1 files changed, 18 insertions, 0 deletions
diff --git a/tests/ui/impl-trait/impl-subtyper.rs b/tests/ui/impl-trait/impl-subtyper.rs
new file mode 100644
index 000000000..2d99cdd4f
--- /dev/null
+++ b/tests/ui/impl-trait/impl-subtyper.rs
@@ -0,0 +1,18 @@
+// check-pass
+
+#![crate_type = "lib"]
+fn checkpoints() -> impl Iterator {
+    Some(()).iter().flat_map(|_| std::iter::once(()))
+}
+
+fn block_checkpoints() -> impl Iterator {
+    checkpoints()
+}
+
+fn iter_raw() -> impl Iterator {
+    let mut iter = block_checkpoints();
+
+    (0..9).map(move |_| {
+        iter.next();
+    })
+}