--- /dev/null
+// compile-flags: -Z mir-opt-level=2
+// build-pass
+
+#![feature(type_alias_impl_trait)]
+
+use std::marker::PhantomData;
+
+trait MyIndex<T> {
+ type O;
+ fn my_index(self) -> Self::O;
+}
+trait MyFrom<T>: Sized {
+ type Error;
+ fn my_from(value: T) -> Result<Self, Self::Error>;
+}
+
+trait F {}
+impl F for () {}
+type DummyT<T> = impl F;
+fn _dummy_t<T>() -> DummyT<T> {}
+
+struct Phantom1<T>(PhantomData<T>);
+struct Phantom2<T>(PhantomData<T>);
+struct Scope<T>(Phantom2<DummyT<T>>);
+
+impl<T> Scope<T> {
+ fn new() -> Self {
+ unimplemented!()
+ }
+}
+
+impl<T> MyFrom<Phantom2<T>> for Phantom1<T> {
+ type Error = ();
+ fn my_from(_: Phantom2<T>) -> Result<Self, Self::Error> {
+ unimplemented!()
+ }
+}
+
+impl<T: MyFrom<Phantom2<DummyT<U>>>, U> MyIndex<Phantom1<T>> for Scope<U> {
+ type O = T;
+ fn my_index(self) -> Self::O {
+ MyFrom::my_from(self.0).ok().unwrap()
+ }
+}
+
+fn main() {
+ let _pos: Phantom1<DummyT<()>> = Scope::new().my_index();
+}