// Original code (./pinned_drop.rs): // // ```rust // #![allow(dead_code)] // // use std::pin::Pin; // // use pin_project::{pin_project, pinned_drop}; // // #[pin_project(PinnedDrop)] // pub struct Struct<'a, T> { // was_dropped: &'a mut bool, // #[pin] // field: T, // } // // #[pinned_drop] // fn drop_Struct(mut this: Pin<&mut Struct<'_, T>>) { // **this.project().was_dropped = true; // } // // fn main() {} // ``` #![allow(dead_code, unused_imports, unused_parens, unknown_lints, renamed_and_removed_lints)] #![allow(clippy::needless_lifetimes, clippy::mut_mut)] use std::pin::Pin; use pin_project::{pin_project, pinned_drop}; // #[pin_project(PinnedDrop)] pub struct Struct<'a, T> { was_dropped: &'a mut bool, // #[pin] field: T, } const _: () = { pub(crate) struct __StructProjection<'pin, 'a, T> where Struct<'a, T>: 'pin, { was_dropped: &'pin mut (&'a mut bool), field: ::pin_project::__private::Pin<&'pin mut (T)>, } pub(crate) struct __StructProjectionRef<'pin, 'a, T> where Struct<'a, T>: 'pin, { was_dropped: &'pin (&'a mut bool), field: ::pin_project::__private::Pin<&'pin (T)>, } impl<'a, T> Struct<'a, T> { pub(crate) fn project<'pin>( self: ::pin_project::__private::Pin<&'pin mut Self>, ) -> __StructProjection<'pin, 'a, T> { unsafe { let Self { was_dropped, field } = self.get_unchecked_mut(); __StructProjection { was_dropped, field: ::pin_project::__private::Pin::new_unchecked(field), } } } pub(crate) fn project_ref<'pin>( self: ::pin_project::__private::Pin<&'pin Self>, ) -> __StructProjectionRef<'pin, 'a, T> { unsafe { let Self { was_dropped, field } = self.get_ref(); __StructProjectionRef { was_dropped, field: ::pin_project::__private::Pin::new_unchecked(field), } } } } // Ensure that it's impossible to use pin projections on a #[repr(packed)] // struct. // // See ./struct-default-expanded.rs and https://github.com/taiki-e/pin-project/pull/34 // for details. #[forbid(unaligned_references, safe_packed_borrows)] fn __assert_not_repr_packed<'a, T>(this: &Struct<'a, T>) { let _ = &this.was_dropped; let _ = &this.field; } impl<'a, T> ::pin_project::__private::Drop for Struct<'a, T> { fn drop(&mut self) { // Safety - we're in 'drop', so we know that 'self' will // never move again. let pinned_self = unsafe { ::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*. unsafe { ::pin_project::__private::PinnedDrop::drop(pinned_self); } } } // Automatically create the appropriate conditional `Unpin` implementation. // // See ./struct-default-expanded.rs and https://github.com/taiki-e/pin-project/pull/53. // for details. pub struct __Struct<'pin, 'a, T> { __pin_project_use_generics: ::pin_project::__private::AlwaysUnpin<'pin, (T)>, __field0: T, __lifetime0: &'a (), } impl<'pin, 'a, T> ::pin_project::__private::Unpin for Struct<'a, T> where __Struct<'pin, 'a, T>: ::pin_project::__private::Unpin { } // A dummy impl of `UnsafeUnpin`, to ensure that the user cannot implement it. #[doc(hidden)] unsafe impl<'pin, 'a, T> ::pin_project::UnsafeUnpin for Struct<'a, T> where __Struct<'pin, 'a, T>: ::pin_project::__private::Unpin { } }; // 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](https://github.com/rust-lang/rust/pull/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, we prevent users from // calling `PinnedDrop::drop`. // // Users can implement [`Drop`] safely using `#[pinned_drop]` and can drop a // type that implements `PinnedDrop` using the [`drop`] function safely. // **Do not call or implement this trait directly.** #[doc(hidden)] impl ::pin_project::__private::PinnedDrop for Struct<'_, T> { // Since calling it twice on the same object would be UB, // this method is unsafe. unsafe fn drop(self: Pin<&mut Self>) { #[allow(clippy::needless_pass_by_value)] fn __drop_inner(__self: Pin<&mut Struct<'_, T>>) { // A dummy `__drop_inner` function to prevent users call outer `__drop_inner`. fn __drop_inner() {} **__self.project().was_dropped = true; } __drop_inner(self); } } fn main() {}