1 use rustc_errors::Applicability;
3 intravisit::{walk_expr, NestedVisitorMap, Visitor},
4 Expr, ExprKind, Stmt, StmtKind,
6 use rustc_lint::{LateContext, LateLintPass};
7 use rustc_middle::hir::map::Map;
8 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 use rustc_span::{source_map::Span, sym, Symbol};
11 use if_chain::if_chain;
13 use clippy_utils::diagnostics::span_lint_and_then;
14 use clippy_utils::is_trait_method;
15 use clippy_utils::source::snippet_with_applicability;
16 use clippy_utils::ty::has_iter_method;
18 declare_clippy_lint! {
20 /// Checks for usage of `for_each` that would be more simply written as a
23 /// ### Why is this bad?
24 /// `for_each` may be used after applying iterator transformers like
25 /// `filter` for better readability and performance. It may also be used to fit a simple
26 /// operation on one line.
27 /// But when none of these apply, a simple `for` loop is more idiomatic.
31 /// let v = vec![0, 1, 2];
32 /// v.iter().for_each(|elem| {
33 /// println!("{}", elem);
38 /// let v = vec![0, 1, 2];
39 /// for elem in v.iter() {
40 /// println!("{}", elem);
43 #[clippy::version = "1.53.0"]
44 pub NEEDLESS_FOR_EACH,
46 "using `for_each` where a `for` loop would be simpler"
49 declare_lint_pass!(NeedlessForEach => [NEEDLESS_FOR_EACH]);
51 impl LateLintPass<'_> for NeedlessForEach {
52 fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
53 let expr = match stmt.kind {
54 StmtKind::Expr(expr) | StmtKind::Semi(expr) => expr,
59 // Check the method name is `for_each`.
60 if let ExprKind::MethodCall(method_name, _, [for_each_recv, for_each_arg], _) = expr.kind;
61 if method_name.ident.name == Symbol::intern("for_each");
62 // Check `for_each` is an associated function of `Iterator`.
63 if is_trait_method(cx, expr, sym::Iterator);
64 // Checks the receiver of `for_each` is also a method call.
65 if let ExprKind::MethodCall(_, _, [iter_recv], _) = for_each_recv.kind;
66 // Skip the lint if the call chain is too long. e.g. `v.field.iter().for_each()` or
67 // `v.foo().iter().for_each()` must be skipped.
70 ExprKind::Array(..) | ExprKind::Call(..) | ExprKind::Path(..)
72 // Checks the type of the `iter` method receiver is NOT a user defined type.
73 if has_iter_method(cx, cx.typeck_results().expr_ty(iter_recv)).is_some();
74 // Skip the lint if the body is not block because this is simpler than `for` loop.
75 // e.g. `v.iter().for_each(f)` is simpler and clearer than using `for` loop.
76 if let ExprKind::Closure(_, _, body_id, ..) = for_each_arg.kind;
77 let body = cx.tcx.hir().body(body_id);
78 if let ExprKind::Block(..) = body.value.kind;
80 let mut ret_collector = RetCollector::default();
81 ret_collector.visit_expr(&body.value);
83 // Skip the lint if `return` is used in `Loop` in order not to suggest using `'label`.
84 if ret_collector.ret_in_loop {
88 let (mut applicability, ret_suggs) = if ret_collector.spans.is_empty() {
89 (Applicability::MachineApplicable, None)
92 Applicability::MaybeIncorrect,
97 .map(|span| (span, "continue".to_string()))
105 snippet_with_applicability(cx, body.params[0].pat.span, "..", &mut applicability),
106 snippet_with_applicability(cx, for_each_recv.span, "..", &mut applicability),
107 snippet_with_applicability(cx, body.value.span, "..", &mut applicability),
110 span_lint_and_then(cx, NEEDLESS_FOR_EACH, stmt.span, "needless use of `for_each`", |diag| {
111 diag.span_suggestion(stmt.span, "try", sugg, applicability);
112 if let Some(ret_suggs) = ret_suggs {
113 diag.multipart_suggestion("...and replace `return` with `continue`", ret_suggs, applicability);
121 /// This type plays two roles.
122 /// 1. Collect spans of `return` in the closure body.
123 /// 2. Detect use of `return` in `Loop` in the closure body.
125 /// NOTE: The functionality of this type is similar to
126 /// [`clippy_utils::visitors::find_all_ret_expressions`], but we can't use
127 /// `find_all_ret_expressions` instead of this type. The reasons are:
128 /// 1. `find_all_ret_expressions` passes the argument of `ExprKind::Ret` to a callback, but what we
129 /// need here is `ExprKind::Ret` itself.
130 /// 2. We can't trace current loop depth with `find_all_ret_expressions`.
132 struct RetCollector {
138 impl<'tcx> Visitor<'tcx> for RetCollector {
139 type Map = Map<'tcx>;
141 fn visit_expr(&mut self, expr: &Expr<'_>) {
143 ExprKind::Ret(..) => {
144 if self.loop_depth > 0 && !self.ret_in_loop {
145 self.ret_in_loop = true;
148 self.spans.push(expr.span);
151 ExprKind::Loop(..) => {
152 self.loop_depth += 1;
153 walk_expr(self, expr);
154 self.loop_depth -= 1;
161 walk_expr(self, expr);
164 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
165 NestedVisitorMap::None