22 lines
997 B
Rust
22 lines
997 B
Rust
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//@ run-pass
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use std::ptr::addr_of;
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// When the unsized tail is a `dyn Trait`, its alignments is only dynamically known. This means the
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// packed(2) needs to be applied at runtime: the actual alignment of the field is `min(2,
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// usual_alignment)`. Here we check that we do this right by comparing size, alignment, and field
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// offset before and after unsizing.
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fn main() {
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#[repr(C, packed(2))]
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struct Packed<T: ?Sized>(u8, core::mem::ManuallyDrop<T>);
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let p = Packed(0, core::mem::ManuallyDrop::new(1));
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let p: &Packed<usize> = &p;
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let sized = (core::mem::size_of_val(p), core::mem::align_of_val(p));
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let sized_offset = unsafe { addr_of!(p.1).cast::<u8>().offset_from(addr_of!(p.0)) };
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let p: &Packed<dyn Send> = p;
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let un_sized = (core::mem::size_of_val(p), core::mem::align_of_val(p));
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let un_sized_offset = unsafe { addr_of!(p.1).cast::<u8>().offset_from(addr_of!(p.0)) };
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assert_eq!(sized, un_sized);
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assert_eq!(sized_offset, un_sized_offset);
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}
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