[TrimmableTypeMap] Handle generic invoker type resolution at runtime

[simonrozsival]

Updated Analysis: Generic Invoker Types Are Not a Real Problem

Original Concern

The legacy GetInvokerType has a MakeGenericType path for generic C# types. The concern was that the trimmable type map would not handle this.

Investigation Result: All Android invokers are non-generic C# types

Java uses type erasure for generics. The Mono.Android binding generator reflects this — all generated interfaces and their invokers are non-generic C# types, even when the Java type has generic parameters:

// java.util.Iterator<E> → non-generic C# interface + non-generic invoker
[Register("java/util/Iterator", "", "Java.Util.IIteratorInvoker")]
[JavaTypeParameters(new string[] {"E"})]  // metadata only, not a C# generic param
public partial interface IIterator : IJavaObject, IJavaPeerable { ... }

[Register("java/util/Iterator", DoNotGenerateAcw=true)]
internal partial class IIteratorInvoker : Java.Lang.Object, IIterator { ... }

The same pattern applies to all 90+ generic Java interfaces:

• java/util/List → IList + IListInvoker (non-generic)
• java/util/Map → IMap + IMapInvoker (non-generic)
• android/os/Parcelable$Creator → IParcelableCreator + IParcelableCreatorInvoker (non-generic)
• etc.

Runtime Flow (Legacy)

1. Java returns an object implementing java.util.Iterator
2. GetJavaToManagedType("java/util/Iterator") → Java.Util.IIterator (non-generic)
3. Since IIterator is an interface, GetInvokerType(typeof(IIterator)) is called
4. IIterator has zero generic arguments → takes the simple path: Assembly.GetType("Java.Util.IIteratorInvoker")
5. IIteratorInvoker is instantiated — no MakeGenericType involved

The MakeGenericType Path Is Dead Code (for Android)

The generic invoker resolution in JavaObjectExtensions.GetInvokerType (lines 137-146) and ManagedTypeManager.GetInvokerTypeCore (lines 48-59) handles C# generics like IFoo<T> → IFooInvoker<T>. But:

• No generated Mono.Android binding produces generic C# invoker types
• No Java.Interop or Java.Base types produce generic C# invoker types
• The code appears to be defensive/future-proofing for a pattern not currently used

Impact on Trimmable Type Map

Low to none. The trimmable path stores InvokerType as a pre-resolved non-generic type reference in the proxy attribute. Since all invokers in Mono.Android are non-generic, this works correctly:

TypeMap entry: "java/util/Iterator" → IIterator_Proxy
IIterator_Proxy.InvokerType → typeof(IIteratorInvoker)  // non-generic, resolves fine

Recommendation

This issue can be deprioritized or closed. The generic invoker scenario is theoretical — it would only matter if:

1. A third-party binding library creates actual C# generic interfaces (not just [JavaTypeParameters])
2. Someone uses the Java.Interop [JniTypeSignature] pattern with generic C# types

Neither scenario is common or blocking for .NET 11.

[simonrozsival]

Closing as not planned — this was a false positive.

Investigation found that generic invoker types don't exist in Mono.Android bindings. Java uses type erasure, and the binding generator reflects this: all 90+ "generic" Java interfaces produce non-generic C# types:

// java.util.Iterator<E> becomes:
[Register("java/util/Iterator", "", "Java.Util.IIteratorInvoker")]
[JavaTypeParameters(new string[] {"E"})]  // metadata only, NOT a C# generic param
public partial interface IIterator : IJavaObject, IJavaPeerable { }

[Register("java/util/Iterator", DoNotGenerateAcw=true)]
internal partial class IIteratorInvoker : Java.Lang.Object, IIterator { }  // non-generic

Same pattern for IList, IMap, IParcelableCreator, IConsumer, IFunction, etc.

The MakeGenericType path in legacy GetInvokerType / GetInvokerTypeCore is effectively dead code for Android — no generated type in Mono.Android, Java.Interop, or Java.Base produces a generic C# invoker.

The trimmable type map's pre-resolved non-generic InvokerType TypeRef on the proxy attribute handles this correctly.