eros 0.8.1

Ergonomic error handling with typed or untyped errors, context, and no enum boilerplate.
Documentation 
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use core::any::Any;

use crate::{AnyError, SendSyncError};

#[doc(hidden)]
pub use crate::narrowing::{GroupNarrow, NarrowTarget, SingleNarrow};
#[doc(hidden)]
pub use crate::recovery::{GroupRecovery, RecoveryHandler, RecoveryTarget, SingleRecovery};

mod sealed {
    pub trait Sealed {}

    // A required method taking this unnameable type seals each relation,
    // including its generic parameters. Sealing only Self would let downstream
    // crates supply a local Index and invent membership or remainder proofs.
    // These methods are never called.
    pub struct Token;
}

// Type-list and index helpers that appear in associated types and inferred proofs.
#[doc(hidden)]
pub enum End {}
#[doc(hidden)]
pub struct Cons<Head, Tail>(core::marker::PhantomData<Head>, Tail);
#[doc(hidden)]
pub struct Recurse<Tail>(Tail);

impl sealed::Sealed for End {}
impl<Head, Tail> sealed::Sealed for Cons<Head, Tail> {}

/// A set of possible errors for an [`ErrorUnion`](crate::ErrorUnion).
///
/// Implemented for tuples of up to 26 [`SendSyncError`] types, the empty tuple
/// `()`, and [`AnyError`].
/// This trait is sealed and cannot be implemented outside Eros.
pub trait TypeSet: sealed::Sealed + Send + Sync + 'static {
    /// The type list used by [`Contains`], [`Narrow`], and [`SupersetOf`].
    type Variants: TupleForm + IsFold;
    /// The owned enum used by [`ErrorUnion::into_enum`](crate::ErrorUnion::into_enum).
    type Enum;
    /// The borrowed enum used by [`ErrorUnion::as_enum`](crate::ErrorUnion::as_enum).
    type RefEnum<'a>
    where
        Self: 'a;
    /// The mutable enum used by [`ErrorUnion::as_mut_enum`](crate::ErrorUnion::as_mut_enum).
    type MutEnum<'a>
    where
        Self: 'a;
}

#[rustfmt::skip]
impl sealed::Sealed for AnyError {}

#[rustfmt::skip]
impl TypeSet for AnyError {
    type Variants = AnyError;
    type Enum = AnyError;
    type RefEnum<'a> = &'a AnyError where Self: 'a;
    type MutEnum<'a> = &'a mut AnyError where Self: 'a;
}

#[rustfmt::skip]
impl sealed::Sealed for () {}

#[rustfmt::skip]
impl TypeSet for () {
    type Variants = End;
    type Enum = core::convert::Infallible;
    type RefEnum<'a> = core::convert::Infallible where Self: 'a;
    type MutEnum<'a> = core::convert::Infallible where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError> sealed::Sealed for (A,) {}

