70 lines
2.2 KiB
Rust
70 lines
2.2 KiB
Rust
//! lint when there is an enum with no variants
|
|
|
|
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.
|
|
///
|
|
/// 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"
|
|
}
|
|
|
|
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;
|
|
}
|
|
|
|
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_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",
|
|
);
|
|
}
|
|
}
|
|
}
|
|
}
|