1 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
2 use clippy_utils::higher::VecArgs;
3 use clippy_utils::source::snippet_opt;
4 use clippy_utils::ty::{implements_trait, type_is_unsafe_function};
5 use clippy_utils::usage::UsedAfterExprVisitor;
6 use clippy_utils::{get_enclosing_loop_or_closure, higher};
7 use clippy_utils::{is_adjusted, iter_input_pats};
8 use if_chain::if_chain;
9 use rustc_errors::Applicability;
10 use rustc_hir::{def_id, Expr, ExprKind, Param, PatKind, QPath};
11 use rustc_lint::{LateContext, LateLintPass, LintContext};
12 use rustc_middle::lint::in_external_macro;
13 use rustc_middle::ty::{self, ClosureKind, Ty};
14 use rustc_session::{declare_lint_pass, declare_tool_lint};
16 declare_clippy_lint! {
17 /// **What it does:** Checks for closures which just call another function where
18 /// the function can be called directly. `unsafe` functions or calls where types
19 /// get adjusted are ignored.
21 /// **Why is this bad?** Needlessly creating a closure adds code for no benefit
22 /// and gives the optimizer more work.
24 /// **Known problems:** If creating the closure inside the closure has a side-
25 /// effect then moving the closure creation out will change when that side-
27 /// See [#1439](https://github.com/rust-lang/rust-clippy/issues/1439) for more details.
32 /// xs.map(|x| foo(x))
37 /// where `foo(_)` is a plain function that takes the exact argument type of
39 pub REDUNDANT_CLOSURE,
41 "redundant closures, i.e., `|a| foo(a)` (which can be written as just `foo`)"
44 declare_clippy_lint! {
45 /// **What it does:** Checks for closures which only invoke a method on the closure
46 /// argument and can be replaced by referencing the method directly.
48 /// **Why is this bad?** It's unnecessary to create the closure.
50 /// **Known problems:** [#3071](https://github.com/rust-lang/rust-clippy/issues/3071),
51 /// [#3942](https://github.com/rust-lang/rust-clippy/issues/3942),
52 /// [#4002](https://github.com/rust-lang/rust-clippy/issues/4002)
57 /// Some('a').map(|s| s.to_uppercase());
59 /// may be rewritten as
61 /// Some('a').map(char::to_uppercase);
63 pub REDUNDANT_CLOSURE_FOR_METHOD_CALLS,
65 "redundant closures for method calls"
68 declare_lint_pass!(EtaReduction => [REDUNDANT_CLOSURE, REDUNDANT_CLOSURE_FOR_METHOD_CALLS]);
70 impl<'tcx> LateLintPass<'tcx> for EtaReduction {
71 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
72 if in_external_macro(cx.sess(), expr.span) {
77 ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args, _) => {
79 // skip `foo(macro!())`
80 if arg.span.ctxt() == expr.span.ctxt() {
81 check_closure(cx, arg);
90 fn check_closure<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
91 if let ExprKind::Closure(_, decl, eid, _, _) = expr.kind {
92 let body = cx.tcx.hir().body(eid);
95 if ex.span.ctxt() != expr.span.ctxt() {
96 if decl.inputs.is_empty() {
97 if let Some(VecArgs::Vec(&[])) = higher::vec_macro(cx, ex) {
98 // replace `|| vec![]` with `Vec::new`
104 "replace the closure with `Vec::new`",
105 "std::vec::Vec::new".into(),
106 Applicability::MachineApplicable,
110 // skip `foo(|| macro!())`
115 if let ExprKind::Call(caller, args) = ex.kind;
117 if let ExprKind::Path(_) = caller.kind;
119 // Not the same number of arguments, there is no way the closure is the same as the function return;
120 if args.len() == decl.inputs.len();
122 // Are the expression or the arguments type-adjusted? Then we need the closure
123 if !(is_adjusted(cx, ex) || args.iter().any(|arg| is_adjusted(cx, arg)));
125 let fn_ty = cx.typeck_results().expr_ty(caller);
127 if matches!(fn_ty.kind(), ty::FnDef(_, _) | ty::FnPtr(_) | ty::Closure(_, _));
129 if !type_is_unsafe_function(cx, fn_ty);
131 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter());
134 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure", |diag| {
135 if let Some(mut snippet) = snippet_opt(cx, caller.span) {
137 if let ty::Closure(_, substs) = fn_ty.kind();
138 if let ClosureKind::FnMut = substs.as_closure().kind();
139 if UsedAfterExprVisitor::is_found(cx, caller)
140 || get_enclosing_loop_or_closure(cx.tcx, expr).is_some();
143 // Mutable closure is used after current expr; we cannot consume it.
