dotnet · simonrozsival · Jul 7, 2026 · Jul 7, 2026 · Jul 7, 2026 · Jul 7, 2026
@@ -161,6 +161,20 @@ static void AssertGetJniTypeInfoForType (Type type, string jniType, bool isKeywo
 			AssertArrayTypesFromSignature<double[]> (manager, "[[D", typeof (JavaObjectArray<JavaPrimitiveArray<double>>));
 			AssertArrayTypesFromSignature<string[]> (manager, "[[Ljava/lang/String;", typeof (JavaObjectArray<JavaObjectArray<string>>));
 
+			// Nullable counterparts of the primitive value types: the boxed reference signatures
+			// java/lang/<Boxed> map to Nullable<T> (see JniBuiltinSimpleReferenceToType /
+			// GetBuiltInTypeForSimpleReference). Unlike the primitive keyword arrays above, these are
+			// non-keyword reference arrays, so the element type is the boxed Nullable<T> and the array
+			// family is T?[] and JavaObjectArray<T?> (no JavaArray<T>/JavaPrimitiveArray<T>).
+			AssertArrayTypesFromSignature<bool?>   (manager, "[Ljava/lang/Boolean;",   typeof (JavaObjectArray<bool?>));
+			AssertArrayTypesFromSignature<sbyte?>  (manager, "[Ljava/lang/Byte;",      typeof (JavaObjectArray<sbyte?>));
+			AssertArrayTypesFromSignature<char?>   (manager, "[Ljava/lang/Character;", typeof (JavaObjectArray<char?>));
+			AssertArrayTypesFromSignature<short?>  (manager, "[Ljava/lang/Short;",     typeof (JavaObjectArray<short?>));
+			AssertArrayTypesFromSignature<int?>    (manager, "[Ljava/lang/Integer;",   typeof (JavaObjectArray<int?>));
+			AssertArrayTypesFromSignature<long?>   (manager, "[Ljava/lang/Long;",      typeof (JavaObjectArray<long?>));
+			AssertArrayTypesFromSignature<float?>  (manager, "[Ljava/lang/Float;",     typeof (JavaObjectArray<float?>));
+			AssertArrayTypesFromSignature<double?> (manager, "[Ljava/lang/Double;",    typeof (JavaObjectArray<double?>));
+
 			// Yes, these look weird...
 			// Assume: class II {}
 			Assert.AreEqual (null, GetType ("II"));

@@ -31,6 +31,21 @@ static class ModelBuilder
 		new ("D", "Double", "System.Double", ["Java.Interop.JavaDoubleArray"]),
 	];
 
+	// Nullable value types map to the boxed java/lang/<Boxed> references (java/lang/Boolean etc.) via
+	// TrimmableTypeMapTypeManager.GetBuiltInTypeForSimpleReference. Like System.String they are neither
+	// scanned Java peers nor primitives, so their array proxies are emitted explicitly. Only the eight
+	// types with a boxed java/lang mapping are included (java/lang/Byte -> sbyte?, not byte?, etc.).
+	static readonly (string Name, string ManagedTypeName) [] NullableArrayProxies = [
+		("Boolean", "System.Boolean"),
+		("SByte",   "System.SByte"),
+		("Char",    "System.Char"),
+		("Int16",   "System.Int16"),
+		("Int32",   "System.Int32"),
+		("Int64",   "System.Int64"),
+		("Single",  "System.Single"),
+		("Double",  "System.Double"),
+	];
+
 	static readonly HashSet<string> EssentialRuntimeTypes = new (StringComparer.Ordinal) {
 		"java/lang/Object",
 		"java/lang/Class",
@@ -55,7 +70,7 @@ static class ModelBuilder
 	/// Emit per-rank array <c>TypeMap</c> entries + <c>__ArrayMapRank{N}</c> sentinels
 	/// for ranks 1..<paramref name="maxArrayRank"/>. 0 disables array entry emission.
 	/// </param>
-	public static TypeMapAssemblyData Build (IReadOnlyList<JavaPeerInfo> peers, string outputPath, string? assemblyName = null, int maxArrayRank = 0)
+	public static TypeMapAssemblyData Build (IReadOnlyList<JavaPeerInfo> peers, string outputPath, string? assemblyName = null, int maxArrayRank = 0, int maxReferenceArrayRank = 0)
 	{
 		if (peers is null) {
 			throw new ArgumentNullException (nameof (peers));
@@ -66,13 +81,20 @@ public static TypeMapAssemblyData Build (IReadOnlyList<JavaPeerInfo> peers, stri
 		if (maxArrayRank < 0) {
 			throw new ArgumentOutOfRangeException (nameof (maxArrayRank), maxArrayRank, "Must be >= 0.");
 		}
+		if (maxReferenceArrayRank < 0) {
+			throw new ArgumentOutOfRangeException (nameof (maxReferenceArrayRank), maxReferenceArrayRank, "Must be >= 0.");
+		}
 
 		assemblyName ??= Path.GetFileNameWithoutExtension (outputPath);
 
 		var model = new TypeMapAssemblyData {
 			AssemblyName = assemblyName,
 			ModuleName = Path.GetFileName (outputPath),
-			MaxArrayRank = maxArrayRank,
+			// The per-assembly __ArrayMapRank{N} anchor count must be uniform across every typemap
+			// assembly (the root generator builds a rectangular [assembly][rank] matrix), so the model
+			// always carries the overall maximum rank. Primitive and reference element types may
+			// populate different rank ranges within that shared anchor set.
+			MaxArrayRank = Math.Max (maxArrayRank, maxReferenceArrayRank),
 		};
 
