mirror of https://github.com/rust-lang/rust
45 lines
1.0 KiB
Rust
45 lines
1.0 KiB
Rust
//! The variants of a union must be padded with uninit bytes such that they have
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//! the same length (in bytes).
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#![crate_type = "lib"]
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#![feature(transmutability)]
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#![allow(dead_code)]
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mod assert {
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use std::mem::{Assume, BikeshedIntrinsicFrom};
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pub fn is_transmutable<Src, Dst>()
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where
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Dst: BikeshedIntrinsicFrom<Src, {
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Assume::ALIGNMENT
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.and(Assume::LIFETIMES)
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.and(Assume::SAFETY)
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.and(Assume::VALIDITY)
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}>
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{}
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}
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#[derive(Clone, Copy)]
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#[repr(C)] struct Zst;
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#[derive(Clone, Copy)]
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#[repr(u8)] enum V0 { V = 0 }
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#[derive(Clone, Copy)]
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#[repr(u8)] enum V2 { V = 2 }
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#[repr(C)]
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union Lopsided {
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smol: Zst,
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lorg: V0,
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}
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#[repr(C)] struct Src(V0, Zst, V2);
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#[repr(C)] struct Dst(V0, Lopsided, V2);
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fn should_pad_variants() {
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// If the implementation (incorrectly) fails to pad `Lopsided::smol` with
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// an uninitialized byte, this transmutation might be (wrongly) accepted:
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assert::is_transmutable::<Src, Dst>(); //~ ERROR cannot be safely transmuted
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}
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