ISet in .NET 8 not populating from configuration as expected in .NET 6

[senabd]

Describe the bug

ISet in .NET 8 not populating from configuration as expected in .NET 6

I have following option definition:

using System.Collections.Generic;

namespace WebApplication3;

public record TestOptions
{
   public ISet<Uri> ISetTest { get; set; } = new HashSet<Uri>();
}

This option class registered in the Startup.cs as usual and In .Net 6 ISetTest property contains values but in .Net 8 it's empty.

Workaround

Use HashSet instead of ISet:

public HashSet<Uri> ISetTest { get; set; } = new HashSet<Uri>();

To Reproduce

Create ASP.NET Core Web API project with .Net 8 LTS.

Create option class:

public record TestOptions
{
	public ISet<Uri> ISetTest { get; set; } = new HashSet<Uri>();
}

Add settings to appsetting.json:

"Tests": {
    "ISetTest": [ "https://testuri.net" ]
}

Register options in Startup.cs or Program.cs:

builder.Services.Configure<TestOptions>(builder.Configuration.GetSection("Tests"));

Resolve TestOptions from a controller:

public WeatherForecastController(IOptions<TestOptions> options)
{
}

Then start the application in debug mode and set a breakpoint on the options variable to check its value. The result should look like:

For .Net 6:

For .Net 8:

Exceptions (if any)

No exception.

Further technical details

• Include the output of dotnet --info

dotnet --info
.NET SDK:
 Version:           8.0.105
 Commit:            eae90abaaf
 Workload version:  8.0.100-manifests.c1c70047

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19045
 OS Platform: Windows
 RID:         win-x64
 Base Path:   C:\Program Files\dotnet\sdk\8.0.105\

.NET workloads installed:
 Workload version: 8.0.100-manifests.c1c70047
 [maui]
   Installation Source: SDK 8.0.100
   Manifest Version:    8.0.3/8.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.maui\8.0.3\WorkloadManifest.json
   Install Type:              Msi

 [maccatalyst]
   Installation Source: VS 17.8.34322.80
   Manifest Version:    17.0.8478/8.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.maccatalyst\17.0.8478\WorkloadManifest.json
   Install Type:              Msi

 [ios]
   Installation Source: VS 17.8.34322.80
   Manifest Version:    17.0.8478/8.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.ios\17.0.8478\WorkloadManifest.json
   Install Type:              Msi

 [maui-windows]
   Installation Source: VS 17.8.34322.80
   Manifest Version:    8.0.3/8.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.maui\8.0.3\WorkloadManifest.json
   Install Type:              Msi

 [wasm-tools]
   Installation Source: VS 17.8.34322.80
   Manifest Version:    8.0.5/8.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.workload.mono.toolchain.current\8.0.5\WorkloadManifest.json
   Install Type:              Msi

 [android]
   Installation Source: VS 17.8.34322.80
   Manifest Version:    34.0.43/8.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.android\34.0.43\WorkloadManifest.json
   Install Type:              Msi

Host:
  Version:      8.0.5
  Architecture: x64
  Commit:       087e15321b

.NET SDKs installed:
  5.0.404 [C:\Program Files\dotnet\sdk]
  6.0.302 [C:\Program Files\dotnet\sdk]
  6.0.422 [C:\Program Files\dotnet\sdk]
  8.0.100 [C:\Program Files\dotnet\sdk]
  8.0.105 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.All 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.22 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.25 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 8.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 8.0.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.22 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.25 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.30 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 7.0.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.22 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.13 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.25 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.30 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 7.0.14 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 8.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 8.0.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
  x86   [C:\Program Files (x86)\dotnet]
    registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

• The IDE (VS / VS Code/ VS4Mac) you're running on, and its version
  Microsoft Visual Studio Professional 2022 (64-bit) - Current Version 17.8.2

[KalleOlaviNiemitalo]

This belongs in dotnet/runtime, area-Extensions-Configuration.

AFAICT, ConfigurationBinder in v6.0.0 does not recognize ISet<>. I guess its BindInstance method gets the existing HashSet<Uri> in the object instance parameter, detects that the instance supports ICollection<Uri>, and calls BindCollection, which then calls the ICollection<Uri>.Add(Uri) method repeatedly.

Between v6.0.0 and v8.0.0, there was a change to make ConfigurationBinder recognize ISet<>: #68133. Now in v8.0.0, BindInstance is told that the type of the property is ISet<Uri>, and presumably calls BindSet, which gives up:

runtime/src/libraries/Microsoft.Extensions.Configuration.Binder/src/ConfigurationBinder.cs

Lines 799 to 803 in 5535e31

	if (elementType != typeof(string) && !elementTypeIsEnum)
	{
	// We only support string and enum keys
	return null;
	}

[KalleOlaviNiemitalo]

Limiting this to strings and enums was requested in #68133 (comment).

[dotnet-policy-service]

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

[tarekgh]

CC @halter73 for the comment #102926 (comment)

[KalleOlaviNiemitalo]

For keys in an IDictionary<TKey, TValue>, the string-or-enum restriction makes some sense, because those are converted from JSON property names that can only be strings.

For elements of ISet<T>, the restriction makes less sense, because they are converted from JSON array elements that can have any JSON type.

[Ricky-Hao]

I also encountered the same issue when I want to use ISet<int> with Configuration Binder.
I think it's no make sense of this string and Enum restriction. The int it's a valid JSON type in JSON array.
Test code with Polyglot notebook

#r "nuget:Microsoft.Extensions.Configuration.Json"
#r "nuget:Microsoft.Extensions.Configuration.Binder"

using Microsoft.Extensions.Configuration;

public class Test
{
    public ISet<int> aaa { get; set; } = new HashSet<int>();
}

var json = """{"aaa": [1, 2, 3, 3]}""";
var builder = new ConfigurationBuilder();
builder.AddJsonStream(new System.IO.MemoryStream(System.Text.Encoding.UTF8.GetBytes(json)));
var config = builder.Build();

var obj = new Test();
config.Bind(obj);

System.Console.WriteLine(obj.aaa.Count);

Output: 0