1 use clippy_utils::higher;
2 use clippy_utils::higher::VecArgs;
3 use clippy_utils::ty::{implements_trait, type_is_unsafe_function};
4 use if_chain::if_chain;
5 use rustc_errors::Applicability;
6 use rustc_hir::{def_id, Expr, ExprKind, Param, PatKind, QPath};
7 use rustc_lint::{LateContext, LateLintPass, LintContext};
8 use rustc_middle::lint::in_external_macro;
9 use rustc_middle::ty::{self, Ty};
10 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 use crate::utils::{is_adjusted, iter_input_pats, snippet_opt, span_lint_and_sugg, span_lint_and_then};
14 declare_clippy_lint! {
15 /// **What it does:** Checks for closures which just call another function where
16 /// the function can be called directly. `unsafe` functions or calls where types
17 /// get adjusted are ignored.
19 /// **Why is this bad?** Needlessly creating a closure adds code for no benefit
20 /// and gives the optimizer more work.
22 /// **Known problems:** If creating the closure inside the closure has a side-
23 /// effect then moving the closure creation out will change when that side-
25 /// See [#1439](https://github.com/rust-lang/rust-clippy/issues/1439) for more details.
30 /// xs.map(|x| foo(x))
35 /// where `foo(_)` is a plain function that takes the exact argument type of
37 pub REDUNDANT_CLOSURE,
39 "redundant closures, i.e., `|a| foo(a)` (which can be written as just `foo`)"
42 declare_clippy_lint! {
43 /// **What it does:** Checks for closures which only invoke a method on the closure
44 /// argument and can be replaced by referencing the method directly.
46 /// **Why is this bad?** It's unnecessary to create the closure.
48 /// **Known problems:** [#3071](https://github.com/rust-lang/rust-clippy/issues/3071),
49 /// [#3942](https://github.com/rust-lang/rust-clippy/issues/3942),
50 /// [#4002](https://github.com/rust-lang/rust-clippy/issues/4002)
55 /// Some('a').map(|s| s.to_uppercase());
57 /// may be rewritten as
59 /// Some('a').map(char::to_uppercase);
61 pub REDUNDANT_CLOSURE_FOR_METHOD_CALLS,
63 "redundant closures for method calls"
66 declare_lint_pass!(EtaReduction => [REDUNDANT_CLOSURE, REDUNDANT_CLOSURE_FOR_METHOD_CALLS]);
68 impl<'tcx> LateLintPass<'tcx> for EtaReduction {
69 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
70 if in_external_macro(cx.sess(), expr.span) {
75 ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args, _) => {
77 // skip `foo(macro!())`
78 if arg.span.ctxt() == expr.span.ctxt() {
79 check_closure(cx, arg)
88 fn check_closure(cx: &LateContext<'_>, expr: &Expr<'_>) {
89 if let ExprKind::Closure(_, ref decl, eid, _, _) = expr.kind {
90 let body = cx.tcx.hir().body(eid);
93 if ex.span.ctxt() != expr.span.ctxt() {
94 if let Some(VecArgs::Vec(&[])) = higher::vec_macro(cx, ex) {
95 // replace `|| vec![]` with `Vec::new`
101 "replace the closure with `Vec::new`",
102 "std::vec::Vec::new".into(),
103 Applicability::MachineApplicable,
106 // skip `foo(|| macro!())`
111 if let ExprKind::Call(ref caller, ref args) = ex.kind;
113 if let ExprKind::Path(_) = caller.kind;
115 // Not the same number of arguments, there is no way the closure is the same as the function return;
116 if args.len() == decl.inputs.len();
118 // Are the expression or the arguments type-adjusted? Then we need the closure
119 if !(is_adjusted(cx, ex) || args.iter().any(|arg| is_adjusted(cx, arg)));
121 let fn_ty = cx.typeck_results().expr_ty(caller);
123 if matches!(fn_ty.kind(), ty::FnDef(_, _) | ty::FnPtr(_) | ty::Closure(_, _));
125 if !type_is_unsafe_function(cx, fn_ty);
