Do not lint use_self on type parameters

Author: camsteffen

clippy_lints/src/use_self.rs

@@ -386,7 +386,7 @@ fn should_lint_ty(hir_ty: &hir::Ty<'_>, ty: Ty<'_>, self_ty: Ty<'_>) -> bool {
         if same_type_and_consts(ty, self_ty);
         if let TyKind::Path(QPath::Resolved(_, path)) = hir_ty.kind;
         then {
-            !matches!(path.res, def::Res::SelfTy(..))
+            !matches!(path.res, Res::SelfTy(..) | Res::Def(DefKind::TyParam, _))
         } else {
             false
         }

tests/ui/use_self.fixed

@@ -492,3 +492,26 @@ mod issue7206 {
         }
     }
 }
+
+mod self_is_ty_param {
+    trait Trait {
+        type Type;
+        type Hi;
+
+        fn test();
+    }
+
+    impl<I> Trait for I
+        where
+            I: Iterator,
+            I::Item: Trait, // changing this to Self would require <Self as Iterator>
+    {
+        type Type = I;
+        type Hi = I::Item;
+
+        fn test() {
+            let _: I::Item;
+            let _: I; // this could lint, but is questionable
+        }
+    }
+}

tests/ui/use_self.rs

@@ -279,7 +279,7 @@ mod generics {
     impl<T> Foo<T> {
         // `Self` is applicable here
         fn foo(value: T) -> Foo<T> {
-            Foo { value }
+            Foo::<T> { value }
         }
 
         // `Cannot` use `Self` as a return type as the generic types are different
@@ -492,3 +492,26 @@ mod issue7206 {
         }
     }
 }
+
+mod self_is_ty_param {
+    trait Trait {
+        type Type;
+        type Hi;
+
+        fn test();
+    }
+
+    impl<I> Trait for I
+        where
+            I: Iterator,
+            I::Item: Trait, // changing this to Self would require <Self as Iterator>
+    {
+        type Type = I;
+        type Hi = I::Item;
+
+        fn test() {
+            let _: I::Item;
+            let _: I; // this could lint, but is questionable
+        }
+    }
+}

tests/ui/use_self.stderr

@@ -153,8 +153,8 @@ LL |         fn foo(value: T) -> Foo<T> {
 error: unnecessary structure name repetition
   --> $DIR/use_self.rs:282:13
    |
-LL |             Foo { value }
-   |             ^^^ help: use the applicable keyword: `Self`
+LL |             Foo::<T> { value }
+   |             ^^^^^^^^ help: use the applicable keyword: `Self`
 
 error: unnecessary structure name repetition
   --> $DIR/use_self.rs:454:13