Fix T89004: Undefined Geometry nodes cause a crash when connected to a Group Output node.

Patch provided by Jacques Lucke.

source/blender/modifiers/intern/MOD_nodes.cc

@@ -1381,6 +1381,10 @@ static void modifyGeometry(ModifierData *md,
     BKE_modifier_set_error(ctx->object, md, "Node group has cycles");
     return;
   }
+  if (tree.has_undefined_nodes_or_sockets()) {
+    BKE_modifier_set_error(ctx->object, md, "Node group has undefined nodes or sockets");
+    return;
+  }
 
   const NodeTreeRef &root_tree_ref = tree.root_context().tree();
   Span<const NodeRef *> input_nodes = root_tree_ref.nodes_by_type("NodeGroupInput");

source/blender/nodes/NOD_derived_node_tree.hh

@@ -170,6 +170,7 @@ class DerivedNodeTree {
   Span<const NodeTreeRef *> used_node_tree_refs() const;
 
   bool has_link_cycles() const;
+  bool has_undefined_nodes_or_sockets() const;
   void foreach_node(FunctionRef<void(DNode)> callback) const;
 
   std::string to_dot() const;

source/blender/nodes/NOD_node_tree_ref.hh

@@ -125,6 +125,7 @@ class SocketRef : NonCopyable, NonMovable {
   bNodeTree *btree() const;
 
   bool is_available() const;
+  bool is_undefined() const;
 
   void *default_value() const;
   template<typename T> T *default_value() const;
@@ -197,6 +198,7 @@ class NodeRef : NonCopyable, NonMovable {
   bool is_group_output_node() const;
   bool is_muted() const;
   bool is_frame() const;
+  bool is_undefined() const;
 
   void *storage() const;
   template<typename T> T *storage() const;
@@ -260,6 +262,7 @@ class NodeTreeRef : NonCopyable, NonMovable {
   Span<const LinkRef *> links() const;
 
   bool has_link_cycles() const;
+  bool has_undefined_nodes_or_sockets() const;
 
   bNodeTree *btree() const;
   StringRefNull name() const;
@@ -417,6 +420,11 @@ inline bool SocketRef::is_available() const
   return (bsocket_->flag & SOCK_UNAVAIL) == 0;
 }
 
+inline bool SocketRef::is_undefined() const
+{
+  return bsocket_->typeinfo == &NodeSocketTypeUndefined;
+}
+
 inline void *SocketRef::default_value() const
 {
   return bsocket_->default_value;
@@ -554,6 +562,11 @@ inline bool NodeRef::is_frame() const
   return bnode_->type == NODE_FRAME;
 }
 
+inline bool NodeRef::is_undefined() const
+{
+  return bnode_->typeinfo == &NodeTypeUndefined;
+}
+
 inline bool NodeRef::is_muted() const
 {
   return (bnode_->flag & NODE_MUTED) != 0;

source/blender/nodes/intern/derived_node_tree.cc

@@ -84,6 +84,16 @@ bool DerivedNodeTree::has_link_cycles() const
   return false;
 }
 
+bool DerivedNodeTree::has_undefined_nodes_or_sockets() const
+{
+  for (const NodeTreeRef *tree_ref : used_node_tree_refs_) {
+    if (tree_ref->has_undefined_nodes_or_sockets()) {
+      return true;
+    }
+  }
+  return false;
+}
+
 /* Calls the given callback on all nodes in the (possibly nested) derived node tree. */
 void DerivedNodeTree::foreach_node(FunctionRef<void(DNode)> callback) const
 {

source/blender/nodes/intern/node_tree_ref.cc

@@ -346,6 +346,21 @@ bool NodeTreeRef::has_link_cycles() const
   return false;
 }
 
+bool NodeTreeRef::has_undefined_nodes_or_sockets() const
+{
+  for (const NodeRef *node : nodes_by_id_) {
+    if (node->is_undefined()) {
+      return true;
+    }
+  }
+  for (const SocketRef *socket : sockets_by_id_) {
+    if (socket->is_undefined()) {
+      return true;
+    }
+  }
+  return true;
+}
+
 std::string NodeTreeRef::to_dot() const
 {
   dot::DirectedGraph digraph;