127 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter());
130 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure", |diag| {
131 if let Some(snippet) = snippet_opt(cx, caller.span) {
132 diag.span_suggestion(
134 "replace the closure with the function itself",
136 Applicability::MachineApplicable,
144 if let ExprKind::MethodCall(ref path, _, ref args, _) = ex.kind;
146 // Not the same number of arguments, there is no way the closure is the same as the function return;
147 if args.len() == decl.inputs.len();
149 // Are the expression or the arguments type-adjusted? Then we need the closure
150 if !(is_adjusted(cx, ex) || args.iter().skip(1).any(|arg| is_adjusted(cx, arg)));
152 let method_def_id = cx.typeck_results().type_dependent_def_id(ex.hir_id).unwrap();
153 if !type_is_unsafe_function(cx, cx.tcx.type_of(method_def_id));
155 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter());
157 if let Some(name) = get_ufcs_type_name(cx, method_def_id, &args[0]);
162 REDUNDANT_CLOSURE_FOR_METHOD_CALLS,
165 "replace the closure with the method itself",
166 format!("{}::{}", name, path.ident.name),
167 Applicability::MachineApplicable,
174 /// Tries to determine the type for universal function call to be used instead of the closure
175 fn get_ufcs_type_name(cx: &LateContext<'_>, method_def_id: def_id::DefId, self_arg: &Expr<'_>) -> Option<String> {
176 let expected_type_of_self = &cx.tcx.fn_sig(method_def_id).inputs_and_output().skip_binder()[0];
177 let actual_type_of_self = &cx.typeck_results().node_type(self_arg.hir_id);
179 if let Some(trait_id) = cx.tcx.trait_of_item(method_def_id) {
180 if match_borrow_depth(expected_type_of_self, &actual_type_of_self)
181 && implements_trait(cx, actual_type_of_self, trait_id, &[])
183 return Some(cx.tcx.def_path_str(trait_id));
187 cx.tcx.impl_of_method(method_def_id).and_then(|_| {
188 //a type may implicitly implement other type's methods (e.g. Deref)
189 if match_types(expected_type_of_self, &actual_type_of_self) {
190 return Some(get_type_name(cx, &actual_type_of_self));
196 fn match_borrow_depth(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
197 match (&lhs.kind(), &rhs.kind()) {
198 (ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_borrow_depth(&t1, &t2),
199 (l, r) => !matches!((l, r), (ty::Ref(_, _, _), _) | (_, ty::Ref(_, _, _))),
203 fn match_types(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
204 match (&lhs.kind(), &rhs.kind()) {
206 | (ty::Char, ty::Char)
207 | (ty::Int(_), ty::Int(_))
208 | (ty::Uint(_), ty::Uint(_))
209 | (ty::Str, ty::Str) => true,
210 (ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_types(t1, t2),
211 (ty::Array(t1, _), ty::Array(t2, _)) | (ty::Slice(t1), ty::Slice(t2)) => match_types(t1, t2),
212 (ty::Adt(def1, _), ty::Adt(def2, _)) => def1 == def2,
217 fn get_type_name(cx: &LateContext<'_>, ty: Ty<'_>) -> String {
219 ty::Adt(t, _) => cx.tcx.def_path_str(t.did),
220 ty::Ref(_, r, _) => get_type_name(cx, &r),
226 closure_inputs: &mut dyn Iterator<Item = &Param<'_>>,
227 call_args: &mut dyn Iterator<Item = &Expr<'_>>,
229 for (closure_input, function_arg) in closure_inputs.zip(call_args) {
230 if let PatKind::Binding(_, _, ident, _) = closure_input.pat.kind {
231 // XXXManishearth Should I be checking the binding mode here?
232 if let ExprKind::Path(QPath::Resolved(None, ref p)) = function_arg.kind {
233 if p.segments.len() != 1 {
234 // If it's a proper path, it can't be a local variable
237 if p.segments[0].ident.name != ident.name {
238 // The two idents should be the same