[TrimmableTypeMap] Fix UCO constructor activations

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

@@ -182,7 +182,7 @@ sealed record UcoMethodData
 /// An [UnmanagedCallersOnly] static wrapper for a constructor callback.
 /// Signature must match the full JNI native method signature (jnienv + self + ctor params)
 /// so the ABI is correct when JNI dispatches the call.
-/// Body: TrimmableNativeRegistration.ActivateInstance(self, typeof(TargetType)).
+/// Body: directly activates the target type using its generated activation ctor.
 /// </summary>
 sealed record UcoConstructorData
 {
@@ -192,7 +192,7 @@ sealed record UcoConstructorData
 	public required string WrapperName { get; init; }
 
 	/// <summary>
-	/// Target type to pass to ActivateInstance.
+	/// Target type to activate in the generated wrapper.
 	/// </summary>
 	public required TypeRefData TargetType { get; init; }
 

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

@@ -239,7 +239,7 @@ TypeDefinitionHandle GetOrCreateSizedType (int size)
 		int typeMethodStart = Metadata.GetRowCount (TableIndex.MethodDef) + 1;
 
 		var handle = Metadata.AddTypeDefinition (
-			TypeAttributes.NestedPrivate | TypeAttributes.ExplicitLayout | TypeAttributes.Sealed | TypeAttributes.AnsiClass,
+			TypeAttributes.NestedAssembly | TypeAttributes.ExplicitLayout | TypeAttributes.Sealed | TypeAttributes.AnsiClass,
 			default,
 			Metadata.GetOrAddString ($"__utf8_{size}"),
 			Metadata.AddTypeReference (SystemRuntimeRef,
@@ -259,7 +259,7 @@ TypeDefinitionHandle GetOrCreateSizedType (int size)
 	/// </summary>
 	public MethodDefinitionHandle EmitBody (string name, MethodAttributes attrs,
 		Action<BlobEncoder> encodeSig, Action<InstructionEncoder> emitIL)
-		=> EmitBody (name, attrs, encodeSig, emitIL, encodeLocals: null);
+		=> EmitBody (name, attrs, encodeSig, emitIL, encodeLocals: null, useBranches: false);
 
 	/// <summary>
 	/// Emits a method body and definition with optional local variable declarations.
@@ -269,9 +269,19 @@ public MethodDefinitionHandle EmitBody (string name, MethodAttributes attrs,
 	/// <see cref="BlobBuilder"/> and must write the full <c>LOCAL_SIG</c> blob (header 0x07,
 	/// compressed count, then each variable type).
 	/// </param>
+	/// <param name="useBranches">
+	/// If true, creates a <see cref="ControlFlowBuilder"/> so the emitted IL can use
+	/// <see cref="InstructionEncoder.DefineLabel"/>, <see cref="InstructionEncoder.Branch"/>,
+	/// and <see cref="InstructionEncoder.MarkLabel"/>.
+	/// </param>
 	public MethodDefinitionHandle EmitBody (string name, MethodAttributes attrs,
 		Action<BlobEncoder> encodeSig, Action<InstructionEncoder> emitIL,
 		Action<BlobBuilder>? encodeLocals)
+		=> EmitBody (name, attrs, encodeSig, emitIL, encodeLocals, useBranches: false);
+
+	public MethodDefinitionHandle EmitBody (string name, MethodAttributes attrs,
+		Action<BlobEncoder> encodeSig, Action<InstructionEncoder> emitIL,
+		Action<BlobBuilder>? encodeLocals, bool useBranches)
 	{
 		_sigBlob.Clear ();
 		encodeSig (new BlobEncoder (_sigBlob));
@@ -287,7 +297,8 @@ public MethodDefinitionHandle EmitBody (string name, MethodAttributes attrs,
 		}
 
 		_codeBlob.Clear ();
-		var encoder = new InstructionEncoder (_codeBlob);
+		ControlFlowBuilder? cfb = useBranches ? new ControlFlowBuilder () : null;
+		var encoder = new InstructionEncoder (_codeBlob, cfb);
 		emitIL (encoder);
 
