1 use rustc_errors::Applicability; 2 use rustc_hir::{ 3 intravisit::{walk_expr, Visitor}, 4 Closure, Expr, ExprKind, Stmt, StmtKind, 5 }; 6 use rustc_lint::{LateContext, LateLintPass}; 7 use rustc_session::{declare_lint_pass, declare_tool_lint}; 8 use rustc_span::{source_map::Span, sym, Symbol}; 9 10 use if_chain::if_chain; 11 12 use clippy_utils::diagnostics::span_lint_and_then; 13 use clippy_utils::is_trait_method; 14 use clippy_utils::source::snippet_with_applicability; 15 use clippy_utils::ty::has_iter_method; 16 17 declare_clippy_lint! { 18 /// ### What it does 19 /// Checks for usage of `for_each` that would be more simply written as a 20 /// `for` loop. 21 /// 22 /// ### Why is this bad? 23 /// `for_each` may be used after applying iterator transformers like 24 /// `filter` for better readability and performance. It may also be used to fit a simple 25 /// operation on one line. 26 /// But when none of these apply, a simple `for` loop is more idiomatic. 27 /// 28 /// ### Example 29 /// ```rust 30 /// let v = vec![0, 1, 2]; 31 /// v.iter().for_each(|elem| { 32 /// println!("{}", elem); 33 /// }) 34 /// ``` 35 /// Use instead: 36 /// ```rust 37 /// let v = vec![0, 1, 2]; 38 /// for elem in v.iter() { 39 /// println!("{}", elem); 40 /// } 41 /// ``` 42 #[clippy::version = "1.53.0"] 43 pub NEEDLESS_FOR_EACH, 44 pedantic, 45 "using `for_each` where a `for` loop would be simpler" 46 } 47 48 declare_lint_pass!(NeedlessForEach => [NEEDLESS_FOR_EACH]); 49 50 impl<'tcx> LateLintPass<'tcx> for NeedlessForEach { check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>)51 fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) { 52 let (StmtKind::Expr(expr) | StmtKind::Semi(expr)) = stmt.kind else { 53 return 54 }; 55 56 if_chain! { 57 // Check the method name is `for_each`. 58 if let ExprKind::MethodCall(method_name, for_each_recv, [for_each_arg], _) = expr.kind; 59 if method_name.ident.name == Symbol::intern("for_each"); 60 // Check `for_each` is an associated function of `Iterator`. 61 if is_trait_method(cx, expr, sym::Iterator); 62 // Checks the receiver of `for_each` is also a method call. 63 if let ExprKind::MethodCall(_, iter_recv, [], _) = for_each_recv.kind; 64 // Skip the lint if the call chain is too long. e.g. `v.field.iter().for_each()` or 65 // `v.foo().iter().for_each()` must be skipped. 66 if matches!( 67 iter_recv.kind, 68 ExprKind::Array(..) | ExprKind::Call(..) | ExprKind::Path(..) 69 ); 70 // Checks the type of the `iter` method receiver is NOT a user defined type. 71 if has_iter_method(cx, cx.typeck_results().expr_ty(iter_recv)).is_some(); 72 // Skip the lint if the body is not block because this is simpler than `for` loop. 73 // e.g. `v.iter().for_each(f)` is simpler and clearer than using `for` loop. 74 if let ExprKind::Closure(&Closure { body, .. }) = for_each_arg.kind; 75 let body = cx.tcx.hir().body(body); 76 if let ExprKind::Block(..) = body.value.kind; 77 then { 78 let mut ret_collector = RetCollector::default(); 79 ret_collector.visit_expr(body.value); 80 81 // Skip the lint if `return` is used in `Loop` in order not to suggest using `'label`. 82 if ret_collector.ret_in_loop { 83 return; 84 } 85 86 let (mut applicability, ret_suggs) = if ret_collector.spans.is_empty() { 87 (Applicability::MachineApplicable, None) 88 } else { 89 ( 90 Applicability::MaybeIncorrect, 91 Some( 92 ret_collector 93 .spans 94 .into_iter() 95 .map(|span| (span, "continue".to_string())) 96 .collect(), 97 ), 98 ) 99 }; 100 101 let sugg = format!( 102 "for {} in {} {}", 103 snippet_with_applicability(cx, body.params[0].pat.span, "..", &mut applicability), 104 snippet_with_applicability(cx, for_each_recv.span, "..", &mut applicability), 105 snippet_with_applicability(cx, body.value.span, "..", &mut applicability), 106 ); 107 108 span_lint_and_then(cx, NEEDLESS_FOR_EACH, stmt.span, "needless use of `for_each`", |diag| { 109 diag.span_suggestion(stmt.span, "try", sugg, applicability); 110 if let Some(ret_suggs) = ret_suggs { 111 diag.multipart_suggestion("...and replace `return` with `continue`", ret_suggs, applicability); 112 } 113 }) 114 } 115 } 116 } 117 } 118 119 /// This type plays two roles. 120 /// 1. Collect spans of `return` in the closure body. 121 /// 2. Detect use of `return` in `Loop` in the closure body. 122 /// 123 /// NOTE: The functionality of this type is similar to 124 /// [`clippy_utils::visitors::find_all_ret_expressions`], but we can't use 125 /// `find_all_ret_expressions` instead of this type. The reasons are: 126 /// 1. `find_all_ret_expressions` passes the argument of `ExprKind::Ret` to a callback, but what we 127 /// need here is `ExprKind::Ret` itself. 128 /// 2. We can't trace current loop depth with `find_all_ret_expressions`. 129 #[derive(Default)] 130 struct RetCollector { 131 spans: Vec<Span>, 132 ret_in_loop: bool, 133 loop_depth: u16, 134 } 135 136 impl<'tcx> Visitor<'tcx> for RetCollector { visit_expr(&mut self, expr: &Expr<'_>)137 fn visit_expr(&mut self, expr: &Expr<'_>) { 138 match expr.kind { 139 ExprKind::Ret(..) => { 140 if self.loop_depth > 0 && !self.ret_in_loop { 141 self.ret_in_loop = true; 142 } 143 144 self.spans.push(expr.span); 145 }, 146 147 ExprKind::Loop(..) => { 148 self.loop_depth += 1; 149 walk_expr(self, expr); 150 self.loop_depth -= 1; 151 return; 152 }, 153 154 _ => {}, 155 } 156 157 walk_expr(self, expr); 158 } 159 } 160