1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::source::{position_before_rarrow, snippet_opt};
3 use if_chain::if_chain;
4 use rustc_ast::{ast, visit::FnKind, ClosureBinder};
5 use rustc_errors::Applicability;
6 use rustc_lint::{EarlyContext, EarlyLintPass};
7 use rustc_session::{declare_lint_pass, declare_tool_lint};
8 use rustc_span::source_map::Span;
9 use rustc_span::BytePos;
11 declare_clippy_lint! {
13 /// Checks for unit (`()`) expressions that can be removed.
15 /// ### Why is this bad?
16 /// Such expressions add no value, but can make the code
17 /// less readable. Depending on formatting they can make a `break` or `return`
18 /// statement look like a function call.
22 /// fn return_unit() -> () {
28 /// fn return_unit() {}
30 #[clippy::version = "1.31.0"]
33 "needless unit expression"
36 declare_lint_pass!(UnusedUnit => [UNUSED_UNIT]);
38 impl EarlyLintPass for UnusedUnit {
39 fn check_fn(&mut self, cx: &EarlyContext<'_>, kind: FnKind<'_>, span: Span, _: ast::NodeId) {
41 if let ast::FnRetTy::Ty(ref ty) = kind.decl().output;
42 if let ast::TyKind::Tup(ref vals) = ty.kind;
43 if vals.is_empty() && !ty.span.from_expansion() && get_def(span) == get_def(ty.span);
45 // implicit types in closure signatures are forbidden when `for<...>` is present
46 if let FnKind::Closure(&ClosureBinder::For { .. }, ..) = kind {
50 lint_unneeded_unit_return(cx, ty, span);
55 fn check_block(&mut self, cx: &EarlyContext<'_>, block: &ast::Block) {
57 if let Some(stmt) = block.stmts.last();
58 if let ast::StmtKind::Expr(ref expr) = stmt.kind;
59 if is_unit_expr(expr);
60 let ctxt = block.span.ctxt();
61 if stmt.span.ctxt() == ctxt && expr.span.ctxt() == ctxt;
68 "unneeded unit expression",
69 "remove the final `()`",
71 Applicability::MachineApplicable,
77 fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
79 ast::ExprKind::Ret(Some(ref expr)) | ast::ExprKind::Break(_, Some(ref expr)) => {
80 if is_unit_expr(expr) && !expr.span.from_expansion() {
88 Applicability::MachineApplicable,
96 fn check_poly_trait_ref(&mut self, cx: &EarlyContext<'_>, poly: &ast::PolyTraitRef) {
97 let segments = &poly.trait_ref.path.segments;
100 if segments.len() == 1;
101 if ["Fn", "FnMut", "FnOnce"].contains(&segments[0].ident.name.as_str());
102 if let Some(args) = &segments[0].args;
103 if let ast::GenericArgs::Parenthesized(generic_args) = &**args;
104 if let ast::FnRetTy::Ty(ty) = &generic_args.output;
105 if ty.kind.is_unit();
107 lint_unneeded_unit_return(cx, ty, generic_args.span);
115 fn get_def(span: Span) -> Option<Span> {
116 if span.from_expansion() {
117 Some(span.ctxt().outer_expn_data().def_site)
123 // is this expr a `()` unit?
124 fn is_unit_expr(expr: &ast::Expr) -> bool {
125 if let ast::ExprKind::Tup(ref vals) = expr.kind {
132 fn lint_unneeded_unit_return(cx: &EarlyContext<'_>, ty: &ast::Ty, span: Span) {
133 let (ret_span, appl) =
134 snippet_opt(cx, span.with_hi(ty.span.hi())).map_or((ty.span, Applicability::MaybeIncorrect), |fn_source| {
135 position_before_rarrow(&fn_source).map_or((ty.span, Applicability::MaybeIncorrect), |rpos| {
137 #[expect(clippy::cast_possible_truncation)]
138 ty.span.with_lo(BytePos(span.lo().0 + rpos as u32)),
139 Applicability::MachineApplicable,
147 "unneeded unit return type",
148 "remove the `-> ()`",