Rollup merge of rust-lang#89918 - JohnTitor:gats-tests, r=jackh726

Add some GATs related regression tests

Closes rust-lang#88287, closes rust-lang#88405

Author: matthiaskrgr

src/test/ui/generic-associated-types/issue-88287.rs

@@ -0,0 +1,39 @@
+// check-pass
+// edition:2018
+
+#![feature(generic_associated_types)]
+#![feature(type_alias_impl_trait)]
+
+use std::future::Future;
+
+trait SearchableResource<Criteria> {
+    type SearchResult;
+}
+
+trait SearchableResourceExt<Criteria>: SearchableResource<Criteria> {
+    type Future<'f, A: 'f + ?Sized, B: 'f>: Future<Output = Result<Vec<A::SearchResult>, ()>> + 'f
+    where
+        A: SearchableResource<B>;
+
+    fn search<'c>(&'c self, client: &'c ()) -> Self::Future<'c, Self, Criteria>;
+}
+
+type SearchFutureTy<'f, A, B: 'f>
+where
+    A: SearchableResource<B> + ?Sized + 'f,
+= impl Future<Output = Result<Vec<A::SearchResult>, ()>> + 'f;
+impl<T, Criteria> SearchableResourceExt<Criteria> for T
+where
+    T: SearchableResource<Criteria>,
+{
+    type Future<'f, A, B: 'f>
+    where
+        A: SearchableResource<B> + ?Sized + 'f,
+    = SearchFutureTy<'f, A, B>;
+
+    fn search<'c>(&'c self, _client: &'c ()) -> Self::Future<'c, Self, Criteria> {
+        async move { todo!() }
+    }
+}
+
+fn main() {}

src/test/ui/generic-associated-types/issue-88405.rs

@@ -0,0 +1,16 @@
+// check-pass
+
+#![feature(generic_associated_types)]
+
+trait SomeTrait {}
+trait OtherTrait {
+    type Item;
+}
+
+trait ErrorSimpleExample {
+    type AssociatedType: SomeTrait;
+    type GatBounded<T: SomeTrait>;
+    type ErrorMinimal: OtherTrait<Item = Self::GatBounded<Self::AssociatedType>>;
+}
+
+fn main() {}