144 snippet = format!("&mut {}", snippet);
147 diag.span_suggestion(
149 "replace the closure with the function itself",
151 Applicability::MachineApplicable,
159 if let ExprKind::MethodCall(path, _, args, _) = ex.kind;
161 // Not the same number of arguments, there is no way the closure is the same as the function return;
162 if args.len() == decl.inputs.len();
164 // Are the expression or the arguments type-adjusted? Then we need the closure
165 if !(is_adjusted(cx, ex) || args.iter().skip(1).any(|arg| is_adjusted(cx, arg)));
167 let method_def_id = cx.typeck_results().type_dependent_def_id(ex.hir_id).unwrap();
168 if !type_is_unsafe_function(cx, cx.tcx.type_of(method_def_id));
170 if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter());
172 if let Some(name) = get_ufcs_type_name(cx, method_def_id, &args[0]);
177 REDUNDANT_CLOSURE_FOR_METHOD_CALLS,
180 "replace the closure with the method itself",
181 format!("{}::{}", name, path.ident.name),
182 Applicability::MachineApplicable,
189 /// Tries to determine the type for universal function call to be used instead of the closure
190 fn get_ufcs_type_name(cx: &LateContext<'_>, method_def_id: def_id::DefId, self_arg: &Expr<'_>) -> Option<String> {
191 let expected_type_of_self = &cx.tcx.fn_sig(method_def_id).inputs_and_output().skip_binder()[0];
192 let actual_type_of_self = &cx.typeck_results().node_type(self_arg.hir_id);
194 if let Some(trait_id) = cx.tcx.trait_of_item(method_def_id) {
195 if match_borrow_depth(expected_type_of_self, actual_type_of_self)
196 && implements_trait(cx, actual_type_of_self, trait_id, &[])
198 return Some(cx.tcx.def_path_str(trait_id));
202 cx.tcx.impl_of_method(method_def_id).and_then(|_| {
203 //a type may implicitly implement other type's methods (e.g. Deref)
204 if match_types(expected_type_of_self, actual_type_of_self) {
205 Some(get_type_name(cx, actual_type_of_self))
212 fn match_borrow_depth(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
213 match (&lhs.kind(), &rhs.kind()) {
214 (ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_borrow_depth(t1, t2),
215 (l, r) => !matches!((l, r), (ty::Ref(_, _, _), _) | (_, ty::Ref(_, _, _))),
219 fn match_types(lhs: Ty<'_>, rhs: Ty<'_>) -> bool {
220 match (&lhs.kind(), &rhs.kind()) {
222 | (ty::Char, ty::Char)
223 | (ty::Int(_), ty::Int(_))
224 | (ty::Uint(_), ty::Uint(_))
225 | (ty::Str, ty::Str) => true,
226 (ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_types(t1, t2),
227 (ty::Array(t1, _), ty::Array(t2, _)) | (ty::Slice(t1), ty::Slice(t2)) => match_types(t1, t2),
228 (ty::Adt(def1, _), ty::Adt(def2, _)) => def1 == def2,
233 fn get_type_name(cx: &LateContext<'_>, ty: Ty<'_>) -> String {
235 ty::Adt(t, _) => cx.tcx.def_path_str(t.did),
236 ty::Ref(_, r, _) => get_type_name(cx, r),
242 closure_inputs: &mut dyn Iterator<Item = &Param<'_>>,
243 call_args: &mut dyn Iterator<Item = &Expr<'_>>,
245 for (closure_input, function_arg) in closure_inputs.zip(call_args) {
246 if let PatKind::Binding(_, _, ident, _) = closure_input.pat.kind {
247 // XXXManishearth Should I be checking the binding mode here?
248 if let ExprKind::Path(QPath::Resolved(None, p)) = function_arg.kind {
249 if p.segments.len() != 1 {
250 // If it's a proper path, it can't be a local variable
253 if p.segments[0].ident.name != ident.name {
254 // The two idents should be the same