1 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
2 use clippy_utils::higher::VecArgs;
3 use clippy_utils::source::snippet_opt;
4 use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
5 use clippy_utils::usage::local_used_after_expr;
6 use clippy_utils::{higher, is_adjusted, path_to_local, path_to_local_id};
7 use if_chain::if_chain;
8 use rustc_errors::Applicability;
9 use rustc_hir::def_id::DefId;
10 use rustc_hir::{Closure, Expr, ExprKind, Param, PatKind, Unsafety};
11 use rustc_lint::{LateContext, LateLintPass};
12 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
13 use rustc_middle::ty::binding::BindingMode;
14 use rustc_middle::ty::{self, Ty, TypeVisitable};
15 use rustc_session::{declare_lint_pass, declare_tool_lint};
16 use rustc_span::symbol::sym;
18 declare_clippy_lint! {
20 /// Checks for closures which just call another function where
21 /// the function can be called directly. `unsafe` functions or calls where types
22 /// get adjusted are ignored.
24 /// ### Why is this bad?
25 /// Needlessly creating a closure adds code for no benefit
26 /// and gives the optimizer more work.
28 /// ### Known problems
29 /// If creating the closure inside the closure has a side-
30 /// effect then moving the closure creation out will change when that side-
32 /// See [#1439](https://github.com/rust-lang/rust-clippy/issues/1439) for more details.
36 /// xs.map(|x| foo(x))
41 /// // where `foo(_)` is a plain function that takes the exact argument type of `x`.
44 #[clippy::version = "pre 1.29.0"]
45 pub REDUNDANT_CLOSURE,
47 "redundant closures, i.e., `|a| foo(a)` (which can be written as just `foo`)"
50 declare_clippy_lint! {
52 /// Checks for closures which only invoke a method on the closure
53 /// argument and can be replaced by referencing the method directly.
55 /// ### Why is this bad?
56 /// It's unnecessary to create the closure.
60 /// Some('a').map(|s| s.to_uppercase());
62 /// may be rewritten as
64 /// Some('a').map(char::to_uppercase);
66 #[clippy::version = "1.35.0"]
67 pub REDUNDANT_CLOSURE_FOR_METHOD_CALLS,
69 "redundant closures for method calls"
72 declare_lint_pass!(EtaReduction => [REDUNDANT_CLOSURE, REDUNDANT_CLOSURE_FOR_METHOD_CALLS]);
74 impl<'tcx> LateLintPass<'tcx> for EtaReduction {
75 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
76 if expr.span.from_expansion() {
79 let body = match expr.kind {
80 ExprKind::Closure(&Closure { body, .. }) => cx.tcx.hir().body(body),
83 if body.value.span.from_expansion() {
84 if body.params.is_empty() {
85 if let Some(VecArgs::Vec(&[])) = higher::VecArgs::hir(cx, body.value) {
86 // replace `|| vec![]` with `Vec::new`
92 "replace the closure with `Vec::new`",
93 "std::vec::Vec::new".into(),
94 Applicability::MachineApplicable,
98 // skip `foo(|| macro!())`
102 let closure_ty = cx.typeck_results().expr_ty(expr);
105 if !is_adjusted(cx, body.value);
106 if let ExprKind::Call(callee, args) = body.value.kind;
107 if let ExprKind::Path(_) = callee.kind;
108 if check_inputs(cx, body.params, None, args);
109 let callee_ty = cx.typeck_results().expr_ty_adjusted(callee);
110 let call_ty = cx.typeck_results().type_dependent_def_id(body.value.hir_id)
111 .map_or(callee_ty, |id| cx.tcx.type_of(id));
112 if check_sig(cx, closure_ty, call_ty);
113 let substs = cx.typeck_results().node_substs(callee.hir_id);
114 // This fixes some false positives that I don't entirely understand
115 if substs.is_empty() || !cx.typeck_results().expr_ty(expr).has_late_bound_regions();
116 // A type param function ref like `T::f` is not 'static, however
117 // it is if cast like `T::f as fn()`. This seems like a rustc bug.
