = None;
+        let mut unsafe_unpin = None;
+        let mut not_unpin = None;
+        let mut project = None;
+        let mut project_ref = None;
+        let mut project_replace_value = None;
+        let mut project_replace_span = None;
+
+        while !input.is_empty() {
+            if input.peek(Token![!]) {
+                let bang: Token![!] = input.parse()?;
+                if input.is_empty() {
+                    bail!(bang, "expected `!Unpin`, found `!`");
+                }
+                let unpin: kw::Unpin = input.parse()?;
+                let span = quote!(#bang #unpin);
+                if not_unpin.replace(span.span()).is_some() {
+                    bail!(span, "duplicate `!Unpin` argument");
+                }
+            } else {
+                let token = input.parse::<Ident>()?;
+                match &*token.to_string() {
+                    "PinnedDrop" => {
+                        if pinned_drop.replace(token.span()).is_some() {
+                            bail!(token, "duplicate `PinnedDrop` argument");
+                        }
+                    }
+                    "UnsafeUnpin" => {
+                        if unsafe_unpin.replace(token.span()).is_some() {
+                            bail!(token, "duplicate `UnsafeUnpin` argument");
+                        }
+                    }
+                    "project" => {
+                        project = Some(parse_value(input, &token, project.is_some())?.0);
+                    }
+                    "project_ref" => {
+                        project_ref = Some(parse_value(input, &token, project_ref.is_some())?.0);
+                    }
+                    "project_replace" => {
+                        if input.peek(Token![=]) {
+                            let (value, span) =
+                                parse_value(input, &token, project_replace_span.is_some())?;
+                            project_replace_value = Some(value);
+                            project_replace_span = Some(span.span());
+                        } else if project_replace_span.is_some() {
+                            bail!(token, "duplicate `project_replace` argument");
+                        } else {
+                            project_replace_span = Some(token.span());
+                        }
+                    }
+                    "Replace" => {
+                        bail!(
+                            token,
+                            "`Replace` argument was removed, use `project_replace` argument instead"
+                        );
+                    }
+                    _ => bail!(token, "unexpected argument: {}", token),
+                }
+            }
+
+            if input.is_empty() {
+                break;
+            }
+            let _: Token![,] = input.parse()?;
+        }
+
+        if project.is_some() || project_ref.is_some() {
+            if project == project_ref {
+                bail!(
+                    project_ref,
+                    "name `{}` is already specified by `project` argument",
+                    project_ref.as_ref().unwrap()
+                );
+            }
+            if let Some(ident) = &project_replace_value {
+                if project == project_replace_value {
+                    bail!(ident, "name `{}` is already specified by `project` argument", ident);
+                } else if project_ref == project_replace_value {
+                    bail!(ident, "name `{}` is already specified by `project_ref` argument", ident);
+                }
+            }
+        }
+
+        if let Some(span) = pinned_drop {
+            if project_replace_span.is_some() {
+                return Err(Error::new(
+                    span,
+                    "arguments `PinnedDrop` and `project_replace` are mutually exclusive",
+                ));
+            }
+        }
+        let project_replace = match (project_replace_span, project_replace_value) {
+            (None, _) => ProjReplace::None,
+            (Some(span), Some(ident)) => ProjReplace::Named { ident, span },
+            (Some(span), None) => ProjReplace::Unnamed { span },
+        };
+        let unpin_impl = match (unsafe_unpin, not_unpin) {
+            (None, None) => UnpinImpl::Default,
+            (Some(span), None) => UnpinImpl::Unsafe(span),
+            (None, Some(span)) => UnpinImpl::Negative(span),
+            (Some(span), Some(_)) => {
+                return Err(Error::new(
+                    span,
+                    "arguments `UnsafeUnpin` and `!Unpin` are mutually exclusive",
+                ));
+            }
+        };
+
+        Ok(Self { pinned_drop, unpin_impl, project, project_ref, project_replace })
+    }
+}
+
+/// `UnsafeUnpin` or `!Unpin` argument.
+#[derive(Clone, Copy)]
+pub(super) enum UnpinImpl {
+    Default,
+    /// `UnsafeUnpin`.
+    Unsafe(Span),
+    /// `!Unpin`.
+    Negative(Span),
+}
+
+/// `project_replace [= <ident>]` argument.
+pub(super) enum ProjReplace {
+    None,
+    /// `project_replace`.
+    Unnamed {
+        span: Span,
+    },
+    /// `project_replace = <ident>`.
+    #[allow(dead_code)] // false positive that fixed in Rust 1.38
+    Named {
+        span: Span,
+        ident: Ident,
+    },
+}
+
+impl ProjReplace {
+    /// Return the span of this argument.
+    pub(super) fn span(&self) -> Option<Span> {
+        match self {
+            Self::None => None,
+            Self::Named { span, .. } | Self::Unnamed { span, .. } => Some(*span),
+        }
+    }
+
+    pub(super) fn ident(&self) -> Option<&Ident> {
+        if let Self::Named { ident, .. } = self {
+            Some(ident)
+        } else {
+            None
+        }
+    }
+}
diff --git a/third_party/rust/pin-project-internal/src/pin_project/attribute.rs b/third_party/rust/pin-project-internal/src/pin_project/attribute.rs
new file mode 100644
index 0000000000..7adfc07d59
--- /dev/null
+++ b/third_party/rust/pin-project-internal/src/pin_project/attribute.rs
@@ -0,0 +1,65 @@
+use proc_macro2::TokenStream;
+use quote::quote;
+use syn::{
+    parse::{Parse, ParseStream},
+    Attribute, Result, Token, Visibility,
+};
+
+use super::PIN;
+use crate::utils::SliceExt;
+
+// To generate the correct `Unpin` implementation and the projection methods,
+// we need to collect the types of the pinned fields.
+// However, since proc-macro-attribute is applied before `cfg` and `cfg_attr`
+// on fields, we cannot be collecting field types properly at this timing.
+// So instead of generating the `Unpin` implementation and the projection
+// methods here, delegate their processing to proc-macro-derive.
+//
+// At this stage, only attributes are parsed and the following attributes are
+// added to the attributes of the item.
+// - `#[derive(InternalDerive)]` - An internal helper macro that does the above
+//   processing.
+// - `#[pin(__private(#args))]` - Pass the argument of `#[pin_project]` to
+//   proc-macro-derive (`InternalDerive`).
+
+pub(super) fn parse_attribute(args: &TokenStream, input: TokenStream) -> Result<TokenStream> {
+    let Input { attrs, body } = syn::parse2(input)?;
+
+    Ok(quote! {
+        #(#attrs)*
+        #[derive(::pin_project::__private::__PinProjectInternalDerive)]
+        // Use `__private` to prevent users from trying to control `InternalDerive`
+        // manually. `__private` does not guarantee compatibility between patch
+        // versions, so it should be sufficient for this purpose in most cases.
+        #[pin(__private(#args))]
+        #body
+    })
+}
+
+#[allow(dead_code)] // false positive that fixed in Rust 1.39
+struct Input {
+    attrs: Vec<Attribute>,
+    body: TokenStream,
+}
+
+impl Parse for Input {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let attrs = input.call(Attribute::parse_outer)?;
+
+        let ahead = input.fork();
+        let _vis: Visibility = ahead.parse()?;
+        if !ahead.peek(Token![struct]) && !ahead.peek(Token![enum]) {
+            // If we check this only on proc-macro-derive, it may generate unhelpful error
+            // messages. So it is preferable to be able to detect it here.
+            bail!(
+                input.parse::<TokenStream>()?,
+                "#[pin_project] attribute may only be used on structs or enums"
+            );
+        } else if let Some(attr) = attrs.find(PIN) {
+            bail!(attr, "#[pin] attribute may only be used on fields of structs or variants");
+        } else if let Some(attr) = attrs.find("pin_project") {
+            bail!(attr, "duplicate #[pin_project] attribute");
+        }
+        Ok(Self { attrs, body: input.parse()? })
+    }
+}
diff --git a/third_party/rust/pin-project-internal/src/pin_project/derive.rs b/third_party/rust/pin-project-internal/src/pin_project/derive.rs
new file mode 100644
index 0000000000..d2b2b5e166
--- /dev/null
+++ b/third_party/rust/pin-project-internal/src/pin_project/derive.rs
@@ -0,0 +1,1122 @@
+use proc_macro2::{Delimiter, Group, Span, TokenStream};
+use quote::{format_ident, quote, quote_spanned, ToTokens};
+use syn::{
+    parse_quote, punctuated::Punctuated, token, visit_mut::VisitMut, Attribute, Data, DataEnum,
+    DeriveInput, Error, Field, Fields, FieldsNamed, FieldsUnnamed, Generics, Ident, Index,
+    Lifetime, LifetimeParam, Meta, Result, Token, Type, Variant, Visibility, WhereClause,
+};
+
+use super::{
+    args::{parse_args, Args, ProjReplace, UnpinImpl},
+    PIN,
+};
+use crate::utils::{
+    determine_lifetime_name, determine_visibility, insert_lifetime_and_bound, ReplaceReceiver,
+    SliceExt, Variants,
+};
+
+pub(super) fn parse_derive(input: TokenStream) -> Result<TokenStream> {
+    let mut input: DeriveInput = syn::parse2(input)?;
+
+    let mut cx;
+    let mut generate = GenerateTokens::default();
+
+    let ident = &input.ident;
+    let ty_generics = input.generics.split_for_impl().1;
+    let self_ty = parse_quote!(#ident #ty_generics);
+    let mut visitor = ReplaceReceiver(&self_ty);
+    visitor.visit_generics_mut(&mut input.generics);
+    visitor.visit_data_mut(&mut input.data);
+
+    match &input.data {
+        Data::Struct(data) => {
+            cx = Context::new(&input.attrs, &input.vis, ident, &mut input.generics, Struct)?;
+            parse_struct(&mut cx, &data.fields, &mut generate)?;
+        }
+        Data::Enum(data) => {
+            cx = Context::new(&input.attrs, &input.vis, ident, &mut input.generics, Enum)?;
+            parse_enum(&mut cx, data, &mut generate)?;
+        }
+        Data::Union(_) => {
+            bail!(input, "#[pin_project] attribute may only be used on structs or enums");
+        }
+    }
+
+    Ok(generate.into_tokens(&cx))
+}
+
+#[derive(Default)]
+struct GenerateTokens {
+    exposed: TokenStream,
+    scoped: TokenStream,
+}
+
+impl GenerateTokens {
+    fn extend(&mut self, expose: bool, tokens: TokenStream) {
+        if expose {
+            self.exposed.extend(tokens);
+        } else {
+            self.scoped.extend(tokens);
+        }
+    }
+
+    fn into_tokens(self, cx: &Context<'_>) -> TokenStream {
+        let mut tokens = self.exposed;
+        let scoped = self.scoped;
+
+        let unpin_impl = make_unpin_impl(cx);
+        let drop_impl = make_drop_impl(cx);
+        let allowed_lints = global_allowed_lints();
+
+        tokens.extend(quote! {
+            // All items except projected types are generated inside a `const` scope.
