From b292a06b3f6e24fd0ab2239f75ea9094327259c9 Mon Sep 17 00:00:00 2001
From: Tobias Gloth <tobias.gloth@3dsystems.com>
Date: Tue, 21 Jul 2026 15:14:14 -0400
Subject: [PATCH] std::set_union expects its inputs to be sorted. (#13928)

---
 src/slic3r/GUI/Tab.cpp | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/slic3r/GUI/Tab.cpp b/src/slic3r/GUI/Tab.cpp
index e2eb67a5fb..6bb47059e2 100644
--- a/src/slic3r/GUI/Tab.cpp
+++ b/src/slic3r/GUI/Tab.cpp
@@ -3299,7 +3299,19 @@ static std::vector<std::string> intersect(std::vector<std::string> const& l, std
 static std::vector<std::string> concat(std::vector<std::string> const& l, std::vector<std::string> const& r)
 {
     std::vector<std::string> t;
-    std::set_union(l.begin(), l.end(), r.begin(), r.end(), std::back_inserter(t));
+    bool l_is_sorted = std::is_sorted(l.begin(), l.end());
+    bool r_is_sorted = std::is_sorted(r.begin(), r.end());
+
+    if (l_is_sorted && r_is_sorted) {
+        std::set_union(l.begin(), l.end(), r.begin(), r.end(), std::back_inserter(t));
+        return t;
+    }
+
+    std::vector<std::string> l_sorted = l;
+    std::vector<std::string> r_sorted = r;
+    std::sort(l_sorted.begin(), l_sorted.end());
+    std::sort(r_sorted.begin(), r_sorted.end());
+    std::set_union(l_sorted.begin(), l_sorted.end(), r_sorted.begin(), r_sorted.end(), std::back_inserter(t));
     return t;
 }