Inline activation ctor in UCO wrappers

- UCO constructors directly call activation ctor (no ActivateInstance indirection)
- WithinNewObjectScope guard prevents double peer creation
- No-op UCO for open generic type definitions
- ControlFlowBuilder support in PEAssemblyBuilder
- Remove TrimmableNativeRegistration wrapper and ActivateInstance

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

Author: simonrozsival

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.
@@ -269,6 +269,11 @@ 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)

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)
@@ -87,7 +89,6 @@ sealed class TypeMapAssemblyEmitter
 	MemberReferenceHandle _jniObjectReferenceCtorRef;
 	MemberReferenceHandle _jniEnvDeleteRefRef;
 	MemberReferenceHandle _withinNewObjectScopeRef;
-	MemberReferenceHandle _activateInstanceRef;
 	MemberReferenceHandle _ucoAttrCtorRef;
 	BlobHandle _ucoAttrBlobHandle;
 	MemberReferenceHandle _typeMapAttrCtorRef2Arg;
@@ -244,17 +245,6 @@ void EmitMemberReferences ()
 				rt => rt.Type ().Boolean (),
 				p => { }));
 
-		// TrimmableTypeMap.ActivateInstance(IntPtr, Type)
-		var trimmableTypeMapRef = _pe.Metadata.AddTypeReference (_pe.MonoAndroidRef,
-			_pe.Metadata.GetOrAddString ("Microsoft.Android.Runtime"), _pe.Metadata.GetOrAddString ("TrimmableTypeMap"));
-		_activateInstanceRef = _pe.AddMemberRef (trimmableTypeMapRef, "ActivateInstance",
-			sig => sig.MethodSignature ().Parameters (2,
-				rt => rt.Void (),
-				p => {
-					p.AddParameter ().Type ().IntPtr ();
-					p.AddParameter ().Type ().Type (_systemTypeRef, false);
-				}));
-
 		// JniNativeMethod..ctor(byte*, byte*, IntPtr)
 		_jniNativeMethodCtorRef = _pe.AddMemberRef (_jniNativeMethodRef, ".ctor",
 			sig => sig.MethodSignature (isInstanceMethod: true).Parameters (3,
@@ -354,6 +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,
@@ -368,14 +368,15 @@ void EmitProxyType (JavaPeerProxyData proxy, Dictionary<string, MethodDefinition
 		}
 
 		// .ctor
-		_pe.EmitBody (".ctor",
+		var ctorHandle = _pe.EmitBody (".ctor",
 			MethodAttributes.Public | MethodAttributes.HideBySig | MethodAttributes.SpecialName | MethodAttributes.RTSpecialName,
 			sig => sig.MethodSignature (isInstanceMethod: true).Parameters (0, rt => rt.Void (), p => { }),
 			encoder => {
 				encoder.OpCode (ILOpCode.Ldarg_0);
 				encoder.Call (_baseCtorRef);
 				encoder.OpCode (ILOpCode.Ret);
 			});
+		metadata.AddCustomAttribute (typeDefHandle, ctorHandle, _ucoAttrBlobHandle);
 
 		// CreateInstance
 		EmitCreateInstance (proxy);
@@ -704,10 +705,14 @@ MethodDefinitionHandle EmitUcoMethod (UcoMethodData 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.
+		// Only jnienv (arg 0) and self (arg 1) are used — the constructor parameters
+		// 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;
 
@@ -733,79 +738,88 @@ MethodDefinitionHandle EmitUcoConstructor (UcoConstructorData uco, JavaPeerProxy
 		}
 
 		MethodDefinitionHandle handle;
+		if (activationCtor.Style == ActivationCtorStyle.JavaInterop) {
+			var ctorRef = AddJavaInteropActivationCtorRef (
+				activationCtor.IsOnLeafType ? targetTypeRef : _pe.ResolveTypeRef (activationCtor.DeclaringType));
 
-		// For non-leaf activation, keep the WithinNewObjectScope guard but route back
-		// through the generated proxy activation path instead of a runtime reflection helper.
-		if (!activationCtor.IsOnLeafType) {
 			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);
 
-					encoder.LoadArgument (1); // jniSelf
-					encoder.OpCode (ILOpCode.Ldtoken);
-					encoder.Token (userTypeRef);
-					encoder.Call (_getTypeFromHandleRef);
-					encoder.Call (_activateInstanceRef);
-
-					encoder.MarkLabel (skipLabel);
-					encoder.OpCode (ILOpCode.Ret);
-				},
-				encodeLocals: null,
-				useBranches: true);
-		} else if (activationCtor.Style == ActivationCtorStyle.JavaInterop) {
-			var ctorRef = AddJavaInteropActivationCtorRef (userTypeRef);
-
-			handle = _pe.EmitBody (uco.WrapperName,
-				MethodAttributes.Public | MethodAttributes.Static | MethodAttributes.HideBySig,
-				encodeSig,
-				encoder => {
-					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);
 
-					encoder.LoadLocalAddress (0);
-					encoder.LoadConstantI4 (1); // JniObjectReferenceOptions.Copy
-					encoder.OpCode (ILOpCode.Newobj);
-					encoder.Token (ctorRef);
-					encoder.OpCode (ILOpCode.Pop);
+					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 (userTypeRef);
+			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);
 
-					encoder.LoadArgument (1); // self
-					encoder.LoadConstantI4 (0); // JniHandleOwnership.DoNotTransfer
-					encoder.OpCode (ILOpCode.Newobj);
-					encoder.Token (ctorRef);
-					encoder.OpCode (ILOpCode.Pop);
+					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)
 	{

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

@@ -189,7 +189,7 @@ public void Generate_LeafCtor_DoesNotUseCreateManagedPeer ()
 	}
 
 	[Fact]
-	public void Generate_InheritedCtor_UcoUsesGuardWithoutReflectionFallback ()
+	public void Generate_InheritedCtor_UcoUsesGuardAndInlinedActivation ()
 	{
 		var peers = ScanFixtures ();
 		var simpleActivity = peers.First (p => p.JavaName == "my/app/SimpleActivity");
@@ -202,7 +202,8 @@ public void Generate_InheritedCtor_UcoUsesGuardWithoutReflectionFallback ()
 		var memberNames = GetMemberRefNames (reader);
 
 		Assert.Contains ("get_WithinNewObjectScope", memberNames);
-		Assert.Contains ("ActivateInstance", memberNames);
+		Assert.Contains ("GetUninitializedObject", memberNames);
+		Assert.DoesNotContain ("ActivateInstance", memberNames);
 		Assert.DoesNotContain ("ActivatePeerFromJavaConstructor", memberNames);
 	}