[typemap] Diagnose unsupported export signatures

Documentation/docs-mobile/TOC.yml

@@ -332,6 +332,8 @@
         href: messages/xa4249.md
       - name: XA4258
         href: messages/xa4258.md
+      - name: XA4263
+        href: messages/xa4263.md
       - name: XA4301
         href: messages/xa4301.md
       - name: XA4302

Documentation/docs-mobile/messages/index.md

@@ -229,6 +229,7 @@ Either change the value in the AndroidManifest.xml to match the $(SupportedOSPla
 + [XA4255](xa4255.md): Generated trimmable type map Java source '{path}' was not found.
 + [XA4256](xa4256.md): Skipping Java peer type '{type}' from assembly '{assembly}' because referenced type '{referencedType}' from assembly '{referencedAssembly}' could not be resolved in '{path}'. This type will not be included in the trimmable type map.
 + [XA4258](xa4258.md): Java name '{name}' contains reserved Java identifier '{identifier}'. Change the package or type name.
++ [XA4263](xa4263.md): The exported member '{member}' has unsupported signature type '{type}'. Use a Java peer type, a supported managed-to-Java mapping, or [ExportParameter].
 + XA4300: Native library '{library}' will not be bundled because it has an unsupported ABI.
 + [XA4301](xa4301.md): Apk already contains the item `xxx`.
 + [XA4302](xa4302.md): Unhandled exception merging \`AndroidManifest.xml\`: {ex}

Documentation/docs-mobile/messages/xa4263.md

@@ -0,0 +1,28 @@
+---
+title: .NET for Android error XA4263
+description: XA4263 error code
+ms.date: 08/31/2026
+f1_keywords:
+  - "XA4263"
+---
+
+# .NET for Android error XA4263
+
+## Example message
+
+```text
+error XA4263: The exported member 'Peer.Get' has unsupported signature type 'ManagedValue'. Use a Java peer type, a supported managed-to-Java mapping, or [ExportParameter].
+```
+
+## Issue
+
+An `[Export]` method or `[ExportField]` initializer uses a managed parameter or return type that has no Java type mapping.
+The type cannot be represented safely in the generated Java declaration.
+This error also occurs when `[ExportParameter]` specifies a Java mapping that is incompatible with the managed type.
+
+## Solution
+
+Use a primitive, string, array, Java peer, or another supported managed-to-Java type.
+Apply input/output stream mappings only to `Stream`, and XML parser mappings only to `XmlReader`.
+Do not apply these scalar mappings to arrays or other wrappers around those types.
+The types must be the framework `System.IO.Stream` and `System.Xml.XmlReader` types, not user-defined types with the same full name.

Xamarin.Android.slnx

@@ -60,8 +60,10 @@
     <Project Path="src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Xamarin.Android.Build.Tests.csproj" />
     <Project Path="src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Xamarin.ProjectTools.csproj" />
     <Project Path="tests/Microsoft.Android.Sdk.TrimmableTypeMap.IntegrationTests/Microsoft.Android.Sdk.TrimmableTypeMap.IntegrationTests.csproj" />
+    <Project Path="tests/Microsoft.Android.Sdk.TrimmableTypeMap.IntegrationTests/SpecialTypeCollisionFixture/SpecialTypeCollisionFixture.csproj" />
     <Project Path="tests/Microsoft.Android.Sdk.TrimmableTypeMap.IntegrationTests/UserTypesFixture/UserTypesFixture.csproj" />
     <Project Path="tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests.csproj" />
+    <Project Path="tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/MonoAndroidFixture/MonoAndroidFixture.csproj" />
     <Project Path="tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/TestAttributeFixtures/TestAttributeFixtures.csproj" />
     <Project Path="tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/TestFixtures/TestFixtures.csproj" />
     <Project Path="tests/MSBuildDeviceIntegration/MSBuildDeviceIntegration.csproj" />

