Support linting self trait bounds for repitition.

Author: Allen Hsu

clippy_lints/src/trait_bounds.rs

@@ -120,6 +120,18 @@ impl<'tcx> LateLintPass<'tcx> for TraitBounds {
         check_bounds_or_where_duplication(cx, gen);
     }
 
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
+        // special handling for self trait bounds as these are not considered generics
+        // ie. trait Foo: Display {}
+        if let Item {
+            kind: ItemKind::Trait(_, _, _, bounds, ..),
+            ..
+        } = item
+        {
+            rollup_traits(cx, bounds, "these bounds contain repeated elements");
+        }
+    }
+
     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
         let mut self_bounds_map = FxHashMap::default();
 

tests/ui/repeated_where_clause_or_trait_bound.fixed

@@ -37,7 +37,7 @@ trait GoodSelfWhereClause {
         Self: Clone + Copy;
 }
 
-trait BadSelfTraitBound: Clone + Clone + Clone {
+trait BadSelfTraitBound: Clone {
     fn f();
 }
 

tests/ui/repeated_where_clause_or_trait_bound.stderr

@@ -16,6 +16,12 @@ error: these where clauses contain repeated elements
 LL |     T: Clone + Clone + Clone + Copy,
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Clone + Copy`
 
+error: these bounds contain repeated elements
+  --> $DIR/repeated_where_clause_or_trait_bound.rs:40:26
+   |
+LL | trait BadSelfTraitBound: Clone + Clone + Clone {
+   |                          ^^^^^^^^^^^^^^^^^^^^^ help: try: `Clone`
+
 error: these where clauses contain repeated elements
   --> $DIR/repeated_where_clause_or_trait_bound.rs:47:15
    |
@@ -40,5 +46,5 @@ error: these bounds contain repeated elements
 LL | fn bad_generic<T: GenericTrait<u64> + GenericTrait<u32> + GenericTrait<u64>>(arg0: T) {
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `GenericTrait<u32> + GenericTrait<u64>`
 
-error: aborting due to 6 previous errors
+error: aborting due to 7 previous errors