Handle repetition of associated constant constraint as well (rust-lang#13723)

changelog: [`trait_duplication_in_bounds`]: trigger on duplicate const
associated constraint as well

~~The first commit is part of rust-lang#13722 which must be merged first.~~

Author: y21

clippy_utils/src/hir_utils.rs

@@ -545,7 +545,7 @@ impl HirEqInterExpr<'_, '_, '_> {
     fn eq_path_parameters(&mut self, left: &GenericArgs<'_>, right: &GenericArgs<'_>) -> bool {
         if left.parenthesized == right.parenthesized {
             over(left.args, right.args, |l, r| self.eq_generic_arg(l, r)) // FIXME(flip1995): may not work
-                && over(left.constraints, right.constraints, |l, r| self.eq_assoc_type_binding(l, r))
+                && over(left.constraints, right.constraints, |l, r| self.eq_assoc_eq_constraint(l, r))
         } else {
             false
         }
@@ -602,8 +602,13 @@ impl HirEqInterExpr<'_, '_, '_> {
         }
     }
 
-    fn eq_assoc_type_binding(&mut self, left: &AssocItemConstraint<'_>, right: &AssocItemConstraint<'_>) -> bool {
-        left.ident.name == right.ident.name && both_some_and(left.ty(), right.ty(), |l, r| self.eq_ty(l, r))
+    /// Checks whether two constraints designate the same equality constraint (same name, and same
+    /// type or const).
+    fn eq_assoc_eq_constraint(&mut self, left: &AssocItemConstraint<'_>, right: &AssocItemConstraint<'_>) -> bool {
+        // TODO: this could be extended to check for identical associated item bound constraints
+        left.ident.name == right.ident.name
+            && (both_some_and(left.ty(), right.ty(), |l, r| self.eq_ty(l, r))
+                || both_some_and(left.ct(), right.ct(), |l, r| self.eq_const_arg(l, r)))
     }
 
     fn check_ctxt(&mut self, left: SyntaxContext, right: SyntaxContext) -> bool {

tests/ui/trait_duplication_in_bounds.fixed

@@ -191,6 +191,7 @@ trait AssocConstTrait {
 }
 fn assoc_const_args<T>()
 where
-    T: AssocConstTrait<ASSOC = 0> + AssocConstTrait<ASSOC = 0>,
+    T: AssocConstTrait<ASSOC = 0>,
+    //~^ trait_duplication_in_bounds
 {
 }

tests/ui/trait_duplication_in_bounds.rs

@@ -192,5 +192,6 @@ trait AssocConstTrait {
 fn assoc_const_args<T>()
 where
     T: AssocConstTrait<ASSOC = 0> + AssocConstTrait<ASSOC = 0>,
+    //~^ trait_duplication_in_bounds
 {
 }

tests/ui/trait_duplication_in_bounds.stderr

@@ -70,5 +70,11 @@ error: these where clauses contain repeated elements
 LL |     T: IntoIterator<Item = U::Owned> + IntoIterator<Item = U::Owned>,
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `IntoIterator<Item = U::Owned>`
 
-error: aborting due to 11 previous errors
+error: these where clauses contain repeated elements
+  --> tests/ui/trait_duplication_in_bounds.rs:194:8
+   |
+LL |     T: AssocConstTrait<ASSOC = 0> + AssocConstTrait<ASSOC = 0>,
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `AssocConstTrait<ASSOC = 0>`
+
+error: aborting due to 12 previous errors