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|
use crate::{LateContext, LateLintPass, LintContext};
use rustc_errors::{fluent, Applicability};
use rustc_hir as hir;
use rustc_middle::ty;
use rustc_middle::ty::adjustment::{Adjust, Adjustment};
use rustc_session::lint::FutureIncompatibilityReason;
use rustc_span::edition::Edition;
use rustc_span::symbol::sym;
use rustc_span::Span;
declare_lint! {
/// The `array_into_iter` lint detects calling `into_iter` on arrays.
///
/// ### Example
///
/// ```rust,edition2018
/// # #![allow(unused)]
/// [1, 2, 3].into_iter().for_each(|n| { *n; });
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Since Rust 1.53, arrays implement `IntoIterator`. However, to avoid
/// breakage, `array.into_iter()` in Rust 2015 and 2018 code will still
/// behave as `(&array).into_iter()`, returning an iterator over
/// references, just like in Rust 1.52 and earlier.
/// This only applies to the method call syntax `array.into_iter()`, not to
/// any other syntax such as `for _ in array` or `IntoIterator::into_iter(array)`.
pub ARRAY_INTO_ITER,
Warn,
"detects calling `into_iter` on arrays in Rust 2015 and 2018",
@future_incompatible = FutureIncompatibleInfo {
reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/IntoIterator-for-arrays.html>",
reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2021),
};
}
#[derive(Copy, Clone, Default)]
pub struct ArrayIntoIter {
for_expr_span: Span,
}
impl_lint_pass!(ArrayIntoIter => [ARRAY_INTO_ITER]);
impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
// Save the span of expressions in `for _ in expr` syntax,
// so we can give a better suggestion for those later.
if let hir::ExprKind::Match(arg, [_], hir::MatchSource::ForLoopDesugar) = &expr.kind {
if let hir::ExprKind::Call(path, [arg]) = &arg.kind {
if let hir::ExprKind::Path(hir::QPath::LangItem(
hir::LangItem::IntoIterIntoIter,
..,
)) = &path.kind
{
self.for_expr_span = arg.span;
}
}
}
// We only care about method call expressions.
if let hir::ExprKind::MethodCall(call, receiver_arg, ..) = &expr.kind {
if call.ident.name != sym::into_iter {
return;
}
// Check if the method call actually calls the libcore
// `IntoIterator::into_iter`.
let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
match cx.tcx.trait_of_item(def_id) {
Some(trait_id) if cx.tcx.is_diagnostic_item(sym::IntoIterator, trait_id) => {}
_ => return,
};
// As this is a method call expression, we have at least one argument.
let receiver_ty = cx.typeck_results().expr_ty(receiver_arg);
let adjustments = cx.typeck_results().expr_adjustments(receiver_arg);
let Some(Adjustment { kind: Adjust::Borrow(_), target }) = adjustments.last() else {
return
};
let types =
std::iter::once(receiver_ty).chain(adjustments.iter().map(|adj| adj.target));
let mut found_array = false;
for ty in types {
match ty.kind() {
// If we run into a &[T; N] or &[T] first, there's nothing to warn about.
// It'll resolve to the reference version.
ty::Ref(_, inner_ty, _) if inner_ty.is_array() => return,
ty::Ref(_, inner_ty, _) if matches!(inner_ty.kind(), ty::Slice(..)) => return,
// Found an actual array type without matching a &[T; N] first.
// This is the problematic case.
ty::Array(..) => {
found_array = true;
break;
}
_ => {}
}
}
if !found_array {
return;
}
// Emit lint diagnostic.
let target = match *target.kind() {
ty::Ref(_, inner_ty, _) if inner_ty.is_array() => "[T; N]",
ty::Ref(_, inner_ty, _) if matches!(inner_ty.kind(), ty::Slice(..)) => "[T]",
// We know the original first argument type is an array type,
// we know that the first adjustment was an autoref coercion
// and we know that `IntoIterator` is the trait involved. The
// array cannot be coerced to something other than a reference
// to an array or to a slice.
_ => bug!("array type coerced to something other than array or slice"),
};
cx.struct_span_lint(
ARRAY_INTO_ITER,
call.ident.span,
fluent::lint_array_into_iter,
|diag| {
diag.set_arg("target", target);
diag.span_suggestion(
call.ident.span,
fluent::use_iter_suggestion,
"iter",
Applicability::MachineApplicable,
);
if self.for_expr_span == expr.span {
diag.span_suggestion(
receiver_arg.span.shrink_to_hi().to(expr.span.shrink_to_hi()),
fluent::remove_into_iter_suggestion,
"",
Applicability::MaybeIncorrect,
);
} else if receiver_ty.is_array() {
diag.multipart_suggestion(
fluent::use_explicit_into_iter_suggestion,
vec![
(expr.span.shrink_to_lo(), "IntoIterator::into_iter(".into()),
(
receiver_arg.span.shrink_to_hi().to(expr.span.shrink_to_hi()),
")".into(),
),
],
Applicability::MaybeIncorrect,
);
}
diag
},
)
}
}
}
|
