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|
use crate::{LateContext, LateLintPass, LintContext};
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_middle::ty;
use rustc_middle::ty::adjustment::{Adjust, Adjustment};
use rustc_session::lint::FutureBreakage;
use rustc_span::symbol::sym;
declare_lint! {
/// The `array_into_iter` lint detects calling `into_iter` on arrays.
///
/// ### Example
///
/// ```rust
/// # #![allow(unused)]
/// [1, 2, 3].into_iter().for_each(|n| { *n; });
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In the future, it is planned to add an `IntoIter` implementation for
/// arrays such that it will iterate over *values* of the array instead of
/// references. Due to how method resolution works, this will change
/// existing code that uses `into_iter` on arrays. The solution to avoid
/// this warning is to use `iter()` instead of `into_iter()`.
///
/// This is a [future-incompatible] lint to transition this to a hard error
/// in the future. See [issue #66145] for more details and a more thorough
/// description of the lint.
///
/// [issue #66145]: https://github.com/rust-lang/rust/issues/66145
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub ARRAY_INTO_ITER,
Warn,
"detects calling `into_iter` on arrays",
@future_incompatible = FutureIncompatibleInfo {
reference: "issue #66145 <https://github.com/rust-lang/rust/issues/66145>",
edition: None,
future_breakage: Some(FutureBreakage {
date: None
})
};
}
declare_lint_pass!(
/// Checks for instances of calling `into_iter` on arrays.
ArrayIntoIter => [ARRAY_INTO_ITER]
);
impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
// We only care about method call expressions.
if let hir::ExprKind::MethodCall(call, span, args, _) = &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_arg = &args[0];
// Peel all `Box<_>` layers. We have to special case `Box` here as
// `Box` is the only thing that values can be moved out of via
// method call. `Box::new([1]).into_iter()` should trigger this
// lint.
let mut recv_ty = cx.typeck_results().expr_ty(receiver_arg);
let mut num_box_derefs = 0;
while recv_ty.is_box() {
num_box_derefs += 1;
recv_ty = recv_ty.boxed_ty();
}
// Make sure we found an array after peeling the boxes.
if !matches!(recv_ty.kind(), ty::Array(..)) {
return;
}
// Make sure that there is an autoref coercion at the expected
// position. The first `num_box_derefs` adjustments are the derefs
// of the box.
match cx.typeck_results().expr_adjustments(receiver_arg).get(num_box_derefs) {
Some(Adjustment { kind: Adjust::Borrow(_), .. }) => {}
_ => return,
}
// Emit lint diagnostic.
let target = match *cx.typeck_results().expr_ty_adjusted(receiver_arg).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, *span, |lint| {
lint.build(&format!(
"this method call currently resolves to `<&{} as IntoIterator>::into_iter` (due \
to autoref coercions), but that might change in the future when \
`IntoIterator` impls for arrays are added.",
target,
))
.span_suggestion(
call.ident.span,
"use `.iter()` instead of `.into_iter()` to avoid ambiguity",
"iter".into(),
Applicability::MachineApplicable,
)
.emit();
})
}
}
}
|
