clippy_lints/src/empty_with_brackets.rs - rust-clippy - Git at Google

 use clippy_utils::attrs::span_contains_cfg;
 use clippy_utils::diagnostics::{span_lint_and_then, span_lint_hir_and_then};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::Applicability;
 use rustc_hir::def::CtorOf;
 use rustc_hir::def::DefKind::Ctor;
 use rustc_hir::def::Res::Def;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::{Expr, ExprKind, Item, ItemKind, Node, Path, QPath, Variant, VariantData};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::impl_lint_pass;
 use rustc_span::Span;

 declare_clippy_lint! {
     /// ### What it does
     /// Finds structs without fields (a so-called "empty struct") that are declared with brackets.
     ///
     /// ### Why restrict this?
     /// Empty brackets after a struct declaration can be omitted,
     /// and it may be desirable to do so consistently for style.
     ///
     /// However, removing the brackets also introduces a public constant named after the struct,
     /// so this is not just a syntactic simplification but an API change, and adding them back
     /// is a *breaking* API change.
     ///
     /// ### Example
     /// ```no_run
     /// struct Cookie {}
     /// struct Biscuit();
     /// ```
     /// Use instead:
     /// ```no_run
     /// struct Cookie;
     /// struct Biscuit;
     /// ```
     #[clippy::version = "1.62.0"]
     pub EMPTY_STRUCTS_WITH_BRACKETS,
     restriction,
     "finds struct declarations with empty brackets"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// Finds enum variants without fields that are declared with empty brackets.
     ///
     /// ### Why restrict this?
     /// Empty brackets after a enum variant declaration are redundant and can be omitted,
     /// and it may be desirable to do so consistently for style.
     ///
     /// However, removing the brackets also introduces a public constant named after the variant,
     /// so this is not just a syntactic simplification but an API change, and adding them back
     /// is a *breaking* API change.
     ///
     /// ### Example
     /// ```no_run
     /// enum MyEnum {
     ///     HasData(u8),
     ///     HasNoData(),       // redundant parentheses
     ///     NoneHereEither {}, // redundant braces
     /// }
     /// ```
     ///
     /// Use instead:
     /// ```no_run
     /// enum MyEnum {
     ///     HasData(u8),
     ///     HasNoData,
     ///     NoneHereEither,
     /// }
     /// ```
     #[clippy::version = "1.77.0"]
     pub EMPTY_ENUM_VARIANTS_WITH_BRACKETS,
     restriction,
     "finds enum variants with empty brackets"
 }

 #[derive(Debug)]
 enum Usage {
     Unused { redundant_use_sites: Vec<Span> },
     Used,
     NoDefinition { redundant_use_sites: Vec<Span> },
 }

 #[derive(Default)]
 pub struct EmptyWithBrackets {
     // Value holds `Usage::Used` if the empty tuple variant was used as a function
     empty_tuple_enum_variants: FxIndexMap<LocalDefId, Usage>,
 }

 impl_lint_pass!(EmptyWithBrackets => [EMPTY_STRUCTS_WITH_BRACKETS, EMPTY_ENUM_VARIANTS_WITH_BRACKETS]);

 impl LateLintPass<'_> for EmptyWithBrackets {
     fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
         // FIXME: handle `struct $name {}`
         if let ItemKind::Struct(ident, generics, var_data) = &item.kind
             && !item.span.from_expansion()
             && !ident.span.from_expansion()
             && has_brackets(var_data)
             && let span_after_ident = item.span.with_lo(generics.span.hi())
             && has_no_fields(cx, var_data, span_after_ident)
         {
             span_lint_and_then(
                 cx,
                 EMPTY_STRUCTS_WITH_BRACKETS,
                 span_after_ident,
                 "found empty brackets on struct declaration",
                 |diagnostic| {
                     diagnostic.span_suggestion_hidden(
                         span_after_ident,
                         "remove the brackets",
                         ";",
                         Applicability::Unspecified,
                     );
                 },
             );
         }
     }

