New lint: empty_enum_variants_with_brackets

CHANGELOG.md

@@ -5105,6 +5105,7 @@ Released 2018-09-13
 [`else_if_without_else`]: https://rust-lang.github.io/rust-clippy/master/index.html#else_if_without_else
 [`empty_drop`]: https://rust-lang.github.io/rust-clippy/master/index.html#empty_drop
 [`empty_enum`]: https://rust-lang.github.io/rust-clippy/master/index.html#empty_enum
+[`empty_enum_variants_with_brackets`]: https://rust-lang.github.io/rust-clippy/master/index.html#empty_enum_variants_with_brackets
 [`empty_line_after_doc_comments`]: https://rust-lang.github.io/rust-clippy/master/index.html#empty_line_after_doc_comments
 [`empty_line_after_outer_attr`]: https://rust-lang.github.io/rust-clippy/master/index.html#empty_line_after_outer_attr
 [`empty_loop`]: https://rust-lang.github.io/rust-clippy/master/index.html#empty_loop

clippy_lints/src/declared_lints.rs

@@ -150,6 +150,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::else_if_without_else::ELSE_IF_WITHOUT_ELSE_INFO,
     crate::empty_drop::EMPTY_DROP_INFO,
     crate::empty_enum::EMPTY_ENUM_INFO,
+    crate::empty_enum_variants_with_brackets::EMPTY_ENUM_VARIANTS_WITH_BRACKETS_INFO,
     crate::empty_structs_with_brackets::EMPTY_STRUCTS_WITH_BRACKETS_INFO,
     crate::endian_bytes::BIG_ENDIAN_BYTES_INFO,
     crate::endian_bytes::HOST_ENDIAN_BYTES_INFO,

clippy_lints/src/empty_enum_variants_with_brackets.rs

@@ -0,0 +1,78 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::source::snippet_opt;
+use rustc_ast::ast::{Variant, VariantData};
+use rustc_errors::Applicability;
+use rustc_lexer::TokenKind;
+use rustc_lint::{EarlyContext, EarlyLintPass};
+use rustc_session::declare_lint_pass;
+use rustc_span::Span;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Finds enum variants without fields that are declared with brackets.
+    /// ### Why is this bad?
+    /// Empty brackets while defining enum variants are redundant and can be omitted.
+    /// ### Example
+    /// ```no_run
+    /// enum Season {
+    ///     Summer(), // redundant parentheses
+    ///     Winter{}, // redundant braces
+    ///     Spring
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// enum Season {
+    ///     Summer,
+    ///     Winter,
+    ///     Spring
+    /// }
+    /// ```
+    #[clippy::version = "1.76.0"]
+    pub EMPTY_ENUM_VARIANTS_WITH_BRACKETS,
+    restriction,
+    "enum variant has empty body with redundant brackets"
+}
+
+declare_lint_pass!(EmptyEnumVariantsWithBrackets => [EMPTY_ENUM_VARIANTS_WITH_BRACKETS]);
+
+impl EarlyLintPass for EmptyEnumVariantsWithBrackets {
+    fn check_variant(&mut self, cx: &EarlyContext<'_>, variant: &Variant) {
+        let span_after_ident = variant.span.with_lo(variant.ident.span.hi());
+        if has_brackets(&variant.data) && has_no_fields(cx, &variant.data, span_after_ident) {
+            span_lint_and_then(
+                cx,
+                EMPTY_ENUM_VARIANTS_WITH_BRACKETS,
+                span_after_ident,
+                "enum variant with brackets has empty body",
+                |diagnostic| {
+                    diagnostic.span_suggestion_hidden(
+                        span_after_ident,
+                        "remove the brackets",
+                        "",
+                        Applicability::MachineApplicable,
+                    );
+                },
+            );
+        }
+    }
+}
+
+fn has_brackets(var_data: &VariantData) -> bool {
+    !matches!(var_data, VariantData::Unit(_))
+}
+
+fn has_no_fields(cx: &EarlyContext<'_>, var_data: &VariantData, braces_span: Span) -> bool {
+    if !var_data.fields().is_empty() {
+        return false;
+    }
+    let Some(braces_span_str) = snippet_opt(cx, braces_span) else {
+        return false;
+    };
+
+    has_no_ident_token(braces_span_str.as_ref())
+}
+
+fn has_no_ident_token(braces_span_str: &str) -> bool {
+    !rustc_lexer::tokenize(braces_span_str).any(|t| t.kind == TokenKind::Ident)
+}

