1 use if_chain::if_chain;
2 use rustc_errors::Applicability;
3 use rustc_hir::{def_id, Expr, ExprKind, Param, PatKind, QPath};
4 use rustc_lint::{LateContext, LateLintPass, LintContext};
5 use rustc_middle::lint::in_external_macro;
6 use rustc_middle::ty::{self, Ty};
7 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 implements_trait, is_adjusted, iter_input_pats, snippet_opt, span_lint_and_sugg, span_lint_and_then,
11 type_is_unsafe_function,
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 check_closure(cx, arg)
85 fn check_closure(cx: &LateContext<'_>, expr: &Expr<'_>) {
86 if let ExprKind::Closure(_, ref decl, eid, _, _) = expr.kind {
87 let body = cx.tcx.hir().body(eid);
91 if let ExprKind::Call(ref caller, ref args) = ex.kind;
93 if let ExprKind::Path(_) = caller.kind;
95 // Not the same number of arguments, there is no way the closure is the same as the function return;
96 if args.len() == decl.inputs.len();
98 // Are the expression or the arguments type-adjusted? Then we need the closure
99 if !(is_adjusted(cx, ex) || args.iter().any(|arg| is_adjusted(cx, arg)));
101 let fn_ty = cx.typeck_results().expr_ty(caller);
103 if matches!(fn_ty.kind(), ty::FnDef(_, _) | ty::FnPtr(_) | ty::Closure(_, _));
105 if !type_is_unsafe_function(cx, fn_ty);
107 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter());
110 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure found", |diag| {
111 if let Some(snippet) = snippet_opt(cx, caller.span) {
112 diag.span_suggestion(
114 "remove closure as shown",
116 Applicability::MachineApplicable,
124 if let ExprKind::MethodCall(ref path, _, ref args, _) = ex.kind;
126 // Not the same number of arguments, there is no way the closure is the same as the function return;
127 if args.len() == decl.inputs.len();
129 // Are the expression or the arguments type-adjusted? Then we need the closure
130 if !(is_adjusted(cx, ex) || args.iter().skip(1).any(|arg| is_adjusted(cx, arg)));
132 let method_def_id = cx.typeck_results().type_dependent_def_id(ex.hir_id).unwrap();
133 if !type_is_unsafe_function(cx, cx.tcx.type_of(method_def_id));
135 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter());
137 if let Some(name) = get_ufcs_type_name(cx, method_def_id, &args[0]);
142 REDUNDANT_CLOSURE_FOR_METHOD_CALLS,
144 "redundant closure found",
145 "remove closure as shown",
146 format!("{}::{}", name, path.ident.name),
147 Applicability::MachineApplicable,
154 /// Tries to determine the type for universal function call to be used instead of the closure
155 fn get_ufcs_type_name(cx: &LateContext<'_>, method_def_id: def_id::DefId, self_arg: &Expr<'_>) -> Option<String> {
156 let expected_type_of_self = &cx.tcx.fn_sig(method_def_id).inputs_and_output().skip_binder()[0];
157 let actual_type_of_self = &cx.typeck_results().node_type(self_arg.hir_id);
159 if let Some(trait_id) = cx.tcx.trait_of_item(method_def_id) {
160 if match_borrow_depth(expected_type_of_self, &actual_type_of_self)
161 && implements_trait(cx, actual_type_of_self, trait_id, &[])
163 return Some(cx.tcx.def_path_str(trait_id));
167 cx.tcx.impl_of_method(method_def_id).and_then(|_| {
168 //a type may implicitly implement other type's methods (e.g. Deref)
169 if match_types(expected_type_of_self, &actual_type_of_self) {
170 return Some(get_type_name(cx, &actual_type_of_self));
176 fn match_borrow_depth(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
177 match (&lhs.kind(), &rhs.kind()) {
178 (ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_borrow_depth(&t1, &t2),
179 (l, r) => !matches!((l, r), (ty::Ref(_, _, _), _) | (_, ty::Ref(_, _, _))),
183 fn match_types(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
184 match (&lhs.kind(), &rhs.kind()) {
186 | (ty::Char, ty::Char)
187 | (ty::Int(_), ty::Int(_))
188 | (ty::Uint(_), ty::Uint(_))
189 | (ty::Str, ty::Str) => true,
190 (ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_types(t1, t2),
191 (ty::Array(t1, _), ty::Array(t2, _)) | (ty::Slice(t1), ty::Slice(t2)) => match_types(t1, t2),
192 (ty::Adt(def1, _), ty::Adt(def2, _)) => def1 == def2,
197 fn get_type_name(cx: &LateContext<'_>, ty: Ty<'_>) -> String {
199 ty::Adt(t, _) => cx.tcx.def_path_str(t.did),
200 ty::Ref(_, r, _) => get_type_name(cx, &r),
206 closure_inputs: &mut dyn Iterator<Item = &Param<'_>>,
207 call_args: &mut dyn Iterator<Item = &Expr<'_>>,
209 for (closure_input, function_arg) in closure_inputs.zip(call_args) {
210 if let PatKind::Binding(_, _, ident, _) = closure_input.pat.kind {
211 // XXXManishearth Should I be checking the binding mode here?
212 if let ExprKind::Path(QPath::Resolved(None, ref p)) = function_arg.kind {
213 if p.segments.len() != 1 {
214 // If it's a proper path, it can't be a local variable
217 if p.segments[0].ident.name != ident.name {
218 // The two idents should be the same