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

@@ -118,6 +118,10 @@ static void WriteUcoConstructor (this BinaryWriter writer, UcoConstructorData co
 		foreach (var parameterType in constructor.ManagedParameterTypes) {
 			writer.WriteTypeRef (parameterType);
 		}
+		writer.Write (constructor.ParameterKinds.Count);
+		foreach (var parameterKind in constructor.ParameterKinds) {
+			writer.Write ((int) parameterKind);
+		}
 	}
 
 	static void WriteNativeRegistration (this BinaryWriter writer, NativeRegistrationData registration)

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

@@ -407,6 +407,11 @@ sealed record UcoConstructorData
 	/// to the corresponding managed type before calling the user ctor.
 	/// </summary>
 	public IReadOnlyList<TypeRefData> ManagedParameterTypes { get; init; } = [];
+
+	/// <summary>
+	/// Per-parameter [ExportParameter] kinds for constructor argument marshalling.
+	/// </summary>
+	public IReadOnlyList<ExportParameterKindInfo> ParameterKinds { get; init; } = [];
 }
 
 /// <summary>

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

@@ -380,6 +380,7 @@ static void BuildUcoConstructors (JavaPeerInfo peer, JavaPeerProxyData proxy)
 					AssemblyName = peer.AssemblyName,
 				},
 				ManagedParameterTypes = ctor.ManagedParameterTypes,
+				ParameterKinds = ctor.ManagedParameterExportKinds,
 				HasMatchingManagedCtor = ctor.HasMatchingManagedCtor,
 			});
 		}

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

@@ -1182,7 +1182,7 @@ MethodDefinitionHandle EmitUcoConstructor (UcoConstructorData uco, JavaPeerProxy
 		if (uco.HasMatchingManagedCtor) {
 			var ctorRef = AddManagedCtorRef (targetTypeRef, uco.ManagedParameterTypes);
 			var managedCtorHandle = EmitUcoConstructorBody (uco.WrapperName, encodeSig,
-				enc => EmitManagedConstructorActivation (enc, targetTypeRef, ctorRef, uco.ManagedParameterTypes, jniParams),
+				enc => EmitManagedConstructorActivation (enc, targetTypeRef, ctorRef, uco.ManagedParameterTypes, uco.ParameterKinds, jniParams),
 				blob => EncodeUcoConstructorLocals_DefaultConstructor (blob, targetTypeRef));
 			AddUnmanagedCallersOnlyAttribute (managedCtorHandle);
 			return managedCtorHandle;
@@ -1278,6 +1278,7 @@ void EmitManagedConstructorActivation (
 		EntityHandle targetTypeRef,
 		MemberReferenceHandle ctorRef,
 		IReadOnlyList<TypeRefData> managedParameterTypes,
+		IReadOnlyList<ExportParameterKindInfo> parameterKinds,
 		IReadOnlyList<JniParamKind> jniParams)
 	{
 		var havePeer = enc.DefineLabel ();
@@ -1303,7 +1304,8 @@ void EmitManagedConstructorActivation (
 		enc.MarkLabel (havePeer);
 		enc.LoadLocal (4);
 		for (int i = 0; i < managedParameterTypes.Count; i++) {
-			EmitManagedConstructorArgument (enc, managedParameterTypes [i], jniParams [i], i + 2);
+			var parameterKind = i < parameterKinds.Count ? parameterKinds [i] : ExportParameterKindInfo.Unspecified;
+			EmitManagedConstructorArgument (enc, managedParameterTypes [i], parameterKind, jniParams [i], i + 2);
 		}
 		enc.Call (ctorRef, managedParameterTypes.Count, isInstance: true);
 
@@ -1383,53 +1385,14 @@ void EmitUcoConstructorBodyWithMarshal (TrackedInstructionEncoder encoder, Contr
 		cfb.AddFinallyRegion (tryStart, finallyStart, finallyStart, afterAll);
 	}
 
