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Rollup merge of #67504 - Mark-Simulacrum:note-data-offset, r=Centril

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Warn against relying on ?Sized being last

Fixes #62522
This commit is contained in:
Mazdak Farrokhzad 2019-12-22 02:40:07 +01:00 • committed by GitHub
commit ca528fcc04
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2
src/liballoc/rc.rs
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@ -2106,6 +2106,8 @@ impl<T: ?Sized> Unpin for Rc<T> { }
unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
// Align the unsized value to the end of the `RcBox`.
// Because it is ?Sized, it will always be the last field in memory.
// Note: This is a detail of the current implementation of the compiler,
// and is not a guaranteed language detail. Do not rely on it outside of std.
data_offset_align(align_of_val(&*ptr))
}

2
src/liballoc/sync.rs
View file

@ -2161,6 +2161,8 @@ impl<T: ?Sized> Unpin for Arc<T> { }
unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
// Align the unsized value to the end of the `ArcInner`.
// Because it is `?Sized`, it will always be the last field in memory.
// Note: This is a detail of the current implementation of the compiler,
// and is not a guaranteed language detail. Do not rely on it outside of std.
data_offset_align(align_of_val(&*ptr))
}