1 use crate::lint::{LateContext, LateLintPass, LintArray, LintContext, LintPass};
4 lint::FutureIncompatibleInfo,
7 adjustment::{Adjust, Adjustment},
10 use rustc_span::symbol::sym;
11 use syntax::errors::Applicability;
16 "detects calling `into_iter` on arrays",
17 @future_incompatible = FutureIncompatibleInfo {
18 reference: "issue #66145 <https://github.com/rust-lang/rust/issues/66145>",
24 /// Checks for instances of calling `into_iter` on arrays.
25 ArrayIntoIter => [ARRAY_INTO_ITER]
28 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ArrayIntoIter {
29 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr<'tcx>) {
30 // We only care about method call expressions.
31 if let hir::ExprKind::MethodCall(call, span, args) = &expr.kind {
32 if call.ident.name != sym::into_iter {
36 // Check if the method call actually calls the libcore
37 // `IntoIterator::into_iter`.
38 let def_id = cx.tables.type_dependent_def_id(expr.hir_id).unwrap();
39 match cx.tcx.trait_of_item(def_id) {
40 Some(trait_id) if cx.tcx.is_diagnostic_item(sym::IntoIterator, trait_id) => {}
44 // As this is a method call expression, we have at least one
46 let receiver_arg = &args[0];
48 // Peel all `Box<_>` layers. We have to special case `Box` here as
49 // `Box` is the only thing that values can be moved out of via
50 // method call. `Box::new([1]).into_iter()` should trigger this
52 let mut recv_ty = cx.tables.expr_ty(receiver_arg);
53 let mut num_box_derefs = 0;
54 while recv_ty.is_box() {
56 recv_ty = recv_ty.boxed_ty();
59 // Make sure we found an array after peeling the boxes.
60 if !matches!(recv_ty.kind, ty::Array(..)) {
64 // Make sure that there is an autoref coercion at the expected
65 // position. The first `num_box_derefs` adjustments are the derefs
67 match cx.tables.expr_adjustments(receiver_arg).get(num_box_derefs) {
68 Some(Adjustment { kind: Adjust::Borrow(_), .. }) => {}
72 // Emit lint diagnostic.
73 let target = match cx.tables.expr_ty_adjusted(receiver_arg).kind {
74 ty::Ref(_, ty::TyS { kind: ty::Array(..), .. }, _) => "[T; N]",
75 ty::Ref(_, ty::TyS { kind: ty::Slice(..), .. }, _) => "[T]",
77 // We know the original first argument type is an array type,
78 // we know that the first adjustment was an autoref coercion
79 // and we know that `IntoIterator` is the trait involved. The
80 // array cannot be coerced to something other than a reference
81 // to an array or to a slice.
82 _ => bug!("array type coerced to something other than array or slice"),
85 "this method call currently resolves to `<&{} as IntoIterator>::into_iter` (due \
86 to autoref coercions), but that might change in the future when \
87 `IntoIterator` impls for arrays are added.",
90 cx.struct_span_lint(ARRAY_INTO_ITER, *span, &msg)
93 "use `.iter()` instead of `.into_iter()` to avoid ambiguity",
95 Applicability::MachineApplicable,