#[rustfmt::skip]
impl<A: SendSyncError> TypeSet for (A,) {
    type Variants = Cons<A, End>;
    type Enum = E1<A>;
    type RefEnum<'a> = E1<&'a A> where Self: 'a;
    type MutEnum<'a> = E1<&'a mut A> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError> sealed::Sealed for (A, B) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError> TypeSet for (A, B) {
    type Variants = Cons<A, Cons<B, End>>;
    type Enum = E2<A, B>;
    type RefEnum<'a> = E2<&'a A, &'a B> where Self: 'a;
    type MutEnum<'a> = E2<&'a mut A, &'a mut B> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError> sealed::Sealed for (A, B, C) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError> TypeSet for (A, B, C) {
    type Variants = Cons<A, Cons<B, Cons<C, End>>>;
    type Enum = E3<A, B, C>;
    type RefEnum<'a> = E3<&'a A, &'a B, &'a C> where Self: 'a;
    type MutEnum<'a> = E3<&'a mut A, &'a mut B, &'a mut C> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError> sealed::Sealed for (A, B, C, D) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError> TypeSet for (A, B, C, D) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, End>>>>;
    type Enum = E4<A, B, C, D>;
    type RefEnum<'a> = E4<&'a A, &'a B, &'a C, &'a D> where Self: 'a;
    type MutEnum<'a> = E4<&'a mut A, &'a mut B, &'a mut C, &'a mut D> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError> sealed::Sealed for (A, B, C, D, E) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError> TypeSet for (A, B, C, D, E) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, End>>>>>;
    type Enum = E5<A, B, C, D, E>;
    type RefEnum<'a> = E5<&'a A, &'a B, &'a C, &'a D, &'a E> where Self: 'a;
    type MutEnum<'a> = E5<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError> sealed::Sealed for (A, B, C, D, E, F) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError> TypeSet for (A, B, C, D, E, F) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, End>>>>>>;
    type Enum = E6<A, B, C, D, E, F>;
    type RefEnum<'a> = E6<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F> where Self: 'a;
    type MutEnum<'a> = E6<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError> TypeSet for (A, B, C, D, E, F, G) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, End>>>>>>>;
    type Enum = E7<A, B, C, D, E, F, G>;
    type RefEnum<'a> = E7<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G> where Self: 'a;
    type MutEnum<'a> = E7<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, End>>>>>>>>;
    type Enum = E8<A, B, C, D, E, F, G, H>;
    type RefEnum<'a> = E8<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H> where Self: 'a;
    type MutEnum<'a> = E8<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, End>>>>>>>>>;
    type Enum = E9<A, B, C, D, E, F, G, H, I>;
    type RefEnum<'a> = E9<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I> where Self: 'a;
    type MutEnum<'a> = E9<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, End>>>>>>>>>>;
    type Enum = E10<A, B, C, D, E, F, G, H, I, J>;
    type RefEnum<'a> = E10<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J> where Self: 'a;
    type MutEnum<'a> = E10<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, End>>>>>>>>>>>;
    type Enum = E11<A, B, C, D, E, F, G, H, I, J, K>;
    type RefEnum<'a> = E11<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K> where Self: 'a;
    type MutEnum<'a> = E11<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, End>>>>>>>>>>>>;
    type Enum = E12<A, B, C, D, E, F, G, H, I, J, K, L>;
    type RefEnum<'a> = E12<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L> where Self: 'a;
    type MutEnum<'a> = E12<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, End>>>>>>>>>>>>>;
    type Enum = E13<A, B, C, D, E, F, G, H, I, J, K, L, M>;
    type RefEnum<'a> = E13<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M> where Self: 'a;
    type MutEnum<'a> = E13<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, End>>>>>>>>>>>>>>;
    type Enum = E14<A, B, C, D, E, F, G, H, I, J, K, L, M, N>;
    type RefEnum<'a> = E14<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N> where Self: 'a;
    type MutEnum<'a> = E14<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, End>>>>>>>>>>>>>>>;
    type Enum = E15<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O>;
    type RefEnum<'a> = E15<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O> where Self: 'a;
    type MutEnum<'a> = E15<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, End>>>>>>>>>>>>>>>>;
    type Enum = E16<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P>;
    type RefEnum<'a> = E16<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P> where Self: 'a;
    type MutEnum<'a> = E16<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, End>>>>>>>>>>>>>>>>>;
    type Enum = E17<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q>;
    type RefEnum<'a> = E17<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P, &'a Q> where Self: 'a;
