extra test for bug i found

src/test/ui/const-generics/generic_arg_infer/dont-use-defaults.rs

@@ -0,0 +1,15 @@
+// run-pass
+#![feature(generic_arg_infer)]
+
+// test that we dont use defaults to aide in type inference
+
+struct Foo<const N: usize = 2>;
+impl<const N: usize> Foo<N> {
+    fn make_arr() -> [(); N] {
+        [(); N]
+    }
+}
+
+fn main() {
+    let [(), (), ()] = Foo::<_>::make_arr();
+}