-	void EmitManagedConstructorArgument (TrackedInstructionEncoder encoder, TypeRefData managedType, JniParamKind jniKind, int argumentIndex)
+	void EmitManagedConstructorArgument (
+		TrackedInstructionEncoder encoder,
+		TypeRefData managedType,
+		ExportParameterKindInfo exportKind,
+		JniParamKind jniKind,
+		int argumentIndex)
 	{
-		if (managedType.ManagedTypeName == "System.Boolean") {
-			encoder.LoadArgument (argumentIndex);
-			encoder.LoadConstantI4 (0);
-			encoder.OpCode (ILOpCode.Cgt_un);
-			return;
-		}
-
-		if (jniKind != JniParamKind.Object) {
-			encoder.LoadArgument (argumentIndex);
-			return;
-		}
-
-		if (managedType.ManagedTypeName == "System.String") {
-			encoder.LoadArgument (argumentIndex);
-			encoder.LoadConstantI4 (0); // JniHandleOwnership.DoNotTransfer
-			encoder.Call (_jniEnvGetStringRef, parameterCount: 2, returnsValue: true);
-			return;
-		}
-
-		if (TryGetSzArrayElementType (managedType.ManagedTypeName, out var elementType)) {
-			var arrayType = ResolveManagedTypeHandle (managedType.ManagedTypeName, managedType.AssemblyName);
-			var elementTypeHandle = ResolveManagedTypeHandle (elementType, managedType.AssemblyName);
-
-			encoder.LoadArgument (argumentIndex);
-			encoder.LoadConstantI4 (0); // JniHandleOwnership.DoNotTransfer
-			encoder.LoadToken (elementTypeHandle);
-			encoder.Call (_getTypeFromHandleRef, parameterCount: 1, returnsValue: true);
-			encoder.Call (_jniEnvGetArrayRef, parameterCount: 3, returnsValue: true);
-			encoder.CastClass (arrayType);
-			return;
-		}
-
-		encoder.LoadArgument (argumentIndex);
-		encoder.LoadConstantI4 (0); // JniHandleOwnership.DoNotTransfer
-		if (managedType.ManagedTypeName == "System.Object") {
-			encoder.OpCode (ILOpCode.Ldnull);
-			encoder.Call (_javaLangObjectGetObjectRef, parameterCount: 3, returnsValue: true);
-			return;
-		}
-
-		var managedTypeHandle = ResolveManagedTypeHandle (managedType.ManagedTypeName, managedType.AssemblyName);
-		encoder.LoadToken (managedTypeHandle);
-		encoder.Call (_getTypeFromHandleRef, parameterCount: 1, returnsValue: true);
-		encoder.Call (_javaLangObjectGetObjectRef, parameterCount: 3, returnsValue: true);
-		encoder.CastClass (managedTypeHandle);
+		GetExportMethodDispatchEmitter ().LoadManagedArgument (encoder, managedType, exportKind, jniKind, argumentIndex);
 	}
 
 	EntityHandle ResolveRuntimeTypeSpec (RuntimeTypeSpec type)

src/Microsoft.Android.Sdk.TrimmableTypeMap/ITrimmableTypeMapLogger.cs

@@ -23,8 +23,10 @@ void LogUnresolvableJavaPeerSkippedWarning (
 	void LogJniAddNativeMethodRegistrationAttributeError (string managedTypeName);
 	void LogInvalidJavaNameError (string javaName, string invalidIdentifier);
 	void LogExportFieldWithParametersError ();
+	void LogExportOnGenericTypeError ();
 	void LogExportFieldOnGenericTypeError ();
 	void LogExportFieldReturnsVoidError ();
+	void LogUnsupportedExportSignatureError (string memberName, string managedTypeName);
 	void LogCustomJavaObjectError (string managedTypeName);
 	void LogCustomJavaObjectWarning (string managedTypeName);
 }

src/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/AssemblyIndex.cs

@@ -30,6 +30,7 @@ sealed class AssemblyIndex : IDisposable
 
 	public MetadataReader Reader { get; }
 	public string AssemblyName { get; }
+	public string MetadataAssemblyName { get; }
 	public string AssemblyPath { get; }
 	internal TypeRefSignatureTypeProvider TypeRefSignatureProvider { get; }
 
@@ -53,6 +54,11 @@ sealed class AssemblyIndex : IDisposable
 	/// </summary>
 	public HashSet<string> ExportedTypeNames { get; } = new (StringComparer.Ordinal);
 
