modify code

[rust.git] / clippy_lints / src / empty_enum.rs

diff --git a/clippy_lints/src/empty_enum.rs b/clippy_lints/src/empty_enum.rs
index 1d7f18befc018865921b1b7187a4909ddeac423a..af9e65e636135d8fb186f7390bb89d8047e46230 100644 (file)
--- a/clippy_lints/src/empty_enum.rs
+++ b/clippy_lints/src/empty_enum.rs
@@ -1,24 +1,40 @@
 //! lint when there is an enum with no variants
 
-use crate::utils::span_lint_and_then;
-use rustc::declare_lint_pass;
-use rustc::hir::*;
-use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
-use rustc_session::declare_tool_lint;
+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.
+    /// ### 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.
+    /// 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.
     ///
-    /// **Known problems:** None.
+    /// ### 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:**
+    ///
+    /// ### Example
+    /// Bad:
     /// ```rust
     /// enum Test {}
     /// ```
+    ///
+    /// Good:
+    /// ```rust
+    /// #![feature(never_type)]
+    ///
+    /// struct Test(!);
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
     pub EMPTY_ENUM,
     pedantic,
     "enum with no variants"
@@ -26,19 +42,26 @@
 
 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);
+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(did);
+            let ty = cx.tcx.type_of(item.def_id);
             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",
+                );
             }
         }
     }