split libcore::mem into multiple files

src/libcore/mem/manually_drop.rs

@@ -0,0 +1,146 @@
+use crate::ptr;
+use crate::ops::{Deref, DerefMut};
+
+/// A wrapper to inhibit compiler from automatically calling `T`’s destructor.
+///
+/// This wrapper is 0-cost.
+///
+/// `ManuallyDrop<T>` is subject to the same layout optimizations as `T`.
+/// As a consequence, it has *no effect* on the assumptions that the compiler makes
+/// about all values being initialized at their type.  In particular, initializing
+/// a `ManuallyDrop<&mut T>` with [`mem::zeroed`] is undefined behavior.
+/// If you need to handle uninitialized data, use [`MaybeUninit<T>`] instead.
+///
+/// # Examples
+///
+/// This wrapper helps with explicitly documenting the drop order dependencies between fields of
+/// the type:
+///
+/// ```rust
+/// use std::mem::ManuallyDrop;
+/// struct Peach;
+/// struct Banana;
+/// struct Melon;
+/// struct FruitBox {
+///     // Immediately clear there’s something non-trivial going on with these fields.
+///     peach: ManuallyDrop<Peach>,
+///     melon: Melon, // Field that’s independent of the other two.
+///     banana: ManuallyDrop<Banana>,
+/// }
+///
+/// impl Drop for FruitBox {
+///     fn drop(&mut self) {
+///         unsafe {
+///             // Explicit ordering in which field destructors are run specified in the intuitive
+///             // location – the destructor of the structure containing the fields.
+///             // Moreover, one can now reorder fields within the struct however much they want.
+///             ManuallyDrop::drop(&mut self.peach);
+///             ManuallyDrop::drop(&mut self.banana);
+///         }
+///         // After destructor for `FruitBox` runs (this function), the destructor for Melon gets
+///         // invoked in the usual manner, as it is not wrapped in `ManuallyDrop`.
+///     }
+/// }
+/// ```
+///
+/// [`mem::zeroed`]: fn.zeroed.html
+/// [`MaybeUninit<T>`]: union.MaybeUninit.html
+#[stable(feature = "manually_drop", since = "1.20.0")]
+#[lang = "manually_drop"]
+#[derive(Copy, Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[repr(transparent)]
+pub struct ManuallyDrop<T: ?Sized> {
+    value: T,
+}
+
+impl<T> ManuallyDrop<T> {
+    /// Wrap a value to be manually dropped.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::mem::ManuallyDrop;
+    /// ManuallyDrop::new(Box::new(()));
+    /// ```
+    #[stable(feature = "manually_drop", since = "1.20.0")]
+    #[inline(always)]
+    pub const fn new(value: T) -> ManuallyDrop<T> {
+        ManuallyDrop { value }
+    }
+
+    /// Extracts the value from the `ManuallyDrop` container.
+    ///
+    /// This allows the value to be dropped again.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::mem::ManuallyDrop;
+    /// let x = ManuallyDrop::new(Box::new(()));
+    /// let _: Box<()> = ManuallyDrop::into_inner(x); // This drops the `Box`.
+    /// ```
+    #[stable(feature = "manually_drop", since = "1.20.0")]
+    #[inline(always)]
+    pub const fn into_inner(slot: ManuallyDrop<T>) -> T {
+        slot.value
+    }
+
+    /// Takes the contained value out.
+    ///
+    /// This method is primarily intended for moving out values in drop.
+    /// Instead of using [`ManuallyDrop::drop`] to manually drop the value,
+    /// you can use this method to take the value and use it however desired.
+    /// `Drop` will be invoked on the returned value following normal end-of-scope rules.
+    ///
+    /// If you have ownership of the container, you can use [`ManuallyDrop::into_inner`] instead.
+    ///
+    /// # Safety
+    ///
+    /// This function semantically moves out the contained value without preventing further usage.
+    /// It is up to the user of this method to ensure that this container is not used again.
+    ///
+    /// [`ManuallyDrop::drop`]: #method.drop
+    /// [`ManuallyDrop::into_inner`]: #method.into_inner
+    #[must_use = "if you don't need the value, you can use `ManuallyDrop::drop` instead"]
+    #[unstable(feature = "manually_drop_take", issue = "55422")]
+    #[inline]
+    pub unsafe fn take(slot: &mut ManuallyDrop<T>) -> T {
+        ManuallyDrop::into_inner(ptr::read(slot))
+    }
+}
+
+impl<T: ?Sized> ManuallyDrop<T> {
+    /// Manually drops the contained value.
+    ///
+    /// If you have ownership of the value, you can use [`ManuallyDrop::into_inner`] instead.
+    ///
+    /// # Safety
+    ///
+    /// This function runs the destructor of the contained value and thus the wrapped value
+    /// now represents uninitialized data. It is up to the user of this method to ensure the
+    /// uninitialized data is not actually used.
+    ///
+    /// [`ManuallyDrop::into_inner`]: #method.into_inner
+    #[stable(feature = "manually_drop", since = "1.20.0")]
+    #[inline]
+    pub unsafe fn drop(slot: &mut ManuallyDrop<T>) {
+        ptr::drop_in_place(&mut slot.value)
+    }
+}
+
+#[stable(feature = "manually_drop", since = "1.20.0")]
+impl<T: ?Sized> Deref for ManuallyDrop<T> {
+    type Target = T;
+    #[inline(always)]
+    fn deref(&self) -> &T {
+        &self.value
+    }
+}
+
+#[stable(feature = "manually_drop", since = "1.20.0")]
+impl<T: ?Sized> DerefMut for ManuallyDrop<T> {
+    #[inline(always)]
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.value
+    }
+}

src/test/ui/consts/const-size_of-cycle.stderr

@@ -5,7 +5,7 @@ LL |     bytes: [u8; std::mem::size_of::<Foo>()]
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: ...which requires const-evaluating `Foo::bytes::{{constant}}#0`...
-  --> $SRC_DIR/libcore/mem.rs:LL:COL
+  --> $SRC_DIR/libcore/mem/mod.rs:LL:COL
    |
 LL |     intrinsics::size_of::<T>()
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^

src/test/ui/type_length_limit.stderr

@@ -1,5 +1,5 @@
 error: reached the type-length limit while instantiating `std::mem::drop::<std::option::Op... G), (G, G, G), (G, G, G))))))>>`
-  --> $SRC_DIR/libcore/mem.rs:LL:COL
+  --> $SRC_DIR/libcore/mem/mod.rs:LL:COL
    |
 LL | pub fn drop<T>(_x: T) { }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^