rust-spec 0.7.1

//! Representation stability and trap/robustness classification.
//!
//! Stability describes whether Rust guarantees a type's layout whereas robustness describes
//! whether the represented value space has invalid bit patterns (i.e. trap values).
//!
//! This module provides the marker types used by [`crate::RustSpec::Layout`] and [`crate::RustSpec::Trap`].
use core::ops::Add;

use crate::{Stable, Unstable};

/// Closed family of representation-stability classifications.
#[sealed::sealed]
pub trait LayoutKind {}

/// Marker for a type whose bit patterns require no representation-validity conversion.
///
/// This marker also includes the validity of pointees, not just the immediate values.
///
/// This marker does not establish provenance, alignment, lifetimes, or aliasing requirements
/// for pointers or references. For example, `Option<&u8>` is `Robust`, but a non-null
/// representation must still be a valid reference before constructing the value.
pub enum Robust {}

/// Marker for a non-robust type that has a trap value.
pub enum NonRobust {}

#[sealed::sealed]
impl LayoutKind for Stable {}

#[sealed::sealed]
impl LayoutKind for Unstable {}

impl<K> Add<K> for NonRobust {
    type Output = Self;

    fn add(self, _: K) -> Self::Output {
        unreachable!()
    }
}

impl<K> Add<K> for Robust {
    type Output = K;

    fn add(self, _: K) -> Self::Output {
        unreachable!()
    }
}

impl<K> Add<K> for Unstable {
    type Output = Self;

    fn add(self, _: K) -> Self::Output {
        unreachable!()
    }
}

impl Add<Unstable> for Stable {
    type Output = Unstable;

    fn add(self, _: Unstable) -> Self::Output {
        unreachable!()
    }
}

impl Add for Stable {
    type Output = Self;

    fn add(self, _: Self) -> Self::Output {
        unreachable!()
    }
}