Handle rustc_on_unimplemented in duplicated_attributes

Author: Noratrieb

clippy_lints/src/attrs/duplicated_attributes.rs

@@ -36,9 +36,10 @@ fn check_duplicated_attr(
     }
     let Some(ident) = attr.ident() else { return };
     let name = ident.name;
-    if name == sym::doc || name == sym::cfg_attr {
+    if name == sym::doc || name == sym::cfg_attr || name == sym::rustc_on_unimplemented {
         // FIXME: Would be nice to handle `cfg_attr` as well. Only problem is to check that cfg
         // conditions are the same.
+        // `#[rustc_on_unimplemented]` contains duplicated subattributes, that's expected.
         return;
     }
     if let Some(direct_parent) = parent.last()

tests/ui/duplicated_attributes.rs

@@ -1,5 +1,5 @@
 //@aux-build:proc_macro_attr.rs
-
+#![feature(rustc_attrs)]
 #![warn(clippy::duplicated_attributes)]
 #![cfg(any(unix, windows))]
 #![allow(dead_code)]
@@ -20,6 +20,10 @@ fn foo() {}
 #[cfg(unix)] // cfgs are not handled
 fn bar() {}
 
+// No warning:
+#[rustc_on_unimplemented(on(_Self = "&str", label = "`a"), on(_Self = "alloc::string::String", label = "a"))]
+trait Abc {}
+
 #[proc_macro_attr::duplicated_attr()] // Should not warn!
 fn babar() {}
 

tests/ui/duplicated_attributes.stderr

@@ -1,35 +1,35 @@
 error: duplicated attribute
-  --> tests/ui/duplicated_attributes.rs:6:10
+  --> tests/ui/duplicated_attributes.rs:7:10
    |
 LL | #![allow(dead_code)]
    |          ^^^^^^^^^
    |
 note: first defined here
-  --> tests/ui/duplicated_attributes.rs:5:10
+  --> tests/ui/duplicated_attributes.rs:6:10
    |
 LL | #![allow(dead_code)]
    |          ^^^^^^^^^
 help: remove this attribute
-  --> tests/ui/duplicated_attributes.rs:6:10
+  --> tests/ui/duplicated_attributes.rs:7:10
    |
 LL | #![allow(dead_code)]
    |          ^^^^^^^^^
    = note: `-D clippy::duplicated-attributes` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::duplicated_attributes)]`
 
 error: duplicated attribute
-  --> tests/ui/duplicated_attributes.rs:14:9
+  --> tests/ui/duplicated_attributes.rs:15:9
    |
 LL | #[allow(dead_code)]
    |         ^^^^^^^^^
    |
 note: first defined here
-  --> tests/ui/duplicated_attributes.rs:13:9
+  --> tests/ui/duplicated_attributes.rs:14:9
    |
 LL | #[allow(dead_code)]
    |         ^^^^^^^^^
 help: remove this attribute
-  --> tests/ui/duplicated_attributes.rs:14:9
+  --> tests/ui/duplicated_attributes.rs:15:9
    |
 LL | #[allow(dead_code)]
    |         ^^^^^^^^^