Assert out if you try to enter a level that's already on the stack.

No current disconnected level supports multiple copies.

1 files changed, 9 insertions, 0 deletions

diff --git a/crawl-ref/source/place.cc b/crawl-ref/source/place.cc
index 9266d724be..7f196f04ec 100644
--- a/crawl-ref/source/place.cc
+++ b/crawl-ref/source/place.cc
@@ -129,3 +129,12 @@ std::vector<level_id> all_dungeon_ids()
     }
     return (out);
 }
+
+bool is_level_on_stack(level_id lev)
+{
+    for (int i = you.level_stack.size() - 1; i >= 0; i--)
+        if (you.level_stack[i].id == lev)
+            return true;
+
+    return false;
+}