NativeAOT does not honor new() constraint

[kant2002]

Description

NativeAOT does not honor new() constraint applied to interface.

Reproduction Steps

using System.Diagnostics.CodeAnalysis;

var serviceCollection = new ServiceCollection();
var w = serviceCollection.GetRequiredService<IGeneric<Target>>();
Console.WriteLine("Working");


class ServiceCollection
{
    public T GetRequiredService<T>()
    {
        return (T)Activator.CreateInstance(typeof(GenericInstantiaion<>).MakeGenericType(typeof(T).GenericTypeArguments[0]))!;
    }
}

interface IGeneric<T> where T: new() {}
class GenericInstantiaion<T> : IGeneric<T> where T: new()
{
    public GenericInstantiaion()
    {
        new T();
    }
}

public class Target {

}

Expected behavior

Do not trim constructor of Target class.

Actual behavior

Exception at runtime.

Regression?

No

Known Workarounds

No response

Configuration

No response

Other information

No response

[ghost]

Tagging subscribers to this area: @agocke, @MichalStrehovsky, @jkotas
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

NativeAOT does not honor new() constraint applied to interface.

Reproduction Steps

using System.Diagnostics.CodeAnalysis;

var serviceCollection = new ServiceCollection();
var w = serviceCollection.GetRequiredService<IGeneric<Target>>();
Console.WriteLine("Working");


class ServiceCollection
{
    public T GetRequiredService<T>()
    {
        return (T)Activator.CreateInstance(typeof(GenericInstantiaion<>).MakeGenericType(typeof(T).GenericTypeArguments[0]))!;
    }
}

interface IGeneric<T> where T: new() {}
class GenericInstantiaion<T> : IGeneric<T> where T: new()
{
    public GenericInstantiaion()
    {
        new T();
    }
}

public class Target {

}

Expected behavior

Do not trim constructor of Target class.

Actual behavior

Exception at runtime.

Regression?

No

Known Workarounds

No response

Configuration

No response

Other information

No response

Author:	kant2002
Assignees:	-
Labels:	area-NativeAOT-coreclr
Milestone:	-

[MichalStrehovsky]

Thanks! Here's a repro that doesn't generate trimming warnings (and is also broken):

IGeneric<Target>.Hey();


interface IGeneric<T> where T: new()
{
    public static void Hey()
    {
        Activator.CreateInstance(typeof(T));
    }

}

public class Target { }

[kant2002]

I think my sample closer to how open generic registered in MEDI. Your example probably different issue :)

[MichalStrehovsky]

The issue would be a won't fix if it required MakeGeneric, especially if it's with something that has a new constraint. If there's a warning, trimming can and will generate broken things. The only aspects that are analysis holes are if there's no warnings.

[kant2002]

I do not want replicate whole DI setup. That’s bigger sample with only one warning from BuildServiceProvider which I believe is fine.

using System.Diagnostics.CodeAnalysis;
using Microsoft.Extensions.DependencyInjection;

var serviceCollection = new ServiceCollection();
serviceCollection.AddSingleton(typeof(IGeneric<>),typeof(GenericInstantiaion<>));
var serviceProvider = serviceCollection.BuildServiceProvider();
var w = serviceProvider.GetRequiredService<IGeneric<Target>>();
Console.WriteLine("Working");




interface IGeneric<T> where T: new() {}
class GenericInstantiaion<T> : IGeneric<T> where T: new()
{
    public GenericInstantiaion()
    {
        new T();
    }
}

public class Target {

}

[kant2002]

We can have situations like in MEDI where library author would support similar pattern for construction as in medi for open generics and just suppress warning like here

runtime/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/CallSiteFactory.cs

Lines 349 to 353 in 199436b

	[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2055:MakeGenericType",
	Justification = "MakeGenericType here is used to create a closed generic implementation type given the closed service type. " +
	"Trimming annotations on the generic types are verified when 'Microsoft.Extensions.DependencyInjection.VerifyOpenGenericServiceTrimmability' is set, which is set by default when PublishTrimmed=true. " +
	"That check informs developers when these generic types don't have compatible trimming annotations.")]
	private ServiceCallSite? TryCreateOpenGeneric(ServiceDescriptor descriptor, Type serviceType, CallSiteChain callSiteChain, int slot, bool throwOnConstraintViolation)

I think it's reasonable to perform analysys on parameters and return types of method when they specified. Develop specify that he need type, and that type guaranteed to return specific type by compiler, so that means that constraints on specific generic type would be satisfied. I honestly did not see how developer can break something with this extra requirement.

Yes, internally it's MakeGenericType probably, but why I cannot suppress usage if I know what I'm doing?

[MichalStrehovsky]

I do not want replicate whole DI setup. That’s bigger sample with only one warning from BuildServiceProvider which I believe is fine.

Oh, I see, it's the pattern from DI. Yes, the suppression in DI relies on the fact that because the interface has a new() constraint and there's a concrete instantiation of the interface with type X, we will not trim the constructor of X. The reduced sample will cover that and it is the same issue. The compiler is not great at detecting all the places where generic instantiations happen.

[MichalStrehovsky]

Vitek fixed this in #82818.