 		while (ILBuilder.Count % 4 != 0) {

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

@@ -43,7 +43,9 @@ namespace Microsoft.Android.Sdk.TrimmableTypeMap;
 ///
 ///     [UnmanagedCallersOnly]
 ///     public static void nctor_0_uco(IntPtr jnienv, IntPtr self)
-///         => TrimmableNativeRegistration.ActivateInstance(self, typeof(Activity));
+///         => new Activity(self, JniHandleOwnership.DoNotTransfer);
+///         // or: var obj = (Activity)RuntimeHelpers.GetUninitializedObject(typeof(Activity));
+///         //     obj.BaseCtor(self, JniHandleOwnership.DoNotTransfer);
 ///
 ///     // Registers JNI native methods (ACWs only):
 ///     public void RegisterNatives(JniType jniType)
@@ -77,7 +79,6 @@ sealed class TypeMapAssemblyEmitter
 	TypeReferenceHandle _systemTypeRef;
 	TypeReferenceHandle _runtimeTypeHandleRef;
 	TypeReferenceHandle _jniTypeRef;
-	TypeReferenceHandle _trimmableNativeRegistrationRef;
 	TypeReferenceHandle _notSupportedExceptionRef;
 	TypeReferenceHandle _runtimeHelpersRef;
 
@@ -87,7 +88,7 @@ sealed class TypeMapAssemblyEmitter
 	MemberReferenceHandle _notSupportedExceptionCtorRef;
 	MemberReferenceHandle _jniObjectReferenceCtorRef;
 	MemberReferenceHandle _jniEnvDeleteRefRef;
-	MemberReferenceHandle _activateInstanceRef;
+	MemberReferenceHandle _withinNewObjectScopeRef;
 	MemberReferenceHandle _ucoAttrCtorRef;
 	BlobHandle _ucoAttrBlobHandle;
 	MemberReferenceHandle _typeMapAttrCtorRef2Arg;
@@ -184,8 +185,6 @@ void EmitTypeReferences ()
 			metadata.GetOrAddString ("System"), metadata.GetOrAddString ("RuntimeTypeHandle"));
 		_jniTypeRef = metadata.AddTypeReference (_javaInteropRef,
 			metadata.GetOrAddString ("Java.Interop"), metadata.GetOrAddString ("JniType"));
-		_trimmableNativeRegistrationRef = metadata.AddTypeReference (_pe.MonoAndroidRef,
-			metadata.GetOrAddString ("Android.Runtime"), metadata.GetOrAddString ("TrimmableNativeRegistration"));
 		_notSupportedExceptionRef = metadata.AddTypeReference (_pe.SystemRuntimeRef,
 			metadata.GetOrAddString ("System"), metadata.GetOrAddString ("NotSupportedException"));
 		_runtimeHelpersRef = metadata.AddTypeReference (_pe.SystemRuntimeRef,
@@ -240,13 +239,11 @@ void EmitMemberReferences ()
 					p.AddParameter ().Type ().Type (_jniHandleOwnershipRef, true);
 				}));
 
-		_activateInstanceRef = _pe.AddMemberRef (_trimmableNativeRegistrationRef, "ActivateInstance",
-			sig => sig.MethodSignature ().Parameters (2,
-				rt => rt.Void (),
-				p => {
-					p.AddParameter ().Type ().IntPtr ();
-					p.AddParameter ().Type ().Type (_systemTypeRef, false);
-				}));
+		// JniEnvironment.get_WithinNewObjectScope() -> bool (static property)
+		_withinNewObjectScopeRef = _pe.AddMemberRef (_jniEnvironmentRef, "get_WithinNewObjectScope",
+			sig => sig.MethodSignature ().Parameters (0,
+				rt => rt.Type ().Boolean (),
+				p => { }));
 
 		// JniNativeMethod..ctor(byte*, byte*, IntPtr)
 		_jniNativeMethodCtorRef = _pe.AddMemberRef (_jniNativeMethodRef, ".ctor",
@@ -347,6 +344,16 @@ void EmitTypeMapAssociationAttributeCtorRef ()
 
 	void EmitProxyType (JavaPeerProxyData proxy, Dictionary<string, MethodDefinitionHandle> wrapperHandles)
 	{
+		if (proxy.IsAcw) {
+			// RegisterNatives uses RVA-backed UTF-8 fields under <PrivateImplementationDetails>.
+			// Materialize those helper types before adding the proxy TypeDef, otherwise the
+			// later RegisterNatives method can be attached to the helper type instead.
+			foreach (var reg in proxy.NativeRegistrations) {
+				_pe.GetOrAddUtf8Field (reg.JniMethodName);
+				_pe.GetOrAddUtf8Field (reg.JniSignature);
+			}
+		}
+
 		var metadata = _pe.Metadata;
 		var typeDefHandle = metadata.AddTypeDefinition (
 			TypeAttributes.Public | TypeAttributes.Sealed | TypeAttributes.Class,
@@ -390,7 +397,7 @@ void EmitProxyType (JavaPeerProxyData proxy, Dictionary<string, MethodDefinition
 		}
 
 		foreach (var uco in proxy.UcoConstructors) {
-			var handle = EmitUcoConstructor (uco);
+			var handle = EmitUcoConstructor (uco, proxy);
 			wrapperHandles [uco.WrapperName] = handle;
 		}
 
