ILLink: extra warning for generic parameter with new constraint and annotation

[sbomer]

Repro:

// IL2026 for type (ILLink produces this twice)
class ClassWithWarningOnGenericArgumentConstructor_NewAndAnnotation : RequiresNewAndConstructors<ClassWithRequires>
{
    // IL2026 (ILLink produces this twice)
    public ClassWithWarningOnGenericArgumentConstructor_NewAndAnnotation()
    {
    }
}

class RequiresNewAndConstructors<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T> where T : new();

[RequiresUnreferencedCode("Message for --ClassWithRequires--")]
class ClassWithRequires;

This produces a warning on the type and on the implicit call to the base constructor (ILLink and ILC both do this). But ILLink produces two of each. That's because:

• ILC handles the new constraint by treating it like PublicParameterlessConstructor annotations
• ILLink handles the new constraint separately, while marking generic argument types

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