2 files changed, 36 insertions, 45 deletions

diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index e5f6b0c0c..a563b2587 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/alloc/src/boxed.rs
@@ -158,7 +158,6 @@ use core::hash::{Hash, Hasher};
 #[cfg(not(no_global_oom_handling))]
 use core::iter::FromIterator;
 use core::iter::{FusedIterator, Iterator};
-#[cfg(not(bootstrap))]
 use core::marker::Tuple;
 use core::marker::{Destruct, Unpin, Unsize};
 use core::mem;
@@ -954,7 +953,7 @@ impl<T: ?Sized> Box<T> {
     /// [`Layout`]: crate::Layout
     #[stable(feature = "box_raw", since = "1.4.0")]
     #[inline]
-    #[must_use = "call `drop(from_raw(ptr))` if you intend to drop the `Box`"]
+    #[must_use = "call `drop(Box::from_raw(ptr))` if you intend to drop the `Box`"]
     pub unsafe fn from_raw(raw: *mut T) -> Self {
         unsafe { Self::from_raw_in(raw, Global) }
     }
@@ -1981,17 +1980,6 @@ impl<I: ExactSizeIterator + ?Sized, A: Allocator> ExactSizeIterator for Box<I, A
 #[stable(feature = "fused", since = "1.26.0")]
 impl<I: FusedIterator + ?Sized, A: Allocator> FusedIterator for Box<I, A> {}
 
-#[cfg(bootstrap)]
-#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
-impl<Args, F: FnOnce<Args> + ?Sized, A: Allocator> FnOnce<Args> for Box<F, A> {
-    type Output = <F as FnOnce<Args>>::Output;
-
-    extern "rust-call" fn call_once(self, args: Args) -> Self::Output {
-        <F as FnOnce<Args>>::call_once(*self, args)
-    }
-}
-
-#[cfg(not(bootstrap))]
 #[stable(feature = "boxed_closure_impls", since = "1.35.0")]
 impl<Args: Tuple, F: FnOnce<Args> + ?Sized, A: Allocator> FnOnce<Args> for Box<F, A> {
     type Output = <F as FnOnce<Args>>::Output;
@@ -2001,15 +1989,6 @@ impl<Args: Tuple, F: FnOnce<Args> + ?Sized, A: Allocator> FnOnce<Args> for Box<F
     }
 }
 
-#[cfg(bootstrap)]
-#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
-impl<Args, F: FnMut<Args> + ?Sized, A: Allocator> FnMut<Args> for Box<F, A> {
-    extern "rust-call" fn call_mut(&mut self, args: Args) -> Self::Output {
-        <F as FnMut<Args>>::call_mut(self, args)
-    }
-}
-
-#[cfg(not(bootstrap))]
 #[stable(feature = "boxed_closure_impls", since = "1.35.0")]
 impl<Args: Tuple, F: FnMut<Args> + ?Sized, A: Allocator> FnMut<Args> for Box<F, A> {
     extern "rust-call" fn call_mut(&mut self, args: Args) -> Self::Output {
@@ -2017,15 +1996,6 @@ impl<Args: Tuple, F: FnMut<Args> + ?Sized, A: Allocator> FnMut<Args> for Box<F,
     }
 }
 
-#[cfg(bootstrap)]
-#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
-impl<Args, F: Fn<Args> + ?Sized, A: Allocator> Fn<Args> for Box<F, A> {
-    extern "rust-call" fn call(&self, args: Args) -> Self::Output {
-        <F as Fn<Args>>::call(self, args)
-    }
-}
-
-#[cfg(not(bootstrap))]
 #[stable(feature = "boxed_closure_impls", since = "1.35.0")]
 impl<Args: Tuple, F: Fn<Args> + ?Sized, A: Allocator> Fn<Args> for Box<F, A> {
     extern "rust-call" fn call(&self, args: Args) -> Self::Output {
@@ -2033,7 +2003,7 @@ impl<Args: Tuple, F: Fn<Args> + ?Sized, A: Allocator> Fn<Args> for Box<F, A> {
     }
 }
 
-#[unstable(feature = "coerce_unsized", issue = "27732")]
+#[unstable(feature = "coerce_unsized", issue = "18598")]
 impl<T: ?Sized + Unsize<U>, U: ?Sized, A: Allocator> CoerceUnsized<Box<U, A>> for Box<T, A> {}
 
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
diff --git a/library/alloc/src/boxed/thin.rs b/library/alloc/src/boxed/thin.rs
index c477c4490..c1a82e452 100644
--- a/library/alloc/src/boxed/thin.rs
+++ b/library/alloc/src/boxed/thin.rs
@@ -226,24 +226,45 @@ impl<H> WithHeader<H> {
     // - Assumes that either `value` can be dereferenced, or is the
     //   `NonNull::dangling()` we use when both `T` and `H` are ZSTs.
     unsafe fn drop<T: ?Sized>(&self, value: *mut T) {
+        struct DropGuard<H> {
+            ptr: NonNull<u8>,
+            value_layout: Layout,
+            _marker: PhantomData<H>,
+        }
+
+        impl<H> Drop for DropGuard<H> {
+            fn drop(&mut self) {
+                unsafe {
+                    // SAFETY: Layout must have been computable if we're in drop
+                    let (layout, value_offset) =
+                        WithHeader::<H>::alloc_layout(self.value_layout).unwrap_unchecked();
+
+                    // Note: Don't deallocate if the layout size is zero, because the pointer
+                    // didn't come from the allocator.
+                    if layout.size() != 0 {
+                        alloc::dealloc(self.ptr.as_ptr().sub(value_offset), layout);
+                    } else {
+                        debug_assert!(
+                            value_offset == 0
+                                && mem::size_of::<H>() == 0
+                                && self.value_layout.size() == 0
+                        );
+                    }
+                }
+            }
+        }
+
         unsafe {
-            let value_layout = Layout::for_value_raw(value);
-            // SAFETY: Layout must have been computable if we're in drop
-            let (layout, value_offset) = Self::alloc_layout(value_layout).unwrap_unchecked();
+            // `_guard` will deallocate the memory when dropped, even if `drop_in_place` unwinds.
+            let _guard = DropGuard {
+                ptr: self.0,
+                value_layout: Layout::for_value_raw(value),
+                _marker: PhantomData::<H>,
+            };
 
             // We only drop the value because the Pointee trait requires that the metadata is copy
             // aka trivially droppable.
             ptr::drop_in_place::<T>(value);
-
-            // Note: Don't deallocate if the layout size is zero, because the pointer
-            // didn't come from the allocator.
-            if layout.size() != 0 {
-                alloc::dealloc(self.0.as_ptr().sub(value_offset), layout);
-            } else {
-                debug_assert!(
-                    value_offset == 0 && mem::size_of::<H>() == 0 && value_layout.size() == 0
-                );
-            }
         }
     }