Compiler error when using configuration binder source generator with custom collections

[adamsitnik]

I've tried to use the new configuration binder source generator to bind a type that contains a custom collection of abstract types.

I got following error:

C:\Users\adsitnik\source\repos\ConfigBindRepro\Microsoft.Extensions.Configuration.Binder.SourceGeneration\Microsoft.Extensions.Configuration.Binder.SourceGeneration.ConfigurationBindingGenerator\BindingExtensions.g.cs(61,29): error CS0
103: The name 'InitializeEndPoint' does not exist in the current context [C:\Users\adsitnik\source\repos\ConfigBindRepro\ConfigBindRepro.csproj]

I would expect it to not produce a compiler error and just try to map what it can, without throwing an exception at runtime (this is what the reflection based binder does in this case).

Repro:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <clear />
    <add key="dotnet8" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet8/nuget/v3/index.json" />
  </packageSources>
</configuration>

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <EnableConfigurationBindingGenerator>true</EnableConfigurationBindingGenerator>
    <Features>InterceptorsPreview</Features>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="8.0.0-rc.2.23429.20" />
    <PackageReference Include="Microsoft.Extensions.Hosting" Version="8.0.0-rc.2.23429.20" />
  </ItemGroup>
</Project>

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using System.Collections.ObjectModel;
using System.Net;

namespace ConfigBindRepro
{
    internal class Program
    {
        static void Main()
        {
            HostApplicationBuilder builder = Host.CreateEmptyApplicationBuilder(settings: null);
            builder.Configuration.AddInMemoryCollection(new KeyValuePair<string, string?>[]
            {
                 new KeyValuePair<string, string?>("ConfigBindRepro:EndPoints:0", "localhost"),
                 new KeyValuePair<string, string?>("ConfigBindRepro:Property", "true")
            });

            AClass instance = new();
#pragma warning disable SYSLIB1100
#pragma warning disable SYSLIB1101
            builder.Configuration.GetSection("ConfigBindRepro").Bind(instance);
#pragma warning restore

            BindToConfiguration(instance, builder.Configuration);
            if (instance.Property && instance.EndPoints.Any())
            {
                Console.WriteLine("OK");
            }
        }

        private static void BindToConfiguration(AClass settings, IConfiguration configuration)
        {
            var endpointsConfig = configuration.GetSection("ConfigBindRepro:EndPoints");
            foreach (var endpoint in endpointsConfig.GetChildren())
            {
                if (endpoint.Value is string)
                {
                    settings.EndPoints.Add(endpoint.Value);
                }
            }
        }
    }

    public class AClass
    {
        public EndPointCollection EndPoints { get; init; } = new EndPointCollection();

        public bool Property { get; set; } = false;
    }

    public sealed class EndPointCollection : Collection<EndPoint>, IEnumerable<EndPoint>
    {
        public EndPointCollection() { }

        public void Add(string hostAndPort)
        {
            EndPoint? endpoint;

            if (IPAddress.TryParse(hostAndPort, out IPAddress? address))
            {
                endpoint = new IPEndPoint(address, 0);
            }
            else
            {
                endpoint = new DnsEndPoint(hostAndPort, 0);
            }

            Add(endpoint);
        }
    }
}

.NET SDK:
 Version:   8.0.100-rc.2.23429.6
 Commit:    4bafa2271a

cc @layomia @eerhardt

[ghost]

Tagging subscribers to this area: @dotnet/area-extensions-configuration
See info in area-owners.md if you want to be subscribed.

Issue Details

---

I've tried to use the new configuration binder source generator to bind a type that contains a custom collection of complex types.

I got following error:

C:\Users\adsitnik\source\repos\ConfigBindRepro\Microsoft.Extensions.Configuration.Binder.SourceGeneration\Microsoft.Extensions.Configuration.Binder.SourceGeneration.ConfigurationBindingGenerator\BindingExtensions.g.cs(61,29): error CS0
103: The name 'InitializeEndPoint' does not exist in the current context [C:\Users\adsitnik\source\repos\ConfigBindRepro\ConfigBindRepro.csproj]

I would expect it to not produce a compiler error and just try to map what it can, without throwing an exception at runtime (this is what the reflection based binder does in this case).