+            // This makes it impossible for user code to refer to these types.
+            // However, this prevents Rustdoc from displaying docs for any
+            // of our types. In particular, users cannot see the
+            // automatically generated `Unpin` impl for the '__UnpinStruct' types
+            //
+            // Previously, we provided a flag to correctly document the
+            // automatically generated `Unpin` impl by using def-site hygiene,
+            // but it is now removed.
+            //
+            // Refs:
+            // - https://github.com/rust-lang/rust/issues/63281
+            // - https://github.com/taiki-e/pin-project/pull/53#issuecomment-525906867
+            // - https://github.com/taiki-e/pin-project/pull/70
+            #allowed_lints
+            #[allow(unused_qualifications)]
+            #[allow(clippy::semicolon_if_nothing_returned)]
+            #[allow(clippy::use_self)]
+            #[allow(clippy::used_underscore_binding)]
+            const _: () = {
+                #[allow(unused_extern_crates)]
+                extern crate pin_project as _pin_project;
+                #scoped
+                #unpin_impl
+                #drop_impl
+            };
+        });
+        tokens
+    }
+}
+
+/// Returns attributes that should be applied to all generated code.
+fn global_allowed_lints() -> TokenStream {
+    quote! {
+        #[allow(box_pointers)] // This lint warns use of the `Box` type.
+        #[allow(deprecated)]
+        #[allow(explicit_outlives_requirements)] // https://github.com/rust-lang/rust/issues/60993
+        #[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
+        #[allow(unreachable_pub)] // This lint warns `pub` field in private struct.
+        #[allow(unused_tuple_struct_fields)]
+        // This lint warns of `clippy::*` generated by external macros.
+        // We allow this lint for compatibility with older compilers.
+        #[allow(clippy::unknown_clippy_lints)]
+        #[allow(clippy::pattern_type_mismatch)]
+        #[allow(clippy::redundant_pub_crate)] // This lint warns `pub(crate)` field in private struct.
+        #[allow(clippy::type_repetition_in_bounds)] // https://github.com/rust-lang/rust-clippy/issues/4326
+    }
+}
+
+/// Returns attributes used on projected types.
+fn proj_allowed_lints(cx: &Context<'_>) -> (TokenStream, TokenStream, TokenStream) {
+    let large_enum_variant = if cx.kind == Enum {
+        Some(quote! {
+            #[allow(variant_size_differences)]
+            #[allow(clippy::large_enum_variant)]
+        })
+    } else {
+        None
+    };
+    let global_allowed_lints = global_allowed_lints();
+    let proj_mut_allowed_lints = if cx.project { Some(&global_allowed_lints) } else { None };
+    let proj_mut = quote! {
+        #proj_mut_allowed_lints
+        #[allow(dead_code)] // This lint warns unused fields/variants.
+        #[allow(clippy::mut_mut)] // This lint warns `&mut &mut <ty>`.
+    };
+    let proj_ref_allowed_lints = if cx.project_ref { Some(&global_allowed_lints) } else { None };
+    let proj_ref = quote! {
+        #proj_ref_allowed_lints
+        #[allow(dead_code)] // This lint warns unused fields/variants.
+        #[allow(clippy::ref_option_ref)] // This lint warns `&Option<&<ty>>`.
+    };
+    let proj_own_allowed_lints =
+        if cx.project_replace.ident().is_some() { Some(&global_allowed_lints) } else { None };
+    let proj_own = quote! {
+        #proj_own_allowed_lints
+        #[allow(dead_code)] // This lint warns unused fields/variants.
+        #large_enum_variant
+    };
+    (proj_mut, proj_ref, proj_own)
+}
+
+struct Context<'a> {
+    /// The original type.
+    orig: OriginalType<'a>,
+    /// The projected types.
+    proj: ProjectedType,
+    /// Types of the pinned fields.
+    pinned_fields: Vec<&'a Type>,
+    /// Kind of the original type: struct or enum
+    kind: TypeKind,
+
+    /// `PinnedDrop` argument.
+    pinned_drop: Option<Span>,
+    /// `UnsafeUnpin` or `!Unpin` argument.
+    unpin_impl: UnpinImpl,
+    /// `project` argument.
+    project: bool,
+    /// `project_ref` argument.
+    project_ref: bool,
+    /// `project_replace [= <ident>]` argument.
+    project_replace: ProjReplace,
+}
+
+impl<'a> Context<'a> {
+    fn new(
+        attrs: &'a [Attribute],
+        vis: &'a Visibility,
+        ident: &'a Ident,
+        generics: &'a mut Generics,
+        kind: TypeKind,
+    ) -> Result<Self> {
+        let Args { pinned_drop, unpin_impl, project, project_ref, project_replace } =
+            parse_args(attrs)?;
+
+        if let Some(name) = [project.as_ref(), project_ref.as_ref(), project_replace.ident()]
+            .iter()
+            .filter_map(Option::as_ref)
+            .find(|name| **name == ident)
+        {
+            bail!(name, "name `{}` is the same as the original type name", name);
+        }
+
+        let mut lifetime_name = String::from("'pin");
+        determine_lifetime_name(&mut lifetime_name, generics);
+        let lifetime = Lifetime::new(&lifetime_name, Span::call_site());
+
+        let ty_generics = generics.split_for_impl().1;
+        let ty_generics_as_generics = parse_quote!(#ty_generics);
+        let mut proj_generics = generics.clone();
+        let pred = insert_lifetime_and_bound(
+            &mut proj_generics,
+            lifetime.clone(),
+            &ty_generics_as_generics,
+            ident,
+        );
+        let mut where_clause = generics.make_where_clause().clone();
+        where_clause.predicates.push(pred);
+
+        let own_ident = project_replace
+            .ident()
+            .cloned()
+            .unwrap_or_else(|| format_ident!("__{}ProjectionOwned", ident));
+
+        Ok(Self {
+            kind,
+            pinned_drop,
+            unpin_impl,
+            project: project.is_some(),
+            project_ref: project_ref.is_some(),
+            project_replace,
+            proj: ProjectedType {
+                vis: determine_visibility(vis),
+                mut_ident: project.unwrap_or_else(|| format_ident!("__{}Projection", ident)),
+                ref_ident: project_ref.unwrap_or_else(|| format_ident!("__{}ProjectionRef", ident)),
+                own_ident,
+                lifetime,
+                generics: proj_generics,
+                where_clause,
+            },
+            orig: OriginalType { attrs, vis, ident, generics },
+            pinned_fields: Vec::new(),
+        })
+    }
+}
+
+#[derive(Copy, Clone, PartialEq)]
+enum TypeKind {
+    Enum,
+    Struct,
+}
+
+use TypeKind::{Enum, Struct};
+
+struct OriginalType<'a> {
+    /// Attributes of the original type.
+    attrs: &'a [Attribute],
+    /// Visibility of the original type.
+    vis: &'a Visibility,
+    /// Name of the original type.
+    ident: &'a Ident,
+    /// Generics of the original type.
+    generics: &'a Generics,
+}
+
+struct ProjectedType {
+    /// Visibility of the projected types.
+    vis: Visibility,
+    /// Name of the projected type returned by `project` method.
+    mut_ident: Ident,
+    /// Name of the projected type returned by `project_ref` method.
+    ref_ident: Ident,
+    /// Name of the projected type returned by `project_replace` method.
+    own_ident: Ident,
+    /// Lifetime on the generated projected types.
+    lifetime: Lifetime,
+    /// Generics of the projected types.
