Fix StackOverflowException of GenerateSerializerCodes with WithNullable and IsRecursive. Issue #121.

This commit removes unnecessary recursion for nullable type. In addition, this commit fixes enum handling bugs for serializer generation.

Author: yfakariya

src/MsgPack/Serialization/CodeDomSerializers/CodeDomSerializerBuilder`1.cs

@@ -320,7 +320,7 @@ protected override CodeDomConstruct MakeCharLiteral( CodeDomContext context, cha
 
 protected override CodeDomConstruct MakeEnumLiteral( CodeDomContext context, Type type, object constant )
 {
-return CodeDomConstruct.Expression( type, new CodePrimitiveExpression( constant ) );
+return CodeDomConstruct.Expression( type, new CodeFieldReferenceExpression( new CodeTypeReferenceExpression( type ), constant.ToString() ) );
 }
 
 protected override CodeDomConstruct MakeDefaultLiteral( CodeDomContext context, Type type )

src/MsgPack/Serialization/SerializerGenerator.cs

@@ -448,17 +448,15 @@ public IEnumerable<SerializerCodeGenerationResult> Generate( IEnumerable<Type> t
 }
 else
 {
-realTargetTypes = targetTypes;
+realTargetTypes =
+targetTypes
+.Where( t => !SerializationTarget.BuiltInSerializerExists( configuration, t, t.GetCollectionTraits() ) );
 }
 
 var generationContext = this.CreateGenerationContext( context, configuration );
 var generatorFactory = this.CreateGeneratorFactory();
 
-foreach ( var targetType in
-realTargetTypes
-.Distinct()
-.Where( t => !SerializationTarget.BuiltInSerializerExists( configuration, t, t.GetCollectionTraits() ) )
-)
+foreach ( var targetType in realTargetTypes.Distinct() )
 {
 var generator = generatorFactory( targetType );
 
@@ -468,9 +466,6 @@ public IEnumerable<SerializerCodeGenerationResult> Generate( IEnumerable<Type> t
 concreteType = context.DefaultCollectionTypes.GetConcreteType( targetType );
 }
 
-#if DEBUG
-Contract.Assert( !SerializationTarget.BuiltInSerializerExists( configuration, targetType, targetType.GetCollectionTraits() ) );
-#endif // DEBUG
 generator.BuildSerializerCode( generationContext, concreteType, null );
 }
 
@@ -485,10 +480,17 @@ private static IEnumerable<Type> ExtractElementTypes( SerializationContext conte
 {
 yield return type;
 
-// Search dependents recursively.
-foreach ( var dependentType in SerializationTarget.Prepare( context, type ).Members.SelectMany( m => ExtractElementTypes( context, configuration, m.Member.GetMemberValueType() ) ) )
+// Search dependents recursively if the type is NOT enum.
+if ( !type.GetIsEnum() )
 {
-yield return dependentType;
+foreach (
+var dependentType in
+SerializationTarget.Prepare( context, type )
+.Members.SelectMany( m => ExtractElementTypes( context, configuration, m.Member.GetMemberValueType() ) ) 
+)
+{
+yield return dependentType;
+}
 }
 }
 
@@ -520,15 +522,7 @@ private static IEnumerable<Type> ExtractElementTypes( SerializationContext conte
 if ( configuration.WithNullableSerializers && type.GetIsValueType() && Nullable.GetUnderlyingType( type ) == null )
 {
 // Retrun nullable companion even if they always have built-in serializers.
-
-var nullableType = typeof( Nullable<> ).MakeGenericType( type );
-
-yield return nullableType;
-
-foreach ( var elementType in ExtractElementTypes( context, configuration, nullableType ) )
-{
-yield return elementType;
-}
+yield return typeof( Nullable<> ).MakeGenericType( type );
 }
 }