1 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
2 use clippy_utils::source::snippet_with_applicability;
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};
12 use rustc_middle::hir::map::Map;
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
33 pub REDUNDANT_CLOSURE_CALL,
35 "throwaway closures called in the expression they are defined"
38 declare_lint_pass!(RedundantClosureCall => [REDUNDANT_CLOSURE_CALL]);
40 // Used to find `return` statements or equivalents e.g., `?`
41 struct ReturnVisitor {
48 Self { found_return: false }
52 impl<'ast> ast_visit::Visitor<'ast> for ReturnVisitor {
53 fn visit_expr(&mut self, ex: &'ast ast::Expr) {
54 if let ast::ExprKind::Ret(_) | ast::ExprKind::Try(_) = ex.kind {
55 self.found_return = true;
58 ast_visit::walk_expr(self, ex);
62 impl EarlyLintPass for RedundantClosureCall {
63 fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
64 if in_external_macro(cx.sess, expr.span) {
68 if let ast::ExprKind::Call(ref paren, _) = expr.kind;
69 if let ast::ExprKind::Paren(ref closure) = paren.kind;
70 if let ast::ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.kind;
72 let mut visitor = ReturnVisitor::new();
73 visitor.visit_expr(block);
74 if !visitor.found_return {
77 REDUNDANT_CLOSURE_CALL,
79 "try not to call a closure in the expression where it is declared",
81 if decl.inputs.is_empty() {
82 let mut app = Applicability::MachineApplicable;
84 snippet_with_applicability(cx, block.span, "..", &mut app).into_owned();
85 diag.span_suggestion(expr.span, "try doing something like", hint, app);
95 impl<'tcx> LateLintPass<'tcx> for RedundantClosureCall {
96 fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
97 fn count_closure_usage<'a, 'tcx>(
98 cx: &'a LateContext<'tcx>,
99 block: &'tcx hir::Block<'_>,
100 path: &'tcx hir::Path<'tcx>,
102 struct ClosureUsageCount<'a, 'tcx> {
103 cx: &'a LateContext<'tcx>,
104 path: &'tcx hir::Path<'tcx>,
107 impl<'a, 'tcx> hir_visit::Visitor<'tcx> for ClosureUsageCount<'a, 'tcx> {
108 type Map = Map<'tcx>;
110 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
112 if let hir::ExprKind::Call(closure, _) = expr.kind;
113 if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = closure.kind;
114 if self.path.segments[0].ident == path.segments[0].ident;
115 if self.path.res == path.res;
120 hir_visit::walk_expr(self, expr);
123 fn nested_visit_map(&mut self) -> hir_visit::NestedVisitorMap<Self::Map> {
124 hir_visit::NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
127 let mut closure_usage_count = ClosureUsageCount { cx, path, count: 0 };
128 closure_usage_count.visit_block(block);
129 closure_usage_count.count
132 for w in block.stmts.windows(2) {
134 if let hir::StmtKind::Local(local) = w[0].kind;
135 if let Option::Some(t) = local.init;
136 if let hir::ExprKind::Closure(..) = t.kind;
137 if let hir::PatKind::Binding(_, _, ident, _) = local.pat.kind;
138 if let hir::StmtKind::Semi(second) = w[1].kind;
139 if let hir::ExprKind::Assign(_, call, _) = second.kind;
140 if let hir::ExprKind::Call(closure, _) = call.kind;
141 if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = closure.kind;
142 if ident == path.segments[0].ident;
143 if count_closure_usage(cx, block, path) == 1;
147 REDUNDANT_CLOSURE_CALL,
149 "closure called just once immediately after it was declared",