+    generics: Generics,
+    /// `where` clause of the projected types. This has an additional
+    /// bound generated by `insert_lifetime_and_bound`
+    where_clause: WhereClause,
+}
+
+struct ProjectedVariants {
+    proj_variants: TokenStream,
+    proj_ref_variants: TokenStream,
+    proj_own_variants: TokenStream,
+    proj_arms: TokenStream,
+    proj_ref_arms: TokenStream,
+    proj_own_arms: TokenStream,
+}
+
+#[derive(Default)]
+struct ProjectedFields {
+    proj_pat: TokenStream,
+    proj_body: TokenStream,
+    proj_own_body: TokenStream,
+    proj_fields: TokenStream,
+    proj_ref_fields: TokenStream,
+    proj_own_fields: TokenStream,
+}
+
+fn validate_struct(ident: &Ident, fields: &Fields) -> Result<()> {
+    if fields.is_empty() {
+        let msg = "#[pin_project] attribute may not be used on structs with zero fields";
+        if let Fields::Unit = fields {
+            bail!(ident, msg)
+        }
+        bail!(fields, msg)
+    }
+    Ok(())
+}
+
+fn validate_enum(brace_token: token::Brace, variants: &Variants) -> Result<()> {
+    if variants.is_empty() {
+        return Err(Error::new(
+            brace_token.span.join(),
+            "#[pin_project] attribute may not be used on enums without variants",
+        ));
+    }
+    let has_field = variants.iter().try_fold(false, |has_field, v| {
+        if let Some((_, e)) = &v.discriminant {
+            bail!(e, "#[pin_project] attribute may not be used on enums with discriminants");
+        } else if let Some(attr) = v.attrs.find(PIN) {
+            bail!(attr, "#[pin] attribute may only be used on fields of structs or variants");
+        } else if v.fields.is_empty() {
+            Ok(has_field)
+        } else {
+            Ok(true)
+        }
+    })?;
+    if has_field {
+        Ok(())
+    } else {
+        bail!(variants, "#[pin_project] attribute may not be used on enums with zero fields");
+    }
+}
+
+fn parse_struct<'a>(
+    cx: &mut Context<'a>,
+    fields: &'a Fields,
+    generate: &mut GenerateTokens,
+) -> Result<()> {
+    // Do this first for a better error message.
+    let packed_check = ensure_not_packed(&cx.orig, Some(fields))?;
+
+    validate_struct(cx.orig.ident, fields)?;
+
+    let ProjectedFields {
+        proj_pat,
+        proj_body,
+        proj_fields,
+        proj_ref_fields,
+        proj_own_fields,
+        proj_own_body,
+    } = match fields {
+        Fields::Named(_) => visit_fields(cx, None, fields, Delimiter::Brace)?,
+        Fields::Unnamed(_) => visit_fields(cx, None, fields, Delimiter::Parenthesis)?,
+        Fields::Unit => unreachable!(),
+    };
+
+    let proj_ident = &cx.proj.mut_ident;
+    let proj_ref_ident = &cx.proj.ref_ident;
+    let proj_own_ident = &cx.proj.own_ident;
+    let vis = &cx.proj.vis;
+    let mut orig_generics = cx.orig.generics.clone();
+    let orig_where_clause = orig_generics.where_clause.take();
+    let proj_generics = &cx.proj.generics;
+    let proj_where_clause = &cx.proj.where_clause;
+
+    // For tuple structs, we need to generate `(T1, T2) where Foo: Bar`
+    // For non-tuple structs, we need to generate `where Foo: Bar { field1: T }`
+    let (where_clause_fields, where_clause_ref_fields, where_clause_own_fields) = match fields {
+        Fields::Named(_) => (
+            quote!(#proj_where_clause #proj_fields),
+            quote!(#proj_where_clause #proj_ref_fields),
+            quote!(#orig_where_clause #proj_own_fields),
+        ),
+        Fields::Unnamed(_) => (
+            quote!(#proj_fields #proj_where_clause;),
+            quote!(#proj_ref_fields #proj_where_clause;),
+            quote!(#proj_own_fields #orig_where_clause;),
+        ),
+        Fields::Unit => unreachable!(),
+    };
+
+    let (proj_attrs, proj_ref_attrs, proj_own_attrs) = proj_allowed_lints(cx);
+    generate.extend(cx.project, quote! {
+        #proj_attrs
+        #vis struct #proj_ident #proj_generics #where_clause_fields
+    });
+    generate.extend(cx.project_ref, quote! {
+        #proj_ref_attrs
+        #vis struct #proj_ref_ident #proj_generics #where_clause_ref_fields
+    });
+    if cx.project_replace.span().is_some() {
+        generate.extend(cx.project_replace.ident().is_some(), quote! {
+            #proj_own_attrs
+            #vis struct #proj_own_ident #orig_generics #where_clause_own_fields
+        });
+    }
+
+    let proj_mut_body = quote! {
+        let Self #proj_pat = self.get_unchecked_mut();
+        #proj_ident #proj_body
+    };
+    let proj_ref_body = quote! {
+        let Self #proj_pat = self.get_ref();
+        #proj_ref_ident #proj_body
+    };
+    let proj_own_body = quote! {
+        let Self #proj_pat = &mut *__self_ptr;
+        #proj_own_body
+    };
+    generate.extend(false, make_proj_impl(cx, &proj_mut_body, &proj_ref_body, &proj_own_body));
+
+    generate.extend(false, packed_check);
+    Ok(())
+}
+
+fn parse_enum<'a>(
+    cx: &mut Context<'a>,
+    DataEnum { brace_token, variants, .. }: &'a DataEnum,
+    generate: &mut GenerateTokens,
+) -> Result<()> {
+    if let ProjReplace::Unnamed { span } = &cx.project_replace {
+        return Err(Error::new(
+            *span,
+            "`project_replace` argument requires a value when used on enums",
+        ));
+    }
+
+    // #[repr(packed)] cannot be apply on enums and will be rejected by rustc.
+    // However, we should not rely on the behavior of rustc that rejects this.
+    // https://github.com/taiki-e/pin-project/pull/324#discussion_r612388001
+    //
+    // Do this first for a better error message.
+    ensure_not_packed(&cx.orig, None)?;
+
+    validate_enum(*brace_token, variants)?;
+
+    let ProjectedVariants {
+        proj_variants,
+        proj_ref_variants,
+        proj_own_variants,
+        proj_arms,
+        proj_ref_arms,
+        proj_own_arms,
+    } = visit_variants(cx, variants)?;
+
+    let proj_ident = &cx.proj.mut_ident;
+    let proj_ref_ident = &cx.proj.ref_ident;
+    let proj_own_ident = &cx.proj.own_ident;
+    let vis = &cx.proj.vis;
+    let mut orig_generics = cx.orig.generics.clone();
+    let orig_where_clause = orig_generics.where_clause.take();
+    let proj_generics = &cx.proj.generics;
+    let proj_where_clause = &cx.proj.where_clause;
+
+    let (proj_attrs, proj_ref_attrs, proj_own_attrs) = proj_allowed_lints(cx);
+    if cx.project {
+        generate.extend(true, quote! {
+            #proj_attrs
+            #vis enum #proj_ident #proj_generics #proj_where_clause {
+                #proj_variants
+            }
+        });
+    }
+    if cx.project_ref {
+        generate.extend(true, quote! {
+            #proj_ref_attrs
+            #vis enum #proj_ref_ident #proj_generics #proj_where_clause {
+                #proj_ref_variants
+            }
+        });
+    }
+    if cx.project_replace.ident().is_some() {
+        generate.extend(true, quote! {
+            #proj_own_attrs
+            #vis enum #proj_own_ident #orig_generics #orig_where_clause {
+                #proj_own_variants
+            }
+        });
+    }
+
+    let proj_mut_body = quote! {
+        match self.get_unchecked_mut() {
+            #proj_arms
+        }
+    };
+    let proj_ref_body = quote! {
+        match self.get_ref() {
+            #proj_ref_arms
+        }
+    };
+    let proj_own_body = quote! {
+        match &mut *__self_ptr {
+            #proj_own_arms
+        }
+    };
+    generate.extend(false, make_proj_impl(cx, &proj_mut_body, &proj_ref_body, &proj_own_body));
+
+    Ok(())
+}
+
+fn visit_variants<'a>(cx: &mut Context<'a>, variants: &'a Variants) -> Result<ProjectedVariants> {
+    let mut proj_variants = TokenStream::new();
+    let mut proj_ref_variants = TokenStream::new();
+    let mut proj_own_variants = TokenStream::new();
+    let mut proj_arms = TokenStream::new();
+    let mut proj_ref_arms = TokenStream::new();
+    let mut proj_own_arms = TokenStream::new();
+
+    for Variant { ident, fields, .. } in variants {
+        let ProjectedFields {
+            proj_pat,
+            proj_body,
+            proj_fields,
+            proj_ref_fields,
+            proj_own_fields,
+            proj_own_body,
+        } = match fields {
+            Fields::Named(_) => visit_fields(cx, Some(ident), fields, Delimiter::Brace)?,
+            Fields::Unnamed(_) => visit_fields(cx, Some(ident), fields, Delimiter::Parenthesis)?,
+            Fields::Unit => ProjectedFields {
+                proj_own_body: proj_own_body(cx, Some(ident), None, &[]),
+                ..Default::default()
+            },
+        };
+
+        let proj_ident = &cx.proj.mut_ident;
+        let proj_ref_ident = &cx.proj.ref_ident;
+        proj_variants.extend(quote! {
+            #ident #proj_fields,
+        });
+        proj_ref_variants.extend(quote! {
+            #ident #proj_ref_fields,
+        });
+        proj_own_variants.extend(quote! {
+            #ident #proj_own_fields,
+        });
+        proj_arms.extend(quote! {
+            Self::#ident #proj_pat => #proj_ident::#ident #proj_body,
+        });
+        proj_ref_arms.extend(quote! {
+            Self::#ident #proj_pat => #proj_ref_ident::#ident #proj_body,
+        });
+        proj_own_arms.extend(quote! {
+            Self::#ident #proj_pat => { #proj_own_body }
+        });
+    }
+
+    Ok(ProjectedVariants {
+        proj_variants,
+        proj_ref_variants,
+        proj_own_variants,
+        proj_arms,
+        proj_ref_arms,
+        proj_own_arms,
+    })
+}
+
+fn visit_fields<'a>(
+    cx: &mut Context<'a>,
+    variant_ident: Option<&Ident>,
+    fields: &'a Fields,
+    delim: Delimiter,
+) -> Result<ProjectedFields> {
+    fn surround(delim: Delimiter, tokens: TokenStream) -> TokenStream {
+        Group::new(delim, tokens).into_token_stream()
