Add explicit formatter declaration for ZeroFormattable attribute

src/ZeroFormatter.Analyzer/ZeroFormatterAnalyzer.cs

@@ -23,6 +23,8 @@ public class ZeroFormatterAnalyzer : DiagnosticAnalyzer
         internal const string UnionAttributeShortName = "UnionAttribute";
         internal const string DynamicUnionAttributeShortName = "DynamicUnionAttribute";
         internal const string UnionKeyAttributeShortName = "UnionKeyAttribute";
+        internal const string ZeroFormattableFormatterProperty = "FormatterType";
+        internal const string FormatterTypeName = "Formatter";
 
         internal static readonly DiagnosticDescriptor TypeMustBeZeroFormattable = new DiagnosticDescriptor(
             id: DiagnosticIdBase + "_" + nameof(TypeMustBeZeroFormattable), title: Title, category: Category,
@@ -102,6 +104,12 @@ public class ZeroFormatterAnalyzer : DiagnosticAnalyzer
             description: "All Union subTypes must be inherited type.",
             defaultSeverity: DiagnosticSeverity.Error, isEnabledByDefault: true);
 
+        internal static readonly DiagnosticDescriptor ExplicitFormatterMustInheritFormatter = new DiagnosticDescriptor(
+            id: DiagnosticIdBase + "_" + nameof(ExplicitFormatterMustInheritFormatter), title: Title, category: Category,
+            messageFormat: "Explicit Formatter type must inherit from Formatter<>. Type: {0}, Formatter: {1}", //  type.Name subType.Name
+            description: "Explicit Formatter type must inherit from Formatter<>.",
+            defaultSeverity: DiagnosticSeverity.Error, isEnabledByDefault: true);
+
         static readonly ImmutableArray<DiagnosticDescriptor> supportedDiagnostics = ImmutableArray.Create(
             TypeMustBeZeroFormattable,
             PublicPropertyNeedsIndex,
@@ -164,9 +172,9 @@ static void Analyze(SyntaxNodeAnalysisContext context)
             if (declaredSymbol == null) return;
 
             var isUnion = declaredSymbol.GetAttributes().FindAttributeShortName(UnionAttributeShortName) != null;
-            var isZeroFormattable = declaredSymbol.GetAttributes().FindAttributeShortName(ZeroFormattableAttributeShortName) != null;
+            var zeroFormattableAttribute = declaredSymbol.GetAttributes().FindAttributeShortName(ZeroFormattableAttributeShortName);
 
-            if (!isUnion && !isZeroFormattable)
+            if (!isUnion && zeroFormattableAttribute == null)
             {
                 return;
             }
@@ -176,8 +184,21 @@ static void Analyze(SyntaxNodeAnalysisContext context)
             {
                 VerifyUnion(reportContext, typeDeclaration.GetLocation(), declaredSymbol);
             }
-            if (isZeroFormattable)
+            if (zeroFormattableAttribute != null)
             {
+                var explicitFormatter =
+                    zeroFormattableAttribute.NamedArguments.Where(
+                        x => x.Key == ZeroFormattableFormatterProperty);
+                if (explicitFormatter.Any())
+                {
+                    if (explicitFormatter.First().Value.Type.BaseType.Name != FormatterTypeName)
+                        reportContext.Add(Diagnostic.Create(ExplicitFormatterMustInheritFormatter,
+                            typeDeclaration.GetLocation(), typeDeclaration.GetLocation(),
+                            explicitFormatter.First().Value.Type));
+
+                    return;
+                }
+
                 VerifyType(reportContext, typeDeclaration.GetLocation(), declaredSymbol, new HashSet<ITypeSymbol>(), null);
             }
 

src/ZeroFormatter.Interfaces.NETCore/ZeroFormatter.Interfaces.NETCore.csproj

@@ -12,8 +12,8 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="System.Runtime" Version="4.1.0" />
-    <PackageReference Include="System.Linq" Version="4.1.0" />
+    <PackageReference Include="System.Runtime" Version="4.3.0" />
+    <PackageReference Include="System.Linq" Version="4.3.0" />
   </ItemGroup>
 
 </Project>

src/ZeroFormatter.Interfaces/Attributes.cs

@@ -5,6 +5,7 @@ namespace ZeroFormatter
     [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, AllowMultiple = false, Inherited = true)]
     public class ZeroFormattableAttribute : Attribute
     {
+        public Type FormatterType { get; set; }
     }
 
     [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false, Inherited = true)]