Repro:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <clear />
    <add key="dotnet8" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet8/nuget/v3/index.json" />
  </packageSources>
</configuration>

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <EnableConfigurationBindingGenerator>true</EnableConfigurationBindingGenerator>
    <Features>InterceptorsPreview</Features>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="8.0.0-rc.2.23429.20" />
    <PackageReference Include="Microsoft.Extensions.Hosting" Version="8.0.0-rc.2.23429.20" />
  </ItemGroup>
</Project>

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using System.Collections.ObjectModel;
using System.Net;

namespace ConfigBindRepro
{
    internal class Program
    {
        static void Main()
        {
            HostApplicationBuilder builder = Host.CreateEmptyApplicationBuilder(settings: null);
            builder.Configuration.AddInMemoryCollection(new KeyValuePair<string, string?>[]
            {
                 new KeyValuePair<string, string?>("ConfigBindRepro:EndPoints:0", "localhost"),
                 new KeyValuePair<string, string?>("ConfigBindRepro:Property", "true")
            });

            AClass instance = new();
#pragma warning disable SYSLIB1100
#pragma warning disable SYSLIB1101
            builder.Configuration.GetSection("ConfigBindRepro").Bind(instance);
#pragma warning restore

            BindToConfiguration(instance, builder.Configuration);
            if (instance.Property && instance.EndPoints.Any())
            {
                Console.WriteLine("OK");
            }
        }

        private static void BindToConfiguration(AClass settings, IConfiguration configuration)
        {
            var endpointsConfig = configuration.GetSection("ConfigBindRepro:EndPoints");
            foreach (var endpoint in endpointsConfig.GetChildren())
            {
                if (endpoint.Value is string)
                {
                    settings.EndPoints.Add(endpoint.Value);
                }
            }
        }
    }

    public class AClass
    {
        public EndPointCollection EndPoints { get; init; } = new EndPointCollection();

        public bool Property { get; set; } = false;
    }

    public sealed class EndPointCollection : Collection<EndPoint>, IEnumerable<EndPoint>
    {
        public EndPointCollection() { }

        public void Add(string hostAndPort)
        {
            EndPoint? endpoint;

            if (IPAddress.TryParse(hostAndPort, out IPAddress? address))
            {
                endpoint = new IPEndPoint(address, 0);
            }
            else
            {
                endpoint = new DnsEndPoint(hostAndPort, 0);
            }

            Add(endpoint);
        }
    }
}

.NET SDK:
 Version:   8.0.100-rc.2.23429.6
 Commit:    4bafa2271a

cc @layomia @eerhardt

Author:	adamsitnik
Assignees:	-
Labels:	area-Extensions-Configuration
Milestone:	-

[layomia]

Thanks, taking a look.

[layomia]

I was able to repro; it's related to #90974. Working on a fix.

[layomia]

Issues isn't really about custom collections. Will address in #90974 & test the scenario.

[ericstj]

Reactivating since we're backporting this to release/8.0.

I confirmed that with the latest from main this issue is fixed. We'll no longer produce bad code when generating for members that have lists of abstract types.

We will, however, skip binding to this member since we cannot create the abstract types. That does seem consistent with what reflection the binder does, and appears to be what you expected based on the repro manually handling the endpoint values.

[adamsitnik]

I confirmed that with the latest from main this issue is fixed.

Great!

That does seem consistent with what reflection the binder does, and appears to be what you expected based on the repro manually handling the endpoint values.

Do we have any plans to be able to hint the binders on how to deal with abstract types? Similarly to what serializers do?
Or perhaps this is an anti-pattern and we should discourage the users from doing that?

[ericstj]

We have an issue tracking user-provided extensibility. #83599
In this case, since you don't own the type it would fall into the registration scenario. I'll add your scenario to that issue.
Closing this, since the fix was merged to RC2 with #92118