Injected service is of wrong type when registered multiple times with generic registration - Microsoft.Extensions.DependecyInjection

[schwarzr]

Description

When registring a service in the IServiceCollection of asp.net core >= 6.0 once with a concrete type and once as a generic registration you get the wrong types of instances from the ServiceProvider.

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddTransient<IProcessor<SampleEntity>, SampleEntityProcessor>();
builder.Services.AddTransient(typeof(IProcessor<>), typeof(GenericProcessor<>));

var app = builder.Build();

// two instances of type SampleEntityProcessor are produced;
var processors = app.Services.GetServices<IProcessor<SampleEntity>>();

app.Run();

Reproduction Steps

Create a new asp.net core 6 Project:

Program.cs

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddTransient<IProcessor<SampleEntity>, SampleEntityProcessor>();
builder.Services.AddTransient(typeof(IProcessor<>), typeof(GenericProcessor<>));

var app = builder.Build();

// two instances of type SampleEntityProcessor are produced;
var processors = app.Services.GetServices<IProcessor<SampleEntity>>();

app.Run();

IProcessor

public interface IProcessor<T>
    where T : class
{
    Task ProcessAsync();
}

GenericProcessor

public class GenericProcessor<T> : IProcessor<T>
    where T : class
{
    public Task ProcessAsync()
    {
        return Task.CompletedTask;
    }
}

SampleEntity

public class SampleEntity
{
    public int Id { get; set; }

    public string Name { get; set; }
}

SampleEntityProcessor

public class SampleEntityProcessor : IProcessor<SampleEntity>
{
    public Task ProcessAsync()
    {
        return Task.CompletedTask;
    }
}

Expected behavior

var processors = app.Services.GetServices<IProcessor<SampleEntity>>();

should return

• instance of SampleEntityProcessor
• instance of GenericProcessor

Actual behavior

var processors = app.Services.GetServices<IProcessor<SampleEntity>>();

currently returns

• instance of SampleEntityProcessor
• instance of SampleEntityProcessor

Regression?

Tested with:

• asp.net 3.1 -> OK
• asp.net 5 -> OK
• asp.net 6 -> Failed (6.0.12)
• asp.net 7 -> Failed (7.0.1)

Known Workarounds

No response

Configuration

Windows 11 x64
.net runtime 6.0.12
.net runtime 7.0.1
Visual Studio 2022

Other information

No response

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[schwarzr]

area-Extensions-DependencyInjection

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

Issue Details

---

Description

When registring a service in the IServiceCollection of asp.net core >= 6.0 once with a concrete type and once as a generic registration you get the wrong types of instances from the ServiceProvider.

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddTransient<IProcessor<SampleEntity>, SampleEntityProcessor>();
builder.Services.AddTransient(typeof(IProcessor<>), typeof(GenericProcessor<>));

var app = builder.Build();

// two instances of type SampleEntityProcessor are produced;
var processors = app.Services.GetServices<IProcessor<SampleEntity>>();

app.Run();

Reproduction Steps

Create a new asp.net core 6 Project:

Program.cs

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddTransient<IProcessor<SampleEntity>, SampleEntityProcessor>();
builder.Services.AddTransient(typeof(IProcessor<>), typeof(GenericProcessor<>));

var app = builder.Build();

// two instances of type SampleEntityProcessor are produced;
var processors = app.Services.GetServices<IProcessor<SampleEntity>>();

app.Run();

IProcessor

public interface IProcessor<T>
    where T : class
{
    Task ProcessAsync();
}

GenericProcessor

public class GenericProcessor<T> : IProcessor<T>
    where T : class
{
    public Task ProcessAsync()
    {
        return Task.CompletedTask;
    }
}

SampleEntity

public class SampleEntity
{
    public int Id { get; set; }

    public string Name { get; set; }
}

SampleEntityProcessor

public class SampleEntityProcessor : IProcessor<SampleEntity>
{
    public Task ProcessAsync()
    {
        return Task.CompletedTask;
    }
}

Expected behavior

var processors = app.Services.GetServices<IProcessor<SampleEntity>>();

should return

• instance of SampleEntityProcessor
• instance of GenericProcessor

Actual behavior

var processors = app.Services.GetServices<IProcessor<SampleEntity>>();

currently returns

• instance of SampleEntityProcessor
• instance of SampleEntityProcessor

Regression?