    type MutEnum<'a> = E17<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P, &'a mut Q> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, End>>>>>>>>>>>>>>>>>>;
    type Enum = E18<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R>;
    type RefEnum<'a> = E18<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P, &'a Q, &'a R> where Self: 'a;
    type MutEnum<'a> = E18<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P, &'a mut Q, &'a mut R> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, End>>>>>>>>>>>>>>>>>>>;
    type Enum = E19<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S>;
    type RefEnum<'a> = E19<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P, &'a Q, &'a R, &'a S> where Self: 'a;
    type MutEnum<'a> = E19<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P, &'a mut Q, &'a mut R, &'a mut S> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, End>>>>>>>>>>>>>>>>>>>>;
    type Enum = E20<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T>;
    type RefEnum<'a> = E20<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P, &'a Q, &'a R, &'a S, &'a T> where Self: 'a;
    type MutEnum<'a> = E20<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P, &'a mut Q, &'a mut R, &'a mut S, &'a mut T> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, End>>>>>>>>>>>>>>>>>>>>>;
    type Enum = E21<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U>;
    type RefEnum<'a> = E21<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P, &'a Q, &'a R, &'a S, &'a T, &'a U> where Self: 'a;
    type MutEnum<'a> = E21<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P, &'a mut Q, &'a mut R, &'a mut S, &'a mut T, &'a mut U> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, Cons<V, End>>>>>>>>>>>>>>>>>>>>>>;
    type Enum = E22<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V>;
    type RefEnum<'a> = E22<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P, &'a Q, &'a R, &'a S, &'a T, &'a U, &'a V> where Self: 'a;
    type MutEnum<'a> = E22<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P, &'a mut Q, &'a mut R, &'a mut S, &'a mut T, &'a mut U, &'a mut V> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, Cons<V, Cons<W, End>>>>>>>>>>>>>>>>>>>>>>>;
    type Enum = E23<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W>;
    type RefEnum<'a> = E23<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P, &'a Q, &'a R, &'a S, &'a T, &'a U, &'a V, &'a W> where Self: 'a;
    type MutEnum<'a> = E23<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P, &'a mut Q, &'a mut R, &'a mut S, &'a mut T, &'a mut U, &'a mut V, &'a mut W> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError, X: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError, X: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, Cons<V, Cons<W, Cons<X, End>>>>>>>>>>>>>>>>>>>>>>>>;
    type Enum = E24<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X>;
    type RefEnum<'a> = E24<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P, &'a Q, &'a R, &'a S, &'a T, &'a U, &'a V, &'a W, &'a X> where Self: 'a;
    type MutEnum<'a> = E24<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P, &'a mut Q, &'a mut R, &'a mut S, &'a mut T, &'a mut U, &'a mut V, &'a mut W, &'a mut X> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError, X: SendSyncError, Y: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError, X: SendSyncError, Y: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, Cons<V, Cons<W, Cons<X, Cons<Y, End>>>>>>>>>>>>>>>>>>>>>>>>>;
    type Enum = E25<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y>;
    type RefEnum<'a> = E25<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P, &'a Q, &'a R, &'a S, &'a T, &'a U, &'a V, &'a W, &'a X, &'a Y> where Self: 'a;
    type MutEnum<'a> = E25<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P, &'a mut Q, &'a mut R, &'a mut S, &'a mut T, &'a mut U, &'a mut V, &'a mut W, &'a mut X, &'a mut Y> where Self: 'a;
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError, X: SendSyncError, Y: SendSyncError, Z: SendSyncError> sealed::Sealed for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z) {}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError, X: SendSyncError, Y: SendSyncError, Z: SendSyncError> TypeSet for (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z) {
    type Variants = Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, Cons<V, Cons<W, Cons<X, Cons<Y, Cons<Z, End>>>>>>>>>>>>>>>>>>>>>>>>>>;
    type Enum = E26<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z>;
    type RefEnum<'a> = E26<&'a A, &'a B, &'a C, &'a D, &'a E, &'a F, &'a G, &'a H, &'a I, &'a J, &'a K, &'a L, &'a M, &'a N, &'a O, &'a P, &'a Q, &'a R, &'a S, &'a T, &'a U, &'a V, &'a W, &'a X, &'a Y, &'a Z> where Self: 'a;
    type MutEnum<'a> = E26<&'a mut A, &'a mut B, &'a mut C, &'a mut D, &'a mut E, &'a mut F, &'a mut G, &'a mut H, &'a mut I, &'a mut J, &'a mut K, &'a mut L, &'a mut M, &'a mut N, &'a mut O, &'a mut P, &'a mut Q, &'a mut R, &'a mut S, &'a mut T, &'a mut U, &'a mut V, &'a mut W, &'a mut X, &'a mut Y, &'a mut Z> where Self: 'a;
}

