From 1ed0ea459dc5456ebcedb798cc88671014cf0f68 Mon Sep 17 00:00:00 2001
From: The 8472 <git@infinite-source.de>
Date: Sat, 4 Jan 2025 19:44:49 +0100
Subject: [PATCH] add regression test for unsound Flatten/FlatMap
 specialization

---
 library/alloc/tests/vec.rs | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/library/alloc/tests/vec.rs b/library/alloc/tests/vec.rs
index 474ea7fe56b8c..2e654d3d1ff1e 100644
--- a/library/alloc/tests/vec.rs
+++ b/library/alloc/tests/vec.rs
@@ -1337,6 +1337,20 @@ fn test_collect_after_iterator_clone() {
     assert_eq!(v, [1, 1, 1, 1, 1]);
     assert!(v.len() <= v.capacity());
 }
+
+// regression test for #135103, similar to the one above Flatten/FlatMap had an unsound InPlaceIterable
+// implementation.
+#[test]
+fn test_flatten_clone() {
+    const S: String = String::new();
+
+    let v = vec![[S, "Hello World!".into()], [S, S]];
+    let mut i = v.into_iter().flatten();
+    let _ = i.next();
+    let result: Vec<String> = i.clone().collect();
+    assert_eq!(result, ["Hello World!", "", ""]);
+}
+
 #[test]
 fn test_cow_from() {
     let borrowed: &[_] = &["borrowed", "(slice)"];