Tested with:

• asp.net 3.1 -> OK
• asp.net 5 -> OK
• asp.net 6 -> Failed (6.0.12)
• asp.net 7 -> Failed (7.0.1)

Known Workarounds

No response

Configuration

Windows 11 x64
.net runtime 6.0.12
.net runtime 7.0.1
Visual Studio 2022

Other information

No response

Author:	schwarzr
Assignees:	-
Labels:	untriaged, area-Extensions-DependencyInjection
Milestone:	-

[madelson]

I'd be interested in working on this.

It would be helpful to confirm my understanding of the precise desired behavior in cases like this, though. Trying to piece together the intent from the code:

• Open generic registrations are always "lower precedence" than exact registrations.
• The default IEnumerable registration is always "lower precedence" than open generic registrations.
• Among otherwise equal registrations, earlier registrations are "lower precedence" than exact registrations.
• When resolving the default IEnumerable registration, registrations are returned in order from lowest precedence to highest precedence.

Is that all correct?

[davidfowl]

I believe it's the same issue as this #68053. We should confirm though, it only happens when the environment is development right?

[madelson]

I believe it's the same issue as this #68053

@davidfowl that seems right; potentially the fix there did not fully resolve the problem.

I believe it's the same issue as this #68053. We should confirm though, it only happens when the environment is development right?

@schwarzr should confirm, but from my repro the code shown requires development environment because in that setup it is being triggered by ValidateOnBuild = true in the ServiceProviderOptions.

However, ValidateOnBuild is not the only way to trigger this. For example the following also repros for me:

void Main()
{
	var sc = new ServiceCollection();
	sc.AddTransient<IProcessor<string>, SampleProcessor>();
	sc.AddTransient(typeof(IProcessor<>), typeof(GenericProcessor<>));
	
        // not using build validation
        using var s = sc.BuildServiceProvider(new ServiceProviderOptions { ValidateOnBuild = false });
        s.GetService(typeof(IProcessor<string>)); // resolve this first: gives SampleProcessor
	s.GetServices<IProcessor<string>>(); // now this gives [SampleProcessor, SampleProcessor]
}

public interface IProcessor<T> { }

public class SampleProcessor : IProcessor<string> { }

public class GenericProcessor<T> : IProcessor<T> { }

[davidfowl]

However, ValidateOnBuild is not the only way to trigger this. For example the following also repros for me:

That raises the priority of this. This was assumed to only be broken in validation scenarios.

[schwarzr]

@madelson

@schwarzr should confirm, but from my repro the code shown requires development environment because in that setup it is being triggered by ValidateOnBuild = true in the ServiceProviderOptions.

I have been able to reproduce this issue outside Visual Studio and without ValidateOnBuild = true. So no, i don't think it is limited do the development environment.

@davidfowl
One thing i recognized when i investigated this issue is, that if you register the generic version twice the resulting instances are: [SampleProcessor, GenericProcessor, SampleProcessor]

void Main()
{
	var sc = new ServiceCollection();
	sc.AddTransient<IProcessor<string>, SampleProcessor>();
	sc.AddTransient(typeof(IProcessor<>), typeof(GenericProcessor<>));
	sc.AddTransient(typeof(IProcessor<>), typeof(GenericProcessor<>));
	
        // not using build validation
        using var s = sc.BuildServiceProvider(new ServiceProviderOptions { ValidateOnBuild = false });
        s.GetService(typeof(IProcessor<string>)); // resolve this first: gives SampleProcessor
	s.GetServices<IProcessor<string>>(); // now this gives [SampleProcessor, GenericProcessor, SampleProcessor]
}

public interface IProcessor<T> { }

public class SampleProcessor : IProcessor<string> { }

public class GenericProcessor<T> : IProcessor<T> { }

and if you register the generic service first, it kind of works as expected.

void Main()
{
	var sc = new ServiceCollection();
	sc.AddTransient(typeof(IProcessor<>), typeof(GenericProcessor<>));
	sc.AddTransient<IProcessor<string>, SampleProcessor>();

        // not using build validation
        using var s = sc.BuildServiceProvider(new ServiceProviderOptions { ValidateOnBuild = false });
        s.GetService(typeof(IProcessor<string>)); // resolve this first: gives SampleProcessor
	s.GetServices<IProcessor<string>>(); // now this gives [GenericProcessor, SampleProcessor]
}

public interface IProcessor<T> { }

public class SampleProcessor : IProcessor<string> { }

public class GenericProcessor<T> : IProcessor<T> { }