1 #![deny(rustc::untranslatable_diagnostic)]
2 #![deny(rustc::diagnostic_outside_of_impl)]
3 use crate::lints::{ArrayIntoIterDiag, ArrayIntoIterDiagSub};
4 use crate::{LateContext, LateLintPass, LintContext};
7 use rustc_middle::ty::adjustment::{Adjust, Adjustment};
8 use rustc_session::lint::FutureIncompatibilityReason;
9 use rustc_span::edition::Edition;
10 use rustc_span::symbol::sym;
14 /// The `array_into_iter` lint detects calling `into_iter` on arrays.
18 /// ```rust,edition2018
19 /// # #![allow(unused)]
20 /// [1, 2, 3].into_iter().for_each(|n| { *n; });
27 /// Since Rust 1.53, arrays implement `IntoIterator`. However, to avoid
28 /// breakage, `array.into_iter()` in Rust 2015 and 2018 code will still
29 /// behave as `(&array).into_iter()`, returning an iterator over
30 /// references, just like in Rust 1.52 and earlier.
31 /// This only applies to the method call syntax `array.into_iter()`, not to
32 /// any other syntax such as `for _ in array` or `IntoIterator::into_iter(array)`.
35 "detects calling `into_iter` on arrays in Rust 2015 and 2018",
36 @future_incompatible = FutureIncompatibleInfo {
37 reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/IntoIterator-for-arrays.html>",
38 reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2021),
42 #[derive(Copy, Clone, Default)]
43 pub struct ArrayIntoIter {
47 impl_lint_pass!(ArrayIntoIter => [ARRAY_INTO_ITER]);
49 impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
50 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
51 // Save the span of expressions in `for _ in expr` syntax,
52 // so we can give a better suggestion for those later.
53 if let hir::ExprKind::Match(arg, [_], hir::MatchSource::ForLoopDesugar) = &expr.kind {
54 if let hir::ExprKind::Call(path, [arg]) = &arg.kind {
55 if let hir::ExprKind::Path(hir::QPath::LangItem(
56 hir::LangItem::IntoIterIntoIter,
60 self.for_expr_span = arg.span;
65 // We only care about method call expressions.
66 if let hir::ExprKind::MethodCall(call, receiver_arg, ..) = &expr.kind {
67 if call.ident.name != sym::into_iter {
71 // Check if the method call actually calls the libcore
72 // `IntoIterator::into_iter`.
73 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
74 match cx.tcx.trait_of_item(def_id) {
75 Some(trait_id) if cx.tcx.is_diagnostic_item(sym::IntoIterator, trait_id) => {}
79 // As this is a method call expression, we have at least one argument.
80 let receiver_ty = cx.typeck_results().expr_ty(receiver_arg);
81 let adjustments = cx.typeck_results().expr_adjustments(receiver_arg);
83 let Some(Adjustment { kind: Adjust::Borrow(_), target }) = adjustments.last() else {
88 std::iter::once(receiver_ty).chain(adjustments.iter().map(|adj| adj.target));
90 let mut found_array = false;
94 // If we run into a &[T; N] or &[T] first, there's nothing to warn about.
95 // It'll resolve to the reference version.
96 ty::Ref(_, inner_ty, _) if inner_ty.is_array() => return,
97 ty::Ref(_, inner_ty, _) if matches!(inner_ty.kind(), ty::Slice(..)) => return,
98 // Found an actual array type without matching a &[T; N] first.
99 // This is the problematic case.
112 // Emit lint diagnostic.
113 let target = match *target.kind() {
114 ty::Ref(_, inner_ty, _) if inner_ty.is_array() => "[T; N]",
115 ty::Ref(_, inner_ty, _) if matches!(inner_ty.kind(), ty::Slice(..)) => "[T]",
116 // We know the original first argument type is an array type,
117 // we know that the first adjustment was an autoref coercion
118 // and we know that `IntoIterator` is the trait involved. The
119 // array cannot be coerced to something other than a reference
120 // to an array or to a slice.
121 _ => bug!("array type coerced to something other than array or slice"),
123 let sub = if self.for_expr_span == expr.span {
124 Some(ArrayIntoIterDiagSub::RemoveIntoIter {
125 span: receiver_arg.span.shrink_to_hi().to(expr.span.shrink_to_hi()),
127 } else if receiver_ty.is_array() {
128 Some(ArrayIntoIterDiagSub::UseExplicitIntoIter {
129 start_span: expr.span.shrink_to_lo(),
130 end_span: receiver_arg.span.shrink_to_hi().to(expr.span.shrink_to_hi()),
135 cx.emit_spanned_lint(
138 ArrayIntoIterDiag { target, suggestion: call.ident.span, sub },