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//! lint when there is an enum with no variants
use crate::utils::span_lint_and_then;
use rustc_hir::*;
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?** 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<'_>) {
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 `!` (never type) or a wrapper \
around it to introduce a type which can't be instantiated",
);
});
}
}
}
}
|
