1 files changed, 73 insertions, 0 deletions
diff --git a/tests/ui/traits/next-solver/generalize/generalize-proj-new-universe-index-1.rs b/tests/ui/traits/next-solver/generalize/generalize-proj-new-universe-index-1.rs
new file mode 100644
index 000000000..4a70bd5f8
--- /dev/null
+++ b/tests/ui/traits/next-solver/generalize/generalize-proj-new-universe-index-1.rs
@@ -0,0 +1,73 @@
+// compile-flags: -Znext-solver
+// check-pass
+
+// A minimization of an ambiguity when using typenum. See
+// https://github.com/rust-lang/trait-system-refactor-initiative/issues/55
+// for more details.
+trait Id {
+    type Assoc: ?Sized;
+}
+impl<T: ?Sized> Id for T {
+    type Assoc = T;
+}
+
+trait WithAssoc<T: ?Sized> {
+    type Assoc: ?Sized;
+}
+
+
+struct Leaf;
+struct Wrapper<U: ?Sized>(U);
+
+impl<U: ?Sized> WithAssoc<U> for Leaf {
+    type Assoc = U;
+}
+
+impl<Ul: ?Sized, Ur: ?Sized> WithAssoc<Wrapper<Ur>> for Wrapper<Ul>
+where
+    Ul: WithAssoc<Ur>,
+{
+    type Assoc = <<Ul as WithAssoc<Ur>>::Assoc as Id>::Assoc;
+}
+
+fn bound<T: ?Sized, U: ?Sized, V: ?Sized>()
+where
+    T: WithAssoc<U, Assoc = V>,
+{
+}
+
+// normalize self type to `Wrapper<Leaf>`
+//   This succeeds, HOWEVER, instantiating the query response previously
+//   incremented the universe index counter.
+// equate impl headers:
+//      <Wrapper<Leaf> as WithAssoc<<Wrapper<Leaf> as Id>::Assoc>>
+//      <Wrapper<?2t> as WithAssoc<Wrapper<?3t>>>
+// ~> AliasRelate(<Wrapper<Leaf> as Id>::Assoc, Equate, Wrapper<?3t>)
+// add where bounds:
+// ~> Leaf: WithAssoc<?3t>
+// equate with assoc type:
+//      ?0t
+//      <Leaf as WithAssoc<?3t>>::Assoc as Id>::Assoc
+// ~> AliasRelate(
+//      <<Leaf as WithAssoc<?3t>>::Assoc as Id>::Assoc,
+//      Equate,
+//      <<Leaf as WithAssoc<?4t>>::Assoc as Id>::Assoc,
+//    )
+//
+// We do not reuse `?3t` during generalization because `?0t` cannot name `?4t` as we created
+// it after incrementing the universe index while normalizing the self type.
+//
+// evaluate_added_goals_and_make_query_response:
+//    AliasRelate(<Wrapper<Leaf> as Id>::Assoc, Equate, Wrapper<?3t>)
+//      YES, constrains ?3t to Leaf
+//    AliasRelate(
+//      <<Leaf as WithAssoc<Leaf>>::Assoc as Id>::Assoc,
+//      Equate,
+//      <<Leaf as WithAssoc<?4t>>::Assoc as Id>::Assoc,
+//    )
+//
+// Normalizing <<Leaf as WithAssoc<?4t>>::Assoc as Id>::Assoc then *correctly*
+// results in ambiguity.
+fn main() {
+    bound::<<Wrapper<Leaf> as Id>::Assoc, <Wrapper<Leaf> as Id>::Assoc, _>()
+}