New upstream version 1.65.0+dfsg1

[rustc.git] / src / test / ui / transmutability / visibility / assume / should_accept_if_dst_has_tricky_unreachable_field.rs

// check-pass
//! Unless visibility is assumed, a transmutation should be rejected if the
//! destination type contains an unreachable field (e.g., a public field with a
//! private type). (This rule is distinct from type privacy, which still may
//! forbid naming such types.)
//!
//! This test exercises a tricky-to-implement instance of this principle: the
//! "pub-in-priv trick". In the below example, the type `dst::private::Zst` is
//! unreachable from `Context`.

#![crate_type = "lib"]
#![feature(transmutability)]
#![allow(dead_code)]

mod assert {
    use std::mem::{Assume, BikeshedIntrinsicFrom};

    pub fn is_transmutable<Src, Dst, Context>()
    where
        Dst: BikeshedIntrinsicFrom<Src, Context, { Assume::SAFETY }>
        // safety IS assumed --------------------^^^^^^^^^^^^^^^^^^
    {}
}

mod src {
    #[repr(C)] pub(in super) struct Zst;

    #[repr(C)] pub(in super) struct Src {
        pub(in super) field: Zst,
    }
}

mod dst {
    mod private {
        #[repr(C)] pub struct Zst; // <- unreachable type
    }

    #[repr(C)] pub(in super) struct Dst {
        pub(in super) field: private::Zst,
    }
}

fn test() {
    struct Context;
    assert::is_transmutable::<src::Src, dst::Dst, Context>();
}