2017-02-05 04:07:54 +00:00
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//! lint when there is an enum with no variants
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2020-04-17 14:01:25 +00:00
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use crate::utils::span_lint_and_help;
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2020-02-21 08:39:38 +00:00
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use rustc_hir::{Item, ItemKind};
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2020-01-12 06:08:41 +00:00
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use rustc_lint::{LateContext, LateLintPass};
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2020-01-11 11:37:08 +00:00
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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2017-02-05 04:07:54 +00:00
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2018-03-28 13:24:26 +00:00
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declare_clippy_lint! {
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2019-03-05 16:50:33 +00:00
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/// **What it does:** Checks for `enum`s with no variants.
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///
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2020-01-24 11:37:16 +00:00
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/// **Why is this bad?** If you want to introduce a type which
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/// can't be instantiated, you should use `!` (the never type),
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/// or a wrapper around it, because `!` has more extensive
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/// compiler support (type inference, etc...) and wrappers
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/// around it are the conventional way to define an uninhabited type.
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/// For further information visit [never type documentation](https://doc.rust-lang.org/std/primitive.never.html)
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///
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2019-03-05 16:50:33 +00:00
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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2020-01-24 11:37:16 +00:00
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///
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/// Bad:
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2019-03-05 16:50:33 +00:00
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/// ```rust
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/// enum Test {}
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/// ```
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2020-01-24 11:37:16 +00:00
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///
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/// Good:
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/// ```rust
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/// #![feature(never_type)]
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///
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/// struct Test(!);
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/// ```
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2017-02-05 04:07:54 +00:00
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pub EMPTY_ENUM,
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2018-03-28 13:24:26 +00:00
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pedantic,
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2017-02-05 04:07:54 +00:00
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"enum with no variants"
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}
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2019-04-08 20:43:55 +00:00
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declare_lint_pass!(EmptyEnum => [EMPTY_ENUM]);
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2017-02-05 04:07:54 +00:00
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EmptyEnum {
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2019-12-22 14:42:41 +00:00
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fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &Item<'_>) {
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2019-07-06 03:52:51 +00:00
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let did = cx.tcx.hir().local_def_id(item.hir_id);
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2019-09-27 15:16:06 +00:00
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if let ItemKind::Enum(..) = item.kind {
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2017-04-27 12:00:35 +00:00
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let ty = cx.tcx.type_of(did);
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2018-11-27 20:14:15 +00:00
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let adt = ty.ty_adt_def().expect("already checked whether this is an enum");
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2017-02-05 04:52:44 +00:00
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if adt.variants.is_empty() {
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2020-04-18 10:28:29 +00:00
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span_lint_and_help(
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2020-04-17 14:01:25 +00:00
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cx,
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EMPTY_ENUM,
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item.span,
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"enum with no variants",
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2020-04-19 18:38:07 +00:00
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None,
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2020-04-18 10:28:29 +00:00
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"consider using the uninhabited type `!` (never type) or a wrapper \
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around it to introduce a type which can't be instantiated",
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2020-04-17 14:01:25 +00:00
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);
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2017-02-05 04:07:54 +00:00
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}
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}
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}
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}
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