Better error handling for setting userdata values

Upsilon/BaseTypes/UserData/UserData.cs

@@ -37,10 +37,10 @@ namespace Upsilon.BaseTypes.UserData
 
         public void Set(Diagnostics diagnostics, TextSpan span, string s, LuaType value)
         {
-            var failed = _typeInfo.Set(Value, s, value);
+            var (failed, error) = _typeInfo.Set(Value, s, value);
             if (failed)
             {
-                diagnostics.LogError($"Cannot find member '{s}' on type '{Value.GetType()}'", span);
+                diagnostics.LogError(error, span);
             }
         }
 

Upsilon/BaseTypes/UserData/UserDataType.cs

@@ -53,23 +53,27 @@ namespace Upsilon.BaseTypes.UserData
             return (null, true);
         }
 
-        public bool Set(object value, string member, LuaType newValue)
+        public (bool failed, string error) Set(object value, string member, LuaType newValue)
         {
             member = member.ToLowerInvariant();
             if (value.GetType() != Type)
-                return true;
+                return (true, "Invalid Type");
             if (Variables.TryGetValue(member, out var info))
             {
                 info.SetValue(value, newValue.ToCSharpObject());
-                return false;
+                return (false, null);
             }
             if (Properties.TryGetValue(member, out var property))
             {
+                if (property.SetMethod == null || property.SetMethod.IsPrivate)
+                {
+                    return (true, $"Property '{member}' on type '{Type}' does not have a publicly available setter.");
+                }
                 property.SetValue(value, newValue.ToCSharpObject());
-                return false;
+                return (false, null);
             }
 
-            return true;
+            return (true, $"Cannot find member '{member}' on type '{Type}'");
         }
 
         public (LuaType Type, bool Failed) BinaryOperator(object value, LuaType par1, OperatorType op, LuaType par2)