1 files changed, 90 insertions, 0 deletions
diff --git a/tests/ui/error_impl_error.rs b/tests/ui/error_impl_error.rs
new file mode 100644
index 00000000000..40ce4181bf3
--- /dev/null
+++ b/tests/ui/error_impl_error.rs
@@ -0,0 +1,90 @@
+#![allow(unused)]
+#![warn(clippy::error_impl_error)]
+#![no_main]
+
+pub mod a {
+    #[derive(Debug)]
+    pub struct Error;
+
+    impl std::fmt::Display for Error {
+        fn fmt(&self, _: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            todo!()
+        }
+    }
+
+    impl std::error::Error for Error {}
+}
+
+mod b {
+    #[derive(Debug)]
+    pub(super) enum Error {}
+
+    impl std::fmt::Display for Error {
+        fn fmt(&self, _: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            todo!()
+        }
+    }
+
+    impl std::error::Error for Error {}
+}
+
+pub mod c {
+    pub union Error {
+        a: u32,
+        b: u32,
+    }
+
+    impl std::fmt::Debug for Error {
+        fn fmt(&self, _: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            todo!()
+        }
+    }
+
+    impl std::fmt::Display for Error {
+        fn fmt(&self, _: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            todo!()
+        }
+    }
+
+    impl std::error::Error for Error {}
+}
+
+pub mod d {
+    pub type Error = std::fmt::Error;
+}
+
+mod e {
+    #[derive(Debug)]
+    pub(super) struct MyError;
+
+    impl std::fmt::Display for MyError {
+        fn fmt(&self, _: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            todo!()
+        }
+    }
+
+    impl std::error::Error for MyError {}
+}
+
+pub mod f {
+    pub type MyError = std::fmt::Error;
+}
+
+// Do not lint module-private types
+
+mod g {
+    #[derive(Debug)]
+    enum Error {}
+
+    impl std::fmt::Display for Error {
+        fn fmt(&self, _: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            todo!()
+        }
+    }
+
+    impl std::error::Error for Error {}
+}
+
+mod h {
+    type Error = std::fmt::Error;
+}