rust-spec 0.7.1

Classification of types in accordance with the Rust specification
Documentation 
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use core::{cell::UnsafeCell, mem::ManuallyDrop};

use rust_spec::{
    RustSpec, Stable, Unstable,
    drop::{CustomDrop, NoDrop},
    layout::Robust,
    mutability::{Exclusive, WithInterior, WithoutInterior},
    niche::WithoutNiche,
    size::{Gt, Sized as SpecSized, Zero},
};
use static_assertions::assert_impl_all;

#[derive(RustSpec)]
pub union RustUnion {
    pub byte: u8,
    _flag: bool,
}

#[derive(RustSpec)]
#[repr(C)]
union ReprCStableUnion {
    byte: u8,
    word: u16,
}

#[derive(RustSpec)]
#[repr(C)]
union ReprCUnion {
    cell: ManuallyDrop<UnsafeCell<u8>>,
    value: u8,
}

#[derive(RustSpec)]
pub union InteriorUnion {
    pub first: ManuallyDrop<UnsafeCell<u8>>,
    pub second: ManuallyDrop<UnsafeCell<u16>>,
}

#[derive(RustSpec)]
#[repr(C)]
union Payload<T>
where
    T: Copy,
{
    fixed: u64,
    value: T,
    unit: (),
}

#[derive(RustSpec)]
#[repr(C)]
pub union Payload2<'a, T>
where
    T: Copy,
{
    fixed: &'a u64,
    value: T,
    item: T,
}

#[derive(RustSpec)]
#[rust_spec(custom_drop)]
pub union CustomDropUnion {
    pub value: u8,
}

impl Drop for CustomDropUnion {
    fn drop(&mut self) {}
}

#[test]
fn union_drop_classification() {
    assert_impl_all!(RustUnion: RustSpec<Drop = NoDrop>);
    assert_impl_all!(CustomDropUnion: RustSpec<Drop = CustomDrop<NoDrop>>);
}

#[test]
fn union_classification() {
    assert_impl_all!(InteriorUnion: RustSpec<Mutability = WithInterior<Robust>>);
    assert_impl_all!(RustUnion:
        RustSpec<
            Layout = Unstable,
            Size = SpecSized<Gt<Zero>>,
            __Alignment = rust_spec::One,
            Trap = Robust,
            Niche = WithoutNiche,
            Mutability = Exclusive<WithoutInterior>,
            __IndirectTrap = Robust,
        >,
    );
    assert_impl_all!(ReprCUnion:
        RustSpec<
            Layout = Stable,
            Size = SpecSized<Gt<Zero>>,
            __Alignment = rust_spec::One,
            Trap = Robust,
            Niche = WithoutNiche,
            Mutability = WithInterior<Robust>,
            __IndirectTrap = Robust,
        >,
    );
    assert_impl_all!(ReprCStableUnion:
        RustSpec<
            Layout = Stable,
            Size = SpecSized<Gt<Zero>>,
            __Alignment = rust_spec::Gt<rust_spec::One>,
            Trap = Robust,
            Niche = WithoutNiche,
            Mutability = Exclusive<WithoutInterior>,
            __IndirectTrap = Robust,
        >,
    );
    assert_impl_all!(Payload<u8>:
        RustSpec<
            Layout = Stable,
            Size = SpecSized<Gt<Zero>>,
            __Alignment = rust_spec::Gt<rust_spec::One>,
            Trap = Robust,
            Niche = WithoutNiche,
            Mutability = Exclusive<WithoutInterior>,
            __IndirectTrap = Robust,
        >,
    );
    assert_impl_all!(Payload<(u32,)>:
        RustSpec<
            Layout = Unstable,
            Size = SpecSized<Gt<Zero>>,
            __Alignment = rust_spec::Gt<rust_spec::One>,
            Trap = Robust,
            Niche = WithoutNiche,
            Mutability = Exclusive<WithoutInterior>,
            __IndirectTrap = Robust,
        >,
    );
}