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Diffstat (limited to 'examples/pinned_drop-expanded.rs')
-rw-r--r-- | examples/pinned_drop-expanded.rs | 154 |
1 files changed, 154 insertions, 0 deletions
diff --git a/examples/pinned_drop-expanded.rs b/examples/pinned_drop-expanded.rs new file mode 100644 index 0000000..15dde89 --- /dev/null +++ b/examples/pinned_drop-expanded.rs @@ -0,0 +1,154 @@ +// Original code (./pinned_drop.rs): +// +// ```rust +// #![allow(dead_code)] +// +// use pin_project::{pin_project, pinned_drop}; +// use std::pin::Pin; +// +// #[pin_project(PinnedDrop)] +// pub struct Struct<'a, T> { +// was_dropped: &'a mut bool, +// #[pin] +// field: T, +// } +// +// #[pinned_drop] +// fn drop_Struct<T>(mut this: Pin<&mut Struct<'_, T>>) { +// **this.project().was_dropped = true; +// } +// +// fn main() {} +// ``` + +#![allow(dead_code, unused_imports, unused_parens)] +#![allow(clippy::no_effect)] + +use pin_project::{pin_project, pinned_drop}; +use std::pin::Pin; + +pub struct Struct<'a, T> { + was_dropped: &'a mut bool, + // #[pin] + field: T, +} + +#[doc(hidden)] +#[allow(clippy::mut_mut)] // This lint warns `&mut &mut <ty>`. +#[allow(dead_code)] // This lint warns unused fields/variants. +#[allow(single_use_lifetimes)] +pub(crate) struct __StructProjection<'pin, 'a, T> +where + Struct<'a, T>: 'pin, +{ + was_dropped: &'pin mut (&'a mut bool), + field: ::pin_project::__reexport::pin::Pin<&'pin mut (T)>, +} +#[doc(hidden)] +#[allow(dead_code)] // This lint warns unused fields/variants. +#[allow(single_use_lifetimes)] +pub(crate) struct __StructProjectionRef<'pin, 'a, T> +where + Struct<'a, T>: 'pin, +{ + was_dropped: &'pin (&'a mut bool), + field: ::pin_project::__reexport::pin::Pin<&'pin (T)>, +} + +#[doc(hidden)] +#[allow(non_upper_case_globals)] +#[allow(single_use_lifetimes)] +const __SCOPE_Struct: () = { + impl<'a, T> Struct<'a, T> { + pub(crate) fn project<'pin>( + self: ::pin_project::__reexport::pin::Pin<&'pin mut Self>, + ) -> __StructProjection<'pin, 'a, T> { + unsafe { + let Self { was_dropped, field } = self.get_unchecked_mut(); + __StructProjection { + was_dropped, + field: ::pin_project::__reexport::pin::Pin::new_unchecked(field), + } + } + } + pub(crate) fn project_ref<'pin>( + self: ::pin_project::__reexport::pin::Pin<&'pin Self>, + ) -> __StructProjectionRef<'pin, 'a, T> { + unsafe { + let Self { was_dropped, field } = self.get_ref(); + __StructProjectionRef { + was_dropped, + field: ::pin_project::__reexport::pin::Pin::new_unchecked(field), + } + } + } + } + + impl<'a, T> ::pin_project::__reexport::ops::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::__reexport::pin::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::__reexport::marker::Unpin for Struct<'a, T> where + __Struct<'pin, 'a, T>: ::pin_project::__reexport::marker::Unpin + { + } + unsafe impl<'a, T> ::pin_project::UnsafeUnpin for Struct<'a, T> {} + + // 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. + #[deny(safe_packed_borrows)] + fn __assert_not_repr_packed<'a, T>(val: &Struct<'a, T>) { + &val.was_dropped; + &val.field; + } +}; + +// 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.** +impl<T> ::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<T>(__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() {} |