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use clippy_utils::{diagnostics::span_lint, get_parent_node, ty::implements_trait};
use rustc_hir::{def_id::LocalDefId, FnSig, ImplItem, ImplItemKind, Item, ItemKind, Node, TraitItem, TraitItemKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::symbol::sym;
declare_clippy_lint! {
/// ### What it does
/// Detects methods named `iter` or `iter_mut` that do not have a return type that implements `Iterator`.
///
/// ### Why is this bad?
/// Methods named `iter` or `iter_mut` conventionally return an `Iterator`.
///
/// ### Example
/// ```rust
/// // `String` does not implement `Iterator`
/// struct Data {}
/// impl Data {
/// fn iter(&self) -> String {
/// todo!()
/// }
/// }
/// ```
/// Use instead:
/// ```rust
/// use std::str::Chars;
/// struct Data {}
/// impl Data {
/// fn iter(&self) -> Chars<'static> {
/// todo!()
/// }
/// }
/// ```
#[clippy::version = "1.57.0"]
pub ITER_NOT_RETURNING_ITERATOR,
pedantic,
"methods named `iter` or `iter_mut` that do not return an `Iterator`"
}
declare_lint_pass!(IterNotReturningIterator => [ITER_NOT_RETURNING_ITERATOR]);
impl<'tcx> LateLintPass<'tcx> for IterNotReturningIterator {
fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
let name = item.ident.name.as_str();
if matches!(name, "iter" | "iter_mut") {
if let TraitItemKind::Fn(fn_sig, _) = &item.kind {
check_sig(cx, name, fn_sig, item.owner_id.def_id);
}
}
}
fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'tcx>) {
let name = item.ident.name.as_str();
if matches!(name, "iter" | "iter_mut")
&& !matches!(
get_parent_node(cx.tcx, item.hir_id()),
Some(Node::Item(Item { kind: ItemKind::Impl(i), .. })) if i.of_trait.is_some()
)
{
if let ImplItemKind::Fn(fn_sig, _) = &item.kind {
check_sig(cx, name, fn_sig, item.owner_id.def_id);
}
}
}
}
fn check_sig(cx: &LateContext<'_>, name: &str, sig: &FnSig<'_>, fn_id: LocalDefId) {
if sig.decl.implicit_self.has_implicit_self() {
let ret_ty = cx.tcx.erase_late_bound_regions(cx.tcx.fn_sig(fn_id).output());
let ret_ty = cx
.tcx
.try_normalize_erasing_regions(cx.param_env, ret_ty)
.unwrap_or(ret_ty);
if cx
.tcx
.get_diagnostic_item(sym::Iterator)
.map_or(false, |iter_id| !implements_trait(cx, ret_ty, iter_id, &[]))
{
span_lint(
cx,
ITER_NOT_RETURNING_ITERATOR,
sig.span,
&format!("this method is named `{name}` but its return type does not implement `Iterator`"),
);
}
}
}
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