+    }
+
+    let mut proj_pat = TokenStream::new();
+    let mut proj_body = TokenStream::new();
+    let mut proj_fields = TokenStream::new();
+    let mut proj_ref_fields = TokenStream::new();
+    let mut proj_own_fields = TokenStream::new();
+    let mut proj_move = TokenStream::new();
+    let mut pinned_bindings = Vec::with_capacity(fields.len());
+
+    for (i, Field { attrs, vis, ident, colon_token, ty, mutability: _ }) in
+        fields.iter().enumerate()
+    {
+        let binding = ident.clone().unwrap_or_else(|| format_ident!("_{}", i));
+        proj_pat.extend(quote!(#binding,));
+        let lifetime = &cx.proj.lifetime;
+        if attrs.position_exact(PIN)?.is_some() {
+            proj_fields.extend(quote! {
+                #vis #ident #colon_token ::pin_project::__private::Pin<&#lifetime mut (#ty)>,
+            });
+            proj_ref_fields.extend(quote! {
+                #vis #ident #colon_token ::pin_project::__private::Pin<&#lifetime (#ty)>,
+            });
+            proj_own_fields.extend(quote! {
+                #vis #ident #colon_token ::pin_project::__private::PhantomData<#ty>,
+            });
+            proj_body.extend(quote! {
+                #ident #colon_token _pin_project::__private::Pin::new_unchecked(#binding),
+            });
+            proj_move.extend(quote! {
+                #ident #colon_token _pin_project::__private::PhantomData,
+            });
+
+            cx.pinned_fields.push(ty);
+            pinned_bindings.push(binding);
+        } else {
+            proj_fields.extend(quote! {
+                #vis #ident #colon_token &#lifetime mut (#ty),
+            });
+            proj_ref_fields.extend(quote! {
+                #vis #ident #colon_token &#lifetime (#ty),
+            });
+            proj_own_fields.extend(quote! {
+                #vis #ident #colon_token #ty,
+            });
+            proj_body.extend(quote! {
+                #binding,
+            });
+            proj_move.extend(quote! {
+                #ident #colon_token _pin_project::__private::ptr::read(#binding),
+            });
+        }
+    }
+
+    let proj_pat = surround(delim, proj_pat);
+    let proj_body = surround(delim, proj_body);
+    let proj_fields = surround(delim, proj_fields);
+    let proj_ref_fields = surround(delim, proj_ref_fields);
+    let proj_own_fields = surround(delim, proj_own_fields);
+
+    let proj_move = Group::new(delim, proj_move);
+    let proj_own_body = proj_own_body(cx, variant_ident, Some(&proj_move), &pinned_bindings);
+
+    Ok(ProjectedFields {
+        proj_pat,
+        proj_body,
+        proj_own_body,
+        proj_fields,
+        proj_ref_fields,
+        proj_own_fields,
+    })
+}
+
+/// Generates the processing that `project_replace` does for the struct or each variant.
+///
+/// Note: `pinned_fields` must be in declaration order.
+fn proj_own_body(
+    cx: &Context<'_>,
+    variant_ident: Option<&Ident>,
+    proj_move: Option<&Group>,
+    pinned_fields: &[Ident],
+) -> TokenStream {
+    let ident = &cx.proj.own_ident;
+    let proj_own = match variant_ident {
+        Some(variant_ident) => quote!(#ident::#variant_ident),
+        None => quote!(#ident),
+    };
+
+    // The fields of the struct and the active enum variant are dropped
+    // in declaration order.
+    // Refs: https://doc.rust-lang.org/reference/destructors.html
+    let pinned_fields = pinned_fields.iter().rev();
+
+    quote! {
+        // First, extract all the unpinned fields.
+        let __result = #proj_own #proj_move;
+
+        // Now create guards to drop all the pinned fields.
+        //
+        // Due to a compiler bug (https://github.com/rust-lang/rust/issues/47949)
+        // this must be in its own scope, or else `__result` will not be dropped
+        // if any of the destructors panic.
+        {
+            #(
+                let __guard = _pin_project::__private::UnsafeDropInPlaceGuard::new(#pinned_fields);
+            )*
+        }
+
+        // Finally, return the result.
+        __result
+    }
+}
+
+/// Creates `Unpin` implementation for the original type.
+///
+/// The kind of `Unpin` impl generated depends on `unpin_impl` field:
+/// - `UnpinImpl::Unsafe` - Implements `Unpin` via `UnsafeUnpin` impl.
+/// - `UnpinImpl::Negative` - Generates `Unpin` impl with bounds that will never be true.
+/// - `UnpinImpl::Default` - Generates `Unpin` impl that requires `Unpin` for all pinned fields.
+fn make_unpin_impl(cx: &Context<'_>) -> TokenStream {
+    match cx.unpin_impl {
+        UnpinImpl::Unsafe(span) => {
+            let mut proj_generics = cx.proj.generics.clone();
+            let orig_ident = cx.orig.ident;
+            let lifetime = &cx.proj.lifetime;
+
+            // Make the error message highlight `UnsafeUnpin` argument.
+            proj_generics.make_where_clause().predicates.push(parse_quote_spanned! { span =>
+                _pin_project::__private::Wrapper<#lifetime, Self>: _pin_project::UnsafeUnpin
+            });
+
+            let (impl_generics, _, where_clause) = proj_generics.split_for_impl();
+            let ty_generics = cx.orig.generics.split_for_impl().1;
+
+            quote_spanned! { span =>
+                impl #impl_generics _pin_project::__private::Unpin for #orig_ident #ty_generics
+                #where_clause
+                {
+                }
+            }
+        }
+        UnpinImpl::Negative(span) => {
+            let mut proj_generics = cx.proj.generics.clone();
+            let orig_ident = cx.orig.ident;
+            let lifetime = &cx.proj.lifetime;
+
+            proj_generics.make_where_clause().predicates.push(parse_quote! {
+                _pin_project::__private::Wrapper<
+                    #lifetime, _pin_project::__private::PhantomPinned
+                >: _pin_project::__private::Unpin
+            });
+
+            let (proj_impl_generics, _, proj_where_clause) = proj_generics.split_for_impl();
+            let ty_generics = cx.orig.generics.split_for_impl().1;
+
+            // For interoperability with `forbid(unsafe_code)`, `unsafe` token should be
+            // call-site span.
+            let unsafety = <Token![unsafe]>::default();
+            quote_spanned! { span =>
+                impl #proj_impl_generics _pin_project::__private::Unpin
+                    for #orig_ident #ty_generics
+                #proj_where_clause
+                {
+                }
+
+                // Generate a dummy impl of `UnsafeUnpin`, to ensure that the user cannot implement it.
+                //
+                // To ensure that users don't accidentally write a non-functional `UnsafeUnpin`
+                // impls, we emit one ourselves. If the user ends up writing an `UnsafeUnpin`
+                // impl, they'll get a "conflicting implementations of trait" error when
+                // coherence checks are run.
+                #[doc(hidden)]
+                #unsafety impl #proj_impl_generics _pin_project::UnsafeUnpin
+                    for #orig_ident #ty_generics
+                #proj_where_clause
+                {
+                }
+            }
+        }
+        UnpinImpl::Default => {
+            let mut full_where_clause = cx.orig.generics.where_clause.clone().unwrap();
+
+            // Generate a field in our new struct for every
+            // pinned field in the original type.
+            let fields = cx.pinned_fields.iter().enumerate().map(|(i, ty)| {
+                let field_ident = format_ident!("__field{}", i);
+                quote!(#field_ident: #ty)
+            });
+
+            // We could try to determine the subset of type parameters
+            // and lifetimes that are actually used by the pinned fields
+            // (as opposed to those only used by unpinned fields).
+            // However, this would be tricky and error-prone, since
+            // it's possible for users to create types that would alias
+            // with generic parameters (e.g. 'struct T').
+            //
+            // Instead, we generate a use of every single type parameter
+            // and lifetime used in the original struct. For type parameters,
+            // we generate code like this:
+            //
+            // ```rust
+            // struct AlwaysUnpin<T: ?Sized>(PhantomData<T>) {}
+            // impl<T: ?Sized> Unpin for AlwaysUnpin<T> {}
+            //
+            // ...
+            // _field: AlwaysUnpin<(A, B, C)>
+            // ```
+            //
+            // This ensures that any unused type parameters
+            // don't end up with `Unpin` bounds.
+            let lifetime_fields = cx.orig.generics.lifetimes().enumerate().map(
+                |(i, LifetimeParam { lifetime, .. })| {
+                    let field_ident = format_ident!("__lifetime{}", i);
+                    quote!(#field_ident: &#lifetime ())
+                },
+            );
+
+            let orig_ident = cx.orig.ident;
+            let struct_ident = format_ident!("__{}", orig_ident);
+            let vis = cx.orig.vis;
+            let lifetime = &cx.proj.lifetime;
+            let type_params = cx.orig.generics.type_params().map(|t| &t.ident);
+            let proj_generics = &cx.proj.generics;
+            let (proj_impl_generics, proj_ty_generics, _) = proj_generics.split_for_impl();
+            let (_, ty_generics, where_clause) = cx.orig.generics.split_for_impl();
+
+            full_where_clause.predicates.push(parse_quote! {
+                #struct_ident #proj_ty_generics: _pin_project::__private::Unpin
+            });
+
+            quote! {
+                // This needs to have the same visibility as the original type,
+                // due to the limitations of the 'public in private' error.
