From d52744e9fc502fcc5ac6fa2003505d9ca0fcb6a4 Mon Sep 17 00:00:00 2001
From: Marijn Schouten <mhkbst@gmail.com>
Date: Thu, 2 Oct 2025 07:12:08 +0000
Subject: [PATCH] iter repeat: panic on last

---
 library/core/src/iter/sources/repeat.rs | 3 ++-
 library/coretests/tests/iter/sources.rs | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/library/core/src/iter/sources/repeat.rs b/library/core/src/iter/sources/repeat.rs
index 4bcd5b16aea6a..ac218e9b617a3 100644
--- a/library/core/src/iter/sources/repeat.rs
+++ b/library/core/src/iter/sources/repeat.rs
@@ -97,8 +97,9 @@ impl<A: Clone> Iterator for Repeat<A> {
         Some(self.element.clone())
     }
 
+    #[track_caller]
     fn last(self) -> Option<A> {
-        Some(self.element)
+        panic!("iterator is infinite");
     }
 
     #[track_caller]
diff --git a/library/coretests/tests/iter/sources.rs b/library/coretests/tests/iter/sources.rs
index 5a391cb67751d..420f3088e6ee4 100644
--- a/library/coretests/tests/iter/sources.rs
+++ b/library/coretests/tests/iter/sources.rs
@@ -37,6 +37,7 @@ fn test_repeat_count() {
 }
 
 #[test]
+#[should_panic = "iterator is infinite"]
 fn test_repeat_last() {
     assert_eq!(repeat(42).last(), Some(42));
 }