2 use rustc::{declare_lint, lint_array};
5 use crate::utils::{is_adjusted, iter_input_pats, snippet_opt, span_lint_and_then};
7 #[allow(missing_copy_implementations)]
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 https://github.com/rust-lang-nursery/rust-clippy/issues/1439 for more
26 /// xs.map(|x| foo(x))
28 /// where `foo(_)` is a plain function that takes the exact argument type of
30 declare_clippy_lint! {
31 pub REDUNDANT_CLOSURE,
33 "redundant closures, i.e. `|a| foo(a)` (which can be written as just `foo`)"
36 impl LintPass for EtaPass {
37 fn get_lints(&self) -> LintArray {
38 lint_array!(REDUNDANT_CLOSURE)
42 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EtaPass {
43 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
45 ExprKind::Call(_, ref args) | ExprKind::MethodCall(_, _, ref args) => for arg in args {
46 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);
57 if let ExprKind::Call(ref caller, ref args) = ex.node {
58 if args.len() != decl.inputs.len() {
59 // Not the same number of arguments, there
60 // is no way the closure is the same as the function
63 if is_adjusted(cx, ex) || args.iter().any(|arg| is_adjusted(cx, arg)) {
64 // Are the expression or the arguments type-adjusted? Then we need the closure
67 let fn_ty = cx.tables.expr_ty(caller);
69 // Is it an unsafe function? They don't implement the closure traits
70 ty::TyFnDef(..) | ty::TyFnPtr(_) => {
71 let sig = fn_ty.fn_sig(cx.tcx);
72 if sig.skip_binder().unsafety == Unsafety::Unsafe || sig.skip_binder().output().sty == ty::TyNever {
78 for (a1, a2) in iter_input_pats(decl, body).zip(args) {
79 if let PatKind::Binding(_, _, ident, _) = a1.pat.node {
80 // XXXManishearth Should I be checking the binding mode here?
81 if let ExprKind::Path(QPath::Resolved(None, ref p)) = a2.node {
82 if p.segments.len() != 1 {
83 // If it's a proper path, it can't be a local variable
86 if p.segments[0].ident.name != ident.name {
87 // The two idents should be the same
97 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure found", |db| {
98 if let Some(snippet) = snippet_opt(cx, caller.span) {
99 db.span_suggestion(expr.span, "remove closure as shown", snippet);