//************************************************************************//

/// Associates a type list with its corresponding error set type.
///
/// For example, `Cons<A, Cons<B, End>>` has `Tuple = (A, B)`.
/// This association determines the error set of the remainder union after
/// [`ErrorUnion::narrow`](crate::ErrorUnion::narrow). This trait is sealed.
pub trait TupleForm: sealed::Sealed {
    /// The corresponding error set.
    type Tuple: TypeSet;
}

impl TupleForm for AnyError {
    type Tuple = AnyError;
}

impl TupleForm for End {
    type Tuple = ();
}

#[rustfmt::skip]
impl<A: SendSyncError> TupleForm
    for Cons<A, End>
{
    type Tuple = (A,);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError> TupleForm
    for Cons<A, Cons<B, End>>
{
    type Tuple = (A, B);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError> TupleForm
    for Cons<A, Cons<B, Cons<C, End>>>
{
    type Tuple = (A, B, C);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError> TupleForm
    for Cons<A, Cons<B, Cons<C, Cons<D, End>>>>
{
    type Tuple = (A, B, C, D);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError> TupleForm
    for Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, End>>>>>
{
    type Tuple = (A, B, C, D, E);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError> TupleForm
    for Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, End>>>>>>
{
    type Tuple = (A, B, C, D, E, F);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError> TupleForm
    for Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, End>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError> TupleForm
    for Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, End>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError> TupleForm
    for Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, End>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, End>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, End>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, End>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, End>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, End>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, End>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, End>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, End>>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, End>>>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, End>>>>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, End>>>>>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, End>>>>>>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, Cons<V, End>>>>>>>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, Cons<V, Cons<W, End>>>>>>>>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError, X: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, Cons<V, Cons<W, Cons<X, End>>>>>>>>>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError, X: SendSyncError, Y: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, Cons<V, Cons<W, Cons<X, Cons<Y, End>>>>>>>>>>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y);
}

#[rustfmt::skip]
impl<A: SendSyncError, B: SendSyncError, C: SendSyncError, D: SendSyncError, E: SendSyncError, F: SendSyncError, G: SendSyncError, H: SendSyncError, I: SendSyncError, J: SendSyncError, K: SendSyncError, L: SendSyncError, M: SendSyncError, N: SendSyncError, O: SendSyncError, P: SendSyncError, Q: SendSyncError, R: SendSyncError, S: SendSyncError, T: SendSyncError, U: SendSyncError, V: SendSyncError, W: SendSyncError, X: SendSyncError, Y: SendSyncError, Z: SendSyncError> TupleForm
    for
    Cons<A, Cons<B, Cons<C, Cons<D, Cons<E, Cons<F, Cons<G, Cons<H, Cons<I, Cons<J, Cons<K, Cons<L, Cons<M, Cons<N, Cons<O, Cons<P, Cons<Q, Cons<R, Cons<S, Cons<T, Cons<U, Cons<V, Cons<W, Cons<X, Cons<Y, Cons<Z, End>>>>>>>>>>>>>>>>>>>>>>>>>>
{
    type Tuple = (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z);
}

//************************************************************************//

/// Tests whether a value's concrete type occurs in a type list.
/// This trait is sealed.
pub trait IsFold: sealed::Sealed {
    /// Returns whether the list contains the value's concrete type.
    fn is_fold(any: &dyn Any) -> bool;
}

impl IsFold for End {
    fn is_fold(_: &dyn Any) -> bool {
        false
    }
}

impl<Head, Tail> IsFold for Cons<Head, Tail>
where
    Head: 'static,
    Tail: IsFold,
{
    fn is_fold(any: &dyn Any) -> bool {
        if any.is::<Head>() {
            true
        } else {
            Tail::is_fold(any)
        }
    }
}

impl IsFold for AnyError {
    fn is_fold(_: &dyn Any) -> bool {
        true
    }
}

//************************************************************************//

impl<A> From<A> for E1<A> {
    fn from(a: A) -> E1<A> {
        E1::A(a)
    }
}

#[rustfmt::skip]
pub enum E1<A> { A(A) }

#[rustfmt::skip]
pub enum E2<A, B> { A(A), B(B) }

#[rustfmt::skip]
pub enum E3<A, B, C> { A(A), B(B), C(C) }

#[rustfmt::skip]
pub enum E4<A, B, C, D> { A(A), B(B), C(C), D(D) }

#[rustfmt::skip]
pub enum E5<A, B, C, D, E> { A(A), B(B), C(C), D(D), E(E) }

#[rustfmt::skip]
pub enum E6<A, B, C, D, E, F> { A(A), B(B), C(C), D(D), E(E), F(F) }

#[rustfmt::skip]
pub enum E7<A, B, C, D, E, F, G> { A(A), B(B), C(C), D(D), E(E), F(F), G(G) }

#[rustfmt::skip]
pub enum E8<A, B, C, D, E, F, G, H> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H) }

#[rustfmt::skip]
pub enum E9<A, B, C, D, E, F, G, H, I> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I) }

#[rustfmt::skip]
pub enum E10<A, B, C, D, E, F, G, H, I, J> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J) }

#[rustfmt::skip]
pub enum E11<A, B, C, D, E, F, G, H, I, J, K> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K) }

#[rustfmt::skip]
pub enum E12<A, B, C, D, E, F, G, H, I, J, K, L> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L) }

#[rustfmt::skip]
pub enum E13<A, B, C, D, E, F, G, H, I, J, K, L, M> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M) }