+                //
+                // Our goal is to implement the public trait `Unpin` for
+                // a potentially public user type. Because of this, rust
+                // requires that any types mentioned in the where clause of
+                // our `Unpin` impl also be public. This means that our generated
+                // `__UnpinStruct` type must also be public.
+                // However, we ensure that the user can never actually reference
+                // this 'public' type by creating this type in the inside of `const`.
+                #[allow(missing_debug_implementations)]
+                #vis struct #struct_ident #proj_generics #where_clause {
+                    __pin_project_use_generics: _pin_project::__private::AlwaysUnpin<
+                        #lifetime, (#(_pin_project::__private::PhantomData<#type_params>),*)
+                    >,
+
+                    #(#fields,)*
+                    #(#lifetime_fields,)*
+                }
+
+                impl #proj_impl_generics _pin_project::__private::Unpin
+                    for #orig_ident #ty_generics
+                #full_where_clause
+                {
+                }
+
+                // Generate a dummy impl of `UnsafeUnpin`, to ensure that the user cannot implement it.
+                //
+                // To ensure that users don't accidentally write a non-functional `UnsafeUnpin`
+                // impls, we emit one ourselves. If the user ends up writing an `UnsafeUnpin`
+                // impl, they'll get a "conflicting implementations of trait" error when
+                // coherence checks are run.
+                #[doc(hidden)]
+                unsafe impl #proj_impl_generics _pin_project::UnsafeUnpin
+                    for #orig_ident #ty_generics
+                #full_where_clause
+                {
+                }
+            }
+        }
+    }
+}
+
+/// Creates `Drop` implementation for the original type.
+///
+/// The kind of `Drop` impl generated depends on `pinned_drop` field:
+/// - `Some` - implements `Drop` via `PinnedDrop` impl.
+/// - `None` - generates code that ensures that `Drop` trait is not implemented,
+///            instead of generating `Drop` impl.
+fn make_drop_impl(cx: &Context<'_>) -> TokenStream {
+    let ident = cx.orig.ident;
+    let (impl_generics, ty_generics, where_clause) = cx.orig.generics.split_for_impl();
+
+    if let Some(span) = cx.pinned_drop {
+        // For interoperability with `forbid(unsafe_code)`, `unsafe` token should be
+        // call-site span.
+        let unsafety = <Token![unsafe]>::default();
+        quote_spanned! { span =>
+            impl #impl_generics _pin_project::__private::Drop for #ident #ty_generics
+            #where_clause
+            {
+                fn drop(&mut self) {
+                    #unsafety {
+                        // Safety - we're in 'drop', so we know that 'self' will
+                        // never move again.
+                        let __pinned_self = _pin_project::__private::Pin::new_unchecked(self);
+                        // We call `pinned_drop` only once. Since `PinnedDrop::drop`
+                        // is an unsafe method and a private API, it is never called again in safe
+                        // code *unless the user uses a maliciously crafted macro*.
+                        _pin_project::__private::PinnedDrop::drop(__pinned_self);
+                    }
+                }
+            }
+        }
+    } else {
+        // If the user does not provide a `PinnedDrop` impl,
+        // we need to ensure that they don't provide a `Drop` impl of their
+        // own.
+        // Based on https://github.com/upsuper/assert-impl/blob/f503255b292ab0ba8d085b657f4065403cfa46eb/src/lib.rs#L80-L87
+        //
+        // We create a new identifier for each struct, so that the traits
+        // for different types do not conflict with each other.
+        //
+        // Another approach would be to provide an empty Drop impl,
+        // which would conflict with a user-provided Drop impl.
+        // However, this would trigger the compiler's special handling
+        // of Drop types (e.g. fields cannot be moved out of a Drop type).
+        // This approach prevents the creation of needless Drop impls,
+        // giving users more flexibility.
+        let trait_ident = format_ident!("{}MustNotImplDrop", ident);
+
+        quote! {
+            // There are two possible cases:
+            // 1. The user type does not implement Drop. In this case,
+            // the first blanked impl will not apply to it. This code
+            // will compile, as there is only one impl of MustNotImplDrop for the user type
+            // 2. The user type does impl Drop. This will make the blanket impl applicable,
+            // which will then conflict with the explicit MustNotImplDrop impl below.
+            // This will result in a compilation error, which is exactly what we want.
+            trait #trait_ident {}
+            #[allow(clippy::drop_bounds, drop_bounds)]
+            impl<T: _pin_project::__private::Drop> #trait_ident for T {}
+            impl #impl_generics #trait_ident for #ident #ty_generics #where_clause {}
+
+            // Generate a dummy impl of `PinnedDrop`, to ensure that the user cannot implement it.
+            // Since the user did not pass `PinnedDrop` to `#[pin_project]`, any `PinnedDrop`
+            // impl will not actually be called. Unfortunately, we can't detect this situation
+            // directly from either the `#[pin_project]` or `#[pinned_drop]` attributes, since
+            // we don't know what other attributes/impl may exist.
+            //
+            // To ensure that users don't accidentally write a non-functional `PinnedDrop`
+            // impls, we emit one ourselves. If the user ends up writing a `PinnedDrop` impl,
+            // they'll get a "conflicting implementations of trait" error when coherence
+            // checks are run.
+            #[doc(hidden)]
+            impl #impl_generics _pin_project::__private::PinnedDrop for #ident #ty_generics
+            #where_clause
+            {
+                unsafe fn drop(self: _pin_project::__private::Pin<&mut Self>) {}
+            }
+        }
+    }
+}
+
+/// Creates an implementation of the projection methods.
+///
+/// On structs, both the `project` and `project_ref` methods are always generated,
+/// and the `project_replace` method is only generated if `ProjReplace::span` is `Some`.
+///
+/// On enums, only methods that the returned projected type is named will be generated.
+fn make_proj_impl(
+    cx: &Context<'_>,
+    proj_body: &TokenStream,
+    proj_ref_body: &TokenStream,
+    proj_own_body: &TokenStream,
+) -> TokenStream {
+    let vis = &cx.proj.vis;
+    let lifetime = &cx.proj.lifetime;
+    let orig_ident = cx.orig.ident;
+    let proj_ident = &cx.proj.mut_ident;
+    let proj_ref_ident = &cx.proj.ref_ident;
+    let proj_own_ident = &cx.proj.own_ident;
+
+    let orig_ty_generics = cx.orig.generics.split_for_impl().1;
+    let proj_ty_generics = cx.proj.generics.split_for_impl().1;
+    let (impl_generics, ty_generics, where_clause) = cx.orig.generics.split_for_impl();
+    // TODO: For enums and project_replace, dead_code warnings should not be
+    // allowed because methods are not generated unless explicitly specified.
+    // However, there is currently no good way to allow warnings for generated
+    // code, so we allow warnings for all methods for now.
+    let allow_dead_code = quote! { #[allow(dead_code)] };
+
+    let mut project = Some(quote! {
+        #allow_dead_code
+        #vis fn project<#lifetime>(
+            self: _pin_project::__private::Pin<&#lifetime mut Self>,
+        ) -> #proj_ident #proj_ty_generics {
+            unsafe {
+                #proj_body
+            }
+        }
+    });
+    let mut project_ref = Some(quote! {
+        #allow_dead_code
+        #[allow(clippy::missing_const_for_fn)]
+        #vis fn project_ref<#lifetime>(
+            self: _pin_project::__private::Pin<&#lifetime Self>,
+        ) -> #proj_ref_ident #proj_ty_generics {
+            unsafe {
+                #proj_ref_body
+            }
+        }
+    });
+    let mut project_replace = cx.project_replace.span().map(|span| {
+        // It is enough to only set the span of the signature.
+        let sig = quote_spanned! { span =>
+            #allow_dead_code
+            #vis fn project_replace(
+                self: _pin_project::__private::Pin<&mut Self>,
+                __replacement: Self,
+            ) -> #proj_own_ident #orig_ty_generics
+        };
+        quote! {
+            #sig {
+                unsafe {
+                    let __self_ptr: *mut Self = self.get_unchecked_mut();
+
+                    // Destructors will run in reverse order, so next create a guard to overwrite
+                    // `self` with the replacement value without calling destructors.
+                    let __guard = _pin_project::__private::UnsafeOverwriteGuard::new(
+                        __self_ptr,
+                        __replacement,
+                    );
+
+                    #proj_own_body
+                }
+            }
+        }
+    });
+
+    if cx.kind == Enum {
+        if !cx.project {
+            project = None;
+        }
+        if !cx.project_ref {
+            project_ref = None;
+        }
+        if cx.project_replace.ident().is_none() {
+            project_replace = None;
+        }
+    }
+
+    quote! {
+        impl #impl_generics #orig_ident #ty_generics #where_clause {
+            #project
+            #project_ref
+            #project_replace
+        }
+    }
+}
+
+/// Checks that the `[repr(packed)]` attribute is not included.
+///
+/// This currently does two checks:
+/// - Checks the attributes of structs to ensure there is no `[repr(packed)]`.
+/// - Generates a function that borrows fields without an unsafe block and
+///   forbidding `unaligned_references` lint.
+fn ensure_not_packed(orig: &OriginalType<'_>, fields: Option<&Fields>) -> Result<TokenStream> {
+    for attr in orig.attrs {
+        if let Meta::List(ref list) = attr.meta {
+            if list.path.is_ident("repr") {
+                for repr in list.parse_args_with(Punctuated::<Meta, Token![,]>::parse_terminated)? {
+                    if repr.path().is_ident("packed") {
+                        let msg = if fields.is_none() {
+                            // #[repr(packed)] cannot be apply on enums and will be rejected by rustc.