118 if !substs.types().any(|t| matches!(t.kind(), ty::Param(_)));
119 let callee_ty_unadjusted = cx.typeck_results().expr_ty(callee).peel_refs();
120 if !is_type_diagnostic_item(cx, callee_ty_unadjusted, sym::Arc);
121 if !is_type_diagnostic_item(cx, callee_ty_unadjusted, sym::Rc);
123 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure", |diag| {
124 if let Some(mut snippet) = snippet_opt(cx, callee.span) {
125 if let Some(fn_mut_id) = cx.tcx.lang_items().fn_mut_trait()
126 && implements_trait(cx, callee_ty.peel_refs(), fn_mut_id, &[])
127 && path_to_local(callee).map_or(false, |l| local_used_after_expr(cx, l, expr))
129 // Mutable closure is used after current expr; we cannot consume it.
130 snippet = format!("&mut {snippet}");
132 diag.span_suggestion(
134 "replace the closure with the function itself",
136 Applicability::MachineApplicable,
144 if !is_adjusted(cx, body.value);
145 if let ExprKind::MethodCall(path, receiver, args, _) = body.value.kind;
146 if check_inputs(cx, body.params, Some(receiver), args);
147 let method_def_id = cx.typeck_results().type_dependent_def_id(body.value.hir_id).unwrap();
148 let substs = cx.typeck_results().node_substs(body.value.hir_id);
149 let call_ty = cx.tcx.bound_type_of(method_def_id).subst(cx.tcx, substs);
150 if check_sig(cx, closure_ty, call_ty);
152 span_lint_and_then(cx, REDUNDANT_CLOSURE_FOR_METHOD_CALLS, expr.span, "redundant closure", |diag| {
153 let name = get_ufcs_type_name(cx, method_def_id);
154 diag.span_suggestion(
156 "replace the closure with the method itself",
157 format!("{name}::{}", path.ident.name),
158 Applicability::MachineApplicable,
167 cx: &LateContext<'_>,
168 params: &[Param<'_>],
169 receiver: Option<&Expr<'_>>,
170 call_args: &[Expr<'_>],
172 if receiver.map_or(params.len() != call_args.len(), |_| params.len() != call_args.len() + 1) {
175 let binding_modes = cx.typeck_results().pat_binding_modes();
176 let check_inputs = |param: &Param<'_>, arg| {
177 match param.pat.kind {
178 PatKind::Binding(_, id, ..) if path_to_local_id(arg, id) => {},
181 // checks that parameters are not bound as `ref` or `ref mut`
182 if let Some(BindingMode::BindByReference(_)) = binding_modes.get(param.pat.hir_id) {
186 match *cx.typeck_results().expr_adjustments(arg) {
190 kind: Adjust::Deref(None),
194 kind: Adjust::Borrow(AutoBorrow::Ref(_, mu2)),
198 // re-borrow with the same mutability is allowed
199 let ty = cx.typeck_results().expr_ty(arg);
200 matches!(*ty.kind(), ty::Ref(.., mu1) if mu1 == mu2.into())
205 std::iter::zip(params, receiver.into_iter().chain(call_args.iter())).all(|(param, arg)| check_inputs(param, arg))
208 fn check_sig<'tcx>(cx: &LateContext<'tcx>, closure_ty: Ty<'tcx>, call_ty: Ty<'tcx>) -> bool {
209 let call_sig = call_ty.fn_sig(cx.tcx);
210 if call_sig.unsafety() == Unsafety::Unsafe {
213 if !closure_ty.has_late_bound_regions() {
216 let ty::Closure(_, substs) = closure_ty.kind() else {
219 let closure_sig = cx.tcx.signature_unclosure(substs.as_closure().sig(), Unsafety::Normal);
220 cx.tcx.erase_late_bound_regions(closure_sig) == cx.tcx.erase_late_bound_regions(call_sig)
223 fn get_ufcs_type_name(cx: &LateContext<'_>, method_def_id: DefId) -> String {
224 let assoc_item = cx.tcx.associated_item(method_def_id);
225 let def_id = assoc_item.container_id(cx.tcx);
226 match assoc_item.container {
227 ty::TraitContainer => cx.tcx.def_path_str(def_id),
228 ty::ImplContainer => {
229 let ty = cx.tcx.type_of(def_id);
231 ty::Adt(adt, _) => cx.tcx.def_path_str(adt.did()),