+	/// <summary>
+	/// Maps forwarded managed type names to the target assembly simple name.
+	/// </summary>
+	public Dictionary<string, string> ForwardedTypeAssemblies { get; } = new (StringComparer.Ordinal);
+
 	/// <summary>
 	/// True iff the assembly's metadata mentions
 	/// <c>Java.Interop.JniAddNativeMethodRegistrationAttribute</c> (as a
@@ -77,6 +83,7 @@ sealed class AssemblyIndex : IDisposable
 		valueTypeReferences = new TypeRefData? [reader.TypeReferences.Count + 1];
 		Reader = reader;
 		AssemblyName = assemblyName;
+		MetadataAssemblyName = reader.GetString (reader.GetAssemblyDefinition ().Name);
 		AssemblyPath = assemblyPath;
 		TypeRefSignatureProvider = new TypeRefSignatureTypeProvider (this);
 	}
@@ -107,7 +114,12 @@ void Build ()
 
 		foreach (var exportedTypeHandle in Reader.ExportedTypes) {
 			var exportedType = Reader.GetExportedType (exportedTypeHandle);
-			ExportedTypeNames.Add (GetExportedTypeFullName (exportedType));
+			var fullName = GetExportedTypeFullName (exportedType);
+			ExportedTypeNames.Add (fullName);
+			var forwardedAssemblyName = GetForwardedAssemblyName (exportedType);
+			if (forwardedAssemblyName is not null) {
+				ForwardedTypeAssemblies [fullName] = forwardedAssemblyName;
+			}
 		}
 
 		foreach (var typeHandle in Reader.TypeDefinitions) {
@@ -146,6 +158,18 @@ string GetExportedTypeFullName (ExportedType exportedType)
 			var ns = Reader.GetString (exportedType.Namespace);
 			return MetadataTypeNameResolver.JoinNamespaceAndName (ns, name);
 		}
+
+		string? GetForwardedAssemblyName (ExportedType exportedType)
+		{
+			if (exportedType.Implementation.Kind == HandleKind.AssemblyReference) {
+				var assemblyReference = Reader.GetAssemblyReference ((AssemblyReferenceHandle) exportedType.Implementation);
+				return Reader.GetString (assemblyReference.Name);
+			}
+			if (exportedType.Implementation.Kind == HandleKind.ExportedType) {
+				return GetForwardedAssemblyName (Reader.GetExportedType ((ExportedTypeHandle) exportedType.Implementation));
+			}
+			return null;
+		}
 	}
 
 	(RegisterInfo? register, TypeAttributeInfo? attrs) ParseAttributes (TypeDefinition typeDef)
@@ -173,8 +197,6 @@ string GetExportedTypeFullName (ExportedType exportedType)
 				registerInfo = registerInfo with { JniName = registerInfo.JniName.Replace ('.', '/') };
 			} else if (attrName == "JniTypeSignatureAttribute") {
 				registerInfo = ParseJniTypeSignatureAttribute (ca);
-			} else if (attrName == "ExportAttribute") {
-				// [Export] is a method-level attribute; it is parsed at scan time by JavaPeerScanner
 			} else if (IsKnownComponentAttribute (attrName)) {
 				attrInfo ??= CreateTypeAttributeInfo (attrName);
 				var value = DecodeAttribute (ca);

src/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/ExportParameterKindInfo.cs

@@ -6,6 +6,7 @@ namespace Microsoft.Android.Sdk.TrimmableTypeMap;
 /// </summary>
 enum ExportParameterKindInfo
 {
+	Invalid = -1,
 	Unspecified = 0,
 	InputStream = 1,
 	OutputStream = 2,

src/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/JavaPeerInfo.cs

@@ -368,6 +368,11 @@ public sealed record JavaConstructorInfo
 	/// </summary>
 	internal IReadOnlyList<TypeRefData> ManagedParameterTypes { get; init; } = [];
 
+	/// <summary>
+	/// Per-parameter [ExportParameter] kinds for constructor argument marshalling.
+	/// </summary>
+	internal IReadOnlyList<ExportParameterKindInfo> ManagedParameterExportKinds { get; init; } = [];
+
 	/// <summary>
 	/// True when this Java constructor has a matching public managed constructor on the target type.
 	/// </summary>