Add tests for issue #53598 and #57700

src/test/ui/type-alias-impl-trait/issue-53598.rs

@@ -0,0 +1,28 @@
+// ignore-tidy-linelength
+#![feature(type_alias_impl_trait)]
+
+use std::fmt::Debug;
+
+pub trait Foo {
+    type Item: Debug;
+
+    fn foo<T: Debug>(_: T) -> Self::Item;
+}
+
+#[derive(Debug)]
+pub struct S<T>(std::marker::PhantomData<T>);
+
+pub struct S2;
+
+impl Foo for S2 {
+    type Item = impl Debug;
+
+    fn foo<T: Debug>(_: T) -> Self::Item {
+    //~^ Error type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
+        S::<T>(Default::default())
+    }
+}
+
+fn main() {
+    S2::foo(123);
+}

src/test/ui/type-alias-impl-trait/issue-53598.stderr

@@ -0,0 +1,12 @@
+error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
+  --> $DIR/issue-53598.rs:20:42
+   |
+LL |       fn foo<T: Debug>(_: T) -> Self::Item {
+   |  __________________________________________^
+LL | |
+LL | |         S::<T>(Default::default())
+LL | |     }
+   | |_____^
+
+error: aborting due to previous error
+

src/test/ui/type-alias-impl-trait/issue-57700.rs

@@ -0,0 +1,22 @@
+// ignore-tidy-linelength
+#![feature(arbitrary_self_types)]
+#![feature(type_alias_impl_trait)]
+
+use std::ops::Deref;
+
+trait Foo {
+    type Bar: Foo;
+
+    fn foo(self: impl Deref<Target = Self>) -> Self::Bar;
+}
+
+impl<C> Foo for C {
+    type Bar = impl Foo;
+
+    fn foo(self: impl Deref<Target = Self>) -> Self::Bar {
+    //~^ Error type parameter `impl Deref<Target = Self>` is part of concrete type but not used in parameter list for the `impl Trait` type alias
+        self
+    }
+}
+
+fn main() {}

src/test/ui/type-alias-impl-trait/issue-57700.stderr

@@ -0,0 +1,12 @@
+error: type parameter `impl Deref<Target = Self>` is part of concrete type but not used in parameter list for the `impl Trait` type alias
+  --> $DIR/issue-57700.rs:16:58
+   |
+LL |       fn foo(self: impl Deref<Target = Self>) -> Self::Bar {
+   |  __________________________________________________________^
+LL | |
+LL | |         self
+LL | |     }
+   | |_____^
+
+error: aborting due to previous error
+