Add a root Node3D automatically if absent when adding preview sun and sky

This makes for a smoother prototyping process compared to displaying
an error message.

editor/plugins/node_3d_editor_plugin.cpp

@@ -6223,8 +6223,9 @@ void Node3DEditor::_add_sun_to_scene() {
 
 	Node *base = get_tree()->get_edited_scene_root();
 	if (!base) {
-		EditorNode::get_singleton()->show_warning(TTR("A root node is needed for this operation"));
-		return;
+		// Create a root node so we can add child nodes to it.
+		EditorNode::get_singleton()->get_scene_tree_dock()->add_root_node(memnew(Node3D));
+		base = get_tree()->get_edited_scene_root();
 	}
 	ERR_FAIL_COND(!base);
 	Node *new_sun = preview_sun->duplicate();
@@ -6241,8 +6242,9 @@ void Node3DEditor::_add_environment_to_scene() {
 
 	Node *base = get_tree()->get_edited_scene_root();
 	if (!base) {
-		EditorNode::get_singleton()->show_warning(TTR("A root node is needed for this operation"));
-		return;
+		// Create a root node so we can add child nodes to it.
+		EditorNode::get_singleton()->get_scene_tree_dock()->add_root_node(memnew(Node3D));
+		base = get_tree()->get_edited_scene_root();
 	}
 	ERR_FAIL_COND(!base);
 

editor/scene_tree_dock.cpp

@@ -1134,12 +1134,7 @@ void SceneTreeDock::_tool_selected(int p_tool, bool p_confirm_override) {
 				}
 			}
 
-			editor_data->get_undo_redo().create_action(TTR("New Scene Root"));
-			editor_data->get_undo_redo().add_do_method(editor, "set_edited_scene", new_node);
-			editor_data->get_undo_redo().add_do_method(scene_tree, "update_tree");
-			editor_data->get_undo_redo().add_do_reference(new_node);
-			editor_data->get_undo_redo().add_undo_method(editor, "set_edited_scene", (Object *)nullptr);
-			editor_data->get_undo_redo().commit_action();
+			add_root_node(new_node);
 
 			editor->edit_node(new_node);
 			editor_selection->clear();
@@ -1162,6 +1157,15 @@ void SceneTreeDock::_tool_selected(int p_tool, bool p_confirm_override) {
 	}
 }
 
+void SceneTreeDock::add_root_node(Node *p_node) {
+	editor_data->get_undo_redo().create_action(TTR("New Scene Root"));
+	editor_data->get_undo_redo().add_do_method(editor, "set_edited_scene", p_node);
+	editor_data->get_undo_redo().add_do_method(scene_tree, "update_tree");
+	editor_data->get_undo_redo().add_do_reference(p_node);
+	editor_data->get_undo_redo().add_undo_method(editor, "set_edited_scene", (Object *)nullptr);
+	editor_data->get_undo_redo().commit_action();
+}
+
 void SceneTreeDock::_node_collapsed(Object *p_obj) {
 	TreeItem *ti = Object::cast_to<TreeItem>(p_obj);
 	if (!ti) {

editor/scene_tree_dock.h

@@ -261,6 +261,7 @@ public:
 	void _focus_node();
 
 	void import_subscene();
+	void add_root_node(Node *p_node);
 	void set_edited_scene(Node *p_scene);
 	void instantiate(const String &p_file);
 	void instantiate_scenes(const Vector<String> &p_files, Node *p_parent = nullptr);