+                            // However, we should not rely on the behavior of rustc that rejects this.
+                            // https://github.com/taiki-e/pin-project/pull/324#discussion_r612388001
+                            "#[repr(packed)] attribute should be applied to a struct or union"
+                        } else if repr.require_name_value().is_ok() {
+                            // #[repr(packed = "")] is not valid format of #[repr(packed)] and will be
+                            // rejected by rustc.
+                            // However, we should not rely on the behavior of rustc that rejects this.
+                            // https://github.com/taiki-e/pin-project/pull/324#discussion_r612388001
+                            "#[repr(packed)] attribute should not be name-value pair"
+                        } else {
+                            "#[pin_project] attribute may not be used on #[repr(packed)] types"
+                        };
+                        bail!(repr, msg);
+                    }
+                }
+            }
+        }
+    }
+
+    let fields = match fields {
+        Some(fields) => fields,
+        None => return Ok(TokenStream::new()),
+    };
+
+    // Workaround for https://github.com/taiki-e/pin-project/issues/32
+    // Through the tricky use of proc macros, it's possible to bypass
+    // the above check for the `repr` attribute.
+    // To ensure that it's impossible to use pin projections on a `#[repr(packed)]`
+    // struct, we generate code like this:
+    //
+    // ```rust
+    // #[forbid(unaligned_references)]
+    // fn assert_not_repr_packed(val: &MyStruct) {
+    //     let _field_1 = &val.field_1;
+    //     let _field_2 = &val.field_2;
+    //     ...
+    //     let _field_n = &val.field_n;
+    // }
+    // ```
+    //
+    // Taking a reference to a packed field is UB, and applying
+    // `#[forbid(unaligned_references)]` makes sure that doing this is a hard error.
+    //
+    // If the struct ends up having `#[repr(packed)]` applied somehow,
+    // this will generate an (unfriendly) error message. Under all reasonable
+    // circumstances, we'll detect the `#[repr(packed)]` attribute, and generate
+    // a much nicer error above.
+    //
+    // There is one exception: If the type of a struct field has an alignment of 1
+    // (e.g. u8), it is always safe to take a reference to it, even if the struct
+    // is `#[repr(packed)]`. If the struct is composed entirely of types of
+    // alignment 1, our generated method will not trigger an error if the
+    // struct is `#[repr(packed)]`.
+    //
+    // Fortunately, this should have no observable consequence - `#[repr(packed)]`
+    // is essentially a no-op on such a type. Nevertheless, we include a test
+    // to ensure that the compiler doesn't ever try to copy the fields on
+    // such a struct when trying to drop it - which is reason we prevent
+    // `#[repr(packed)]` in the first place.
+    //
+    // See also https://github.com/taiki-e/pin-project/pull/34.
+    //
+    // Note:
+    // - Lint-based tricks aren't perfect, but they're much better than nothing:
+    //   https://github.com/taiki-e/pin-project-lite/issues/26
+    //
+    // - Enable both unaligned_references and safe_packed_borrows lints
+    //   because unaligned_references lint does not exist in older compilers:
+    //   https://github.com/taiki-e/pin-project-lite/pull/55
+    //   https://github.com/rust-lang/rust/pull/82525
+    let mut field_refs = vec![];
+    match fields {
+        Fields::Named(FieldsNamed { named, .. }) => {
+            for Field { ident, .. } in named {
+                field_refs.push(quote!(&this.#ident));
+            }
+        }
+        Fields::Unnamed(FieldsUnnamed { unnamed, .. }) => {
+            for (index, _) in unnamed.iter().enumerate() {
+                let index = Index::from(index);
+                field_refs.push(quote!(&this.#index));
+            }
+        }
+        Fields::Unit => {}
+    }
+
+    let (impl_generics, ty_generics, where_clause) = orig.generics.split_for_impl();
+    let ident = orig.ident;
+    Ok(quote! {
+        #[forbid(unaligned_references, safe_packed_borrows)]
+        fn __assert_not_repr_packed #impl_generics (this: &#ident #ty_generics) #where_clause {
+            #(let _ = #field_refs;)*
+        }
+    })
+}
diff --git a/third_party/rust/pin-project-internal/src/pin_project/mod.rs b/third_party/rust/pin-project-internal/src/pin_project/mod.rs
new file mode 100644
index 0000000000..2dce78f37f
--- /dev/null
+++ b/third_party/rust/pin-project-internal/src/pin_project/mod.rs
@@ -0,0 +1,17 @@
+mod args;
+mod attribute;
+mod derive;
+
+use proc_macro2::TokenStream;
+use syn::Error;
+
+/// The annotation for pinned type.
+const PIN: &str = "pin";
+
+pub(crate) fn attribute(args: &TokenStream, input: TokenStream) -> TokenStream {
+    attribute::parse_attribute(args, input).unwrap_or_else(Error::into_compile_error)
+}
+
+pub(crate) fn derive(input: TokenStream) -> TokenStream {
+    derive::parse_derive(input).unwrap_or_else(Error::into_compile_error)
+}
diff --git a/third_party/rust/pin-project-internal/src/pinned_drop.rs b/third_party/rust/pin-project-internal/src/pinned_drop.rs
new file mode 100644
index 0000000000..d30ecbebaa
--- /dev/null
+++ b/third_party/rust/pin-project-internal/src/pinned_drop.rs
@@ -0,0 +1,235 @@
+use proc_macro2::TokenStream;
+use quote::{format_ident, quote, ToTokens};
+use syn::{
+    parse_quote, spanned::Spanned, token::Colon, visit_mut::VisitMut, Error, FnArg,
+    GenericArgument, Ident, ImplItem, ItemImpl, Pat, PatIdent, PatType, Path, PathArguments,
+    Result, ReturnType, Signature, Token, Type, TypePath, TypeReference,
+};
+
+use crate::utils::{ReplaceReceiver, SliceExt};
+
+pub(crate) fn attribute(args: &TokenStream, mut input: ItemImpl) -> TokenStream {
+    let res = (|| -> Result<()> {
+        if !args.is_empty() {
+            bail!(args, "unexpected argument: `{}`", args)
+        }
+        validate_impl(&input)?;
+        expand_impl(&mut input);
+        Ok(())
+    })();
+
+    if let Err(e) = res {
+        let mut tokens = e.to_compile_error();
+        if let Type::Path(self_ty) = &*input.self_ty {
+            let (impl_generics, _, where_clause) = input.generics.split_for_impl();
+
+            // Generate a dummy impl of `PinnedDrop`.
+            // In many cases, `#[pinned_drop] impl` is declared after `#[pin_project]`.
+            // Therefore, if `pinned_drop` compile fails, you will also get an error
+            // about `PinnedDrop` not being implemented.
+            // This can be prevented to some extent by generating a dummy
+            // `PinnedDrop` implementation.
+            // We already know that we will get a compile error, so this won't
+            // accidentally compile successfully.
+            //
+            // However, if `input.self_ty` is not Type::Path, there is a high possibility that
+            // the type does not exist (since #[pin_project] can only be used on struct/enum
+            // definitions), so do not generate a dummy impl.
+            tokens.extend(quote! {
+                impl #impl_generics ::pin_project::__private::PinnedDrop for #self_ty
+                #where_clause
+                {
+                    unsafe fn drop(self: ::pin_project::__private::Pin<&mut Self>) {}
+                }
+            });
+        }
+        tokens
+    } else {
+        input.into_token_stream()
+    }
+}
+
+/// Validates the signature of given `PinnedDrop` impl.
+fn validate_impl(item: &ItemImpl) -> Result<()> {
+    const INVALID_ITEM: &str =
+        "#[pinned_drop] may only be used on implementation for the `PinnedDrop` trait";
+
+    if let Some(attr) = item.attrs.find("pinned_drop") {
+        bail!(attr, "duplicate #[pinned_drop] attribute");
+    }
+
+    if let Some((_, path, _)) = &item.trait_ {
+        if !path.is_ident("PinnedDrop") {
+            bail!(path, INVALID_ITEM);
+        }
+    } else {
+        bail!(item.self_ty, INVALID_ITEM);
+    }
+
+    if item.unsafety.is_some() {
+        bail!(item.unsafety, "implementing the trait `PinnedDrop` is not unsafe");
+    }
+    if item.items.is_empty() {
+        bail!(item, "not all trait items implemented, missing: `drop`");
+    }
+
+    match &*item.self_ty {
+        Type::Path(_) => {}
+        ty => {
+            bail!(ty, "implementing the trait `PinnedDrop` on this type is unsupported");
+        }
+    }
+
+    item.items.iter().enumerate().try_for_each(|(i, item)| match item {
+        ImplItem::Const(item) => {
+            bail!(item, "const `{}` is not a member of trait `PinnedDrop`", item.ident)
+        }
+        ImplItem::Type(item) => {
+            bail!(item, "type `{}` is not a member of trait `PinnedDrop`", item.ident)
+        }
+        ImplItem::Fn(method) => {
+            validate_sig(&method.sig)?;
+            if i == 0 {
+                Ok(())
+            } else {
+                bail!(method, "duplicate definitions with name `drop`")
+            }
+        }
+        _ => unreachable!("unexpected ImplItem"),
+    })
+}
+
+/// Validates the signature of given `PinnedDrop::drop` method.