     fn check_variant(&mut self, cx: &LateContext<'_>, variant: &Variant<'_>) {
         // FIXME: handle `$name {}`
         if !variant.span.from_expansion()
             && !variant.ident.span.from_expansion()
             && let span_after_ident = variant.span.with_lo(variant.ident.span.hi())
             && has_no_fields(cx, &variant.data, span_after_ident)
         {
             match variant.data {
                 VariantData::Struct { .. } => {
                     // Empty struct variants can be linted immediately
                     span_lint_and_then(
                         cx,
                         EMPTY_ENUM_VARIANTS_WITH_BRACKETS,
                         span_after_ident,
                         "enum variant has empty brackets",
                         |diagnostic| {
                             diagnostic.span_suggestion_hidden(
                                 span_after_ident,
                                 "remove the brackets",
                                 "",
                                 Applicability::MaybeIncorrect,
                             );
                         },
                     );
                 },
                 VariantData::Tuple(.., local_def_id) => {
                     // Don't lint reachable tuple enums
                     if cx.effective_visibilities.is_reachable(variant.def_id) {
                         return;
                     }
                     if let Some(entry) = self.empty_tuple_enum_variants.get_mut(&local_def_id) {
                         // empty_tuple_enum_variants contains Usage::NoDefinition if the variant was called before the
                         // definition was encountered. Now that there's a definition, convert it
                         // to Usage::Unused.
                         if let Usage::NoDefinition { redundant_use_sites } = entry {
                             *entry = Usage::Unused {
                                 redundant_use_sites: redundant_use_sites.clone(),
                             };
                         }
                     } else {
                         self.empty_tuple_enum_variants.insert(
                             local_def_id,
                             Usage::Unused {
                                 redundant_use_sites: vec![],
                             },
                         );
                     }
                 },
                 VariantData::Unit(..) => {},
             }
         }
     }

     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
         if let Some(def_id) = check_expr_for_enum_as_function(expr) {
             if let Some(parentheses_span) = call_parentheses_span(cx.tcx, expr) {
                 // Do not count expressions from macro expansion as a redundant use site.
                 if expr.span.from_expansion() {
                     return;
                 }
                 match self.empty_tuple_enum_variants.get_mut(&def_id) {
                     Some(
                         &mut (Usage::Unused {
                             ref mut redundant_use_sites,
                         }
                         | Usage::NoDefinition {
                             ref mut redundant_use_sites,
                         }),
                     ) => {
                         redundant_use_sites.push(parentheses_span);
                     },
                     None => {
                         // The variant isn't in the IndexMap which means its definition wasn't encountered yet.
                         self.empty_tuple_enum_variants.insert(
                             def_id,
                             Usage::NoDefinition {
                                 redundant_use_sites: vec![parentheses_span],
                             },
                         );
                     },
                     _ => {},
                 }
             } else {
                 // The parentheses are not redundant.
                 self.empty_tuple_enum_variants.insert(def_id, Usage::Used);
             }
         }
     }

     fn check_crate_post(&mut self, cx: &LateContext<'_>) {
         for (local_def_id, usage) in &self.empty_tuple_enum_variants {
             // Ignore all variants with Usage::Used or Usage::NoDefinition
             let Usage::Unused { redundant_use_sites } = usage else {
                 continue;
             };
             // Attempt to fetch the Variant from LocalDefId.
             let Node::Variant(variant) = cx.tcx.hir_node(
                 cx.tcx
                     .local_def_id_to_hir_id(cx.tcx.parent(local_def_id.to_def_id()).expect_local()),
             ) else {
                 continue;
             };
             // Span of the parentheses in variant definition
             let span = variant.span.with_lo(variant.ident.span.hi());
             span_lint_hir_and_then(
                 cx,
                 EMPTY_ENUM_VARIANTS_WITH_BRACKETS,
                 variant.hir_id,
                 span,
                 "enum variant has empty brackets",
                 |diagnostic| {
                     if redundant_use_sites.is_empty() {
                         // If there's no redundant use sites, the definition is the only place to modify.
                         diagnostic.span_suggestion_hidden(
                             span,
                             "remove the brackets",
                             "",
                             Applicability::MaybeIncorrect,
                         );
                     } else {
                         let mut parentheses_spans: Vec<_> =
                             redundant_use_sites.iter().map(|span| (*span, String::new())).collect();
                         parentheses_spans.push((span, String::new()));
                         diagnostic.multipart_suggestion(
                             "remove the brackets",
                             parentheses_spans,
                             Applicability::MaybeIncorrect,
                         );
                     }
                 },
             );
         }
     }
 }

