use if_chain::if_chain; use rustc_errors::Applicability; use rustc_hir::{def_id, Expr, ExprKind, Param, PatKind, QPath}; use rustc_lint::{LateContext, LateLintPass, LintContext}; use rustc_middle::lint::in_external_macro; use rustc_middle::ty::{self, Ty}; use rustc_session::{declare_lint_pass, declare_tool_lint}; use crate::utils::{ implements_trait, is_adjusted, iter_input_pats, snippet_opt, span_lint_and_then, type_is_unsafe_function, }; declare_clippy_lint! { /// **What it does:** Checks for closures which just call another function where /// the function can be called directly. `unsafe` functions or calls where types /// get adjusted are ignored. /// /// **Why is this bad?** Needlessly creating a closure adds code for no benefit /// and gives the optimizer more work. /// /// **Known problems:** If creating the closure inside the closure has a side- /// effect then moving the closure creation out will change when that side- /// effect runs. /// See rust-lang/rust-clippy#1439 for more details. /// /// **Example:** /// ```rust,ignore /// xs.map(|x| foo(x)) /// ``` /// where `foo(_)` is a plain function that takes the exact argument type of /// `x`. pub REDUNDANT_CLOSURE, style, "redundant closures, i.e., `|a| foo(a)` (which can be written as just `foo`)" } declare_clippy_lint! { /// **What it does:** Checks for closures which only invoke a method on the closure /// argument and can be replaced by referencing the method directly. /// /// **Why is this bad?** It's unnecessary to create the closure. /// /// **Known problems:** rust-lang/rust-clippy#3071, rust-lang/rust-clippy#4002, /// rust-lang/rust-clippy#3942 /// /// /// **Example:** /// ```rust,ignore /// Some('a').map(|s| s.to_uppercase()); /// ``` /// may be rewritten as /// ```rust,ignore /// Some('a').map(char::to_uppercase); /// ``` pub REDUNDANT_CLOSURE_FOR_METHOD_CALLS, pedantic, "redundant closures for method calls" } declare_lint_pass!(EtaReduction => [REDUNDANT_CLOSURE, REDUNDANT_CLOSURE_FOR_METHOD_CALLS]); impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EtaReduction { fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) { if in_external_macro(cx.sess(), expr.span) { return; } match expr.kind { ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args) => { for arg in args { check_closure(cx, arg) } }, _ => (), } } } fn check_closure(cx: &LateContext<'_, '_>, expr: &Expr<'_>) { if let ExprKind::Closure(_, ref decl, eid, _, _) = expr.kind { let body = cx.tcx.hir().body(eid); let ex = &body.value; if_chain!( if let ExprKind::Call(ref caller, ref args) = ex.kind; if let ExprKind::Path(_) = caller.kind; // Not the same number of arguments, there is no way the closure is the same as the function return; if args.len() == decl.inputs.len(); // Are the expression or the arguments type-adjusted? Then we need the closure if !(is_adjusted(cx, ex) || args.iter().any(|arg| is_adjusted(cx, arg))); let fn_ty = cx.tables.expr_ty(caller); if matches!(fn_ty.kind, ty::FnDef(_, _) | ty::FnPtr(_) | ty::Closure(_, _)); if !type_is_unsafe_function(cx, fn_ty); if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter()); then { span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure found", |diag| { if let Some(snippet) = snippet_opt(cx, caller.span) { diag.span_suggestion( expr.span, "remove closure as shown", snippet, Applicability::MachineApplicable, ); } }); } ); if_chain!( if let ExprKind::MethodCall(ref path, _, ref args) = ex.kind; // Not the same number of arguments, there is no way the closure is the same as the function return; if args.len() == decl.inputs.len(); // Are the expression or the arguments type-adjusted? Then we need the closure if !(is_adjusted(cx, ex) || args.iter().skip(1).any(|arg| is_adjusted(cx, arg))); let method_def_id = cx.tables.type_dependent_def_id(ex.hir_id).unwrap(); if !type_is_unsafe_function(cx, cx.tcx.type_of(method_def_id)); if compare_inputs(&mut iter_input_pats(decl, body), &mut args.iter()); if let Some(name) = get_ufcs_type_name(cx, method_def_id, &args[0]); then { span_lint_and_then(cx, REDUNDANT_CLOSURE_FOR_METHOD_CALLS, expr.span, "redundant closure found", |diag| { diag.span_suggestion( expr.span, "remove closure as shown", format!("{}::{}", name, path.ident.name), Applicability::MachineApplicable, ); }); } ); } } /// Tries to determine the type for universal function call to be used instead of the closure fn get_ufcs_type_name(cx: &LateContext<'_, '_>, method_def_id: def_id::DefId, self_arg: &Expr<'_>) -> Option { let expected_type_of_self = &cx.tcx.fn_sig(method_def_id).inputs_and_output().skip_binder()[0]; let actual_type_of_self = &cx.tables.node_type(self_arg.hir_id); if let Some(trait_id) = cx.tcx.trait_of_item(method_def_id) { if match_borrow_depth(expected_type_of_self, &actual_type_of_self) && implements_trait(cx, actual_type_of_self, trait_id, &[]) { return Some(cx.tcx.def_path_str(trait_id)); } } cx.tcx.impl_of_method(method_def_id).and_then(|_| { //a type may implicitly implement other type's methods (e.g. Deref) if match_types(expected_type_of_self, &actual_type_of_self) { return Some(get_type_name(cx, &actual_type_of_self)); } None }) } fn match_borrow_depth(lhs: Ty<'_>, rhs: Ty<'_>) -> bool { match (&lhs.kind, &rhs.kind) { (ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_borrow_depth(&t1, &t2), (l, r) => match (l, r) { (ty::Ref(_, _, _), _) | (_, ty::Ref(_, _, _)) => false, (_, _) => true, }, } } fn match_types(lhs: Ty<'_>, rhs: Ty<'_>) -> bool { match (&lhs.kind, &rhs.kind) { (ty::Bool, ty::Bool) | (ty::Char, ty::Char) | (ty::Int(_), ty::Int(_)) | (ty::Uint(_), ty::Uint(_)) | (ty::Str, ty::Str) => true, (ty::Ref(_, t1, mut1), ty::Ref(_, t2, mut2)) => mut1 == mut2 && match_types(t1, t2), (ty::Array(t1, _), ty::Array(t2, _)) | (ty::Slice(t1), ty::Slice(t2)) => match_types(t1, t2), (ty::Adt(def1, _), ty::Adt(def2, _)) => def1 == def2, (_, _) => false, } } fn get_type_name(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> String { match ty.kind { ty::Adt(t, _) => cx.tcx.def_path_str(t.did), ty::Ref(_, r, _) => get_type_name(cx, &r), _ => ty.to_string(), } } fn compare_inputs( closure_inputs: &mut dyn Iterator>, call_args: &mut dyn Iterator>, ) -> bool { for (closure_input, function_arg) in closure_inputs.zip(call_args) { if let PatKind::Binding(_, _, ident, _) = closure_input.pat.kind { // XXXManishearth Should I be checking the binding mode here? if let ExprKind::Path(QPath::Resolved(None, ref p)) = function_arg.kind { if p.segments.len() != 1 { // If it's a proper path, it can't be a local variable return false; } if p.segments[0].ident.name != ident.name { // The two idents should be the same return false; } } else { return false; } } else { return false; } } true }