--- /dev/null
+// build-pass
+
+trait AssociatedConstant {
+ const DATA: ();
+}
+
+impl<F, T> AssociatedConstant for F
+where
+ F: FnOnce() -> T,
+ T: AssociatedConstant,
+{
+ const DATA: () = T::DATA;
+}
+
+impl AssociatedConstant for () {
+ const DATA: () = ();
+}
+
+fn foo() -> impl AssociatedConstant {
+ ()
+}
+
+fn get_data<T: AssociatedConstant>(_: T) -> &'static () {
+ &T::DATA
+}
+
+fn main() {
+ get_data(foo);
+}
--- /dev/null
+// build-pass
+
+#![feature(type_alias_impl_trait)]
+
+use std::marker::PhantomData;
+
+/* copied Index and TryFrom for convinience (and simplicity) */
+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>;
+}
+
+/* MCVE starts here */
+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();
+}