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_then, type_is_unsafe_function,
13 declare_clippy_lint! {
14 /// **What it does:** Checks for closures which just call another function where
15 /// the function can be called directly. `unsafe` functions or calls where types
16 /// get adjusted are ignored.
18 /// **Why is this bad?** Needlessly creating a closure adds code for no benefit
19 /// and gives the optimizer more work.
21 /// **Known problems:** If creating the closure inside the closure has a side-
22 /// effect then moving the closure creation out will change when that side-
24 /// See rust-lang/rust-clippy#1439 for more details.
28 /// xs.map(|x| foo(x))
30 /// where `foo(_)` is a plain function that takes the exact argument type of
32 pub REDUNDANT_CLOSURE,
34 "redundant closures, i.e., `|a| foo(a)` (which can be written as just `foo`)"
37 declare_clippy_lint! {
38 /// **What it does:** Checks for closures which only invoke a method on the closure
39 /// argument and can be replaced by referencing the method directly.
41 /// **Why is this bad?** It's unnecessary to create the closure.
43 /// **Known problems:** rust-lang/rust-clippy#3071, rust-lang/rust-clippy#4002,
44 /// rust-lang/rust-clippy#3942
49 /// Some('a').map(|s| s.to_uppercase());
51 /// may be rewritten as
53 /// Some('a').map(char::to_uppercase);
55 pub REDUNDANT_CLOSURE_FOR_METHOD_CALLS,
57 "redundant closures for method calls"
60 declare_lint_pass!(EtaReduction => [REDUNDANT_CLOSURE, REDUNDANT_CLOSURE_FOR_METHOD_CALLS]);
62 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EtaReduction {
63 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
64 if in_external_macro(cx.sess(), expr.span) {
69 ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args) => {
71 check_closure(cx, arg)
79 fn check_closure(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
80 if let ExprKind::Closure(_, ref decl, eid, _, _) = expr.kind {
81 let body = cx.tcx.hir().body(eid);
85 if let ExprKind::Call(ref caller, ref args) = ex.kind;
87 if let ExprKind::Path(_) = caller.kind;
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().any(|arg| is_adjusted(cx, arg)));
95 let fn_ty = cx.tables.expr_ty(caller);
97 if matches!(fn_ty.kind, ty::FnDef(_, _) | ty::FnPtr(_) | ty::Closure(_, _));
99 if !type_is_unsafe_function(cx, fn_ty);
101 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter());
104 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure found", |db| {
105 if let Some(snippet) = snippet_opt(cx, caller.span) {
108 "remove closure as shown",
110 Applicability::MachineApplicable,
118 if let ExprKind::MethodCall(ref path, _, ref args) = ex.kind;
120 // Not the same number of arguments, there is no way the closure is the same as the function return;
121 if args.len() == decl.inputs.len();
123 // Are the expression or the arguments type-adjusted? Then we need the closure
124 if !(is_adjusted(cx, ex) || args.iter().skip(1).any(|arg| is_adjusted(cx, arg)));
126 let method_def_id = cx.tables.type_dependent_def_id(ex.hir_id).unwrap();
127 if !type_is_unsafe_function(cx, cx.tcx.type_of(method_def_id));
129 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter());
131 if let Some(name) = get_ufcs_type_name(cx, method_def_id, &args[0]);
134 span_lint_and_then(cx, REDUNDANT_CLOSURE_FOR_METHOD_CALLS, expr.span, "redundant closure found", |db| {
137 "remove closure as shown",
138 format!("{}::{}", name, path.ident.name),
139 Applicability::MachineApplicable,
147 /// Tries to determine the type for universal function call to be used instead of the closure
148 fn get_ufcs_type_name(cx: &LateContext<'_, '_>, method_def_id: def_id::DefId, self_arg: &Expr<'_>) -> Option<String> {
149 let expected_type_of_self = &cx.tcx.fn_sig(method_def_id).inputs_and_output().skip_binder()[0];
150 let actual_type_of_self = &cx.tables.node_type(self_arg.hir_id);
152 if let Some(trait_id) = cx.tcx.trait_of_item(method_def_id) {
153 if match_borrow_depth(expected_type_of_self, &actual_type_of_self)
154 && implements_trait(cx, actual_type_of_self, trait_id, &[])
156 return Some(cx.tcx.def_path_str(trait_id));
160 cx.tcx.impl_of_method(method_def_id).and_then(|_| {
161 //a type may implicitly implement other type's methods (e.g. Deref)
162 if match_types(expected_type_of_self, &actual_type_of_self) {
163 return Some(get_type_name(cx, &actual_type_of_self));
169 fn match_borrow_depth(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
170 match (&lhs.kind, &rhs.kind) {
171 (ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_borrow_depth(&t1, &t2),
172 (l, r) => match (l, r) {
173 (ty::Ref(_, _, _), _) | (_, ty::Ref(_, _, _)) => false,
179 fn match_types(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
180 match (&lhs.kind, &rhs.kind) {
182 | (ty::Char, ty::Char)
183 | (ty::Int(_), ty::Int(_))
184 | (ty::Uint(_), ty::Uint(_))
185 | (ty::Str, ty::Str) => true,
186 (ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_types(t1, t2),
187 (ty::Array(t1, _), ty::Array(t2, _)) | (ty::Slice(t1), ty::Slice(t2)) => match_types(t1, t2),
188 (ty::Adt(def1, _), ty::Adt(def2, _)) => def1 == def2,
193 fn get_type_name(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> String {
195 ty::Adt(t, _) => cx.tcx.def_path_str(t.did),
196 ty::Ref(_, r, _) => get_type_name(cx, &r),
202 closure_inputs: &mut dyn Iterator<Item = &Param<'_>>,
203 call_args: &mut dyn Iterator<Item = &Expr<'_>>,
205 for (closure_input, function_arg) in closure_inputs.zip(call_args) {
206 if let PatKind::Binding(_, _, ident, _) = closure_input.pat.kind {
207 // XXXManishearth Should I be checking the binding mode here?
208 if let ExprKind::Path(QPath::Resolved(None, ref p)) = function_arg.kind {
209 if p.segments.len() != 1 {
210 // If it's a proper path, it can't be a local variable
213 if p.segments[0].ident.name != ident.name {
214 // The two idents should be the same