1 use crate::utils::{is_adjusted, iter_input_pats, snippet_opt, span_lint_and_then};
3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
5 use rustc::{declare_tool_lint, lint_array};
6 use rustc_errors::Applicability;
10 /// **What it does:** Checks for closures which just call another function where
11 /// the function can be called directly. `unsafe` functions or calls where types
12 /// get adjusted are ignored.
14 /// **Why is this bad?** Needlessly creating a closure adds code for no benefit
15 /// and gives the optimizer more work.
17 /// **Known problems:** If creating the closure inside the closure has a side-
18 /// effect then moving the closure creation out will change when that side-
20 /// See https://github.com/rust-lang/rust-clippy/issues/1439 for more
25 /// xs.map(|x| foo(x))
27 /// where `foo(_)` is a plain function that takes the exact argument type of
29 declare_clippy_lint! {
30 pub REDUNDANT_CLOSURE,
32 "redundant closures, i.e. `|a| foo(a)` (which can be written as just `foo`)"
35 impl LintPass for EtaPass {
36 fn get_lints(&self) -> LintArray {
37 lint_array!(REDUNDANT_CLOSURE)
40 fn name(&self) -> &'static str {
45 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EtaPass {
46 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
48 ExprKind::Call(_, ref args) | ExprKind::MethodCall(_, _, ref args) => {
50 check_closure(cx, arg)
58 fn check_closure(cx: &LateContext<'_, '_>, expr: &Expr) {
59 if let ExprKind::Closure(_, ref decl, eid, _, _) = expr.node {
60 let body = cx.tcx.hir().body(eid);
62 if let ExprKind::Call(ref caller, ref args) = ex.node {
63 if args.len() != decl.inputs.len() {
64 // Not the same number of arguments, there
65 // is no way the closure is the same as the function
68 if is_adjusted(cx, ex) || args.iter().any(|arg| is_adjusted(cx, arg)) {
69 // Are the expression or the arguments type-adjusted? Then we need the closure
72 let fn_ty = cx.tables.expr_ty(caller);
74 // Is it an unsafe function? They don't implement the closure traits
75 ty::FnDef(..) | ty::FnPtr(_) => {
76 let sig = fn_ty.fn_sig(cx.tcx);
77 if sig.skip_binder().unsafety == Unsafety::Unsafe || sig.skip_binder().output().sty == ty::Never {
83 for (a1, a2) in iter_input_pats(decl, body).zip(args) {
84 if let PatKind::Binding(_, _, ident, _) = a1.pat.node {
85 // XXXManishearth Should I be checking the binding mode here?
86 if let ExprKind::Path(QPath::Resolved(None, ref p)) = a2.node {
87 if p.segments.len() != 1 {
88 // If it's a proper path, it can't be a local variable
91 if p.segments[0].ident.name != ident.name {
92 // The two idents should be the same
102 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure found", |db| {
103 if let Some(snippet) = snippet_opt(cx, caller.span) {
106 "remove closure as shown",
108 Applicability::MachineApplicable,