Trimmer implementation of type hierarchy marking shows order dependent behavior

[vitek-karas]

This bug is only observable after a fix from: #86635
But the bug exists in the code base today, it's just that without the PR above it actually shows even wrong marking behavior.

class UseByDerived
{
    [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods)]
    class AnnotatedBase
    {
        [RequiresUnreferencedCode("--AnnotatedBase.VirtualMethodWithRequires--")]
        public virtual void VirtualMethodWithRequires() { }
    }

    // BUG
    // IL2113 - AnnotatedBase.VirtualMethodWithRequires
    class Derived : AnnotatedBase
    {
        [RequiresUnreferencedCode("--Derived.VirtualMethodWithRequires--")]
        public override void VirtualMethodWithRequires() { }
    }

    static void TestMethodOnDerived(Derived instance)
    {
        instance.GetType().GetMethod("MethodWithRequires");
    }

    public static void Test()
    {
        TestMethodOnDerived(new Derived());
    }
}

In the above example, the type hierarchy marking is triggered by:

Derived instance;
instance.GetType()...

In this case the trimmer produces IL2113 because the marking is first triggered on Derived and that triggers marking of methods which show up as accessible through Derived but declared on Base (IL2113 is for methods from base, IL2112 is for method on the type itself).

But if the same is triggered by:

AnnotatedBase instance;
instance.GetType()...

Then there will be no IL2113 instead there will be IL2112 on the Base.VirtualMethodWithRequires directly.

So if the program has both access patterns in it, then the diagnostics behavior is dependent on which order trimmer will process it in. The behavior should be consistent.

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Issue Details

---

This bug is only observable after a fix from: <PR TBD - chicken and egg problem>
But the bug exists in the code base today, it's just that without the PR above it actually shows even wrong marking behavior.

class UseByDerived
{
    [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods)]
    class AnnotatedBase
    {
        [RequiresUnreferencedCode("--AnnotatedBase.VirtualMethodWithRequires--")]
        public virtual void VirtualMethodWithRequires() { }
    }

    // BUG
    // IL2113 - AnnotatedBase.VirtualMethodWithRequires
    class Derived : AnnotatedBase
    {
        [RequiresUnreferencedCode("--Derived.VirtualMethodWithRequires--")]
        public override void VirtualMethodWithRequires() { }
    }

    static void TestMethodOnDerived(Derived instance)
    {
        instance.GetType().GetMethod("MethodWithRequires");
    }

    public static void Test()
    {
        TestMethodOnDerived(new Derived());
    }
}

In the above example, the type hierarchy marking is triggered by:

Derived instance;
instance.GetType()...

In this case the trimmer produces IL2113 because the marking is first triggered on Derived and that triggers marking of methods which show up as accessible through Derived but declared on Base (IL2113 is for methods from base, IL2112 is for method on the type itself).

But if the same is triggered by:

AnnotatedBase instance;
instance.GetType()...

Then there will be no IL2113 instead there will be IL2112 on the Base.VirtualMethodWithRequires directly.

So if the program has both access patterns in it, then the diagnostics behavior is dependent on which order trimmer will process it in. The behavior should be consistent.

Author:	vitek-karas
Assignees:	-
Labels:	area-Tools-ILLink
Milestone:	-