[TrimmableTypeMap] Use non-generic JavaPeerProxy base for interface proxies

The generated proxy for an interface peer (e.g. a binding listener interface
like ApxLabs.FastAndroidCamera.INonMarshalingPreviewCallback) derived from the
closed generic JavaPeerProxy<TInterface>. That base annotates its type parameter
with [DynamicallyAccessedMembers(PublicConstructors | NonPublicConstructors)] and
returns new JavaPeerContainerFactory<T>() from GetContainerFactory(). Closing the
generic over an interface -- which has no constructors -- makes ILC fail to load
the closed type ("Failed to load type JavaPeerProxy1<...INonMarshalingPreviewCallback>
from assembly Mono.Android"), which fails the whole NativeAOT build
(ManifestTest.RemovePermissionTest, which pulls in ZXing.Net.Mobile ->
ApxLabs.FastAndroidCamera).

Interface peers now derive from the non-generic JavaPeerProxy base (the same base
already used for open generic definitions), passing the interface as the TargetType
constructor argument so runtime TargetType identity is unchanged. Instances are
still created from the InvokerType in CreateInstance, so behaviour is preserved;
abstract classes keep the generic base since they have constructors.

Reproduced locally with ZXing.Net.Mobile (3.0.0-beta5): NativeAOT build failed with
the TypeLoadException before, builds successfully after. Basic Mono.Android listener
apps (IOnClickListener/IOnLongClickListener) and AndroidX.Fragment still build clean.
Fixes RemovePermissionTest.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: simonrozsival

src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/Model/TypeMapAssemblyData.cs

@@ -173,6 +173,16 @@ sealed class JavaPeerProxyData
 	/// </summary>
 	public bool IsGenericDefinition { get; init; }
 
+	/// <summary>
+	/// True if the proxied peer type is a Java interface. Interfaces have no constructors, so
+	/// the proxy must derive from the non-generic <c>JavaPeerProxy</c> base instead of
+	/// <c>JavaPeerProxy&lt;T&gt;</c>: closing the generic (whose <c>T</c> is annotated with
+	/// <c>[DynamicallyAccessedMembers(PublicConstructors|NonPublicConstructors)]</c>) over an
+	/// interface makes ILC fail to load the type (TypeLoadException). Instances are still created
+	/// from <see cref="InvokerType"/> in CreateInstance.
+	/// </summary>
+	public bool IsInterface { get; init; }
+
 	/// <summary>
 	/// True when the Java stub must not call RegisterNatives from a static initializer because
 	/// the type can be instantiated before the runtime is fully ready (for example Application

src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/ModelBuilder.cs

@@ -318,6 +318,7 @@ static JavaPeerProxyData BuildProxyType (JavaPeerInfo peer, string jniName, Hash
 			},
 			IsAcw = isAcw,
 			IsGenericDefinition = peer.IsGenericDefinition,
+			IsInterface = peer.IsInterface,
 			CannotRegisterInStaticConstructor = peer.CannotRegisterInStaticConstructor,
 		};
 

src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/TypeMapAssemblyEmitter.cs

@@ -719,9 +719,16 @@ void EmitProxyType (JavaPeerProxyData proxy, Dictionary<UcoWrapperTargetData, Me
 		// placeholder like `Java.Lang.Object` leaks an incorrect TargetType into the typemap.
 		// The non-generic base takes `targetType` as a ctor parameter, so we can pass the real
 		// open-generic type token (a TypeRef, not a closed TypeSpec) and keep TargetType correct.
+		//
+		// Interface peers also use the non-generic base: `JavaPeerProxy<T>` annotates T with
+		// [DynamicallyAccessedMembers(PublicConstructors|NonPublicConstructors)], and closing it
+		// over an interface (which has no constructors) makes ILC fail to load the type
+		// (TypeLoadException: "Failed to load type 'JavaPeerProxy`1<ISomeInterface>'"). The peer is
+		// still activated from its InvokerType in CreateInstance, so behaviour is unchanged.
+		bool useNonGenericBase = proxy.IsGenericDefinition || proxy.IsInterface;
 		EntityHandle proxyBaseType;
 		MemberReferenceHandle baseCtorRef;
-		if (proxy.IsGenericDefinition) {
+		if (useNonGenericBase) {
 			proxyBaseType = _javaPeerProxyNonGenericRef;
 			baseCtorRef = _pe.AddMemberRef (_javaPeerProxyNonGenericRef, ".ctor",
 				sig => sig.MethodSignature (isInstanceMethod: true).Parameters (3,
@@ -763,9 +770,9 @@ void EmitProxyType (JavaPeerProxyData proxy, Dictionary<UcoWrapperTargetData, Me
 			encoder => {
 				encoder.OpCode (ILOpCode.Ldarg_0);
 				encoder.LoadString (metadata.GetOrAddUserString (proxy.JniName));
-				if (proxy.IsGenericDefinition) {
-					// Non-generic base ctor signature: (string, Type, Type?). Push the open-generic
-					// target type as the second argument.
+				if (useNonGenericBase) {
+					// Non-generic base ctor signature: (string, Type, Type?). Push the
+					// target type (open-generic definition or interface) as the second argument.
 					encoder.LoadToken (targetTypeRef);
 					encoder.Call (_getTypeFromHandleRef, parameterCount: 1, returnsValue: true);
 				}
@@ -775,7 +782,7 @@ void EmitProxyType (JavaPeerProxyData proxy, Dictionary<UcoWrapperTargetData, Me
 				} else {
 					encoder.OpCode (ILOpCode.Ldnull);
 				}
-				encoder.Call (baseCtorRef, parameterCount: proxy.IsGenericDefinition ? 3 : 2, isInstance: true);
+				encoder.Call (baseCtorRef, parameterCount: useNonGenericBase ? 3 : 2, isInstance: true);
 				encoder.Return ();
 			});
 