src/ZeroFormatter.NETCore/ZeroFormatter.NETCore.csproj

@@ -26,20 +26,20 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="System.Reflection.Emit" Version="4.0.1" />
-    <PackageReference Include="System.Runtime" Version="4.1.0" />
-    <PackageReference Include="System.Runtime.Extensions" Version="4.1.0" />
-    <PackageReference Include="System.Collections" Version="4.0.11" />
-    <PackageReference Include="System.Linq" Version="4.1.0" />
-    <PackageReference Include="System.Linq.Expressions" Version="4.1.0" />
-    <PackageReference Include="System.Runtime.InteropServices" Version="4.1.0" />
-    <PackageReference Include="System.Reflection" Version="4.1.0" />
-    <PackageReference Include="System.Reflection.Extensions" Version="4.0.1" />
-    <PackageReference Include="System.Threading" Version="4.0.11" />
-    <PackageReference Include="System.Text.Encoding" Version="4.0.11" />
-    <PackageReference Include="System.Text.Encoding.Extensions" Version="4.0.11" />
-    <PackageReference Include="System.Collections.Concurrent" Version="4.0.12" />
-    <PackageReference Include="System.ObjectModel" Version="4.0.12" />
+    <PackageReference Include="System.Reflection.Emit" Version="4.3.0" />
+    <PackageReference Include="System.Runtime" Version="4.3.0" />
+    <PackageReference Include="System.Runtime.Extensions" Version="4.3.0" />
+    <PackageReference Include="System.Collections" Version="4.3.0" />
+    <PackageReference Include="System.Linq" Version="4.3.0" />
+    <PackageReference Include="System.Linq.Expressions" Version="4.3.0" />
+    <PackageReference Include="System.Runtime.InteropServices" Version="4.3.0" />
+    <PackageReference Include="System.Reflection" Version="4.3.0" />
+    <PackageReference Include="System.Reflection.Extensions" Version="4.3.0" />
+    <PackageReference Include="System.Threading" Version="4.3.0" />
+    <PackageReference Include="System.Text.Encoding" Version="4.3.0" />
+    <PackageReference Include="System.Text.Encoding.Extensions" Version="4.3.0" />
+    <PackageReference Include="System.Collections.Concurrent" Version="4.3.0" />
+    <PackageReference Include="System.ObjectModel" Version="4.3.0" />
   </ItemGroup>
 
 </Project>

src/ZeroFormatter/Formatters/Formatter.cs

@@ -105,7 +105,33 @@ static Formatter()
             var resolver = ResolverCache<TTypeResolver>.Default;
             try
             {
-                formatter = resolver.ResolveFormatter(t);
+
+#if NET_CORE
+                var ti = t.GetTypeInfo();
+#else
+                var ti = t;
+#endif
+                var attribute = (ZeroFormattableAttribute) ti.GetCustomAttributes(typeof(ZeroFormattableAttribute))
+                    .FirstOrDefault();
+                if (attribute != null && attribute.FormatterType != null)
+                {
+                    Type[] genericArguments;
+                    if (ti.IsGenericType)
+                    {
+                        var classTypes = ti.GetGenericArguments();
+                        genericArguments = new Type[1 + classTypes.Length];
+                        genericArguments[0] = typeof(TTypeResolver);
+                        Array.Copy(classTypes, 0, genericArguments, 1, classTypes.Length);
+                    }
+                    else
+                        genericArguments = new[] {typeof(TTypeResolver)};
+
+                    formatter = Activator.CreateInstance(
+                        attribute.FormatterType.MakeGenericType(genericArguments));
+                }
+
+                if (formatter == null)
+                    formatter = resolver.ResolveFormatter(t);
 
                 // If Unity, should avoid long static constructor and <T> code because IL2CPP generate every <T>.
                 if (formatter == null && resolver.IsUseBuiltinSerializer)

tests/ZeroFormatter.Tests/ZeroFormatter.Tests.csproj

@@ -97,6 +97,7 @@
     <Compile Include="EqTest.cs" />
     <Compile Include="VersiongTest.cs" />
     <Compile Include="ZeroArgumentTest.cs" />
+    <Compile Include="ZeroFormatterAttributeTest.cs" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="ChainingAssertion.Ext.cs" />

tests/ZeroFormatter.Tests/ZeroFormatterAttributeTest.cs

@@ -0,0 +1,55 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using ZeroFormatter.Formatters;
+using ZeroFormatter.Internal;
+
+namespace ZeroFormatter.Tests
+{
+    [TestClass]
+    public class ZeroFormatterAttributeTest
+    {
+        [TestMethod]
+        public void Serialize()
+        {
+            var customClass = new CustomClass("Hello World");
+
+            var data = ZeroFormatterSerializer.Serialize(customClass);
+            var result = ZeroFormatterSerializer.Deserialize<CustomClass>(data);
+            result.Test.Is(customClass.Test);
+        }
+
+        [ZeroFormattable(FormatterType = typeof(CustomClassFormatter<>))]
+        public class CustomClass
+        {
+            public CustomClass(string test)
+            {
+                Test = test;
+            }
+
+            public string Test { get; }
+        }
+
+        public class CustomClassFormatter<TTypeResolver> : Formatter<TTypeResolver, CustomClass>
+            where TTypeResolver : ITypeResolver, new()
+        {
+            public override int? GetLength()
+            {
+                return null;
+            }
+
+            public override int Serialize(ref byte[] bytes, int offset, CustomClass value)
+            {
+                var stringLength = BinaryUtil.WriteString(ref bytes, offset + 4, value.Test);
+                BinaryUtil.WriteInt32Unsafe(ref bytes, offset, stringLength);
+                return stringLength + 4;
+            }
+
+            public override CustomClass Deserialize(ref byte[] bytes, int offset, DirtyTracker tracker,
+                out int byteSize)
+            {
+                var length = BinaryUtil.ReadInt32(ref bytes, offset);
+                byteSize = 4 + length;
+                return new CustomClass(BinaryUtil.ReadString(ref bytes, offset + 4, length));
+            }
+        }
+    }
+}