Auto merge of #11107 - Centri3:error_impl_error, r=Jarcho

New lint [`error_impl_error`]

Closes #11101

changelog: New lint [`error_impl_error`]

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;
+}

tests/ui/error_impl_error.stderr

@@ -0,0 +1,45 @@
+error: exported type named `Error` that implements `Error`
+  --> $DIR/error_impl_error.rs:7:16
+   |
+LL |     pub struct Error;
+   |                ^^^^^
+   |
+note: `Error` was implemented here
+  --> $DIR/error_impl_error.rs:15:5
+   |
+LL |     impl std::error::Error for Error {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: `-D clippy::error-impl-error` implied by `-D warnings`
+
+error: exported type named `Error` that implements `Error`
+  --> $DIR/error_impl_error.rs:20:21
+   |
+LL |     pub(super) enum Error {}
+   |                     ^^^^^
+   |
+note: `Error` was implemented here
+  --> $DIR/error_impl_error.rs:28:5
+   |
+LL |     impl std::error::Error for Error {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: exported type named `Error` that implements `Error`
+  --> $DIR/error_impl_error.rs:32:15
+   |
+LL |     pub union Error {
+   |               ^^^^^
+   |
+note: `Error` was implemented here
+  --> $DIR/error_impl_error.rs:49:5
+   |
+LL |     impl std::error::Error for Error {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: exported type alias named `Error` that implements `Error`
+  --> $DIR/error_impl_error.rs:53:14
+   |
+LL |     pub type Error = std::fmt::Error;
+   |              ^^^^^
+
+error: aborting due to 4 previous errors
+