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/TypeMapAssemblyGeneratorTests.cs

@@ -178,13 +178,13 @@ public void Generate_ProxyType_UsesGenericJavaPeerProxyBase ()
 		Assert.All (proxyTypes, proxyType => {
 			switch (proxyType.BaseType.Kind) {
 			case HandleKind.TypeSpecification:
-				// Non-generic target types derive from the closed `JavaPeerProxy<T>`.
+				// Concrete (constructible) target types derive from the closed `JavaPeerProxy<T>`.
 				var baseTypeSpec = reader.GetTypeSpecification ((TypeSpecificationHandle) proxyType.BaseType);
 				var baseTypeName = baseTypeSpec.DecodeSignature (SignatureTypeProvider.Instance, genericContext: null);
 				Assert.StartsWith ("Java.Interop.JavaPeerProxy`1<", baseTypeName, StringComparison.Ordinal);
 				break;
 			case HandleKind.TypeReference:
-				// Open generic target types derive from the non-generic `JavaPeerProxy`.
+				// Open generic definitions and interfaces derive from the non-generic `JavaPeerProxy`.
 				var baseTypeRef = reader.GetTypeReference ((TypeReferenceHandle) proxyType.BaseType);
 				Assert.Equal ("Java.Interop", reader.GetString (baseTypeRef.Namespace));
 				Assert.Equal ("JavaPeerProxy", reader.GetString (baseTypeRef.Name));
@@ -201,6 +201,29 @@ public void Generate_ProxyType_UsesGenericJavaPeerProxyBase ()
 			objectProxyBaseType.DecodeSignature (SignatureTypeProvider.Instance, genericContext: null));
 	}
 
+	[Fact]
+	public void Generate_InterfaceProxyType_UsesNonGenericJavaPeerProxyBase ()
+	{
+		// JavaPeerProxy<T> annotates T with [DynamicallyAccessedMembers(Constructors)]. Closing it
+		// over an interface (which has no constructors) makes ILC fail to load the closed generic
+		// type ("Failed to load type 'JavaPeerProxy`1<ISomeInterface>'"). Interface proxies must
+		// therefore derive from the non-generic JavaPeerProxy base (a plain TypeReference).
+		var peers = ScanFixtures ();
+		using var stream = GenerateAssembly (peers);
+		using var pe = new PEReader (stream);
+		var reader = pe.GetMetadataReader ();
+
+		var interfaceProxy = reader.TypeDefinitions
+			.Select (h => reader.GetTypeDefinition (h))
+			.Where (t => reader.GetString (t.Namespace) == "_TypeMap.Proxies")
+			.First (t => reader.GetString (t.Name) == "Android_Views_IOnClickListener_Proxy");
+
+		Assert.Equal (HandleKind.TypeReference, interfaceProxy.BaseType.Kind);
+		var baseTypeRef = reader.GetTypeReference ((TypeReferenceHandle) interfaceProxy.BaseType);
+		Assert.Equal ("Java.Interop", reader.GetString (baseTypeRef.Namespace));
+		Assert.Equal ("JavaPeerProxy", reader.GetString (baseTypeRef.Name));
+	}
+
 	// Regression test: every generated proxy type must carry a custom attribute whose
 	// constructor points at the proxy's own TypeDefinitionHandle (either as a MemberRef
 	// parented on the TypeDef, or as a MethodDefinition on the TypeDef). This is how