Expose DasherContext.IsValidTopLevelType and tweak logic/errors a bit.

Author: drewnoakes

Dasher.Tests/Dasher.Tests.csproj

@@ -58,6 +58,7 @@
     </Reference>
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="DasherContextTests.cs" />
     <Compile Include="DeserialiserPerfTests.cs" />
     <Compile Include="PackerPerfTests.cs" />
     <Compile Include="PackerTests.cs" />

Dasher.Tests/DasherContextTests.cs

@@ -0,0 +1,44 @@
+using System;
+using Xunit;
+
+// ReSharper disable EmptyConstructor
+// ReSharper disable UnusedParameter.Local
+// ReSharper disable UnassignedGetOnlyAutoProperty
+// ReSharper disable MemberCanBePrivate.Local
+// ReSharper disable UnusedAutoPropertyAccessor.Local
+// ReSharper disable UnusedMember.Local
+
+namespace Dasher.Tests
+{
+    public sealed class DasherContextTests
+    {
+        private class Invalid1 { }
+        private class Invalid2 { public Invalid2() {} }
+        private class Invalid3 { private Invalid3(int i) {} public int I { get; } }
+
+        private class Valid1 { public Valid1(int i) {} public int I { get; } }
+        private struct Valid2 { public Valid2(int i, float f) { I = i; } public int I { get; } }
+
+        [Fact]
+        public void IsValidTopLevelType()
+        {
+            var context = new DasherContext();
+
+            Assert.False(context.IsValidTopLevelType(typeof(string)));
+            Assert.False(context.IsValidTopLevelType(typeof(int)));
+            Assert.False(context.IsValidTopLevelType(typeof(int?)));
+            Assert.False(context.IsValidTopLevelType(typeof(Tuple<int, float>)));
+            Assert.False(context.IsValidTopLevelType(typeof(TimeSpan)));
+            Assert.False(context.IsValidTopLevelType(typeof(DateTime)));
+            Assert.False(context.IsValidTopLevelType(typeof(Guid)));
+            Assert.False(context.IsValidTopLevelType(typeof(Version)));
+            Assert.False(context.IsValidTopLevelType(typeof(Invalid1)));
+            Assert.False(context.IsValidTopLevelType(typeof(decimal)));
+            Assert.False(context.IsValidTopLevelType(typeof(Union<int, string>)));
+
+            Assert.True(context.IsValidTopLevelType(typeof(Valid1)));
+            Assert.True(context.IsValidTopLevelType(typeof(Valid2)));
+            Assert.True(context.IsValidTopLevelType(typeof(Union<Valid1, Valid2>)));
+        }
+    }
+}

Dasher.Tests/DeserialiserTests.cs

@@ -51,7 +51,7 @@ public void MultiplePropertiesExactMatch()
         public void DisallowsPrimitiveTypes()
         {
             var exception = Assert.Throws<DeserialisationException>(() => new Deserialiser<int>());
-            Assert.Equal("Cannot deserialise type \"System.Int32\": Top-level primitive types are not supported. An object with properties supports future versioning.", exception.Message);
+            Assert.Equal("Cannot deserialise type \"System.Int32\": Top level types must be complex to support future versioning.", exception.Message);
         }
 
         [Fact]

Dasher.Tests/SerialiserTests.cs

@@ -34,7 +34,7 @@ public sealed class SerialiserTests
         public void DisallowsPrimitiveTypes()
         {
             var exception = Assert.Throws<SerialisationException>(() => new Serialiser<int>());
-            Assert.Equal("Cannot serialise type \"System.Int32\": Top-level primitive types are not supported. An object with properties supports future versioning.", exception.Message);
+            Assert.Equal("Cannot serialise type \"System.Int32\": Top level types must be complex to support future versioning.", exception.Message);
         }
 
         [Fact]

Dasher/DasherContext.cs

@@ -99,11 +99,26 @@ internal bool TryGetTypeProvider(Type type, ICollection<string> errors, out ITyp
 
         internal void ValidateTopLevelType(Type type, ICollection<string> errors)
         {
-            if (type.IsPrimitive)
-                errors.Add("Top-level primitive types are not supported. An object with properties supports future versioning.");
-
-            if (!_typeProviders.Any(p => p.CanProvide(type)))
+            if (Union.IsUnionType(type))
+            {
+                foreach (var memberType in Union.GetTypes(type))
+                    ValidateTopLevelType(memberType, errors);
+            }
+            else if (_typeProviders.Any(p => p.CanProvide(type)))
+            {
+                errors.Add("Top level types must be complex to support future versioning.");
+            }
+            else
+            {
                 ComplexTypeProvider.TryValidateComplexType(type, errors);
+            }
+        }
+
+        public bool IsValidTopLevelType(Type type)
+        {
+            var errors = new List<string>(capacity: 0);
+            ValidateTopLevelType(type, errors);
+            return errors.Count == 0;
         }
     }
 }

Dasher/UnionTypes.cs

@@ -23,6 +23,8 @@
 #endregion
 
 using System;
+using System.Collections.Generic;
+using System.Reflection;
 
 // ReSharper disable AssignNullToNotNullAttribute
 // ReSharper disable FieldCanBeMadeReadOnly.Local
@@ -32,6 +34,23 @@ namespace Dasher
 {
     // NOTE this file is generated
 
+    internal static class Union
+    {
+        public static bool IsUnionType(Type type)
+        {
+            return type.FullName.StartsWith("Dasher.Union`", StringComparison.Ordinal)
+                && type.Assembly == Assembly.GetExecutingAssembly();
+        }
+
+        public static IReadOnlyList<Type> GetTypes(Type type)
+        {
+            if (!IsUnionType(type))
+                throw new ArgumentException("Must be a union type.", nameof(type));
+
+            return type.GetGenericArguments();
+        }
+    }
+
     /// <summary>
     /// Models a value which may be of one of 2 types.
     /// </summary>

Dasher/UnionTypes.tt

@@ -28,6 +28,8 @@
 #endregion
 
 using System;
+using System.Collections.Generic;
+using System.Reflection;
 
 // ReSharper disable AssignNullToNotNullAttribute
 // ReSharper disable FieldCanBeMadeReadOnly.Local
@@ -36,6 +38,23 @@ using System;
 namespace Dasher
 {
     // NOTE this file is generated
+
+    internal static class Union
+    {
+        public static bool IsUnionType(Type type)
+        {
+            return type.FullName.StartsWith("Dasher.Union`", StringComparison.Ordinal)
+                && type.Assembly == Assembly.GetExecutingAssembly();
+        }
+
+        public static IReadOnlyList<Type> GetTypes(Type type)
+        {
+            if (!IsUnionType(type))
+                throw new ArgumentException("Must be a union type.", nameof(type));
+
+            return type.GetGenericArguments();
+        }
+    }
 <#
 for (var level = 2; level <= 16; level++)
 {