 fn has_brackets(var_data: &VariantData<'_>) -> bool {
     !matches!(var_data, VariantData::Unit(..))
 }

 fn has_no_fields(cx: &LateContext<'_>, var_data: &VariantData<'_>, braces_span: Span) -> bool {
     var_data.fields().is_empty() &&
     // there might still be field declarations hidden from the AST
     // (conditionally compiled code using #[cfg(..)])
     !span_contains_cfg(cx, braces_span)
 }

 // If expression HIR ID and callee HIR ID are same, returns the span of the parentheses, else,
 // returns None.
 fn call_parentheses_span(tcx: TyCtxt<'_>, expr: &Expr<'_>) -> Option<Span> {
     if let Node::Expr(parent) = tcx.parent_hir_node(expr.hir_id)
         && let ExprKind::Call(callee, ..) = parent.kind
         && callee.hir_id == expr.hir_id
     {
         Some(parent.span.with_lo(expr.span.hi()))
     } else {
         None
     }
 }

 // Returns the LocalDefId of the variant being called as a function if it exists.
 fn check_expr_for_enum_as_function(expr: &Expr<'_>) -> Option<LocalDefId> {
     if let ExprKind::Path(QPath::Resolved(
         _,
         Path {
             res: Def(Ctor(CtorOf::Variant, _), def_id),
             ..
         },
     )) = expr.kind
     {
         def_id.as_local()
     } else {
         None
     }
 }
	use clippy_utils::attrs::span_contains_cfg;
	use clippy_utils::diagnostics::{span_lint_and_then, span_lint_hir_and_then};
	use rustc_data_structures::fx::FxIndexMap;
	use rustc_errors::Applicability;
	use rustc_hir::def::CtorOf;
	use rustc_hir::def::DefKind::Ctor;
	use rustc_hir::def::Res::Def;
	use rustc_hir::def_id::LocalDefId;
	use rustc_hir::{Expr, ExprKind, Item, ItemKind, Node, Path, QPath, Variant, VariantData};
	use rustc_lint::{LateContext, LateLintPass};
	use rustc_middle::ty::TyCtxt;
	use rustc_session::impl_lint_pass;
	use rustc_span::Span;

	declare_clippy_lint! {
	/// ### What it does
	/// Finds structs without fields (a so-called "empty struct") that are declared with brackets.
	///
	/// ### Why restrict this?
	/// Empty brackets after a struct declaration can be omitted,
	/// and it may be desirable to do so consistently for style.
	///
	/// However, removing the brackets also introduces a public constant named after the struct,
	/// so this is not just a syntactic simplification but an API change, and adding them back
	/// is a breaking API change.
	///
	/// ### Example
	/// ```no_run
	/// struct Cookie {}
	/// struct Biscuit();
	/// ```
	/// Use instead:
	/// ```no_run
	/// struct Cookie;
	/// struct Biscuit;
	/// ```
	#[clippy::version = "1.62.0"]
	pub EMPTY_STRUCTS_WITH_BRACKETS,
	restriction,
	"finds struct declarations with empty brackets"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// Finds enum variants without fields that are declared with empty brackets.
	///
	/// ### Why restrict this?
	/// Empty brackets after a enum variant declaration are redundant and can be omitted,
	/// and it may be desirable to do so consistently for style.
	///
	/// However, removing the brackets also introduces a public constant named after the variant,
	/// so this is not just a syntactic simplification but an API change, and adding them back
	/// is a breaking API change.
	///
	/// ### Example
	/// ```no_run
	/// enum MyEnum {
	/// HasData(u8),
	/// HasNoData(), // redundant parentheses
	/// NoneHereEither {}, // redundant braces
	/// }
	/// ```
	///
	/// Use instead:
	/// ```no_run
	/// enum MyEnum {
	/// HasData(u8),
	/// HasNoData,
	/// NoneHereEither,
	/// }
	/// ```
	#[clippy::version = "1.77.0"]
	pub EMPTY_ENUM_VARIANTS_WITH_BRACKETS,
	restriction,
	"finds enum variants with empty brackets"
	}

