Custom types with the Configuration-binding source generator

[jamescrosswell]

I'm trying to get source generated configuration binders working with the settings for our library. Or settings class has a number of properties with custom types and this causes the binding to fail.

For example, trying to create a binding for the following type:

public class AppSettings
{
    public string? ExampleString { get; set; }
    public int? Number { get; set; }
    public SubstringOrRegexPattern? Pattern { get; set; }
}

This produces a couple of warnings:

0>AppSettingsSetup.cs(29,9): Warning SYSLIB1100 : Cannot create instance of type 'ConsoleApp4.SubstringOrRegexPattern?' because it has multiple public parameterized constructors. (https://learn.microsoft.com/dotnet/fundamentals/syslib-diagnostics/syslib1100)
0>AppSettingsSetup.cs(29,9): Warning SYSLIB1101 : Property 'Pattern' on type 'ConsoleApp4.AppSettings' is not supported. (https://learn.microsoft.com/dotnet/fundamentals/syslib-diagnostics/syslib1101)

... and if I ignore the warnings and just run the program anyway, stepping into the generated code I see:

        public static void BindCore(IConfiguration configuration, ref AppSettings instance, bool defaultValueIfNotFound, BinderOptions? binderOptions)
        {
            ValidateConfigurationKeys(typeof(AppSettings), s_configKeys_AppSettings, configuration, binderOptions);

            if (configuration["ExampleString"] is string value0)
            {
                instance.ExampleString = value0;
            }

            if (configuration["Number"] is string value1)
            {
                instance.Number = ParseInt(value1, () => configuration.GetSection("Number").Path);
            }

            if (AsConfigWithChildren(configuration.GetSection("Pattern")) is IConfigurationSection section2)
            {
                throw new InvalidOperationException("Cannot create instance of type 'ConsoleApp4.SubstringOrRegexPattern' because one or more parameters cannot be bound to. Constructor parameters must have corresponding properties. Fields are not supported. Missing properties are: 'substringOrRegexPattern,comparison'");
            }
        }

So the generated code just throws an InvalidOperationException... With the source generators for JsonSerialization, it's easy enough to work around things like this by providing custom JsonConverters. What's the recommended way of dealing with this for Confituration Binding Source Generators though?