Implement !Unpin option

ci.sh

@@ -12,7 +12,7 @@ echo "Running 'cargo fmt -- --check'"
 cargo +nightly fmt --all -- --check
 
 echo "Running 'cargo clippy'"
-cargo +nightly clippy --all --all-features
+cargo +nightly clippy --all --all-features --all-targets
 
 echo "Running 'cargo test'"
 cargo +nightly test --all --all-features

pin-project-internal/src/lib.rs

@@ -220,6 +220,40 @@ use crate::utils::{Immutable, Mutable, Owned};
 ///
 /// See also [`project`] and [`project_ref`] attributes.
 ///
+/// ## `!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, U> {
+///     #[pin]
+///     pinned: T,
+///     unpinned: U,
+/// }
+/// ```
+///
+/// You can also ensure `!Unpin` by using `#[pin]` attribute for [`PhantomPinned`] field.
+///
+/// ```rust
+/// use pin_project::pin_project;
+/// use std::marker::PhantomPinned;
+///
+/// #[pin_project]
+/// struct Struct<T, U> {
+///     #[pin]
+///     pinned: T,
+///     unpinned: U,
+///     #[pin]
+///     _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`