@@ -695,39 +702,123 @@ MethodDefinitionHandle EmitUcoMethod (UcoMethodData uco)
 		return handle;
 	}
 
-	MethodDefinitionHandle EmitUcoConstructor (UcoConstructorData uco)
+	MethodDefinitionHandle EmitUcoConstructor (UcoConstructorData uco, JavaPeerProxyData proxy)
 	{
-		var userTypeRef = _pe.ResolveTypeRef (uco.TargetType);
+		var targetTypeRef = _pe.ResolveTypeRef (uco.TargetType);
+		var activationCtor = proxy.ActivationCtor ?? throw new InvalidOperationException (
+			$"UCO constructor wrapper requires an activation ctor for '{uco.TargetType.ManagedTypeName}'");
 
 		// UCO constructor wrappers must match the JNI native method signature exactly.
-		// The Java JCW declares e.g. "private native void nctor_0(Context p0)" and calls
-		// it with arguments. JNI dispatches with (JNIEnv*, jobject, <ctor params...>),
-		// so the wrapper signature must include all parameters to match the ABI.
 		// Only jnienv (arg 0) and self (arg 1) are used — the constructor parameters
-		// are not forwarded because ActivateInstance creates the managed peer using the
+		// are not forwarded because we create the managed peer using the
 		// activation ctor (IntPtr, JniHandleOwnership), not the user-visible constructor.
 		var jniParams = JniSignatureHelper.ParseParameterTypes (uco.JniSignature);
 		int paramCount = 2 + jniParams.Count;
 
-		var handle = _pe.EmitBody (uco.WrapperName,
-			MethodAttributes.Public | MethodAttributes.Static | MethodAttributes.HideBySig,
-			sig => sig.MethodSignature ().Parameters (paramCount,
-				rt => rt.Void (),
-				p => {
-					p.AddParameter ().Type ().IntPtr (); // jnienv
-					p.AddParameter ().Type ().IntPtr (); // self
-					for (int j = 0; j < jniParams.Count; j++)
-						JniSignatureHelper.EncodeClrType (p.AddParameter ().Type (), jniParams [j]);
-				}),
-			encoder => {
-				encoder.LoadArgument (1); // self
-				encoder.OpCode (ILOpCode.Ldtoken);
-				encoder.Token (userTypeRef);
-				encoder.Call (_getTypeFromHandleRef);
-				encoder.Call (_activateInstanceRef);
-				encoder.OpCode (ILOpCode.Ret);
+		Action<BlobEncoder> encodeSig = sig => sig.MethodSignature ().Parameters (paramCount,
+			rt => rt.Void (),
+			p => {
+				p.AddParameter ().Type ().IntPtr (); // jnienv
+				p.AddParameter ().Type ().IntPtr (); // self
+				for (int j = 0; j < jniParams.Count; j++)
+					JniSignatureHelper.EncodeClrType (p.AddParameter ().Type (), jniParams [j]);
 			});
 
