//! lint when there is an enum with no variants
-use crate::utils::span_lint_and_then;
-use rustc::hir::*;
-use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
-use rustc::{declare_lint_pass, declare_tool_lint};
+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};
declare_clippy_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.
+ /// **Why is this bad?** If you want to introduce a type which
+ /// can't be instantiated, you should use `!` (the never type),
+ /// 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"
declare_lint_pass!(EmptyEnum => [EMPTY_ENUM]);
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EmptyEnum {
- fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &Item) {
+impl<'tcx> LateLintPass<'tcx> for EmptyEnum {
+ fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
let did = cx.tcx.hir().local_def_id(item.hir_id);
if let ItemKind::Enum(..) = item.kind {
let ty = cx.tcx.type_of(did);
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",
+ );
}
}
}