Fix crash when opening graph resource with a missing function reference.

Also try to not interpret the graph as "new" in the editor if it actually
failed, so don't load default preset.

Godot reports this to the user with a dialog when opening scenes, or when
opening resources for the first time, but not always: if you open a scene
with the missing dependency, it still loads the scene, and if you open
the graph after that, it opens without showing you the dialog again....
so we have to handle the mess ourselves in such cases.

editor/graph/voxel_graph_editor.cpp

@@ -278,9 +278,9 @@ void VoxelGraphEditor::set_generator(Ref<VoxelGeneratorGraph> generator) {
  Ref<VoxelGraphFunction> graph = generator->get_main_function();
 
  // Load a default preset when creating new graphs.
- // TODO Downside is, an empty graph cannot be seen.
- // But Godot doesnt let us know if the resource has been created from the inspector or not
- if (graph->get_nodes_count() == 0) {
+ // Downside is, an empty graph cannot be seen. But Godot doesnt let us know if the resource has been created
+ // from the inspector or not, so we had to introduce a special boolean...
+ if (graph->get_nodes_count() == 0 && graph->can_load_default_graph()) {
  _generator->load_plane_preset();
  }
 

generators/graph/voxel_graph_function.cpp

@@ -17,6 +17,9 @@ const char *VoxelGraphFunction::SIGNAL_NODE_NAME_CHANGED = "node_name_changed";
 void VoxelGraphFunction::clear() {
  unregister_subresources();
  _graph.clear();
+#ifdef TOOLS_ENABLED
+ _can_load_default_graph = false;
+#endif
 }
 
 ProgramGraph::Node *create_node_internal(ProgramGraph &graph, VoxelGraphFunction::NodeTypeID type_id, Vector2 position,
@@ -843,7 +846,7 @@ static bool var_to_id(Variant v, uint32_t &out_id, uint32_t min = 0) {
  return true;
 }
 
-static bool load_graph_from_variant_data(ProgramGraph &graph, Dictionary data) {
+static bool load_graph_from_variant_data(ProgramGraph &graph, Dictionary data, String resource_path) {
  Dictionary nodes_data = data["nodes"];
  Array connections_data = data["connections"];
  const NodeTypeDB &type_db = NodeTypeDB::get_singleton();
@@ -880,9 +883,14 @@ static bool load_graph_from_variant_data(ProgramGraph &graph, Dictionary data) {
  const String func_key = ntype.params[0].name;
  Ref<VoxelGraphFunction> function = node_data[func_key];
  if (function.is_null()) {
- ERR_PRINT(String("Unable to load external function referenced in {0}")
- .format(varray(VoxelGraphFunction::get_class_static())));
- continue;
+ ERR_PRINT(String("Unable to load external function referenced in {0} {}")
+ .format(varray(VoxelGraphFunction::get_class_static(), resource_path)));
+ // continue;
+ // Cancel, connections to that node cause crashes if we carry on loading. Perhaps we could try using a
+ // placeholder in the future so the graph can still be opened?
+ // We should also report the missing dependencies in the editor somehow, because Godot doesn't do it for
+ // us if the resource is opened in some cases
+ return false;
  }
  setup_function(*node, function);
  // TODO Create a placeholder node in case a function isn't found to avoid loss of data?
@@ -970,7 +978,7 @@ static bool load_graph_from_variant_data(ProgramGraph &graph, Dictionary data) {
 bool VoxelGraphFunction::load_graph_from_variant_data(Dictionary data) {
  clear();
 
- if (zylann::voxel::pg::load_graph_from_variant_data(_graph, data)) {
+ if (zylann::voxel::pg::load_graph_from_variant_data(_graph, data, get_path())) {
  register_subresources();
  return true;
 

generators/graph/voxel_graph_function.h

@@ -218,6 +218,12 @@ class VoxelGraphFunction : public Resource {
 
  void update_function_nodes(std::vector<ProgramGraph::Connection> *removed_connections);
 
+#ifdef TOOLS_ENABLED
+ bool can_load_default_graph() const {
+ return _can_load_default_graph;
+ }
+#endif
+
 private:
  void register_subresource(Resource &resource);
  void unregister_subresource(Resource &resource);
@@ -244,6 +250,13 @@ class VoxelGraphFunction : public Resource {
  ProgramGraph _graph;
  std::vector<Port> _inputs;
  std::vector<Port> _outputs;
+#ifdef TOOLS_ENABLED
+ // Godot doesn't make a difference between a resource newly created in the inspector and an empty one or one created
+ // from script... It is necessary to know that in order to load a "hello world" graph in the editor when creating a
+ // new graph. True by default after being created, but will become false if cleared (which means it's not a brand
+ // new instance).
+ bool _can_load_default_graph = true;
+#endif
 };
 
 ProgramGraph::Node *create_node_internal(ProgramGraph &graph, VoxelGraphFunction::NodeTypeID type_id, Vector2 position,