NativeAOT fails when calling through generic method with reference type using reflection

[davidfowl]

Description

This might be by design by I don't know why so consider this both a bug and a question. I thought the only problems with using MakeGenericType and NativeAOT was the fact that value types needed unique code and that had to be generated ahead of time (since we don't have the fallback to universal shared generics). So for example, if I called MakeGenericMethod(reference type) it would be fine because that would use a shared implementation and wouldn't need to generate new code.

I found that to be mostly true until I tried to call a static abstract interface method via reflection.

Reproduction Steps

// Reflection for calling Parser.Parse<StringWrapper>("Hello");
var method = typeof(Parser).GetMethod(nameof(Parser.Parse), BindingFlags.Public | BindingFlags.Static)!.MakeGenericMethod(typeof(StringWrapper));
var r = (StringWrapper)method.Invoke(null, new[] { "Hello" })!;
Console.WriteLine(r);

class Parser
{
    // A generic callsite that lets use the static abstract interface method
    public static T Parse<T>(string s) where T : IParsable<T>
    {
        return T.Parse(s, CultureInfo.InvariantCulture);
    }
}

class StringWrapper : IParsable<StringWrapper>
{
    private string _data;
    public StringWrapper(string data)
    {
        _data = data;
    }

    public static StringWrapper Parse(string s, IFormatProvider? provider)
    {
        return new StringWrapper(s);
    }

    public static bool TryParse([NotNullWhen(true)] string? s, IFormatProvider? provider, out StringWrapper result)
    {
        result = new(s);
        return true;
    }

    public override string ToString() => _data;
}

Expected behavior

This should print Hello to the console.

Actual behavior

I get this exception.

Unhandled Exception: EETypeRva:0x018EB208(System.Reflection.MissingRuntimeArtifactException): MakeGenericMethod() cannot create this generic method instantiation because no code was generated for it: 'Parser.Parse<StringWrapper>(System.String)'.
   at System.Reflection.Runtime.MethodInfos.RuntimeNamedMethodInfo`1.GetUncachedMethodInvoker(RuntimeTypeInfo[], MemberInfo) + 0x113
   at System.Reflection.Runtime.MethodInfos.RuntimeMethodInfo.get_MethodInvoker() + 0xa1
   at System.Reflection.Runtime.MethodInfos.RuntimeNamedMethodInfo`1.MakeGenericMethod(Type[]) + 0x183
   at Program.<Main>$(String[]) + 0x7b
   at WebApplication35!<BaseAddress>+0xc23123

Regression?

No response

Known Workarounds

No response

Configuration

.NET 7.0.100-preview.6.22314.18

Other information

No response

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

Issue Details

---

Description

This might be by design by I don't know why so consider this both a bug and a question. I thought the only problems with using MakeGenericType and NativeAOT was the fact that value types needed unique code and that had to be generated ahead of time (since we don't have the fallback to universal shared generics). So for example, if I called MakeGenericMethod(reference type) it would be fine because that would use a shared implementation and wouldn't need to generate new code.

I found that to be mostly true until I tried to call a static abstract interface method via reflection.

Reproduction Steps

// Reflection for calling Parser.Parse<StringWrapper>("Hello");
var method = typeof(Parser).GetMethod(nameof(Parser.Parse), BindingFlags.Public | BindingFlags.Static)!.MakeGenericMethod(typeof(StringWrapper));
var r = (StringWrapper)method.Invoke(null, new[] { "Hello" })!;
Console.WriteLine(r);

class Parser
{
    // A generic callsite that lets use the static abstract interface method
    public static T Parse<T>(string s) where T : IParsable<T>
    {
        return T.Parse(s, CultureInfo.InvariantCulture);
    }
}

class StringWrapper : IParsable<StringWrapper>
{
    private string _data;
    public StringWrapper(string data)
    {
        _data = data;
    }

    public static StringWrapper Parse(string s, IFormatProvider? provider)
    {
        return new StringWrapper(s);
    }

    public static bool TryParse([NotNullWhen(true)] string? s, IFormatProvider? provider, out StringWrapper result)
    {
        result = new(s);
        return true;
    }

    public override string ToString() => _data;
}

Expected behavior

This should print Hello to the console.

Actual behavior

I get this exception.

Unhandled Exception: EETypeRva:0x018EB208(System.Reflection.MissingRuntimeArtifactException): MakeGenericMethod() cannot create this generic method instantiation because no code was generated for it: 'Parser.Parse<StringWrapper>(System.String)'.
   at System.Reflection.Runtime.MethodInfos.RuntimeNamedMethodInfo`1.GetUncachedMethodInvoker(RuntimeTypeInfo[], MemberInfo) + 0x113
   at System.Reflection.Runtime.MethodInfos.RuntimeMethodInfo.get_MethodInvoker() + 0xa1
   at System.Reflection.Runtime.MethodInfos.RuntimeNamedMethodInfo`1.MakeGenericMethod(Type[]) + 0x183
   at Program.<Main>$(String[]) + 0x7b
   at WebApplication35!<BaseAddress>+0xc23123

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

Author:	davidfowl
Assignees:	-
Labels:	area-System.Reflection, untriaged
Milestone:	-

[davidfowl]

cc @davidwrighton You were looking for cases where we would want a late bound API for calling into static interface methods. This is it. Today we do this manually by writing a generic method stub with a constraint, and using MakeGenericMethod method to specialize to the right type.

[MichalStrehovsky]

This is #67745 - right now you either need to add a static call to Parse<StringWrapper> or add the specific method to RD.XML.

[davidfowl]

This is #67745 - right now you either need to add a static call to Parse or add the specific method to RD.XML.

Is RD.xml documented?

[MichalStrehovsky]

It's documented here: https://github.com/dotnet/runtime/blob/main/src/coreclr/nativeaot/docs/rd-xml-format.md

But writing any sort of XML (be it this one, or the ILLink trim ones) is such a bad experience that it's sometimes better to forget it exists. I'm working on a fix for this right now, so if it's not urgent, wait a day or two and this problem will go away.

[davidfowl]

It's not urgent, I'm looking at other ways to make value types work though. We will just say its not supported at the moment, but motivated individuals can use RD.xml to preserve the internal generic methods that get called.