From 2fbb793f4e32cbf866da8d832c87c663fa32e67b Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Tue, 16 Sep 2025 23:05:09 +0800
Subject: [PATCH] fixes #25173; SinglyLinkedList.remove broken /
 AssertionDefect (#25175)

fixes #25173

(cherry picked from commit 51a9ada0436958ba3c3423802dd0d26dec88e18b)
---
 lib/pure/collections/lists.nim |  2 ++
 tests/stdlib/tlists.nim        | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/lib/pure/collections/lists.nim b/lib/pure/collections/lists.nim
index 0e52d5ca00..81983269ef 100644
--- a/lib/pure/collections/lists.nim
+++ b/lib/pure/collections/lists.nim
@@ -710,6 +710,8 @@ proc remove*[T](L: var SinglyLinkedList[T], n: SinglyLinkedNode[T]): bool {.disc
     L.head = n.next
     if L.tail.next == n:
       L.tail.next = L.head # restore cycle
+    if L.tail == n:
+      L.tail = nil # reset tail if we removed the last node
   else:
     var prev = L.head
     while prev.next != n and prev.next != nil:
diff --git a/tests/stdlib/tlists.nim b/tests/stdlib/tlists.nim
index 5993278c79..9339a6df05 100644
--- a/tests/stdlib/tlists.nim
+++ b/tests/stdlib/tlists.nim
@@ -273,5 +273,17 @@ template main =
     list.add(n4)
     doAssert list.toSeq == @["sonic", "the", "hedgehog"]
 
+
+  block:
+    var list = initSinglyLinkedList[int]()
+
+    list.add(4)
+    list.remove(list.head)
+
+    list.add(5)
+    list.remove(list.head)
+
+    list.add(6)
+
 static: main()
 main()