126 lines
5.0 KiB
Rust
126 lines
5.0 KiB
Rust
use crate::{LateContext, LateLintPass, LintContext};
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use rustc_errors::Applicability;
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use rustc_hir as hir;
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use rustc_middle::ty;
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use rustc_middle::ty::adjustment::{Adjust, Adjustment};
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use rustc_session::lint::FutureBreakage;
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use rustc_span::symbol::sym;
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declare_lint! {
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/// The `array_into_iter` lint detects calling `into_iter` on arrays.
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///
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/// ### Example
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///
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/// ```rust
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/// # #![allow(unused)]
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/// [1, 2, 3].into_iter().for_each(|n| { *n; });
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/// ```
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///
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/// {{produces}}
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///
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/// ### Explanation
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///
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/// In the future, it is planned to add an `IntoIter` implementation for
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/// arrays such that it will iterate over *values* of the array instead of
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/// references. Due to how method resolution works, this will change
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/// existing code that uses `into_iter` on arrays. The solution to avoid
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/// this warning is to use `iter()` instead of `into_iter()`.
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///
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/// This is a [future-incompatible] lint to transition this to a hard error
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/// in the future. See [issue #66145] for more details and a more thorough
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/// description of the lint.
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///
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/// [issue #66145]: https://github.com/rust-lang/rust/issues/66145
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/// [future-incompatible]: ../index.md#future-incompatible-lints
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pub ARRAY_INTO_ITER,
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Warn,
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"detects calling `into_iter` on arrays",
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@future_incompatible = FutureIncompatibleInfo {
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reference: "issue #66145 <https://github.com/rust-lang/rust/issues/66145>",
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edition: None,
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future_breakage: Some(FutureBreakage {
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date: None
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})
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};
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}
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declare_lint_pass!(
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/// Checks for instances of calling `into_iter` on arrays.
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ArrayIntoIter => [ARRAY_INTO_ITER]
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);
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impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
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// We only care about method call expressions.
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if let hir::ExprKind::MethodCall(call, span, args, _) = &expr.kind {
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if call.ident.name != sym::into_iter {
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return;
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}
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// Check if the method call actually calls the libcore
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// `IntoIterator::into_iter`.
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let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
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match cx.tcx.trait_of_item(def_id) {
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Some(trait_id) if cx.tcx.is_diagnostic_item(sym::IntoIterator, trait_id) => {}
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_ => return,
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};
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// As this is a method call expression, we have at least one
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// argument.
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let receiver_arg = &args[0];
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// Peel all `Box<_>` layers. We have to special case `Box` here as
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// `Box` is the only thing that values can be moved out of via
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// method call. `Box::new([1]).into_iter()` should trigger this
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// lint.
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let mut recv_ty = cx.typeck_results().expr_ty(receiver_arg);
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let mut num_box_derefs = 0;
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while recv_ty.is_box() {
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num_box_derefs += 1;
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recv_ty = recv_ty.boxed_ty();
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}
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// Make sure we found an array after peeling the boxes.
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if !matches!(recv_ty.kind(), ty::Array(..)) {
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return;
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}
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// Make sure that there is an autoref coercion at the expected
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// position. The first `num_box_derefs` adjustments are the derefs
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// of the box.
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match cx.typeck_results().expr_adjustments(receiver_arg).get(num_box_derefs) {
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Some(Adjustment { kind: Adjust::Borrow(_), .. }) => {}
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_ => return,
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}
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// Emit lint diagnostic.
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let target = match *cx.typeck_results().expr_ty_adjusted(receiver_arg).kind() {
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ty::Ref(_, inner_ty, _) if inner_ty.is_array() => "[T; N]",
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ty::Ref(_, inner_ty, _) if matches!(inner_ty.kind(), ty::Slice(..)) => "[T]",
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// We know the original first argument type is an array type,
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// we know that the first adjustment was an autoref coercion
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// and we know that `IntoIterator` is the trait involved. The
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// array cannot be coerced to something other than a reference
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// to an array or to a slice.
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_ => bug!("array type coerced to something other than array or slice"),
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};
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cx.struct_span_lint(ARRAY_INTO_ITER, *span, |lint| {
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lint.build(&format!(
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"this method call currently resolves to `<&{} as IntoIterator>::into_iter` (due \
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to autoref coercions), but that might change in the future when \
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`IntoIterator` impls for arrays are added.",
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target,
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))
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.span_suggestion(
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call.ident.span,
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"use `.iter()` instead of `.into_iter()` to avoid ambiguity",
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"iter".into(),
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Applicability::MachineApplicable,
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)
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.emit();
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})
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}
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}
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}
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