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
81 lines
2.2 KiB
Rust
81 lines
2.2 KiB
Rust
//@ check-pass
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//! Adapted from https://rust-lang.github.io/unsafe-code-guidelines/layout/enums.html#explicit-repr-annotation-without-c-compatibility
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#![crate_type = "lib"]
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#![feature(transmutability)]
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#![allow(dead_code, incomplete_features, non_camel_case_types)]
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use std::mem::MaybeUninit;
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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 {
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alignment: false,
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lifetimes: false,
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safety: true,
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validity: false,
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}
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}>
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{}
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pub fn is_maybe_transmutable<Src, Dst>()
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where
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Dst: TransmuteFrom<Src, {
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Assume {
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alignment: false,
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lifetimes: false,
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safety: true,
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validity: true,
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}
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}>
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{}
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}
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#[repr(u8)] enum V0 { V = 0 }
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#[repr(u8)] enum V1 { V = 1 }
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fn repr_u8() {
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#[repr(u8)]
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enum TwoCases {
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A(u8, u16), // 0x00 INIT INIT INIT
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B(u16), // 0x01 PADD INIT INIT
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}
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const _: () = {
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assert!(std::mem::size_of::<TwoCases>() == 4);
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};
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#[repr(C)] struct TwoCasesA(V0, u8, u8, u8);
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#[repr(C)] struct TwoCasesB(V1, MaybeUninit<u8>, u8, u8);
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assert::is_transmutable::<TwoCasesA, TwoCases>();
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assert::is_transmutable::<TwoCasesB, TwoCases>();
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assert::is_maybe_transmutable::<TwoCases, TwoCasesA>();
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assert::is_maybe_transmutable::<TwoCases, TwoCasesB>();
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}
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fn repr_c_u8() {
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#[repr(C, u8)]
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enum TwoCases {
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A(u8, u16), // 0x00 PADD INIT PADD INIT INIT
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B(u16), // 0x01 PADD INIT INIT PADD PADD
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}
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const _: () = {
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assert!(std::mem::size_of::<TwoCases>() == 6);
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};
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#[repr(C)] struct TwoCasesA(V0, MaybeUninit<u8>, u8, MaybeUninit<u8>, u8, u8);
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#[repr(C)] struct TwoCasesB(V1, MaybeUninit<u8>, u8, u8, MaybeUninit<u8>, MaybeUninit<u8>);
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assert::is_transmutable::<TwoCasesA, TwoCases>();
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assert::is_transmutable::<TwoCasesB, TwoCases>();
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assert::is_maybe_transmutable::<TwoCases, TwoCasesA>();
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assert::is_maybe_transmutable::<TwoCases, TwoCasesB>();
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}
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