From 4176a2a551eba3d81ccdc6ea2a923277955ce7f6 Mon Sep 17 00:00:00 2001
From: Andreas Fabri <andreas.fabri@geometryfactory.com>
Date: Fri, 26 Sep 2025 12:09:13 +0100
Subject: [PATCH] Surface_mesh: Fix collect_garbage in case mesh is not valid

---
 .../include/CGAL/Surface_mesh/Surface_mesh.h  | 11 +++++---
 Surface_mesh/test/Surface_mesh/issue_9086.cpp | 26 +++++++++++++++++++
 2 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 Surface_mesh/test/Surface_mesh/issue_9086.cpp

diff --git a/Surface_mesh/include/CGAL/Surface_mesh/Surface_mesh.h b/Surface_mesh/include/CGAL/Surface_mesh/Surface_mesh.h
index d38d7ffeabd..ad339ef5ca7 100644
--- a/Surface_mesh/include/CGAL/Surface_mesh/Surface_mesh.h
+++ b/Surface_mesh/include/CGAL/Surface_mesh/Surface_mesh.h
@@ -2680,8 +2680,12 @@ collect_garbage(Visitor &visitor)
     for (i=0; i<nH; ++i)
     {
         h = Halfedge_index(i);
-        set_target(h, vmap[target(h)]);
-        set_next(h, hmap[next(h)]);
+        if(target(h) != null_vertex()){
+          set_target(h, vmap[target(h)]);
+        }
+        if(next(h) != null_halfedge()){
+          set_next(h, hmap[next(h)]);
+        }
         if (!is_border(h))
             set_face(h, fmap[face(h)]);
     }
@@ -2691,7 +2695,8 @@ collect_garbage(Visitor &visitor)
     for (i=0; i<nF; ++i)
     {
         f = Face_index(i);
-        set_halfedge(f, hmap[halfedge(f)]);
+        if( halfedge(f) != null_halfedge())
+          set_halfedge(f, hmap[halfedge(f)]);
     }
 
     //apply visitor before invalidating the maps
diff --git a/Surface_mesh/test/Surface_mesh/issue_9086.cpp b/Surface_mesh/test/Surface_mesh/issue_9086.cpp
new file mode 100644
index 00000000000..ef3ee449771
--- /dev/null
+++ b/Surface_mesh/test/Surface_mesh/issue_9086.cpp
@@ -0,0 +1,26 @@
+#include <CGAL/Surface_mesh/Surface_mesh.h>
+#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
+
+
+typedef CGAL::Exact_predicates_inexact_constructions_kernel   Epick;
+
+int main()
+{
+CGAL::Surface_mesh<CGAL::Epick::Point_3> mesh;
+  auto f0 = mesh.add_face();
+  auto f1 = mesh.add_face();  // If this line is commented out, it will not crash.
+  mesh.remove_face(f0);
+
+  auto v0 = mesh.add_vertex();
+  auto v1 = mesh.add_vertex();  // If this line is commented out, it will not crash.
+  mesh.remove_vertex(v0);
+
+  auto e0 = mesh.add_edge();
+  auto e1 = mesh.add_edge();  // If this line is commented out, it will not crash.
+  mesh.remove_edge(edge(e0,mesh));
+
+
+  mesh.collect_garbage();
+
+  return 0;
+}
\ No newline at end of file