Little fix: don't create an empty undo/redo command when trying to add a second Input GraphNode

scene/resources/shader_graph.cpp

@@ -142,6 +142,15 @@ ShaderGraph::GraphError ShaderGraph::get_graph_error(ShaderType p_type) const {
 	return shader[p_type].error;
 }
 
+int ShaderGraph::node_count(ShaderType p_which, int p_type)
+{
+	int count=0;
+	for (Map<int,Node>::Element *E=shader[p_which].node_map.front();E;E=E->next())
+		if (E->get().type==p_type)
+			count++;
+	return count;
+}
+
 void ShaderGraph::_bind_methods() {
 
 	ObjectTypeDB::bind_method(_MD("_update_shader"),&ShaderGraph::_update_shader);

scene/resources/shader_graph.h

@@ -365,6 +365,8 @@ public:
 
 	GraphError get_graph_error(ShaderType p_type) const;
 
+	int node_count(ShaderType p_which, int p_type);
+
 	static int get_type_input_count(NodeType p_type);
 	static int get_type_output_count(NodeType p_type);
 	static SlotType get_type_input_type(NodeType p_type,int p_idx);

tools/editor/plugins/shader_graph_editor_plugin.cpp

@@ -2162,6 +2162,9 @@ void ShaderGraphView::_notification(int p_what) {
 
 void ShaderGraphView::add_node(int p_type, const Vector2 &location) {
 
+	if ((p_type==ShaderGraph::NODE_INPUT||p_type==ShaderGraph::NODE_INPUT) && graph->node_count(type, p_type)>0)
+		return;
+
 	List<int> existing;
 	graph->get_node_list(type,&existing);
 	existing.sort();