Merge pull request #1514 from pengowen123/patch-empty_enum

Add empty_enum lint for enums with no variants

CHANGELOG.md

@@ -306,6 +306,7 @@ All notable changes to this project will be documented in this file.
 [`double_parens`]: https://github.com/Manishearth/rust-clippy/wiki#double_parens
 [`drop_ref`]: https://github.com/Manishearth/rust-clippy/wiki#drop_ref
 [`duplicate_underscore_argument`]: https://github.com/Manishearth/rust-clippy/wiki#duplicate_underscore_argument
+[`empty_enum`]: https://github.com/Manishearth/rust-clippy/wiki#empty_enum
 [`empty_loop`]: https://github.com/Manishearth/rust-clippy/wiki#empty_loop
 [`enum_clike_unportable_variant`]: https://github.com/Manishearth/rust-clippy/wiki#enum_clike_unportable_variant
 [`enum_glob_use`]: https://github.com/Manishearth/rust-clippy/wiki#enum_glob_use

README.md

@@ -180,7 +180,7 @@ transparently:
 
 ## Lints
 
-There are 184 lints included in this crate:
+There are 185 lints included in this crate:
 
 name                                                                                                                   | default | triggers on
 -----------------------------------------------------------------------------------------------------------------------|---------|----------------------------------------------------------------------------------------------------------------------------------
@@ -220,6 +220,7 @@ name
 [double_parens](https://github.com/Manishearth/rust-clippy/wiki#double_parens)                                         | warn    | Warn on unnecessary double parentheses
 [drop_ref](https://github.com/Manishearth/rust-clippy/wiki#drop_ref)                                                   | warn    | calls to `std::mem::drop` with a reference instead of an owned value
 [duplicate_underscore_argument](https://github.com/Manishearth/rust-clippy/wiki#duplicate_underscore_argument)         | warn    | function arguments having names which only differ by an underscore
+[empty_enum](https://github.com/Manishearth/rust-clippy/wiki#empty_enum)                                               | allow   | enum with no variants
 [empty_loop](https://github.com/Manishearth/rust-clippy/wiki#empty_loop)                                               | warn    | empty `loop {}`, which should block or sleep
 [enum_clike_unportable_variant](https://github.com/Manishearth/rust-clippy/wiki#enum_clike_unportable_variant)         | warn    | C-like enums that are `repr(isize/usize)` and have values that don't fit into an `i32`
 [enum_glob_use](https://github.com/Manishearth/rust-clippy/wiki#enum_glob_use)                                         | allow   | use items that import all variants of an enum

clippy_lints/src/empty_enum.rs

@@ -0,0 +1,46 @@
+//! lint when there is an enum with no variants
+
+use rustc::lint::*;
+use rustc::hir::*;
+use utils::span_lint_and_then;
+
+/// **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.
+///
+/// **Known problems:** None.
+///
+/// **Example:**
+/// ```rust
+/// enum Test {}
+/// ```
+declare_lint! {
+    pub EMPTY_ENUM,
+    Allow,
+    "enum with no variants"
+}
+
+#[derive(Copy,Clone)]
+pub struct EmptyEnum;
+
+impl LintPass for EmptyEnum {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(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.id);
+        if let ItemEnum(..) = item.node {
+            let ty = cx.tcx.item_type(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 `!` or a wrapper around it");
+                });
+            }
+        }
+    }
+}

clippy_lints/src/lib.rs

@@ -72,6 +72,7 @@ pub mod derive;
 pub mod doc;
 pub mod double_parens;
 pub mod drop_forget_ref;
+pub mod empty_enum;
 pub mod entry;
 pub mod enum_clike;
 pub mod enum_glob_use;
@@ -265,6 +266,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
         max_single_char_names: conf.max_single_char_names,
     });
     reg.register_late_lint_pass(box drop_forget_ref::Pass);
+    reg.register_late_lint_pass(box empty_enum::EmptyEnum);
     reg.register_late_lint_pass(box types::AbsurdExtremeComparisons);
     reg.register_late_lint_pass(box types::InvalidUpcastComparisons);
     reg.register_late_lint_pass(box regex::Pass::default());
@@ -304,6 +306,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
 
     reg.register_lint_group("clippy_pedantic", vec![
         booleans::NONMINIMAL_BOOL,
+        empty_enum::EMPTY_ENUM,
         enum_glob_use::ENUM_GLOB_USE,
         enum_variants::PUB_ENUM_VARIANT_NAMES,
         enum_variants::STUTTER,

tests/compile-fail/empty_enum.rs

@@ -0,0 +1,11 @@
+#![feature(plugin)]
+#![plugin(clippy)]
+
+#![allow(dead_code)]
+#![deny(empty_enum)]
+
+enum Empty {} //~ ERROR enum with no variants
+    //~^ HELP consider using the uninhabited type `!` or a wrapper around it
+
+fn main() {
+}

tests/compile-fail/enum_glob_use.rs

@@ -5,7 +5,9 @@
 
 use std::cmp::Ordering::*; //~ ERROR: don't use glob imports for enum variants
 
-enum Enum {}
+enum Enum {
+    _Foo,
+}
 
 use self::Enum::*; //~ ERROR: don't use glob imports for enum variants