clippy_lints/src/lib.rs

@@ -115,6 +115,7 @@ mod duplicate_mod;
 mod else_if_without_else;
 mod empty_drop;
 mod empty_enum;
+mod empty_enum_variants_with_brackets;
 mod empty_structs_with_brackets;
 mod endian_bytes;
 mod entry;
@@ -1081,6 +1082,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(|_| Box::new(uninhabited_references::UninhabitedReferences));
     store.register_late_pass(|_| Box::new(ineffective_open_options::IneffectiveOpenOptions));
     store.register_late_pass(|_| Box::new(unconditional_recursion::UnconditionalRecursion));
+    store.register_early_pass(|| Box::new(empty_enum_variants_with_brackets::EmptyEnumVariantsWithBrackets));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

tests/ui/empty_enum_variants_with_brackets.fixed

@@ -0,0 +1,24 @@
+#![warn(clippy::empty_enum_variants_with_brackets)]
+
+enum TestEnum {
+    // These two enums should not trigger the lint.
+    NonEmptyBrace { x: i32, y: i32 },
+    NonEmptyParentheses(i32, i32),
+
+    // Enum variant with braces and no data
+    EmptyBrace, //~ ERROR: enum variant with brackets has empty body
+
+    // Enum variant with parentheses and no data
+    EmptyParentheses, //~ ERROR: enum variant with brackets has empty body
+}
+
+enum TestEnumWithFeature {
+    // These two enums should not trigger the lint.
+    NonEmptyBrace {
+        #[cfg(feature = "thisisneverenabled")]
+        x: i32,
+    },
+    NonEmptyParentheses(#[cfg(feature = "thisisneverenabled")] i32),
+}
+
+fn main() {}

tests/ui/empty_enum_variants_with_brackets.rs

@@ -0,0 +1,24 @@
+#![warn(clippy::empty_enum_variants_with_brackets)]
+
+enum TestEnum {
+    // These two enums should not trigger the lint.
+    NonEmptyBrace { x: i32, y: i32 },
+    NonEmptyParentheses(i32, i32),
+
+    // Enum variant with braces and no data
+    EmptyBrace {}, //~ ERROR: enum variant with brackets has empty body
+
+    // Enum variant with parentheses and no data
+    EmptyParentheses(), //~ ERROR: enum variant with brackets has empty body
+}
+
+enum TestEnumWithFeature {
+    // These two enums should not trigger the lint.
+    NonEmptyBrace {
+        #[cfg(feature = "thisisneverenabled")]
+        x: i32,
+    },
+    NonEmptyParentheses(#[cfg(feature = "thisisneverenabled")] i32),
+}
+
+fn main() {}

tests/ui/empty_enum_variants_with_brackets.stderr

@@ -0,0 +1,20 @@
+error: enum variant with brackets has empty body
+  --> $DIR/empty_enum_variants_with_brackets.rs:9:15
+   |
+LL |     EmptyBrace {},
+   |               ^^^
+   |
+   = note: `-D clippy::empty-enum-variants-with-brackets` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::empty_enum_variants_with_brackets)]`
+   = help: remove the brackets
+
+error: enum variant with brackets has empty body
+  --> $DIR/empty_enum_variants_with_brackets.rs:12:21
+   |
+LL |     EmptyParentheses(),
+   |                     ^^
+   |
+   = help: remove the brackets
+
+error: aborting due to 2 previous errors
+