Fix IndexOutOfRangeException when an Enum's MetadataToken collides with Nullable<T>

Orm/Xtensive.Orm.Tests.Core/Tuples/NullableTokenCollisionTest.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Reflection;
+using System.Reflection.Emit;
+using NUnit.Framework;
+
+namespace Xtensive.Tuples;
+
+[TestFixture]
+public class NullableTokenCollisionTest
+{
+  [Test]
+  public void EnumWithNullableMetadataTokenIsNotTreatedAsNullable()
+  {
+    var nullableToken = typeof(Nullable<>).MetadataToken;
+    var enumType = EmitEnumWithMetadataToken(nullableToken);
+
+    Assert.That(enumType.IsEnum, Is.True);
+    Assert.That(enumType.MetadataToken, Is.EqualTo(nullableToken));
+    Assert.That(enumType.Module, Is.Not.EqualTo(typeof(Nullable<>).Module));
+    Assert.DoesNotThrow(() =>TupleDescriptor.Create(new[] { enumType}));
+  }
+
+  [Test]
+  public void GenuineNullableEnumStillResolves()
+  {
+    var nullableToken = typeof(Nullable<>).MetadataToken;
+    var enumType = EmitEnumWithMetadataToken(nullableToken);
+    var nullableEnum = typeof(Nullable<>).MakeGenericType(enumType);
+
+    Assert.DoesNotThrow(() => TupleDescriptor.Create(new[] { nullableEnum }));
+  }
+
+  private static Type EmitEnumWithMetadataToken(int targetToken)
+  {
+    var rowId = targetToken & 0X00FFFFFF;
+    var assembly = AssemblyBuilder.DefineDynamicAssembly(
+      new AssemblyName("NullableTokenCollisionAsm"), AssemblyBuilderAccess.Run);
+    var module = assembly.DefineDynamicModule("NullableTokenCollisionModule");
+
+    //Starting at 2 because module is at 1 and then we add fake test until we reach the desired value
+    for (var i = 2; i < rowId; i++) {
+      module.DefineType("Filler" + i, TypeAttributes.Public).CreateType();
+    }
+
+    var enumBuilder = module.DefineEnum("CollidingStatus", TypeAttributes.Public, typeof(int));
+    enumBuilder.DefineLiteral("FirstOption", 0);
+    enumBuilder.DefineLiteral("SecondOption", 1);
+    return enumBuilder.CreateType();
+  }
+}

Orm/Xtensive.Orm/Tuples/Packed/TupleLayout.cs

@@ -5,6 +5,7 @@
 // Created:    2012.12.29
 
 using System;
+using System.Reflection;
 using System.Runtime.CompilerServices;
 using Xtensive.Reflection;
 
@@ -54,10 +55,11 @@ private static class ValueFieldAccessorResolver
       private static readonly ValueFieldAccessor DateTimeOffsetAccessor = new DateTimeOffsetFieldAccessor();
 
       private static readonly int NullableTypeMetadataToken = WellKnownTypes.NullableOfT.MetadataToken;
+      private static readonly Module NullableTypeModule = WellKnownTypes.NullableOfT.Module;
 
       public static ValueFieldAccessor GetValue(Type probeType)
       {
-        return (probeType.MetadataToken ^ NullableTypeMetadataToken) == 0
+        return probeType.MetadataToken == NullableTypeMetadataToken && probeType.Module == NullableTypeModule
           ? (ResolveByNullableType(probeType) ?? TryResolveNullableEnum(probeType))
           : (ResolveByType(probeType) ?? TryResolveEnum(probeType));
       }