1 use if_chain::if_chain;
3 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
4 use rustc::ty::{self, Ty};
5 use rustc::{declare_lint_pass, declare_tool_lint};
6 use rustc_errors::Applicability;
8 use crate::utils::{is_adjusted, iter_input_pats, snippet_opt, span_lint_and_then, type_is_unsafe_function};
10 declare_clippy_lint! {
11 /// **What it does:** Checks for closures which just call another function where
12 /// the function can be called directly. `unsafe` functions or calls where types
13 /// get adjusted are ignored.
15 /// **Why is this bad?** Needlessly creating a closure adds code for no benefit
16 /// and gives the optimizer more work.
18 /// **Known problems:** If creating the closure inside the closure has a side-
19 /// effect then moving the closure creation out will change when that side-
21 /// See rust-lang/rust-clippy#1439 for more details.
25 /// xs.map(|x| foo(x))
27 /// where `foo(_)` is a plain function that takes the exact argument type of
29 pub REDUNDANT_CLOSURE,
31 "redundant closures, i.e., `|a| foo(a)` (which can be written as just `foo`)"
34 declare_lint_pass!(EtaReduction => [REDUNDANT_CLOSURE]);
36 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EtaReduction {
37 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
38 if in_external_macro(cx.sess(), expr.span) {
43 ExprKind::Call(_, ref args) | ExprKind::MethodCall(_, _, ref args) => {
45 check_closure(cx, arg)
53 fn check_closure(cx: &LateContext<'_, '_>, expr: &Expr) {
54 if let ExprKind::Closure(_, ref decl, eid, _, _) = expr.node {
55 let body = cx.tcx.hir().body(eid);
59 if let ExprKind::Call(ref caller, ref args) = ex.node;
61 // Not the same number of arguments, there is no way the closure is the same as the function return;
62 if args.len() == decl.inputs.len();
64 // Are the expression or the arguments type-adjusted? Then we need the closure
65 if !(is_adjusted(cx, ex) || args.iter().any(|arg| is_adjusted(cx, arg)));
67 let fn_ty = cx.tables.expr_ty(caller);
68 if !type_is_unsafe_function(cx, fn_ty);
70 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.into_iter());
73 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure found", |db| {
74 if let Some(snippet) = snippet_opt(cx, caller.span) {
77 "remove closure as shown",
79 Applicability::MachineApplicable,
87 if let ExprKind::MethodCall(ref path, _, ref args) = ex.node;
89 // Not the same number of arguments, there is no way the closure is the same as the function return;
90 if args.len() == decl.inputs.len();
92 // Are the expression or the arguments type-adjusted? Then we need the closure
93 if !(is_adjusted(cx, ex) || args.iter().skip(1).any(|arg| is_adjusted(cx, arg)));
95 let method_def_id = cx.tables.type_dependent_def_id(ex.hir_id).unwrap();
96 if !type_is_unsafe_function(cx, cx.tcx.type_of(method_def_id));
98 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.into_iter());
100 if let Some(name) = get_ufcs_type_name(cx, method_def_id, &args[0]);
103 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure found", |db| {
106 "remove closure as shown",
107 format!("{}::{}", name, path.ident.name),
108 Applicability::MachineApplicable,
116 /// Tries to determine the type for universal function call to be used instead of the closure
117 fn get_ufcs_type_name(
118 cx: &LateContext<'_, '_>,
119 method_def_id: def_id::DefId,
121 ) -> std::option::Option<String> {
122 let expected_type_of_self = &cx.tcx.fn_sig(method_def_id).inputs_and_output().skip_binder()[0];
123 let actual_type_of_self = &cx.tables.node_type(self_arg.hir_id);
125 if let Some(trait_id) = cx.tcx.trait_of_item(method_def_id) {
126 if match_borrow_depth(expected_type_of_self, &actual_type_of_self) {
127 return Some(cx.tcx.def_path_str(trait_id));
131 cx.tcx.impl_of_method(method_def_id).and_then(|_| {
132 //a type may implicitly implement other type's methods (e.g. Deref)
133 if match_types(expected_type_of_self, &actual_type_of_self) {
134 return Some(get_type_name(cx, &actual_type_of_self));
140 fn match_borrow_depth(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
141 match (&lhs.sty, &rhs.sty) {
142 (ty::Ref(_, t1, _), ty::Ref(_, t2, _)) => match_borrow_depth(&t1, &t2),
143 (l, r) => match (l, r) {
144 (ty::Ref(_, _, _), _) | (_, ty::Ref(_, _, _)) => false,
150 fn match_types(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
151 match (&lhs.sty, &rhs.sty) {
153 | (ty::Char, ty::Char)
154 | (ty::Int(_), ty::Int(_))
155 | (ty::Uint(_), ty::Uint(_))
156 | (ty::Str, ty::Str) => true,
157 (ty::Ref(_, t1, _), ty::Ref(_, t2, _))
158 | (ty::Array(t1, _), ty::Array(t2, _))
159 | (ty::Slice(t1), ty::Slice(t2)) => match_types(t1, t2),
160 (ty::Adt(def1, _), ty::Adt(def2, _)) => def1 == def2,
165 fn get_type_name(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> String {
167 ty::Adt(t, _) => cx.tcx.def_path_str(t.did),
168 ty::Ref(_, r, _) => get_type_name(cx, &r),
173 fn compare_inputs(closure_inputs: &mut dyn Iterator<Item = &Arg>, call_args: &mut dyn Iterator<Item = &Expr>) -> bool {
174 for (closure_input, function_arg) in closure_inputs.zip(call_args) {
175 if let PatKind::Binding(_, _, ident, _) = closure_input.pat.node {
176 // XXXManishearth Should I be checking the binding mode here?
177 if let ExprKind::Path(QPath::Resolved(None, ref p)) = function_arg.node {
178 if p.segments.len() != 1 {
179 // If it's a proper path, it can't be a local variable
182 if p.segments[0].ident.name != ident.name {
183 // The two idents should be the same