	#[derive(Debug)]
	enum Usage {
	Unused { redundant_use_sites: Vec<Span> },
	Used,
	NoDefinition { redundant_use_sites: Vec<Span> },
	}

	#[derive(Default)]
	pub struct EmptyWithBrackets {
	// Value holds `Usage::Used` if the empty tuple variant was used as a function
	empty_tuple_enum_variants: FxIndexMap<LocalDefId, Usage>,
	}

	impl_lint_pass!(EmptyWithBrackets => [EMPTY_STRUCTS_WITH_BRACKETS, EMPTY_ENUM_VARIANTS_WITH_BRACKETS]);

	impl LateLintPass<'_> for EmptyWithBrackets {
	fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
	// FIXME: handle `struct $name {}`
	if let ItemKind::Struct(ident, generics, var_data) = &item.kind
	&& !item.span.from_expansion()
	&& !ident.span.from_expansion()
	&& has_brackets(var_data)
	&& let span_after_ident = item.span.with_lo(generics.span.hi())
	&& has_no_fields(cx, var_data, span_after_ident)
	{
	span_lint_and_then(
	cx,
	EMPTY_STRUCTS_WITH_BRACKETS,
	span_after_ident,
	"found empty brackets on struct declaration",
	\|diagnostic\| {
	diagnostic.span_suggestion_hidden(
	span_after_ident,
	"remove the brackets",
	";",
	Applicability::Unspecified,
	);
	},
	);
	}
	}

	fn check_variant(&mut self, cx: &LateContext<'_>, variant: &Variant<'_>) {
	// FIXME: handle `$name {}`
	if !variant.span.from_expansion()
	&& !variant.ident.span.from_expansion()
	&& let span_after_ident = variant.span.with_lo(variant.ident.span.hi())
	&& has_no_fields(cx, &variant.data, span_after_ident)
	{
	match variant.data {
	VariantData::Struct { .. } => {
	// Empty struct variants can be linted immediately
	span_lint_and_then(
	cx,
	EMPTY_ENUM_VARIANTS_WITH_BRACKETS,
	span_after_ident,
	"enum variant has empty brackets",
	\|diagnostic\| {
	diagnostic.span_suggestion_hidden(
	span_after_ident,
	"remove the brackets",
	"",
	Applicability::MaybeIncorrect,
	);
	},
	);
	},
	VariantData::Tuple(.., local_def_id) => {
	// Don't lint reachable tuple enums
	if cx.effective_visibilities.is_reachable(variant.def_id) {
	return;
	}
	if let Some(entry) = self.empty_tuple_enum_variants.get_mut(&local_def_id) {
	// empty_tuple_enum_variants contains Usage::NoDefinition if the variant was called before the
	// definition was encountered. Now that there's a definition, convert it
	// to Usage::Unused.
	if let Usage::NoDefinition { redundant_use_sites } = entry {
	*entry = Usage::Unused {
	redundant_use_sites: redundant_use_sites.clone(),
	};
	}
	} else {
	self.empty_tuple_enum_variants.insert(
	local_def_id,
	Usage::Unused {
	redundant_use_sites: vec![],
	},
	);
	}
	},
	VariantData::Unit(..) => {},
	}
	}
	}

	fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
	if let Some(def_id) = check_expr_for_enum_as_function(expr) {
	if let Some(parentheses_span) = call_parentheses_span(cx.tcx, expr) {
	// Do not count expressions from macro expansion as a redundant use site.
	if expr.span.from_expansion() {
	return;
	}
	match self.empty_tuple_enum_variants.get_mut(&def_id) {
	Some(
	&mut (Usage::Unused {
	ref mut redundant_use_sites,
	}
	\| Usage::NoDefinition {
	ref mut redundant_use_sites,
	}),
	) => {
	redundant_use_sites.push(parentheses_span);
	},
	None => {
	// The variant isn't in the IndexMap which means its definition wasn't encountered yet.
	self.empty_tuple_enum_variants.insert(
	def_id,
	Usage::NoDefinition {
	redundant_use_sites: vec![parentheses_span],
	},
	);
	},
	_ => {},
	}
	} else {
	// The parentheses are not redundant.
	self.empty_tuple_enum_variants.insert(def_id, Usage::Used);
	}
	}
	}

	fn check_crate_post(&mut self, cx: &LateContext<'_>) {
	for (local_def_id, usage) in &self.empty_tuple_enum_variants {
	// Ignore all variants with Usage::Used or Usage::NoDefinition
	let Usage::Unused { redundant_use_sites } = usage else {
	continue;
	};
	// Attempt to fetch the Variant from LocalDefId.
	let Node::Variant(variant) = cx.tcx.hir_node(
	cx.tcx
	.local_def_id_to_hir_id(cx.tcx.parent(local_def_id.to_def_id()).expect_local()),
	) else {
	continue;
	};
	// Span of the parentheses in variant definition
	let span = variant.span.with_lo(variant.ident.span.hi());
	span_lint_hir_and_then(
	cx,
	EMPTY_ENUM_VARIANTS_WITH_BRACKETS,
	variant.hir_id,
	span,
	"enum variant has empty brackets",
	\|diagnostic\| {
	if redundant_use_sites.is_empty() {
	// If there's no redundant use sites, the definition is the only place to modify.
	diagnostic.span_suggestion_hidden(
	span,
	"remove the brackets",
	"",
	Applicability::MaybeIncorrect,
	);
	} else {
	let mut parentheses_spans: Vec<_> =
	redundant_use_sites.iter().map(\|span\| (*span, String::new())).collect();
	parentheses_spans.push((span, String::new()));
	diagnostic.multipart_suggestion(
	"remove the brackets",
	parentheses_spans,
	Applicability::MaybeIncorrect,
	);
	}
	},
	);
	}
	}
	}

	fn has_brackets(var_data: &VariantData<'_>) -> bool {
	!matches!(var_data, VariantData::Unit(..))
	}

	fn has_no_fields(cx: &LateContext<'_>, var_data: &VariantData<'_>, braces_span: Span) -> bool {
	var_data.fields().is_empty() &&
	// there might still be field declarations hidden from the AST
	// (conditionally compiled code using #[cfg(..)])
	!span_contains_cfg(cx, braces_span)
	}

	// If expression HIR ID and callee HIR ID are same, returns the span of the parentheses, else,
	// returns None.
	fn call_parentheses_span(tcx: TyCtxt<'_>, expr: &Expr<'_>) -> Option<Span> {
	if let Node::Expr(parent) = tcx.parent_hir_node(expr.hir_id)
	&& let ExprKind::Call(callee, ..) = parent.kind
	&& callee.hir_id == expr.hir_id
	{
	Some(parent.span.with_lo(expr.span.hi()))
	} else {
	None
	}
	}

	// Returns the LocalDefId of the variant being called as a function if it exists.
	fn check_expr_for_enum_as_function(expr: &Expr<'_>) -> Option<LocalDefId> {
	if let ExprKind::Path(QPath::Resolved(
	_,
	Path {
	res: Def(Ctor(CtorOf::Variant, _), def_id),
	..
	},
	)) = expr.kind
	{
	def_id.as_local()
	} else {
	None
	}
	}