Make reference names editable throught text field and add reference name sanitation

com.unity.shadergraph/Editor/Data/Graphs/AbstractMaterialGraph.cs

         public string SanitizePropertyReferenceName(string referenceName)
         {
             referenceName = referenceName.Trim();
+            referenceName = Regex.Replace(referenceName, @"\s+", "_");
+            referenceName = Regex.Replace(referenceName, @"^[^A-Za-z_]", "_");
+            referenceName = Regex.Replace(referenceName, @"[^A-Za-z_0-9]", "_");
+
+            // Similat to teh property names, duplicate names are handled by appending `_n`
+            // to the end of the referene name.
+            if (m_Properties.Any(p => p.referenceName == referenceName && p.guid != guid))
+            {
+                // Strip out the "_n" part of the name.
+                var baseRegex = new Regex(@"^(.*)_(\d+)$");
+                var baseMatch = baseRegex.Match(referenceName);
+                if (baseMatch.Success)
+                    referenceName = baseMatch.Groups[1].Value;
+
+                var regex = new Regex(@"^" + Regex.Escape(referenceName) + @"_(\d+)$");
+                var existingDuplicateNumbers = m_Properties.Where(p => p.guid != guid).Select(p => regex.Match(p.referenceName)).Where(m => m.Success).Select(m => int.Parse(m.Groups[1].Value)).Where(n => n > 0).Distinct().ToList();
+
+                var duplicateNumber = 1;
+                existingDuplicateNumbers.Sort();
+                if (existingDuplicateNumbers.Any() && existingDuplicateNumbers.First() == 1)
+                {
+                    duplicateNumber = existingDuplicateNumbers.Last() + 1;
+                    for (var i = 1; i < existingDuplicateNumbers.Count; i++)
+                    {
+                        if (existingDuplicateNumbers[i - 1] != existingDuplicateNumbers[i] - 1)
+                        {
+                            duplicateNumber = existingDuplicateNumbers[i - 1] + 1;
+                            break;
+                        }
+                    }
+                }
+
+                referenceName = string.Format("{0}_{1}", referenceName, duplicateNumber);
+            }
+
             return referenceName;
         }
 

com.unity.shadergraph/Editor/Data/Graphs/AbstractShaderProperty.cs

         private string m_Name;
 
         [SerializeField]
-        private string m_CustomReferenceName;
-
-        [SerializeField]
-
-        [SerializeField]
-        private bool m_UseCustomReferenceName = false;
 
         [SerializeField]
         private SerializableGuid m_Guid = new SerializableGuid();
             set { m_Name = value; }
         }
 
-        public string customReferenceName
-        {
-            get
-            {
-                if (string.IsNullOrEmpty(m_CustomReferenceName))
-                    m_CustomReferenceName = "_" + displayName;
-                return m_CustomReferenceName;
-            }
-            set { m_CustomReferenceName = value; }
-        }
-
         string m_DefaultReferenceName;
 
         public string referenceName
-                if (useCustomReferenceName)
-                {
-                    return customReferenceName;
-                }
-
                 if (string.IsNullOrEmpty(overrideReferenceName))
                 {
                     if (string.IsNullOrEmpty(m_DefaultReferenceName))
             }
         }
 
-        public string overrideReferenceName { get; set; }
+        [SerializeField]
+        string m_OverrideReferenceName;
+
+        public string overrideReferenceName
+        {
+            get { return m_OverrideReferenceName; }
+            set { m_OverrideReferenceName = value; }
+        }
 
         public abstract PropertyType propertyType { get; }
 
         {
             get { return m_GeneratePropertyBlock; }
             set { m_GeneratePropertyBlock = value; }
-        }
-
-        public bool useCustomReferenceName
-        {
-            get { return m_UseCustomReferenceName; }
-            set { m_UseCustomReferenceName = value; }
         }
 
         public abstract Vector4 defaultValue { get; }

com.unity.shadergraph/Editor/Data/Graphs/IShaderProperty.cs

         PropertyType propertyType { get; }
         Guid guid { get; }
         bool generatePropertyBlock { get; set; }
-        bool useCustomReferenceName { get; set; }
-        string customReferenceName { get; set; }
         Vector4 defaultValue { get; }
         string overrideReferenceName { get; set; }
 

com.unity.shadergraph/Editor/Drawing/Blackboard/BlackboardFieldPropertyView.cs

 using System;
+using System.Linq;
+using UnityEditor.Graphing.Util;
+using UnityEngine.Experimental.UIElements.StyleSheets;
 using Toggle = UnityEngine.Experimental.UIElements.Toggle;
 
 namespace UnityEditor.ShaderGraph.Drawing
         readonly AbstractMaterialGraph m_Graph;
 
-        Toggle m_UseCustomReferenceNameToggle;
+        IShaderProperty m_Property;
+
+        static Type s_ContextualMenuManipulator = AppDomain.CurrentDomain.GetAssemblies().SelectMany(x => x.GetTypesOrNothing()).FirstOrDefault(t => t.FullName == "UnityEngine.Experimental.UIElements.ContextualMenuManipulator");
+            m_Property = property;
-            m_UseCustomReferenceNameToggle = new Toggle(() =>
-            {
-                property.useCustomReferenceName = m_UseCustomReferenceNameToggle.on;
-                m_ReferenceNameField.SetEnabled(property.useCustomReferenceName);
-                m_ReferenceNameField.value = property.referenceName;
-                DirtyNodes(ModificationScope.Graph);
-            });
-            m_UseCustomReferenceNameToggle.on = property.useCustomReferenceName;
-            m_ReferenceNameField.SetEnabled(property.useCustomReferenceName);
-                if (!property.useCustomReferenceName)
-                    return;
-                property.customReferenceName = newName.newValue;
+                string newReferenceName = m_Graph.SanitizePropertyReferenceName(newName.newValue);
+                property.overrideReferenceName = newReferenceName;
+                m_ReferenceNameField.value = newReferenceName;
+                m_ReferenceNameField.style.fontStyle = StyleValue<FontStyle>.Create(FontStyle.Bold);
-            AddRow("Specify reference name", m_UseCustomReferenceNameToggle);
+
+            if (!string.IsNullOrEmpty(property.overrideReferenceName))
+                m_ReferenceNameField.style.fontStyle = StyleValue<FontStyle>.Create(FontStyle.Bold);
 
             if (property is Vector1ShaderProperty)
             {
 
 
             AddToClassList("sgblackboardFieldPropertyView");
+
+            this.AddManipulator((IManipulator)Activator.CreateInstance(s_ContextualMenuManipulator, (Action<ContextualMenuPopulateEvent>)BuildContextualMenu));
+        }
+
+        void BuildContextualMenu(ContextualMenuPopulateEvent evt)
+        {
+            evt.menu.AppendAction("Reset reference name", e =>
+            {
+                m_Property.overrideReferenceName = null;
+                m_ReferenceNameField.value = m_Property.referenceName;
+                m_ReferenceNameField.style.fontStyle = StyleValue<FontStyle>.Create(FontStyle.Normal);
+                DirtyNodes(ModificationScope.Graph);
+            }, ContextualMenu.MenuAction.AlwaysEnabled);
         }
 
         VisualElement AddRow(string labelText, VisualElement control)