1 files changed, 21 insertions, 0 deletions
diff --git a/tests/ui/traits/next-solver/closure-signature-inference-2.rs b/tests/ui/traits/next-solver/closure-signature-inference-2.rs
new file mode 100644
index 000000000..8fece7ba9
--- /dev/null
+++ b/tests/ui/traits/next-solver/closure-signature-inference-2.rs
@@ -0,0 +1,21 @@
+// compile-flags: -Znext-solver
+// check-pass
+
+fn map<T: Default, U, F: FnOnce(T) -> U>(f: F) {
+    f(T::default());
+}
+
+fn main() {
+    map::<i32, _ /* ?U */, _ /* ?F */>(|x| x.to_string());
+    // PREVIOUSLY when confirming the `map` call, we register:
+    //
+    // (1.) ?F: FnOnce<(i32,)>
+    // (2.) <?F as FnOnce<(i32,)>>::Output projects-to ?U
+    //
+    // While (1.) is ambiguous, (2.) immediately gets processed
+    // and we infer `?U := <?F as FnOnce<(i32,)>>::Output`.
+    //
+    // Thus, the only pending obligation that remains is (1.).
+    // Since it is a trait obligation, we don't use it to deduce
+    // the closure signature, and we fail!
+}