1 files changed, 14 insertions, 0 deletions
diff --git a/tests/ui/borrowck/borrow-immutable-upvar-mutation-impl-trait.rs b/tests/ui/borrowck/borrow-immutable-upvar-mutation-impl-trait.rs
new file mode 100644
index 00000000000..57198cb95e7
--- /dev/null
+++ b/tests/ui/borrowck/borrow-immutable-upvar-mutation-impl-trait.rs
@@ -0,0 +1,14 @@
+#![feature(unboxed_closures)]
+
+// Tests that we can't assign to or mutably borrow upvars from `Fn`
+// closures (issue #17780)
+
+fn main() {}
+
+fn bar() -> impl Fn() -> usize {
+    let mut x = 0;
+    move || {
+        x += 1; //~ ERROR cannot assign
+        x
+    }
+}