| //! lint when there is an enum with no variants |
| |
| 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_tool_lint}; |
| |
| 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) |
| /// |
| /// |
| /// ### Example |
| /// ```no_run |
| /// enum Test {} |
| /// ``` |
| /// |
| /// Use instead: |
| /// ```no_run |
| /// #![feature(never_type)] |
| /// |
| /// struct Test(!); |
| /// ``` |
| #[clippy::version = "pre 1.29.0"] |
| pub EMPTY_ENUM, |
| pedantic, |
| "enum with no variants" |
| } |
| |
| declare_lint_pass!(EmptyEnum => [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; |
| } |
| |
| if let ItemKind::Enum(..) = item.kind { |
| let ty = cx.tcx.type_of(item.owner_id).instantiate_identity(); |
| let adt = ty.ty_adt_def().expect("already checked whether this is an enum"); |
| if adt.variants().is_empty() { |
| 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", |
| ); |
| } |
| } |
| } |
| } |