+		// Open generic types can't be activated — emit a no-op UCO.
+		if (proxy.IsGenericDefinition) {
+			var noopHandle = _pe.EmitBody (uco.WrapperName,
+				MethodAttributes.Public | MethodAttributes.Static | MethodAttributes.HideBySig,
+				encodeSig,
+				encoder => {
+					encoder.OpCode (ILOpCode.Ret);
+				});
+			AddUnmanagedCallersOnlyAttribute (noopHandle);
+			return noopHandle;
+		}
+
+		MethodDefinitionHandle handle;
+		if (activationCtor.Style == ActivationCtorStyle.JavaInterop) {
+			var ctorRef = AddJavaInteropActivationCtorRef (
+				activationCtor.IsOnLeafType ? targetTypeRef : _pe.ResolveTypeRef (activationCtor.DeclaringType));
+
+			handle = _pe.EmitBody (uco.WrapperName,
+				MethodAttributes.Public | MethodAttributes.Static | MethodAttributes.HideBySig,
+				encodeSig,
+				encoder => {
+					// Skip activation if the object is being created from managed code
+					// (e.g., JNIEnv.StartCreateInstance / JNIEnv.NewObject).
+					var skipLabel = encoder.DefineLabel ();
+					encoder.Call (_withinNewObjectScopeRef);
+					encoder.Branch (ILOpCode.Brtrue, skipLabel);
+
+					if (!activationCtor.IsOnLeafType) {
+						encoder.OpCode (ILOpCode.Ldtoken);
+						encoder.Token (targetTypeRef);
+						encoder.Call (_getTypeFromHandleRef);
+						encoder.Call (_getUninitializedObjectRef);
+						encoder.OpCode (ILOpCode.Castclass);
+						encoder.Token (targetTypeRef);
+					}
+
+					encoder.LoadLocalAddress (0);
+					encoder.LoadArgument (1); // self
+					encoder.Call (_jniObjectReferenceCtorRef);
+
+					if (activationCtor.IsOnLeafType) {
+						encoder.LoadLocalAddress (0);
+						encoder.LoadConstantI4 (1); // JniObjectReferenceOptions.Copy
+						encoder.OpCode (ILOpCode.Newobj);
+						encoder.Token (ctorRef);
+						encoder.OpCode (ILOpCode.Pop);
+					} else {
+						encoder.LoadLocalAddress (0);
+						encoder.LoadConstantI4 (1); // JniObjectReferenceOptions.Copy
+						encoder.Call (ctorRef);
+					}
+
+					encoder.MarkLabel (skipLabel);
+					encoder.OpCode (ILOpCode.Ret);
+				},
+				EncodeJniObjectReferenceLocal,
+				useBranches: true);
+		} else {
+			var ctorRef = AddActivationCtorRef (
+				activationCtor.IsOnLeafType ? targetTypeRef : _pe.ResolveTypeRef (activationCtor.DeclaringType));
+
+			handle = _pe.EmitBody (uco.WrapperName,
+				MethodAttributes.Public | MethodAttributes.Static | MethodAttributes.HideBySig,
+				encodeSig,
+				encoder => {
+					// Skip activation if the object is being created from managed code
+					var skipLabel = encoder.DefineLabel ();
+					encoder.Call (_withinNewObjectScopeRef);
+					encoder.Branch (ILOpCode.Brtrue, skipLabel);
+
+					if (activationCtor.IsOnLeafType) {
+						encoder.LoadArgument (1); // self
+						encoder.LoadConstantI4 (0); // JniHandleOwnership.DoNotTransfer
+						encoder.OpCode (ILOpCode.Newobj);
+						encoder.Token (ctorRef);
+						encoder.OpCode (ILOpCode.Pop);
+					} else {
+						encoder.OpCode (ILOpCode.Ldtoken);
+						encoder.Token (targetTypeRef);
+						encoder.Call (_getTypeFromHandleRef);
+						encoder.Call (_getUninitializedObjectRef);
+						encoder.OpCode (ILOpCode.Castclass);
+						encoder.Token (targetTypeRef);
+
+						encoder.LoadArgument (1); // self
+						encoder.LoadConstantI4 (0); // JniHandleOwnership.DoNotTransfer
+						encoder.Call (ctorRef);
+					}
+
+					encoder.MarkLabel (skipLabel);
+					encoder.OpCode (ILOpCode.Ret);
+				},
+				encodeLocals: null,
+				useBranches: true);
+		}
 		AddUnmanagedCallersOnlyAttribute (handle);
 		return handle;
 	}

src/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMap.cs

@@ -147,39 +147,6 @@ internal bool TryCreatePeer (Type type, IntPtr handle, JniHandleOwnership transf
 		return GetProxyForManagedType (type)?.GetContainerFactory ();
 	}
 
