|
| 1 | +use rustc_errors::Applicability; |
| 2 | +use rustc_hir::{ |
| 3 | + intravisit::{walk_expr, NestedVisitorMap, Visitor}, |
| 4 | + Expr, ExprKind, Stmt, StmtKind, |
| 5 | +}; |
| 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}; |
| 10 | + |
| 11 | +use if_chain::if_chain; |
| 12 | + |
| 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; |
| 17 | + |
| 18 | +declare_clippy_lint! { |
| 19 | + /// **What it does:** Checks for usage of `for_each` that would be more simply written as a |
| 20 | + /// `for` loop. |
| 21 | + /// |
| 22 | + /// **Why is this bad?** `for_each` may be used after applying iterator transformers like |
| 23 | + /// `filter` for better readability and performance. It may also be used to fit a simple |
| 24 | + /// operation on one line. |
| 25 | + /// But when none of these apply, a simple `for` loop is more idiomatic. |
| 26 | + /// |
| 27 | + /// **Known problems:** None. |
| 28 | + /// |
| 29 | + /// **Example:** |
| 30 | + /// |
| 31 | + /// ```rust |
| 32 | + /// let v = vec![0, 1, 2]; |
| 33 | + /// v.iter().for_each(|elem| { |
| 34 | + /// println!("{}", elem); |
| 35 | + /// }) |
| 36 | + /// ``` |
| 37 | + /// Use instead: |
| 38 | + /// ```rust |
| 39 | + /// let v = vec![0, 1, 2]; |
| 40 | + /// for elem in v.iter() { |
| 41 | + /// println!("{}", elem); |
| 42 | + /// } |
| 43 | + /// ``` |
| 44 | + pub NEEDLESS_FOR_EACH, |
| 45 | + pedantic, |
| 46 | + "using `for_each` where a `for` loop would be simpler" |
| 47 | +} |
| 48 | + |
| 49 | +declare_lint_pass!(NeedlessForEach => [NEEDLESS_FOR_EACH]); |
| 50 | + |
| 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, |
| 55 | + _ => return, |
| 56 | + }; |
| 57 | + |
| 58 | + if_chain! { |
| 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. |
| 68 | + if matches!( |
| 69 | + iter_recv.kind, |
| 70 | + ExprKind::Array(..) | ExprKind::Call(..) | ExprKind::Path(..) |
| 71 | + ); |
| 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; |
| 79 | + then { |
| 80 | + let mut ret_collector = RetCollector::default(); |
| 81 | + ret_collector.visit_expr(&body.value); |
| 82 | + |
| 83 | + // Skip the lint if `return` is used in `Loop` in order not to suggest using `'label`. |
| 84 | + if ret_collector.ret_in_loop { |
| 85 | + return; |
| 86 | + } |
| 87 | + |
| 88 | + let (mut applicability, ret_suggs) = if ret_collector.spans.is_empty() { |
| 89 | + (Applicability::MachineApplicable, None) |
| 90 | + } else { |
| 91 | + ( |
| 92 | + Applicability::MaybeIncorrect, |
| 93 | + Some( |
| 94 | + ret_collector |
| 95 | + .spans |
| 96 | + .into_iter() |
| 97 | + .map(|span| (span, "continue".to_string())) |
| 98 | + .collect(), |
| 99 | + ), |
| 100 | + ) |
| 101 | + }; |
| 102 | + |
| 103 | + let sugg = format!( |
| 104 | + "for {} in {} {}", |
| 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), |
| 108 | + ); |
| 109 | + |
| 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); |
| 114 | + } |
| 115 | + }) |
| 116 | + } |
| 117 | + } |
| 118 | + } |
| 119 | +} |
| 120 | + |
| 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. |
| 124 | +/// |
| 125 | +/// NOTE: The functionality of this type is similar to |
| 126 | +/// [`crate::utilts::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`. |
| 131 | +#[derive(Default)] |
| 132 | +struct RetCollector { |
| 133 | + spans: Vec<Span>, |
| 134 | + ret_in_loop: bool, |
| 135 | + loop_depth: u16, |
| 136 | +} |
| 137 | + |
| 138 | +impl<'tcx> Visitor<'tcx> for RetCollector { |
| 139 | + type Map = Map<'tcx>; |
| 140 | + |
| 141 | + fn visit_expr(&mut self, expr: &Expr<'_>) { |
| 142 | + match expr.kind { |
| 143 | + ExprKind::Ret(..) => { |
| 144 | + if self.loop_depth > 0 && !self.ret_in_loop { |
| 145 | + self.ret_in_loop = true |
| 146 | + } |
| 147 | + |
| 148 | + self.spans.push(expr.span) |
| 149 | + }, |
| 150 | + |
| 151 | + ExprKind::Loop(..) => { |
| 152 | + self.loop_depth += 1; |
| 153 | + walk_expr(self, expr); |
| 154 | + self.loop_depth -= 1; |
| 155 | + return; |
| 156 | + }, |
| 157 | + |
| 158 | + _ => {}, |
| 159 | + } |
| 160 | + |
| 161 | + walk_expr(self, expr); |
| 162 | + } |
| 163 | + |
| 164 | + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { |
| 165 | + NestedVisitorMap::None |
| 166 | + } |
| 167 | +} |
0 commit comments