1 files changed, 11 insertions, 0 deletions
diff --git a/tests/ui/lint/unused/unused-supertrait.rs b/tests/ui/lint/unused/unused-supertrait.rs
new file mode 100644
index 000000000..64a8e5204
--- /dev/null
+++ b/tests/ui/lint/unused/unused-supertrait.rs
@@ -0,0 +1,11 @@
+#![deny(unused_must_use)]
+
+fn it() -> impl ExactSizeIterator<Item = ()> {
+    let x: Box<dyn ExactSizeIterator<Item = ()>> = todo!();
+    x
+}
+
+fn main() {
+    it();
+    //~^ ERROR unused implementer of `Iterator` that must be used
+}