1 files changed, 33 insertions, 0 deletions
diff --git a/src/test/ui/nll/relate_tys/impl-fn-ignore-binder-via-bottom.rs b/src/test/ui/nll/relate_tys/impl-fn-ignore-binder-via-bottom.rs
new file mode 100644
index 000000000..c4db6fc97
--- /dev/null
+++ b/src/test/ui/nll/relate_tys/impl-fn-ignore-binder-via-bottom.rs
@@ -0,0 +1,33 @@
+// Test that the NLL solver cannot find a solution
+// for `exists<R1> { forall<R1> { R2: R1 } }`.
+//
+// In this test, the impl should match `fn(T)` for some `T`,
+// but we ask it to match `for<'a> fn(&'a ())`. Due to argument
+// contravariance, this effectively requires a `T = &'b ()` where
+// `forall<'a> { 'a: 'b }`. Therefore, we get an error.
+//
+// Note the use of `-Zno-leak-check` here. This is presently required in order
+// to skip the leak-check errors.
+//
+// c.f. Issue #57642.
+//
+// compile-flags:-Zno-leak-check
+
+trait Y {
+    type F;
+    fn make_f() -> Self::F;
+}
+
+impl<T> Y for fn(T) {
+    type F = fn(T);
+
+    fn make_f() -> Self::F {
+        |_| {}
+    }
+}
+
+fn main() {
+    let _x = <fn(&())>::make_f();
+    //~^ ERROR implementation of `Y` is not general enough
+    //~| ERROR implementation of `Y` is not general enough
+}