-// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-
//! lint when there is an enum with no variants
-use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
-use crate::rustc::{declare_tool_lint, lint_array};
-use crate::rustc::hir::*;
-use crate::utils::span_lint_and_then;
+use crate::utils::span_lint_and_help;
+use rustc_hir::{Item, ItemKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
-/// **What it does:** Checks for `enum`s with no variants.
-///
-/// **Why is this bad?** Enum's with no variants should be replaced with `!`,
-/// the uninhabited type,
-/// or a wrapper around it.
-///
-/// **Known problems:** None.
-///
-/// **Example:**
-/// ```rust
-/// enum Test {}
-/// ```
declare_clippy_lint! {
+ /// **What it does:** Checks for `enum`s with no variants.
+ ///
+ /// As of this writing, the `never_type` is still a
+ /// nightly-only experimental API. Therefore, this lint is only triggered
+ /// if the `never_type` is enabled.
+ ///
+ /// **Why is this bad?** If you want to introduce a type which
+ /// can't be instantiated, you should use `!` (the primitive type "never"),
+ /// or a wrapper around it, because `!` has more extensive
+ /// compiler support (type inference, etc...) and wrappers
+ /// around it are the conventional way to define an uninhabited type.
+ /// For further information visit [never type documentation](https://doc.rust-lang.org/std/primitive.never.html)
+ ///
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ ///
+ /// Bad:
+ /// ```rust
+ /// enum Test {}
+ /// ```
+ ///
+ /// Good:
+ /// ```rust
+ /// #![feature(never_type)]
+ ///
+ /// struct Test(!);
+ /// ```
pub EMPTY_ENUM,
pedantic,
"enum with no variants"
}
-#[derive(Copy, Clone)]
-pub struct EmptyEnum;
+declare_lint_pass!(EmptyEnum => [EMPTY_ENUM]);
-impl LintPass for EmptyEnum {
- fn get_lints(&self) -> LintArray {
- lint_array!(EMPTY_ENUM)
- }
-}
+impl<'tcx> LateLintPass<'tcx> for EmptyEnum {
+ fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
+ // Only suggest the `never_type` if the feature is enabled
+ if !cx.tcx.features().never_type {
+ return;
+ }
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EmptyEnum {
- fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &Item) {
- let did = cx.tcx.hir.local_def_id(item.id);
- if let ItemKind::Enum(..) = item.node {
- let ty = cx.tcx.type_of(did);
- let adt = ty.ty_adt_def()
- .expect("already checked whether this is an enum");
+ if let ItemKind::Enum(..) = item.kind {
+ let ty = cx.tcx.type_of(item.def_id);
+ let adt = ty.ty_adt_def().expect("already checked whether this is an enum");
if adt.variants.is_empty() {
- span_lint_and_then(cx, EMPTY_ENUM, item.span, "enum with no variants", |db| {
- db.span_help(item.span, "consider using the uninhabited type `!` or a wrapper around it");
- });
+ span_lint_and_help(
+ cx,
+ EMPTY_ENUM,
+ item.span,
+ "enum with no variants",
+ None,
+ "consider using the uninhabited type `!` (never type) or a wrapper \
+ around it to introduce a type which can't be instantiated",
+ );
}
}
}