ScriptableRenderPipeline/MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Presenters/Nodes/SubgraphIONodePresenter.cs

using System;
using System.Collections.Generic;
using UnityEditor.Experimental.UIElements.GraphView;
using UnityEngine;
using UnityEngine.MaterialGraph;

namespace UnityEditor.MaterialGraph.Drawing
{
    [Serializable]
    class SubgraphIONodeControlPresenter : GraphControlPresenter
    {
        public override void OnGUIHandler()
        {
            base.OnGUIHandler();

            var ioNode = node as SubGraphOutputNode;
            if (ioNode == null)
                return;

            if (GUILayout.Button("Add Slot"))
                ioNode.AddSlot();
            if (GUILayout.Button("Remove Slot"))
                ioNode.RemoveSlot();
        }

        public override float GetHeight()
        {
            return EditorGUIUtility.singleLineHeight * 2 + 3 * EditorGUIUtility.standardVerticalSpacing;
        }
    }

    [Serializable]
    public class SubgraphIONodePresenter : MaterialNodePresenter
    {
        protected override IEnumerable<GraphControlPresenter> GetControlData()
        {
            var instance = CreateInstance<SubgraphIONodeControlPresenter>();
            instance.Initialize(node);
            return new List<GraphControlPresenter> { instance };
        }
    }
}