1ad218f3af
As our implementation of MCP411 nears completion and we begin to solicit testing, it's no longer reasonable to expect testers to type or remember `BikeshedIntrinsicFrom`. The name degrades the ease-of-reading of documentation, and the overall experience of using compiler safe transmute. Tentatively, we'll instead adopt `TransmuteFrom`. This name seems to be the one most likely to be stabilized, after discussion on Zulip [1]. We may want to revisit the ordering of `Src` and `Dst` before stabilization, at which point we'd likely consider `TransmuteInto` or `Transmute`. [1] https://rust-lang.zulipchat.com/#narrow/stream/216762-project-safe-transmute/topic/What.20should.20.60BikeshedIntrinsicFrom.60.20be.20named.3F
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, TransmuteFrom};
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pub fn is_transmutable<Src, Dst>()
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where
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Dst: TransmuteFrom<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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