1 files changed, 87 insertions, 0 deletions
diff --git a/clippy_lints/src/error_impl_error.rs b/clippy_lints/src/error_impl_error.rs
new file mode 100644
index 00000000000..379af9b2234
--- /dev/null
+++ b/clippy_lints/src/error_impl_error.rs
@@ -0,0 +1,87 @@
+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
+    )
+}