GetTypeInfo().GetDeclaredMethod() generates a false positive warning

[roji]

It seems that while the linker properly recognizes Type.GetMethod() and Type.GetTypeInfo().GetMethod(), it generates a warning when Type.GetTypeInfo().GetDeclaredMethod() is used (but the program does work):

class Program
{
    public static void Main()
    {
        // These works:
        // var openMethod = typeof(Program).GetMethod("Foo")!;
        // var openMethod = typeof(Program).GetTypeInfo().GetMethod(nameof(Foo))!;

        // This works, but generates a warning:
        var openMethod = typeof(Program).GetTypeInfo().GetDeclaredMethod(nameof(Foo))!;

        var method = openMethod.MakeGenericMethod(typeof(string));
        method.Invoke(null, null);
    }

    public static void Foo<T>()
        => Console.WriteLine("Foo" + default(T));
}

/cc @vitek-karas

[vitek-karas]

What is the warning it generates?

The GetDeclaredMethod is annotated like this:

[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
public virtual MethodInfo? GetDeclaredMethod(string name) ...

Meaning that the "this" passed to it must keep all methods (public and private).

Unlike Type.GetMethod trimmer doesn't have a special case for this, so it doesn't matter if the name of the method is statically known or not, the trimmer will simply keep all methods on the target type.

[roji]

Sorry for leaving out the details. The problem isn't with GetDeclaredMethod, it's with MakeGenericMethod called on its result:

/home/roji/projects/test/Program.cs(20,9): Trim analysis warning IL2060: Program.Main(): Call to 'System.Reflection.MethodInfo System.Reflection.MethodInfo::MakeGenericMethod(System.Type[])' can not be statically analyzed. It's not possible to guarantee the availability of requirements of the generic method. [/home/roji/projects/test/Test.csproj]

[vitek-karas]

I see - that's the same root cause as I mentioned above that there's no intrinsic handling for TypeInfo.GetDeclaredMethod - meaning linker doesn't know which method the MakeGenericMethod is called on.

We could add that if necessary... it's just that for now we didn't find the need.

(Given that TypeInfo is basically obsolete now)

[roji]

We have quite a lot of usage of TypeInfo in the code base - I can't say it's super important or anything, mainly that the APIs there are sometimes slightly easier to use. If TypeInfo really is discouraged by now, we can make the switch where necessary...

[MichalStrehovsky]

Yeah, it's pretty discouraged: dotnet/runtime#61122

[roji]

Thanks @MichalStrehovsky, I'll go ahead and close this, and remove any problematic references to TypeInfo.