Add a test for TAIT used with impl/dyn Trait inside RPIT

src/test/ui/type-alias-impl-trait/issue-101750.rs

@@ -0,0 +1,37 @@
+#![feature(type_alias_impl_trait)]
+
+// check-pass
+
+trait Trait {}
+
+type TAIT = impl Trait;
+
+struct Concrete;
+impl Trait for Concrete {}
+
+fn tait() -> TAIT {
+    Concrete
+}
+
+trait OuterTrait {
+    type Item;
+}
+struct Dummy<T> {
+    t: T,
+}
+impl<T> OuterTrait for Dummy<T> {
+    type Item = T;
+}
+
+fn tait_and_impl_trait() -> impl OuterTrait<Item = (TAIT, impl Trait)> {
+    Dummy {
+        t: (tait(), Concrete),
+    }
+}
+
+fn tait_and_dyn_trait() -> impl OuterTrait<Item = (TAIT, Box<dyn Trait>)> {
+    let b: Box<dyn Trait> = Box::new(Concrete);
+    Dummy { t: (tait(), b) }
+}
+
+fn main() {}