+///
+/// The correct signature is: `(mut) self: (<path>::)Pin<&mut Self>`
+fn validate_sig(sig: &Signature) -> Result<()> {
+    fn get_ty_path(ty: &Type) -> Option<&Path> {
+        if let Type::Path(TypePath { qself: None, path }) = ty {
+            Some(path)
+        } else {
+            None
+        }
+    }
+
+    const INVALID_ARGUMENT: &str = "method `drop` must take an argument `self: Pin<&mut Self>`";
+
+    if sig.ident != "drop" {
+        bail!(sig.ident, "method `{}` is not a member of trait `PinnedDrop", sig.ident,);
+    }
+
+    if let ReturnType::Type(_, ty) = &sig.output {
+        match &**ty {
+            Type::Tuple(ty) if ty.elems.is_empty() => {}
+            _ => bail!(ty, "method `drop` must return the unit type"),
+        }
+    }
+
+    match sig.inputs.len() {
+        1 => {}
+        0 => return Err(Error::new(sig.paren_token.span.join(), INVALID_ARGUMENT)),
+        _ => bail!(sig.inputs, INVALID_ARGUMENT),
+    }
+
+    if let Some(arg) = sig.receiver() {
+        // (mut) self: <path>
+        if let Some(path) = get_ty_path(&arg.ty) {
+            let ty =
+                path.segments.last().expect("Type paths should always have at least one segment");
+            if let PathArguments::AngleBracketed(args) = &ty.arguments {
+                // (mut) self: (<path>::)<ty><&mut <elem>..>
+                if let Some(GenericArgument::Type(Type::Reference(TypeReference {
+                    mutability: Some(_),
+                    elem,
+                    ..
+                }))) = args.args.first()
+                {
+                    // (mut) self: (<path>::)Pin<&mut Self>
+                    if args.args.len() == 1
+                        && ty.ident == "Pin"
+                        && get_ty_path(elem).map_or(false, |path| path.is_ident("Self"))
+                    {
+                        if sig.unsafety.is_some() {
+                            bail!(sig.unsafety, "implementing the method `drop` is not unsafe");
+                        }
+                        return Ok(());
+                    }
+                }
+            }
+        }
+    }
+
+    bail!(sig.inputs[0], INVALID_ARGUMENT)
+}
+
+// from:
+//
+// fn drop(self: Pin<&mut Self>) {
+//     // ...
+// }
+//
+// into:
+//
+// unsafe fn drop(self: Pin<&mut Self>) {
+//     fn __drop_inner<T>(__self: Pin<&mut Foo<'_, T>>) {
+//         fn __drop_inner() {}
+//         // ...
+//     }
+//     __drop_inner(self);
+// }
+//
+fn expand_impl(item: &mut ItemImpl) {
+    // `PinnedDrop` is a private trait and should not appear in docs.
+    item.attrs.push(parse_quote!(#[doc(hidden)]));
+
+    let path = &mut item.trait_.as_mut().expect("unexpected inherent impl").1;
+    *path = parse_quote_spanned! { path.span() =>
+        ::pin_project::__private::PinnedDrop
+    };
+
+    let method =
+        if let ImplItem::Fn(method) = &mut item.items[0] { method } else { unreachable!() };
+
+    // `fn drop(mut self: Pin<&mut Self>)` -> `fn __drop_inner<T>(mut __self: Pin<&mut Receiver>)`
+    let drop_inner = {
+        let mut drop_inner = method.clone();
+        let ident = format_ident!("__drop_inner");
+        // Add a dummy `__drop_inner` function to prevent users call outer `__drop_inner`.
+        drop_inner.block.stmts.insert(0, parse_quote!(fn #ident() {}));
+        drop_inner.sig.ident = ident;
+        drop_inner.sig.generics = item.generics.clone();
+        let receiver = drop_inner.sig.receiver().expect("drop() should have a receiver").clone();
+        let pat = Box::new(Pat::Ident(PatIdent {
+            attrs: Vec::new(),
+            by_ref: None,
+            mutability: receiver.mutability,
+            ident: Ident::new("__self", receiver.self_token.span()),
+            subpat: None,
+        }));
+        drop_inner.sig.inputs[0] = FnArg::Typed(PatType {
+            attrs: receiver.attrs,
+            pat,
+            colon_token: Colon::default(),
+            ty: receiver.ty,
+        });
+        let self_ty = if let Type::Path(ty) = &*item.self_ty { ty } else { unreachable!() };
+        let mut visitor = ReplaceReceiver(self_ty);
+        visitor.visit_signature_mut(&mut drop_inner.sig);
+        visitor.visit_block_mut(&mut drop_inner.block);
+        drop_inner
+    };
+
+    // `fn drop(mut self: Pin<&mut Self>)` -> `unsafe fn drop(self: Pin<&mut Self>)`
+    method.sig.unsafety = Some(<Token![unsafe]>::default());
+    let self_token = if let FnArg::Receiver(ref mut rec) = method.sig.inputs[0] {
+        rec.mutability = None;
+        &rec.self_token
+    } else {
+        panic!("drop() should have a receiver")
+    };
+
+    method.block.stmts = parse_quote! {
+        #[allow(clippy::needless_pass_by_value)] // This lint does not warn the receiver.
+        #drop_inner
+        __drop_inner(#self_token);
+    };
+}
diff --git a/third_party/rust/pin-project-internal/src/utils.rs b/third_party/rust/pin-project-internal/src/utils.rs
new file mode 100644
index 0000000000..3f4ec8524f
--- /dev/null
+++ b/third_party/rust/pin-project-internal/src/utils.rs
@@ -0,0 +1,383 @@
+use std::{iter::FromIterator, mem};
+
+use proc_macro2::{Group, Spacing, Span, TokenStream, TokenTree};
+use quote::{quote, quote_spanned, ToTokens};
+use syn::{
+    parse::{Parse, ParseBuffer, ParseStream},
+    parse_quote,
+    punctuated::Punctuated,
+    token,
+    visit_mut::{self, VisitMut},
+    Attribute, ExprPath, ExprStruct, Generics, Ident, Item, Lifetime, LifetimeParam, Macro,
+    PatStruct, PatTupleStruct, Path, PathArguments, PredicateType, QSelf, Result, Token, Type,
+    TypeParamBound, TypePath, Variant, Visibility, WherePredicate,
+};
+
+pub(crate) type Variants = Punctuated<Variant, Token![,]>;
+
+macro_rules! format_err {
+    ($span:expr, $msg:expr $(,)?) => {
+        syn::Error::new_spanned(&$span as &dyn quote::ToTokens, &$msg as &dyn std::fmt::Display)
+    };
+    ($span:expr, $($tt:tt)*) => {
+        format_err!($span, format!($($tt)*))
+    };
+}
+
+macro_rules! bail {
+    ($($tt:tt)*) => {
+        return Err(format_err!($($tt)*))
+    };
+}
+
+macro_rules! parse_quote_spanned {
+    ($span:expr => $($tt:tt)*) => {
+        syn::parse2(quote::quote_spanned!($span => $($tt)*)).unwrap_or_else(|e| panic!("{}", e))
+    };
+}
+
+/// Determines the lifetime names. Ensure it doesn't overlap with any existing
+/// lifetime names.
+pub(crate) fn determine_lifetime_name(lifetime_name: &mut String, generics: &mut Generics) {
+    struct CollectLifetimes(Vec<String>);
+
+    impl VisitMut for CollectLifetimes {
+        fn visit_lifetime_param_mut(&mut self, def: &mut LifetimeParam) {
+            self.0.push(def.lifetime.to_string());
+        }
+    }
+
+    debug_assert!(lifetime_name.starts_with('\''));
+
+    let mut lifetimes = CollectLifetimes(Vec::new());
+    lifetimes.visit_generics_mut(generics);
+
+    while lifetimes.0.iter().any(|name| name.starts_with(&**lifetime_name)) {
+        lifetime_name.push('_');
+    }
+}
+
+/// Like `insert_lifetime`, but also generates a bound of the form
+/// `OriginalType<A, B>: 'lifetime`. Used when generating the definition
+/// of a projection type
+pub(crate) fn insert_lifetime_and_bound(
+    generics: &mut Generics,
+    lifetime: Lifetime,
+    orig_generics: &Generics,
+    orig_ident: &Ident,
+) -> WherePredicate {
+    insert_lifetime(generics, lifetime.clone());
+
+    let orig_type: Type = parse_quote!(#orig_ident #orig_generics);
+    let mut punct = Punctuated::new();
+    punct.push(TypeParamBound::Lifetime(lifetime));
+
+    WherePredicate::Type(PredicateType {
+        lifetimes: None,
+        bounded_ty: orig_type,
+        colon_token: <Token![:]>::default(),
+        bounds: punct,
+    })
+}
+
+/// Inserts a `lifetime` at position `0` of `generics.params`.
+pub(crate) fn insert_lifetime(generics: &mut Generics, lifetime: Lifetime) {
+    generics.lt_token.get_or_insert_with(<Token![<]>::default);
+    generics.gt_token.get_or_insert_with(<Token![>]>::default);
+    generics.params.insert(0, LifetimeParam::new(lifetime).into());
+}
+
+/// Determines the visibility of the projected types and projection methods.
+///
+/// If given visibility is `pub`, returned visibility is `pub(crate)`.
+/// Otherwise, returned visibility is the same as given visibility.
+pub(crate) fn determine_visibility(vis: &Visibility) -> Visibility {
+    if let Visibility::Public(token) = vis {
+        parse_quote_spanned!(token.span => pub(crate))
+    } else {
+        vis.clone()
+    }
+}
+
+pub(crate) fn respan<T>(node: &T, span: Span) -> T
+where
+    T: ToTokens + Parse,
+{
+    let tokens = node.to_token_stream();
+    let respanned = respan_tokens(tokens, span);
+    syn::parse2(respanned).unwrap()
+}
+
+fn respan_tokens(tokens: TokenStream, span: Span) -> TokenStream {
+    tokens
+        .into_iter()
+        .map(|mut token| {
+            token.set_span(span);
+            token
+        })
+        .collect()
+}
+
+// =================================================================================================
+// extension traits
+
+pub(crate) trait SliceExt {
+    fn position_exact(&self, ident: &str) -> Result<Option<usize>>;
+    fn find(&self, ident: &str) -> Option<&Attribute>;
+}
+
+impl SliceExt for [Attribute] {
+    /// # Errors
+    ///
+    /// - There are multiple specified attributes.
