Add regression test for rust-lang#112515

tests/rustdoc/issue-112515-impl-ty-alias.rs

@@ -0,0 +1,30 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/112515>.
+// It's to ensure that this code doesn't have infinite loop in rustdoc when
+// trying to retrive type alias implementations.
+
+// ignore-tidy-linelength
+
+pub type Boom = S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<S<u64, u8>, ()>, ()>, ()>, u8>, ()>, u8>, ()>, u8>, u8>, ()>, ()>, ()>, u8>, u8>, u8>, ()>, ()>, u8>, ()>, ()>, ()>, u8>, u8>, ()>, ()>, ()>, ()>, ()>, u8>, ()>, ()>, u8>, ()>, ()>, ()>, u8>, ()>, ()>, u8>, u8>, u8>, u8>, ()>, u8>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>, ()>;
+pub struct S<T, U>(T, U);
+
+pub trait A {}
+
+pub trait B<T> {
+    type P;
+}
+
+impl A for u64 {}
+
+impl<T, U> A for S<T, U> {}
+
+impl<T> B<u8> for S<T, ()>
+where
+    T: B<u8>,
+    <T as B<u8>>::P: A,
+{
+    type P = ();
+}
+
+impl<T: A, U, V> B<T> for S<U, V> {
+    type P = ();
+}