1 use rustc_errors::Applicability;
3 intravisit::{walk_expr, Visitor},
4 Closure, Expr, ExprKind, Stmt, StmtKind,
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};
10 use if_chain::if_chain;
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;
17 declare_clippy_lint! {
19 /// Checks for usage of `for_each` that would be more simply written as a
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.
30 /// let v = vec![0, 1, 2];
31 /// v.iter().for_each(|elem| {
32 /// println!("{}", elem);
37 /// let v = vec![0, 1, 2];
38 /// for elem in v.iter() {
39 /// println!("{}", elem);
42 #[clippy::version = "1.53.0"]
43 pub NEEDLESS_FOR_EACH,
45 "using `for_each` where a `for` loop would be simpler"
48 declare_lint_pass!(NeedlessForEach => [NEEDLESS_FOR_EACH]);
50 impl<'tcx> LateLintPass<'tcx> for NeedlessForEach {
51 fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
52 let (StmtKind::Expr(expr) | StmtKind::Semi(expr)) = stmt.kind else {
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.
68 ExprKind::Array(..) | ExprKind::Call(..) | ExprKind::Path(..)
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;
78 let mut ret_collector = RetCollector::default();
79 ret_collector.visit_expr(body.value);
81 // Skip the lint if `return` is used in `Loop` in order not to suggest using `'label`.
82 if ret_collector.ret_in_loop {
86 let (mut applicability, ret_suggs) = if ret_collector.spans.is_empty() {
87 (Applicability::MachineApplicable, None)
90 Applicability::MaybeIncorrect,
95 .map(|span| (span, "continue".to_string()))
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),
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);
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.
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`.
130 struct RetCollector {
136 impl<'tcx> Visitor<'tcx> for RetCollector {
137 fn visit_expr(&mut self, expr: &Expr<'_>) {
139 ExprKind::Ret(..) => {
140 if self.loop_depth > 0 && !self.ret_in_loop {
141 self.ret_in_loop = true;
144 self.spans.push(expr.span);
147 ExprKind::Loop(..) => {
148 self.loop_depth += 1;
149 walk_expr(self, expr);
150 self.loop_depth -= 1;
157 walk_expr(self, expr);