Enable C#12 (#657)

+semver:minor

Author: hazzik

src/Directory.Build.props

@@ -15,7 +15,7 @@
     <IncludeSymbols>true</IncludeSymbols>
     <EmbedUntrackedSources>true</EmbedUntrackedSources>
     <AllowedOutputExtensionsInPackageBuildOutputFolder>$(AllowedOutputExtensionsInPackageBuildOutputFolder);.pdb</AllowedOutputExtensionsInPackageBuildOutputFolder>
-    <LangVersion>10</LangVersion>
+    <LangVersion>12</LangVersion>
     <NoWarn>$(NoWarn);1591</NoWarn>
   </PropertyGroup>
 
@@ -31,5 +31,6 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="All"/>
+    <PackageReference Include="Polyfill" Version="3.0.0" PrivateAssets="All"/>
   </ItemGroup>
 </Project>

src/FluentNHibernate/Automapping/Steps/PropertyStep.cs

@@ -117,7 +117,7 @@ static TypeReference GetDefaultType(Member property)
         if (property.PropertyType.IsEnum())
             type = new TypeReference(typeof(EnumStringType<>).MakeGenericType(property.PropertyType));
 
-        if (property.PropertyType.IsNullable() && property.PropertyType.IsEnum())
+        if (property.PropertyType.IsNullableType() && property.PropertyType.IsEnum())
             type = new TypeReference(typeof(EnumStringType<>).MakeGenericType(property.PropertyType.GetGenericArguments()[0]));
 
         return type;

src/FluentNHibernate/Mapping/PropertyPart.cs

@@ -324,7 +324,7 @@ PropertyMapping IPropertyMappingProvider.GetPropertyMapping()
 
         foreach (var column in mapping.Columns)
         {
-            if (member.PropertyType.IsNullable() && member.PropertyType.IsEnum())
+            if (member.PropertyType.IsNullableType() && member.PropertyType.IsEnum())
                 column.Set(x => x.NotNull, Layer.Defaults, false);
 
             column.MergeAttributes(columnAttributes);
@@ -343,7 +343,7 @@ TypeReference GetDefaultType()
         if (member.PropertyType.IsEnum())
             type = new TypeReference(typeof(EnumStringType<>).MakeGenericType(member.PropertyType));
 
-        if (member.PropertyType.IsNullable() && member.PropertyType.IsEnum())
+        if (member.PropertyType.IsNullableType() && member.PropertyType.IsEnum())
             type = new TypeReference(typeof(EnumStringType<>).MakeGenericType(member.PropertyType.GetGenericArguments()[0]));
 
         return type;

src/FluentNHibernate/Utils/Extensions.cs

@@ -35,13 +35,19 @@ public static bool ClosesInterface(this Type type, Type openGenericInterface)
 
     public static bool IsEnum(this Type type)
     {
-        if (type.IsNullable())
+        if (type.IsNullableType())
             return type.GetGenericArguments()[0].IsEnum;
 
         return type.IsEnum;
     }
 
+    [Obsolete("Please use IsNullableType(Type type)")]
     public static bool IsNullable(this Type type)
+    {
+        return type.IsNullableType();
+    }
+
+    public static bool IsNullableType(this Type type)
     {
         return type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>);
     }