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use clippy_utils::diagnostics::{span_lint, span_lint_hir_and_then};
use clippy_utils::path_res;
use clippy_utils::ty::implements_trait;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::{Item, ItemKind};
use rustc_hir_analysis::hir_ty_to_ty;
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::Visibility;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for types named `Error` that implement `Error`.
///
/// ### Why is this bad?
/// It can become confusing when a codebase has 20 types all named `Error`, requiring either
/// aliasing them in the `use` statement or qualifying them like `my_module::Error`. This
/// hinders comprehension, as it requires you to memorize every variation of importing `Error`
/// used across a codebase.
///
/// ### Example
/// ```rust,ignore
/// #[derive(Debug)]
/// pub enum Error { ... }
///
/// impl std::fmt::Display for Error { ... }
///
/// impl std::error::Error for Error { ... }
/// ```
#[clippy::version = "1.72.0"]
pub ERROR_IMPL_ERROR,
restriction,
"exported types named `Error` that implement `Error`"
}
declare_lint_pass!(ErrorImplError => [ERROR_IMPL_ERROR]);
impl<'tcx> LateLintPass<'tcx> for ErrorImplError {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
let Some(error_def_id) = cx.tcx.get_diagnostic_item(sym::Error) else {
return;
};
match item.kind {
ItemKind::TyAlias(ty, _) if implements_trait(cx, hir_ty_to_ty(cx.tcx, ty), error_def_id, &[])
&& item.ident.name == sym::Error
&& is_visible_outside_module(cx, item.owner_id.def_id) =>
{
span_lint(
cx,
ERROR_IMPL_ERROR,
item.ident.span,
"exported type alias named `Error` that implements `Error`",
);
},
ItemKind::Impl(imp) if let Some(trait_def_id) = imp.of_trait.and_then(|t| t.trait_def_id())
&& error_def_id == trait_def_id
&& let Some(def_id) = path_res(cx, imp.self_ty).opt_def_id().and_then(DefId::as_local)
&& let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id)
&& let Some(ident) = cx.tcx.opt_item_ident(def_id.to_def_id())
&& ident.name == sym::Error
&& is_visible_outside_module(cx, def_id) =>
{
span_lint_hir_and_then(
cx,
ERROR_IMPL_ERROR,
hir_id,
ident.span,
"exported type named `Error` that implements `Error`",
|diag| {
diag.span_note(item.span, "`Error` was implemented here");
}
);
}
_ => {},
}
}
}
/// Do not lint private `Error`s, i.e., ones without any `pub` (minus `pub(self)` of course) and
/// which aren't reexported
fn is_visible_outside_module(cx: &LateContext<'_>, def_id: LocalDefId) -> bool {
!matches!(
cx.tcx.visibility(def_id),
Visibility::Restricted(mod_def_id) if cx.tcx.parent_module_from_def_id(def_id).to_def_id() == mod_def_id
)
}
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