use clippy_utils::diagnostics::span_lint_and_help;

use rustc_hir::{Item, ItemKind};

use rustc_lint::{LateContext, LateLintPass};

use rustc_session::declare_lint_pass;

declare_clippy_lint! {

/// ### What it does

/// Checks for `enum`s with no variants, which therefore are uninhabited types

/// (cannot be instantiated).

///

/// As of this writing, the `never_type` is still a nightly-only experimental API.

/// Therefore, this lint is only triggered if `#![feature(never_type)]` is enabled.

///

/// ### Why is this bad?

/// * If you only want a type which can’t be instantiated, you should use [`!`]

/// (the primitive type "never"), because [`!`] has more extensive compiler support

/// (type inference, etc.) and implementations of common traits.

///

/// * If you need to introduce a distinct type, consider using a [newtype] `struct`

/// containing [`!`] instead (`struct MyType(pub !)`), because it is more idiomatic

/// to use a `struct` rather than an `enum` when an `enum` is unnecessary.

///

/// If you do this, note that the [visibility] of the [`!`] field determines whether

/// the uninhabitedness is visible in documentation, and whether it can be pattern

/// matched to mark code unreachable. If the field is not visible, then the struct

/// acts like any other struct with private fields.

///

/// * If the enum has no variants only because all variants happen to be

/// [disabled by conditional compilation][cfg], then it would be appropriate

/// to allow the lint, with `#[allow(empty_enum)]`.

///

/// For further information, visit

/// [the never type’s documentation][`!`].

///

/// ### Example

/// ```no_run

/// enum CannotExist {}

/// ```

///

/// Use instead:

/// ```no_run

/// #![feature(never_type)]

///

/// /// Use the `!` type directly...

/// type CannotExist = !;

///

/// /// ...or define a newtype which is distinct.

/// struct CannotExist2(pub !);

/// ```

///

/// [`!`]: https://doc.rust-lang.org/std/primitive.never.html

/// [cfg]: https://doc.rust-lang.org/reference/conditional-compilation.html

/// [newtype]: https://doc.rust-lang.org/book/ch19-04-advanced-types.html#using-the-newtype-pattern-for-type-safety-and-abstraction

/// [visibility]: https://doc.rust-lang.org/reference/visibility-and-privacy.html

#[clippy::version = "pre 1.29.0"]

pub EMPTY_ENUM,

pedantic,

"enum with no variants"

}

declare_lint_pass!(EmptyEnum => [EMPTY_ENUM]);

impl LateLintPass<'_> for EmptyEnum {

}