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