#[rustfmt::skip]
pub enum E14<A, B, C, D, E, F, G, H, I, J, K, L, M, N> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N) }

#[rustfmt::skip]
pub enum E15<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O) }

#[rustfmt::skip]
pub enum E16<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P) }

#[rustfmt::skip]
pub enum E17<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P), Q(Q) }

#[rustfmt::skip]
pub enum E18<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P), Q(Q), R(R) }

#[rustfmt::skip]
pub enum E19<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P), Q(Q), R(R), S(S) }

#[rustfmt::skip]
pub enum E20<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P), Q(Q), R(R), S(S), T(T) }

#[rustfmt::skip]
pub enum E21<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P), Q(Q), R(R), S(S), T(T), U(U) }

#[rustfmt::skip]
pub enum E22<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P), Q(Q), R(R), S(S), T(T), U(U), V(V) }

#[rustfmt::skip]
pub enum E23<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P), Q(Q), R(R), S(S), T(T), U(U), V(V), W(W) }

#[rustfmt::skip]
pub enum E24<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P), Q(Q), R(R), S(S), T(T), U(U), V(V), W(W), X(X) }

#[rustfmt::skip]
pub enum E25<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P), Q(Q), R(R), S(S), T(T), U(U), V(V), W(W), X(X), Y(Y) }

#[rustfmt::skip]
pub enum E26<A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z> { A(A), B(B), C(C), D(D), E(E), F(F), G(G), H(H), I(I), J(J), K(K), L(L), M(M), N(N), O(O), P(P), Q(Q), R(R), S(S), T(T), U(U), V(V), W(W), X(X), Y(Y), Z(Z) }

//************************************************************************//

/// A type list that contains `T`.
///
/// Applied to [`TypeSet::Variants`] when constructing an error union.
/// `Index` is inferred at call sites. This trait is sealed.
pub trait Contains<T, Index> {
    #[doc(hidden)]
    fn __seal(_: sealed::Token);
}

/// Base case implementation for when the Cons Head is T.
impl<T, Tail> Contains<T, End> for Cons<T, Tail> {
    fn __seal(_: sealed::Token) {}
}

/// Recursive case for when the Cons Tail contains T.
impl<T, Index, Head, Tail> Contains<T, Cons<Index, ()>> for Cons<Head, Tail>
where
    Tail: Contains<T, Index>,
{
    fn __seal(_: sealed::Token) {}
}

impl<T> Contains<T, End> for AnyError {
    fn __seal(_: sealed::Token) {}
}

//************************************************************************//

/// A type list from which `T` can be removed.
///
/// Applied to [`TypeSet::Variants`] by [`ErrorUnion::narrow`](crate::ErrorUnion::narrow).
/// `Index` is inferred at call sites. This trait is sealed.
pub trait Narrow<T, Index>: TupleForm {
    /// The type list remaining after removing `T`.
    type Remainder: TupleForm;

    #[doc(hidden)]
    fn __seal(_: sealed::Token);
}

/// Base case where the search Target is in the Head of the Variants.
impl<Target, Tail> Narrow<Target, End> for Cons<Target, Tail>
where
    Tail: TupleForm,
    Cons<Target, Tail>: TupleForm,
{
    type Remainder = Tail;

    fn __seal(_: sealed::Token) {}
}

/// Recursive case where the search Target is in the Tail of the Variants.
impl<Head, Tail, Target, Index> Narrow<Target, Recurse<Index>> for Cons<Head, Tail>
where
    Tail: Narrow<Target, Index>,
    Tail: TupleForm,
    Cons<Head, Tail>: TupleForm,
    Cons<Head, <Tail as Narrow<Target, Index>>::Remainder>: TupleForm,
{
    type Remainder = Cons<Head, <Tail as Narrow<Target, Index>>::Remainder>;

    fn __seal(_: sealed::Token) {}
}

fn _narrow_test() {
    use core::{fmt::Error, num::ParseIntError};
    fn can_narrow<Types, Target, Remainder, Index>()
    where
        Types: Narrow<Target, Index, Remainder = Remainder>,
    {
    }

    type T0 = <(Error, ParseIntError) as TypeSet>::Variants;

    can_narrow::<T0, Error, _, _>();
    can_narrow::<T0, ParseIntError, Cons<Error, End>, _>();
}

