Auto merge of #53227 - nivkner:pin_move, r=RalfJung

move the Pin API into its own module for centralized documentation

This implements the change proposed by @withoutboats in #49150, as suggested by @RalfJung in the review of #53104,
along with the documentation that was originally in it, that was deemed more appropriate in module-level documentation.

r? @RalfJung

Author: bors

src/liballoc/boxed.rs

@@ -64,12 +64,14 @@ use core::future::{Future, FutureObj, LocalFutureObj, UnsafeFutureObj};
 use core::hash::{Hash, Hasher};
 use core::iter::FusedIterator;
 use core::marker::{Unpin, Unsize};
-use core::mem::{self, PinMut};
+use core::mem;
+use core::pin::PinMut;
 use core::ops::{CoerceUnsized, Deref, DerefMut, Generator, GeneratorState};
 use core::ptr::{self, NonNull, Unique};
 use core::task::{Context, Poll, Spawn, SpawnErrorKind, SpawnObjError};
 
 use raw_vec::RawVec;
+use pin::PinBox;
 use str::from_boxed_utf8_unchecked;
 
 /// A pointer type for heap allocation.
@@ -758,166 +760,6 @@ impl<T> Generator for Box<T>
     }
 }
 
-/// A pinned, heap allocated reference.
-#[unstable(feature = "pin", issue = "49150")]
-#[fundamental]
-#[repr(transparent)]
-pub struct PinBox<T: ?Sized> {
-    inner: Box<T>,
-}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T> PinBox<T> {
-    /// Allocate memory on the heap, move the data into it and pin it.
-    #[unstable(feature = "pin", issue = "49150")]
-    pub fn new(data: T) -> PinBox<T> {
-        PinBox { inner: Box::new(data) }
-    }
-}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T: ?Sized> PinBox<T> {
-    /// Get a pinned reference to the data in this PinBox.
-    #[inline]
-    pub fn as_pin_mut<'a>(&'a mut self) -> PinMut<'a, T> {
-        unsafe { PinMut::new_unchecked(&mut *self.inner) }
-    }
-
-    /// Constructs a `PinBox` from a raw pointer.
-    ///
-    /// After calling this function, the raw pointer is owned by the
-    /// resulting `PinBox`. Specifically, the `PinBox` destructor will call
-    /// the destructor of `T` and free the allocated memory. Since the
-    /// way `PinBox` allocates and releases memory is unspecified, the
-    /// only valid pointer to pass to this function is the one taken
-    /// from another `PinBox` via the [`PinBox::into_raw`] function.
-    ///
-    /// This function is unsafe because improper use may lead to
-    /// memory problems. For example, a double-free may occur if the
-    /// function is called twice on the same raw pointer.
-    ///
-    /// [`PinBox::into_raw`]: struct.PinBox.html#method.into_raw
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(pin)]
-    /// use std::boxed::PinBox;
-    /// let x = PinBox::new(5);
-    /// let ptr = PinBox::into_raw(x);
-    /// let x = unsafe { PinBox::from_raw(ptr) };
-    /// ```
-    #[inline]
-    pub unsafe fn from_raw(raw: *mut T) -> Self {
-        PinBox { inner: Box::from_raw(raw) }
-    }
-
-    /// Consumes the `PinBox`, returning the wrapped raw pointer.
-    ///
-    /// After calling this function, the caller is responsible for the
-    /// memory previously managed by the `PinBox`. In particular, the
-    /// caller should properly destroy `T` and release the memory. The
-    /// proper way to do so is to convert the raw pointer back into a
-    /// `PinBox` with the [`PinBox::from_raw`] function.
-    ///
-    /// Note: this is an associated function, which means that you have
-    /// to call it as `PinBox::into_raw(b)` instead of `b.into_raw()`. This
-    /// is so that there is no conflict with a method on the inner type.
-    ///
-    /// [`PinBox::from_raw`]: struct.PinBox.html#method.from_raw
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(pin)]
-    /// use std::boxed::PinBox;
-    /// let x = PinBox::new(5);
-    /// let ptr = PinBox::into_raw(x);
-    /// ```
-    #[inline]
-    pub fn into_raw(b: PinBox<T>) -> *mut T {
-        Box::into_raw(b.inner)
-    }
-
-    /// Get a mutable reference to the data inside this PinBox.
-    ///
-    /// This function is unsafe. Users must guarantee that the data is never
-    /// moved out of this reference.
-    #[inline]
-    pub unsafe fn get_mut<'a>(this: &'a mut PinBox<T>) -> &'a mut T {
-        &mut *this.inner
-    }
-
-    /// Convert this PinBox into an unpinned Box.
-    ///
-    /// This function is unsafe. Users must guarantee that the data is never
-    /// moved out of the box.
-    #[inline]
-    pub unsafe fn unpin(this: PinBox<T>) -> Box<T> {
-        this.inner
-    }
-}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T: ?Sized> From<Box<T>> for PinBox<T> {
-    fn from(boxed: Box<T>) -> PinBox<T> {
-        PinBox { inner: boxed }
-    }
-}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T: Unpin + ?Sized> From<PinBox<T>> for Box<T> {
-    fn from(pinned: PinBox<T>) -> Box<T> {
-        pinned.inner
-    }
-}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T: ?Sized> Deref for PinBox<T> {
-    type Target = T;
-
-    fn deref(&self) -> &T {
-        &*self.inner
-    }
-}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T: Unpin + ?Sized> DerefMut for PinBox<T> {
-    fn deref_mut(&mut self) -> &mut T {
-        &mut *self.inner
-    }
-}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T: fmt::Display + ?Sized> fmt::Display for PinBox<T> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        fmt::Display::fmt(&*self.inner, f)
-    }
-}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T: fmt::Debug + ?Sized> fmt::Debug for PinBox<T> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        fmt::Debug::fmt(&*self.inner, f)
-    }
-}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T: ?Sized> fmt::Pointer for PinBox<T> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        // It's not possible to extract the inner Uniq directly from the Box,
-        // instead we cast it to a *const which aliases the Unique
-        let ptr: *const T = &*self.inner;
-        fmt::Pointer::fmt(&ptr, f)
-    }
-}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<PinBox<U>> for PinBox<T> {}
-
-#[unstable(feature = "pin", issue = "49150")]
-impl<T: ?Sized> Unpin for PinBox<T> {}
-
 #[unstable(feature = "futures_api", issue = "50547")]
 impl<F: ?Sized + Future + Unpin> Future for Box<F> {
     type Output = F::Output;
@@ -927,15 +769,6 @@ impl<F: ?Sized + Future + Unpin> Future for Box<F> {
     }
 }
 
