1 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
2 use clippy_utils::sugg::Sugg;
3 use if_chain::if_chain;
5 use rustc_ast::visit as ast_visit;
6 use rustc_ast::visit::Visitor as AstVisitor;
7 use rustc_errors::Applicability;
9 use rustc_hir::intravisit as hir_visit;
10 use rustc_hir::intravisit::Visitor as HirVisitor;
11 use rustc_lint::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
12 use rustc_middle::hir::nested_filter;
13 use rustc_middle::lint::in_external_macro;
14 use rustc_session::{declare_lint_pass, declare_tool_lint};
16 declare_clippy_lint! {
18 /// Detects closures called in the same expression where they
21 /// ### Why is this bad?
22 /// It is unnecessarily adding to the expression's
27 /// let a = (|| 42)();
34 #[clippy::version = "pre 1.29.0"]
35 pub REDUNDANT_CLOSURE_CALL,
37 "throwaway closures called in the expression they are defined"
40 declare_lint_pass!(RedundantClosureCall => [REDUNDANT_CLOSURE_CALL]);
42 // Used to find `return` statements or equivalents e.g., `?`
43 struct ReturnVisitor {
50 Self { found_return: false }
54 impl<'ast> ast_visit::Visitor<'ast> for ReturnVisitor {
55 fn visit_expr(&mut self, ex: &'ast ast::Expr) {
56 if let ast::ExprKind::Ret(_) | ast::ExprKind::Try(_) = ex.kind {
57 self.found_return = true;
60 ast_visit::walk_expr(self, ex);
64 impl EarlyLintPass for RedundantClosureCall {
65 fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
66 if in_external_macro(cx.sess(), expr.span) {
70 if let ast::ExprKind::Call(ref paren, _) = expr.kind;
71 if let ast::ExprKind::Paren(ref closure) = paren.kind;
72 if let ast::ExprKind::Closure(box ast::Closure { ref asyncness, ref fn_decl, ref body, .. }) = closure.kind;
74 let mut visitor = ReturnVisitor::new();
75 visitor.visit_expr(body);
76 if !visitor.found_return {
79 REDUNDANT_CLOSURE_CALL,
81 "try not to call a closure in the expression where it is declared",
83 if fn_decl.inputs.is_empty() {
84 let mut app = Applicability::MachineApplicable;
85 let mut hint = Sugg::ast(cx, body, "..", closure.span.ctxt(), &mut app);
87 if asyncness.is_async() {
88 // `async x` is a syntax error, so it becomes `async { x }`
89 if !matches!(body.kind, ast::ExprKind::Block(_, _)) {
90 hint = hint.blockify();
93 hint = hint.asyncify();
96 diag.span_suggestion(expr.span, "try doing something like", hint.to_string(), app);
106 impl<'tcx> LateLintPass<'tcx> for RedundantClosureCall {
107 fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
108 fn count_closure_usage<'tcx>(
109 cx: &LateContext<'tcx>,
110 block: &'tcx hir::Block<'_>,
111 path: &'tcx hir::Path<'tcx>,
113 struct ClosureUsageCount<'a, 'tcx> {
114 cx: &'a LateContext<'tcx>,
115 path: &'tcx hir::Path<'tcx>,
118 impl<'a, 'tcx> hir_visit::Visitor<'tcx> for ClosureUsageCount<'a, 'tcx> {
119 type NestedFilter = nested_filter::OnlyBodies;
121 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
123 if let hir::ExprKind::Call(closure, _) = expr.kind;
124 if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = closure.kind;
125 if self.path.segments[0].ident == path.segments[0].ident;
126 if self.path.res == path.res;
131 hir_visit::walk_expr(self, expr);
134 fn nested_visit_map(&mut self) -> Self::Map {
138 let mut closure_usage_count = ClosureUsageCount { cx, path, count: 0 };
139 closure_usage_count.visit_block(block);
140 closure_usage_count.count
143 for w in block.stmts.windows(2) {
145 if let hir::StmtKind::Local(local) = w[0].kind;
146 if let Option::Some(t) = local.init;
147 if let hir::ExprKind::Closure { .. } = t.kind;
148 if let hir::PatKind::Binding(_, _, ident, _) = local.pat.kind;
149 if let hir::StmtKind::Semi(second) = w[1].kind;
150 if let hir::ExprKind::Assign(_, call, _) = second.kind;
151 if let hir::ExprKind::Call(closure, _) = call.kind;
152 if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = closure.kind;
153 if ident == path.segments[0].ident;
154 if count_closure_usage(cx, block, path) == 1;
158 REDUNDANT_CLOSURE_CALL,
160 "closure called just once immediately after it was declared",