//************************************************************************//

/// A type list containing every member of `Other`.
///
/// Applied to [`TypeSet::Variants`] by [`ErrorUnion::widen`](crate::ErrorUnion::widen)
/// and [`ErrorUnion::narrow`](crate::ErrorUnion::narrow).
/// `Index` is inferred at call sites. This trait is sealed.
pub trait SupersetOf<Other, Index> {
    /// The type list remaining after removing the members of `Other`.
    type Remainder: TupleForm;

    #[doc(hidden)]
    fn __seal(_: sealed::Token);
}

/// Base case
impl<T: TupleForm> SupersetOf<End, End> for T {
    type Remainder = T;

    fn __seal(_: sealed::Token) {}
}

/// Recursive case - more complex because we have to reason about the Index itself as a
/// heterogenous list.
impl<SubHead, SubTail, SuperHead, SuperTail, HeadIndex, TailIndex>
    SupersetOf<Cons<SubHead, SubTail>, Cons<HeadIndex, TailIndex>> for Cons<SuperHead, SuperTail>
where
    Cons<SuperHead, SuperTail>: Narrow<SubHead, HeadIndex>,
    <Cons<SuperHead, SuperTail> as Narrow<SubHead, HeadIndex>>::Remainder:
        SupersetOf<SubTail, TailIndex>,
{
    type Remainder =
        <<Cons<SuperHead, SuperTail> as Narrow<SubHead, HeadIndex>>::Remainder as SupersetOf<
            SubTail,
            TailIndex,
        >>::Remainder;

    fn __seal(_: sealed::Token) {}
}

impl SupersetOf<AnyError, End> for AnyError {
    type Remainder = AnyError;

    fn __seal(_: sealed::Token) {}
}

fn _superset_test() {
    use core::{
        cell::{BorrowError, BorrowMutError},
        fmt::Error,
        num::{ParseFloatError, ParseIntError, TryFromIntError},
        str::Utf8Error,
    };
    fn is_superset<S1, S2, Remainder, Index>()
    where
        S1: SupersetOf<S2, Index, Remainder = Remainder>,
    {
    }

    type T0 = <(Error,) as TypeSet>::Variants;
    type T1A = <(Error, ParseIntError) as TypeSet>::Variants;
    type T1B = <(ParseIntError, Error) as TypeSet>::Variants;
    type T2 = <(ParseIntError, ParseFloatError, Error) as TypeSet>::Variants;
    type T3 = <(
        BorrowError,
        BorrowMutError,
        Error,
        TryFromIntError,
        ParseIntError,
        Utf8Error,
        ParseFloatError,
    ) as TypeSet>::Variants;

    is_superset::<T0, T0, _, _>();
    is_superset::<T1A, T1A, _, _>();
    is_superset::<T1A, T1B, _, _>();
    is_superset::<T1B, T1A, _, _>();
    is_superset::<T2, T2, _, _>();
    is_superset::<T1A, T0, _, _>();
    is_superset::<T1B, T0, _, _>();
    is_superset::<T2, T0, <(ParseIntError, ParseFloatError) as TypeSet>::Variants, _>();
    is_superset::<T2, T1A, <(ParseFloatError,) as TypeSet>::Variants, _>();
    is_superset::<T2, T1B, <(ParseFloatError,) as TypeSet>::Variants, _>();
    is_superset::<
        T3,
        T1A,
        <(
            BorrowError,
            BorrowMutError,
            TryFromIntError,
            Utf8Error,
            ParseFloatError,
        ) as TypeSet>::Variants,
        _,
    >();
    is_superset::<T3, T1B, _, _>();
    is_superset::<T3, T0, _, _>();
    is_superset::<T3, T2, _, _>();

    type T5sup =
        <(BorrowError, BorrowMutError, Error, Utf8Error, ParseIntError) as TypeSet>::Variants;
    type T5sub = <(BorrowError, ParseIntError) as TypeSet>::Variants;
    type T5rem = <(BorrowMutError, Error, Utf8Error) as TypeSet>::Variants;

    is_superset::<T5sup, T5sub, T5rem, _>();
}

impl<Target: SendSyncError> Narrow<Target, End> for AnyError {
    type Remainder = AnyError;
    fn __seal(_: sealed::Token) {}
}

impl<Head, Tail, TailIndex> SupersetOf<Cons<Head, Tail>, Cons<End, TailIndex>> for AnyError
where
    Head: SendSyncError,
    AnyError: SupersetOf<Tail, TailIndex>,
{
    type Remainder = AnyError;
    fn __seal(_: sealed::Token) {}
}