-#[unstable(feature = "futures_api", issue = "50547")]
-impl<F: ?Sized + Future> Future for PinBox<F> {
-    type Output = F::Output;
-
-    fn poll(mut self: PinMut<Self>, cx: &mut Context) -> Poll<Self::Output> {
-        self.as_pin_mut().poll(cx)
-    }
-}
-
 #[unstable(feature = "futures_api", issue = "50547")]
 unsafe impl<'a, T, F> UnsafeFutureObj<'a, T> for Box<F>
     where F: Future<Output = T> + 'a
@@ -955,25 +788,6 @@ unsafe impl<'a, T, F> UnsafeFutureObj<'a, T> for Box<F>
     }
 }
 
-#[unstable(feature = "futures_api", issue = "50547")]
-unsafe impl<'a, T, F> UnsafeFutureObj<'a, T> for PinBox<F>
-    where F: Future<Output = T> + 'a
-{
-    fn into_raw(self) -> *mut () {
-        PinBox::into_raw(self) as *mut ()
-    }
-
-    unsafe fn poll(ptr: *mut (), cx: &mut Context) -> Poll<T> {
-        let ptr = ptr as *mut F;
-        let pin: PinMut<F> = PinMut::new_unchecked(&mut *ptr);
-        pin.poll(cx)
-    }
-
-    unsafe fn drop(ptr: *mut ()) {
-        drop(PinBox::from_raw(ptr as *mut F))
-    }
-}
-
 #[unstable(feature = "futures_api", issue = "50547")]
 impl<Sp> Spawn for Box<Sp>
     where Sp: Spawn + ?Sized
@@ -990,13 +804,6 @@ impl<Sp> Spawn for Box<Sp>
     }
 }
 
-#[unstable(feature = "futures_api", issue = "50547")]
-impl<'a, F: Future<Output = ()> + Send + 'a> From<PinBox<F>> for FutureObj<'a, ()> {
-    fn from(boxed: PinBox<F>) -> Self {
-        FutureObj::new(boxed)
-    }
-}
-
 #[unstable(feature = "futures_api", issue = "50547")]
 impl<'a, F: Future<Output = ()> + Send + 'a> From<Box<F>> for FutureObj<'a, ()> {
     fn from(boxed: Box<F>) -> Self {
@@ -1005,15 +812,15 @@ impl<'a, F: Future<Output = ()> + Send + 'a> From<Box<F>> for FutureObj<'a, ()>
 }
 
 #[unstable(feature = "futures_api", issue = "50547")]
-impl<'a, F: Future<Output = ()> + 'a> From<PinBox<F>> for LocalFutureObj<'a, ()> {
-    fn from(boxed: PinBox<F>) -> Self {
+impl<'a, F: Future<Output = ()> + 'a> From<Box<F>> for LocalFutureObj<'a, ()> {
+    fn from(boxed: Box<F>) -> Self {
         LocalFutureObj::new(boxed)
     }
 }
 
-#[unstable(feature = "futures_api", issue = "50547")]
-impl<'a, F: Future<Output = ()> + 'a> From<Box<F>> for LocalFutureObj<'a, ()> {
-    fn from(boxed: Box<F>) -> Self {
-        LocalFutureObj::new(boxed)
+#[unstable(feature = "pin", issue = "49150")]
+impl<T: Unpin + ?Sized> From<PinBox<T>> for Box<T> {
+    fn from(pinned: PinBox<T>) -> Box<T> {
+        unsafe { PinBox::unpin(pinned) }
     }
 }

src/liballoc/lib.rs

@@ -160,6 +160,7 @@ pub mod collections;
 pub mod sync;
 pub mod rc;
 pub mod raw_vec;
+pub mod pin;
 pub mod prelude;
 pub mod borrow;
 pub mod fmt;