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use clippy_utils::diagnostics::span_lint_and_note;
use clippy_utils::ty::is_copy;
use rustc_hir::{Impl, Item, ItemKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::declare_lint_pass;
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for types that implement `Copy` as well as
/// `Iterator`.
///
/// ### Why is this bad?
/// Implicit copies can be confusing when working with
/// iterator combinators.
///
/// ### Example
/// ```rust,ignore
/// #[derive(Copy, Clone)]
/// struct Countdown(u8);
///
/// impl Iterator for Countdown {
/// // ...
/// }
///
/// let a: Vec<_> = my_iterator.take(1).collect();
/// let b: Vec<_> = my_iterator.collect();
/// ```
#[clippy::version = "1.30.0"]
pub COPY_ITERATOR,
pedantic,
"implementing `Iterator` on a `Copy` type"
}
declare_lint_pass!(CopyIterator => [COPY_ITERATOR]);
impl<'tcx> LateLintPass<'tcx> for CopyIterator {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
if let ItemKind::Impl(Impl {
of_trait: Some(trait_ref),
..
}) = item.kind
&& let ty = cx.tcx.type_of(item.owner_id).instantiate_identity()
&& is_copy(cx, ty)
&& let Some(trait_id) = trait_ref.trait_def_id()
&& cx.tcx.is_diagnostic_item(sym::Iterator, trait_id)
{
span_lint_and_note(
cx,
COPY_ITERATOR,
item.span,
"you are implementing `Iterator` on a `Copy` type",
None,
"consider implementing `IntoIterator` instead",
);
}
}
}
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