ConfigurationField: Validate field on construction

This lets us check whether fields are defaulted to an allowed value,
ex. one of the entries in ConfigurationListRestrictedField attribute.
Validation failure throws a ConfigurationFieldException.

Author: lookeypl

LukeBot.Common/Configuration.cs

@@ -290,7 +290,14 @@ private ConfigurationField AllocateFieldAccessor(object owner, FieldInfo fi, Con
             }
 
             // how does this spaghetti work I still have no idea
-            return Activator.CreateInstance(constructedType, constructorArgs) as ConfigurationField;
+            try
+            {
+                return Activator.CreateInstance(constructedType, constructorArgs) as ConfigurationField;
+            }
+            catch (TargetInvocationException e)
+            {
+                throw e.InnerException;
+            }
         }
 
         private void RegisterConfigurationFields(object fieldRef, string prefix = "")

LukeBot.Common/ConfigurationField.cs

@@ -12,6 +12,9 @@
 namespace LukeBot.Common
 {
     // Validator definition
+    // Note that ConfigurationField constructor WILL run the validator when initializing the accessor.
+    // This means your object should be defaulted to a value that makes the validation pass.
+    // If validation during Field construction fails, ConfigurationFieldException will be thrown.
     public interface IConfigurationFieldValidator<T>
     {
         public bool Validate(T input);
@@ -314,6 +317,11 @@ public ConfigurationFieldAccessor(string name, Expression<Func<T>> expression, I
             );
             Setter = Expression.Lambda<Action<T>>(body, parameter).Compile();
             Getter = expression.Compile();
+
+            if (!mValidator.Validate(Getter()))
+            {
+                throw new ConfigurationFieldException("Default value \"{0}\" that field {1} is set to is invalid", Getter(), Name);
+            }
         }
 
         public void Set(T v) => Setter(v);

Tools/LukeBot.Tests/Common/ConfigurationTests.cs

@@ -233,10 +233,22 @@ public class DefaultRestrictedFieldTestConfiguration: Configuration<DefaultRestr
             public string restrictedSetToSecond = "second";
 
             [ConfigurationListRestrictedField<string>(new string[] { "first", "second", "third" })]
-            public string restrictedEmpty;
+            public string restrictedSetToFirst = "first";
 
+            [ConfigurationListRestrictedField<int>(new int[] { 10, 20, 30 })]
+            public int restrictedSetTo30 = 30;
+        }
+
+        public class EmptyRestrictedFieldTestConfiguration: Configuration<EmptyRestrictedFieldTestConfiguration>
+        {
+            [ConfigurationListRestrictedField<string>(new string[] { "first", "second", "third" })]
+            public string restrictedEmpty = "";
+        }
+
+        public class WrongDefaultRestrictedFieldTestConfiguration: Configuration<WrongDefaultRestrictedFieldTestConfiguration>
+        {
             [ConfigurationListRestrictedField<string>(new string[] { "first", "second", "third" })]
-            public string restrictedBadDefault = "wrong";
+            public string badDefaultRestricted = "wrong";
         }
 
 
@@ -434,8 +446,9 @@ public void Configuration_RestrictedDefaults()
             // default value that is part of the restriction list should be left alone
             Assert.AreEqual("second", conf.restrictedSetToSecond);
 
-            // empty
-            Assert.AreEqual("first", conf.restrictedEmpty);
+            // empty or incorrect fields should be default-assigned to first value on the list
+            Assert.ThrowsException<ConfigurationFieldException>(() => new EmptyRestrictedFieldTestConfiguration());
+            Assert.ThrowsException<ConfigurationFieldException>(() => new WrongDefaultRestrictedFieldTestConfiguration());
         }
     }
 }