-	/// <summary>
-	/// Creates a managed peer instance for a Java object being constructed.
-	/// Called from generated UCO constructor wrappers (nctor_*_uco).
-	/// </summary>
-	internal static void ActivateInstance (IntPtr self, Type targetType)
-	{
-		var instance = s_instance;
-		if (instance is null) {
-			throw new InvalidOperationException ("TrimmableTypeMap has not been initialized.");
-		}
-
-		// Look up the proxy via JNI class name → TypeMap dictionary.
-		// We can't use targetType.GetCustomAttribute<JavaPeerProxy>() because the
-		// self-application attribute is on the proxy type, not the target type.
-		var selfRef = new JniObjectReference (self);
-		var jniClass = JniEnvironment.Types.GetObjectClass (selfRef);
-		var className = JniEnvironment.Types.GetJniTypeNameFromClass (jniClass);
-		JniObjectReference.Dispose (ref jniClass);
-
-		if (className is null || !instance._typeMap.TryGetValue (className, out var proxyType)) {
-			throw new InvalidOperationException (
-				$"Failed to create peer for type '{targetType.FullName}' (jniClass='{className}'). " +
-				"Ensure the type has a generated proxy in the TypeMap assembly.");
-		}
-
-		var proxy = proxyType.GetCustomAttribute<JavaPeerProxy> (inherit: false);
-		if (proxy is null || proxy.CreateInstance (self, JniHandleOwnership.DoNotTransfer) is null) {
-			throw new InvalidOperationException (
-				$"Failed to create peer for type '{targetType.FullName}'. " +
-				"Ensure the type has a generated proxy in the TypeMap assembly.");
-		}
-	}
-
 	[UnmanagedCallersOnly]
 	static void OnRegisterNatives (IntPtr jnienv, IntPtr klass, IntPtr nativeClassHandle)
 	{
@@ -208,4 +175,5 @@ static void OnRegisterNatives (IntPtr jnienv, IntPtr klass, IntPtr nativeClassHa
 			Environment.FailFast ($"TrimmableTypeMap: Failed to register natives for class '{className}'.", ex);
 		}
 	}
+
 }

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

@@ -188,6 +188,25 @@ public void Generate_LeafCtor_DoesNotUseCreateManagedPeer ()
 		Assert.True (ctorRefs.Count >= 2, "Should have ctor refs for proxy base + target type");
 	}
 
+	[Fact]
+	public void Generate_InheritedCtor_UcoUsesGuardAndInlinedActivation ()
+	{
+		var peers = ScanFixtures ();
+		var simpleActivity = peers.First (p => p.JavaName == "my/app/SimpleActivity");
+		Assert.NotNull (simpleActivity.ActivationCtor);
+		Assert.NotEqual (simpleActivity.ManagedTypeName, simpleActivity.ActivationCtor.DeclaringTypeName);
+
+		using var stream = GenerateAssembly (new [] { simpleActivity }, "InheritedCtorUcoTest");
+		using var pe = new PEReader (stream);
+		var reader = pe.GetMetadataReader ();
+		var memberNames = GetMemberRefNames (reader);
+
+		Assert.Contains ("get_WithinNewObjectScope", memberNames);
+		Assert.Contains ("GetUninitializedObject", memberNames);
+		Assert.DoesNotContain ("ActivateInstance", memberNames);
+		Assert.DoesNotContain ("ActivatePeerFromJavaConstructor", memberNames);
+	}
+
 	[Fact]
 	public void Generate_GenericType_ThrowsNotSupportedException ()
 	{
@@ -422,14 +441,26 @@ public void Generate_AcwProxy_HasRegisterNativesAndUcoMethods ()
 		using var pe = new PEReader (stream);
 		var reader = pe.GetMetadataReader ();
 
-		var memberNames = GetMemberRefNames (reader);
+		var proxyType = reader.TypeDefinitions
+			.Select (h => reader.GetTypeDefinition (h))
+			.Single (t =>
+				reader.GetString (t.Namespace) == "_TypeMap.Proxies" &&
+				reader.GetString (t.Name) == "MyApp_MainActivity_Proxy");
+		var proxyMethodNames = proxyType.GetMethods ()
+			.Select (h => reader.GetMethodDefinition (h))
+			.Select (m => reader.GetString (m.Name))
+			.ToList ();
+		Assert.Contains ("RegisterNatives", proxyMethodNames);
+		Assert.Contains (proxyMethodNames, name => name.Contains ("_uco_"));
 
-		// RegisterNatives is a method definition on the proxy type, not a member reference
-		var methodDefs = reader.MethodDefinitions
+		var privateImplDetailsType = reader.TypeDefinitions
+			.Select (h => reader.GetTypeDefinition (h))
+			.Single (t => reader.GetString (t.Name) == "<PrivateImplementationDetails>");
+		var privateImplMethodNames = privateImplDetailsType.GetMethods ()
 			.Select (h => reader.GetMethodDefinition (h))
 			.Select (m => reader.GetString (m.Name))
 			.ToList ();
-		Assert.Contains ("RegisterNatives", methodDefs);
+		Assert.DoesNotContain ("RegisterNatives", privateImplMethodNames);
 	}
 
 	[Fact]