1 use if_chain::if_chain;
4 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
5 use rustc::ty::{self, Ty};
6 use rustc::{declare_lint_pass, declare_tool_lint};
7 use rustc_errors::Applicability;
9 use crate::utils::{is_adjusted, iter_input_pats, snippet_opt, span_lint_and_then, type_is_unsafe_function};
11 declare_clippy_lint! {
12 /// **What it does:** Checks for closures which just call another function where
13 /// the function can be called directly. `unsafe` functions or calls where types
14 /// get adjusted are ignored.
16 /// **Why is this bad?** Needlessly creating a closure adds code for no benefit
17 /// and gives the optimizer more work.
19 /// **Known problems:** If creating the closure inside the closure has a side-
20 /// effect then moving the closure creation out will change when that side-
22 /// See rust-lang/rust-clippy#1439 for more details.
26 /// xs.map(|x| foo(x))
28 /// where `foo(_)` is a plain function that takes the exact argument type of
30 pub REDUNDANT_CLOSURE,
32 "redundant closures, i.e., `|a| foo(a)` (which can be written as just `foo`)"
35 declare_clippy_lint! {
36 /// **What it does:** Checks for closures which only invoke a method on the closure
37 /// argument and can be replaced by referencing the method directly.
39 /// **Why is this bad?** It's unnecessary to create the closure.
43 /// Some('a').map(|s| s.to_uppercase());
45 /// may be rewritten as
47 /// Some('a').map(char::to_uppercase);
49 pub REDUNDANT_CLOSURES_FOR_METHOD_CALLS,
51 "redundant closures for method calls"
54 declare_lint_pass!(EtaReduction => [REDUNDANT_CLOSURE, REDUNDANT_CLOSURES_FOR_METHOD_CALLS]);
56 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EtaReduction {
57 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
58 if in_external_macro(cx.sess(), expr.span) {
63 ExprKind::Call(_, ref args) | ExprKind::MethodCall(_, _, ref args) => {
65 check_closure(cx, arg)
73 fn check_closure(cx: &LateContext<'_, '_>, expr: &Expr) {
74 if let ExprKind::Closure(_, ref decl, eid, _, _) = expr.node {
75 let body = cx.tcx.hir().body(eid);
79 if let ExprKind::Call(ref caller, ref args) = ex.node;
81 // Not the same number of arguments, there is no way the closure is the same as the function return;
82 if args.len() == decl.inputs.len();
84 // Are the expression or the arguments type-adjusted? Then we need the closure
85 if !(is_adjusted(cx, ex) || args.iter().any(|arg| is_adjusted(cx, arg)));
87 let fn_ty = cx.tables.expr_ty(caller);
89 if matches!(fn_ty.sty, ty::FnDef(_, _) | ty::FnPtr(_) | ty::Closure(_, _));
91 if !type_is_unsafe_function(cx, fn_ty);
93 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.into_iter());
96 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure found", |db| {
97 if let Some(snippet) = snippet_opt(cx, caller.span) {
100 "remove closure as shown",
102 Applicability::MachineApplicable,
110 if let ExprKind::MethodCall(ref path, _, ref args) = ex.node;
112 // Not the same number of arguments, there is no way the closure is the same as the function return;
113 if args.len() == decl.inputs.len();
115 // Are the expression or the arguments type-adjusted? Then we need the closure
116 if !(is_adjusted(cx, ex) || args.iter().skip(1).any(|arg| is_adjusted(cx, arg)));
118 let method_def_id = cx.tables.type_dependent_def_id(ex.hir_id).unwrap();
119 if !type_is_unsafe_function(cx, cx.tcx.type_of(method_def_id));
121 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.into_iter());
123 if let Some(name) = get_ufcs_type_name(cx, method_def_id, &args[0]);
126 span_lint_and_then(cx, REDUNDANT_CLOSURES_FOR_METHOD_CALLS, expr.span, "redundant closure found", |db| {
129 "remove closure as shown",
130 format!("{}::{}", name, path.ident.name),
131 Applicability::MachineApplicable,
139 /// Tries to determine the type for universal function call to be used instead of the closure
140 fn get_ufcs_type_name(
141 cx: &LateContext<'_, '_>,
142 method_def_id: def_id::DefId,
144 ) -> std::option::Option<String> {
145 let expected_type_of_self = &cx.tcx.fn_sig(method_def_id).inputs_and_output().skip_binder()[0];
146 let actual_type_of_self = &cx.tables.node_type(self_arg.hir_id);
148 if let Some(trait_id) = cx.tcx.trait_of_item(method_def_id) {
149 if match_borrow_depth(expected_type_of_self, &actual_type_of_self) {
150 return Some(cx.tcx.def_path_str(trait_id));
154 cx.tcx.impl_of_method(method_def_id).and_then(|_| {
155 //a type may implicitly implement other type's methods (e.g. Deref)
156 if match_types(expected_type_of_self, &actual_type_of_self) {
157 return Some(get_type_name(cx, &actual_type_of_self));
163 fn match_borrow_depth(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
164 match (&lhs.sty, &rhs.sty) {
165 (ty::Ref(_, t1, _), ty::Ref(_, t2, _)) => match_borrow_depth(&t1, &t2),
166 (l, r) => match (l, r) {
167 (ty::Ref(_, _, _), _) | (_, ty::Ref(_, _, _)) => false,
173 fn match_types(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
174 match (&lhs.sty, &rhs.sty) {
176 | (ty::Char, ty::Char)
177 | (ty::Int(_), ty::Int(_))
178 | (ty::Uint(_), ty::Uint(_))
179 | (ty::Str, ty::Str) => true,
180 (ty::Ref(_, t1, _), ty::Ref(_, t2, _))
181 | (ty::Array(t1, _), ty::Array(t2, _))
182 | (ty::Slice(t1), ty::Slice(t2)) => match_types(t1, t2),
183 (ty::Adt(def1, _), ty::Adt(def2, _)) => def1 == def2,
188 fn get_type_name(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> String {
190 ty::Adt(t, _) => cx.tcx.def_path_str(t.did),
191 ty::Ref(_, r, _) => get_type_name(cx, &r),
196 fn compare_inputs(closure_inputs: &mut dyn Iterator<Item = &Arg>, call_args: &mut dyn Iterator<Item = &Expr>) -> bool {
197 for (closure_input, function_arg) in closure_inputs.zip(call_args) {
198 if let PatKind::Binding(_, _, ident, _) = closure_input.pat.node {
199 // XXXManishearth Should I be checking the binding mode here?
200 if let ExprKind::Path(QPath::Resolved(None, ref p)) = function_arg.node {
201 if p.segments.len() != 1 {
202 // If it's a proper path, it can't be a local variable
205 if p.segments[0].ident.name != ident.name {
206 // The two idents should be the same