+    /// - The `Attribute::tokens` field of the specified attribute is not empty.
+    fn position_exact(&self, ident: &str) -> Result<Option<usize>> {
+        self.iter()
+            .try_fold((0, None), |(i, mut prev), attr| {
+                if attr.path().is_ident(ident) {
+                    if prev.replace(i).is_some() {
+                        bail!(attr, "duplicate #[{}] attribute", ident);
+                    }
+                    attr.meta.require_path_only()?;
+                }
+                Ok((i + 1, prev))
+            })
+            .map(|(_, pos)| pos)
+    }
+
+    fn find(&self, ident: &str) -> Option<&Attribute> {
+        self.iter().position(|attr| attr.path().is_ident(ident)).map(|i| &self[i])
+    }
+}
+
+pub(crate) trait ParseBufferExt<'a> {
+    fn parenthesized(self) -> Result<ParseBuffer<'a>>;
+}
+
+impl<'a> ParseBufferExt<'a> for ParseStream<'a> {
+    fn parenthesized(self) -> Result<ParseBuffer<'a>> {
+        let content;
+        let _: token::Paren = syn::parenthesized!(content in self);
+        Ok(content)
+    }
+}
+
+impl<'a> ParseBufferExt<'a> for ParseBuffer<'a> {
+    fn parenthesized(self) -> Result<ParseBuffer<'a>> {
+        let content;
+        let _: token::Paren = syn::parenthesized!(content in self);
+        Ok(content)
+    }
+}
+
+// =================================================================================================
+// visitors
+
+// Replace `self`/`Self` with `__self`/`self_ty`.
+// Based on:
+// - https://github.com/dtolnay/async-trait/blob/0.1.35/src/receiver.rs
+// - https://github.com/dtolnay/async-trait/commit/6029cbf375c562ca98fa5748e9d950a8ff93b0e7
+
+pub(crate) struct ReplaceReceiver<'a>(pub(crate) &'a TypePath);
+
+impl ReplaceReceiver<'_> {
+    fn self_ty(&self, span: Span) -> TypePath {
+        respan(self.0, span)
+    }
+
+    fn self_to_qself(&self, qself: &mut Option<QSelf>, path: &mut Path) {
+        if path.leading_colon.is_some() {
+            return;
+        }
+
+        let first = &path.segments[0];
+        if first.ident != "Self" || !first.arguments.is_empty() {
+            return;
+        }
+
+        if path.segments.len() == 1 {
+            self.self_to_expr_path(path);
+            return;
+        }
+
+        let span = first.ident.span();
+        *qself = Some(QSelf {
+            lt_token: Token![<](span),
+            ty: Box::new(self.self_ty(span).into()),
+            position: 0,
+            as_token: None,
+            gt_token: Token![>](span),
+        });
+
+        path.leading_colon = Some(**path.segments.pairs().next().unwrap().punct().unwrap());
+
+        let segments = mem::replace(&mut path.segments, Punctuated::new());
+        path.segments = segments.into_pairs().skip(1).collect();
+    }
+
+    fn self_to_expr_path(&self, path: &mut Path) {
+        if path.leading_colon.is_some() {
+            return;
+        }
+
+        let first = &path.segments[0];
+        if first.ident != "Self" || !first.arguments.is_empty() {
+            return;
+        }
+
+        let self_ty = self.self_ty(first.ident.span());
+        let variant = mem::replace(path, self_ty.path);
+        for segment in &mut path.segments {
+            if let PathArguments::AngleBracketed(bracketed) = &mut segment.arguments {
+                if bracketed.colon2_token.is_none() && !bracketed.args.is_empty() {
+                    bracketed.colon2_token = Some(<Token![::]>::default());
+                }
+            }
+        }
+        if variant.segments.len() > 1 {
+            path.segments.push_punct(<Token![::]>::default());
+            path.segments.extend(variant.segments.into_pairs().skip(1));
+        }
+    }
+
+    fn visit_token_stream(&self, tokens: &mut TokenStream) -> bool {
+        let mut out = Vec::new();
+        let mut modified = false;
+        let mut iter = tokens.clone().into_iter().peekable();
+        while let Some(tt) = iter.next() {
+            match tt {
+                TokenTree::Ident(mut ident) => {
+                    modified |= prepend_underscore_to_self(&mut ident);
+                    if ident == "Self" {
+                        modified = true;
+                        let self_ty = self.self_ty(ident.span());
+                        match iter.peek() {
+                            Some(TokenTree::Punct(p))
+                                if p.as_char() == ':' && p.spacing() == Spacing::Joint =>
+                            {
+                                let next = iter.next().unwrap();
+                                match iter.peek() {
+                                    Some(TokenTree::Punct(p)) if p.as_char() == ':' => {
+                                        let span = ident.span();
+                                        out.extend(quote_spanned!(span=> <#self_ty>));
+                                    }
+                                    _ => out.extend(quote!(#self_ty)),
+                                }
+                                out.push(next);
+                            }
+                            _ => out.extend(quote!(#self_ty)),
+                        }
+                    } else {
+                        out.push(TokenTree::Ident(ident));
+                    }
+                }
+                TokenTree::Group(group) => {
+                    let mut content = group.stream();
+                    modified |= self.visit_token_stream(&mut content);
+                    let mut new = Group::new(group.delimiter(), content);
+                    new.set_span(group.span());
+                    out.push(TokenTree::Group(new));
+                }
+                other => out.push(other),
+            }
+        }
+        if modified {
+            *tokens = TokenStream::from_iter(out);
+        }
+        modified
+    }
+}
+
+impl VisitMut for ReplaceReceiver<'_> {
+    // `Self` -> `Receiver`
+    fn visit_type_mut(&mut self, ty: &mut Type) {
+        if let Type::Path(node) = ty {
+            if node.qself.is_none() && node.path.is_ident("Self") {
+                *ty = self.self_ty(node.path.segments[0].ident.span()).into();
+            } else {
+                self.visit_type_path_mut(node);
+            }
+        } else {
+            visit_mut::visit_type_mut(self, ty);
+        }
+    }
+
+    // `Self::Assoc` -> `<Receiver>::Assoc`
+    fn visit_type_path_mut(&mut self, ty: &mut TypePath) {
+        if ty.qself.is_none() {
+            self.self_to_qself(&mut ty.qself, &mut ty.path);
+        }
+        visit_mut::visit_type_path_mut(self, ty);
+    }
+
+    // `Self::method` -> `<Receiver>::method`
+    fn visit_expr_path_mut(&mut self, expr: &mut ExprPath) {
+        if expr.qself.is_none() {
+            self.self_to_qself(&mut expr.qself, &mut expr.path);
+        }
+        visit_mut::visit_expr_path_mut(self, expr);
+    }
+
+    fn visit_expr_struct_mut(&mut self, expr: &mut ExprStruct) {
+        self.self_to_expr_path(&mut expr.path);
+        visit_mut::visit_expr_struct_mut(self, expr);
+    }
+
+    fn visit_pat_struct_mut(&mut self, pat: &mut PatStruct) {
+        self.self_to_expr_path(&mut pat.path);
+        visit_mut::visit_pat_struct_mut(self, pat);
+    }
+
+    fn visit_pat_tuple_struct_mut(&mut self, pat: &mut PatTupleStruct) {
+        self.self_to_expr_path(&mut pat.path);
+        visit_mut::visit_pat_tuple_struct_mut(self, pat);
+    }
+
+    fn visit_path_mut(&mut self, path: &mut Path) {
+        if path.segments.len() == 1 {
+            // Replace `self`, but not `self::function`.
+            prepend_underscore_to_self(&mut path.segments[0].ident);
+        }
+        for segment in &mut path.segments {
+            self.visit_path_arguments_mut(&mut segment.arguments);
+        }
+    }
+
+    fn visit_item_mut(&mut self, item: &mut Item) {
+        match item {
+            // Visit `macro_rules!` because locally defined macros can refer to `self`.
+            Item::Macro(item) if item.mac.path.is_ident("macro_rules") => {
+                self.visit_macro_mut(&mut item.mac);
+            }
+            // Otherwise, do not recurse into nested items.
+            _ => {}
+        }
+    }
+
+    fn visit_macro_mut(&mut self, mac: &mut Macro) {
+        // We can't tell in general whether `self` inside a macro invocation
+        // refers to the self in the argument list or a different self
+        // introduced within the macro. Heuristic: if the macro input contains
+        // `fn`, then `self` is more likely to refer to something other than the
+        // outer function's self argument.
+        if !contains_fn(mac.tokens.clone()) {
+            self.visit_token_stream(&mut mac.tokens);
+        }
+    }
+}
+
+fn contains_fn(tokens: TokenStream) -> bool {
+    tokens.into_iter().any(|tt| match tt {
+        TokenTree::Ident(ident) => ident == "fn",
+        TokenTree::Group(group) => contains_fn(group.stream()),
+        _ => false,
+    })
+}
+
+pub(crate) fn prepend_underscore_to_self(ident: &mut Ident) -> bool {
+    let modified = ident == "self";
+    if modified {
+        *ident = Ident::new("__self", ident.span());
+    }
+    modified
+}