 		// Invoker types are NOT emitted as separate proxies or TypeMap entries.
@@ -109,12 +131,13 @@ public static TypeMapAssemblyData Build (IReadOnlyList<JavaPeerInfo> peers, stri
 
 			EmitPeers (model, jniName, peersForName, assemblyName, usedProxyNames);
 
-			if (maxArrayRank > 0) {
-				EmitArrayEntries (model, jniName, peersForName, maxArrayRank);
+			// Java peer types are reference types: emit array proxies only up to the reference rank.
+			if (maxReferenceArrayRank > 0) {
+				EmitArrayEntries (model, jniName, peersForName, maxReferenceArrayRank);
 			}
 		}
 
-		if (maxArrayRank > 0 && string.Equals (assemblyName, "_Java.Interop.TypeMap", StringComparison.Ordinal)) {
+		if (string.Equals (assemblyName, "_Java.Interop.TypeMap", StringComparison.Ordinal)) {
 			EmitPrimitiveArrayEntries (model, maxArrayRank);
 		}
 
@@ -541,6 +564,26 @@ static TypeMapAttributeData BuildEntry (JavaPeerInfo peer, JavaPeerProxyData? pr
 	static string AssemblyQualify (string typeName, string assemblyName)
 		=> $"{typeName}, {assemblyName}";
 
+	static string AssemblyQualify (TypeRefData type)
+	{
+		if (type.GenericArguments.Count == 0) {
+			return AssemblyQualify (type.ManagedTypeName, type.AssemblyName);
+		}
+
+		var builder = new StringBuilder ();
+		builder.Append (type.ManagedTypeName);
+		builder.Append ("[[");
+		for (int i = 0; i < type.GenericArguments.Count; i++) {
+			if (i > 0) {
+				builder.Append ("],[");
+			}
+			builder.Append (AssemblyQualify (type.GenericArguments [i]));
+		}
+		builder.Append ("]], ");
+		builder.Append (type.AssemblyName);
+		return builder.ToString ();
+	}
+
 	static string AddArrayRank (string typeReference, int rank)
 	{
 		if (rank == 0) {
@@ -569,7 +612,7 @@ static string MakeNestedJavaObjectArrayTypeReference (string elementTypeReferenc
 
 	static IReadOnlyList<string> GetArrayTypeReferences (ArrayProxyData proxy)
 	{
-		var elementType = AssemblyQualify (proxy.ElementType.ManagedTypeName, proxy.ElementType.AssemblyName);
+		var elementType = AssemblyQualify (proxy.ElementType);
 		if (proxy.Primitive is null) {
 			var rankOneTypes = new [] {
 				MakeGenericTypeReference ("Java.Interop.JavaObjectArray`1", "Java.Interop", elementType),
@@ -585,7 +628,7 @@ static IReadOnlyList<string> GetArrayTypeReferences (ArrayProxyData proxy)
 			MakeGenericTypeReference ("Java.Interop.JavaPrimitiveArray`1", "Java.Interop", elementType),
 		];
 		foreach (var concreteArrayType in proxy.Primitive.ConcreteArrayTypes) {
-			rankOnePrimitiveTypes.Add (AssemblyQualify (concreteArrayType.ManagedTypeName, concreteArrayType.AssemblyName));
+			rankOnePrimitiveTypes.Add (AssemblyQualify (concreteArrayType));
 		}
 		return ExpandRankOneTypes (rankOnePrimitiveTypes, proxy.Rank);
 	}
@@ -616,7 +659,7 @@ static void AddArrayProxyAssociations (TypeMapAssemblyData model, ArrayProxyData
 	}
 
 	static string GetArrayProxyMapKey (TypeRefData elementType)
-		=> AssemblyQualify (elementType.ManagedTypeName, elementType.AssemblyName);
+		=> AssemblyQualify (elementType);
 
 	/// <summary>
 	/// Emits per-rank array TypeMap entries for one peer, anchored to the per-assembly
@@ -665,6 +708,13 @@ static void EmitArrayEntriesForPeer (TypeMapAssemblyData model, JavaPeerInfo pee
 		}
 	}
 
+	// Emits array proxies for the built-in element types that are not scanned Java peers:
+	//   * the keyword primitives (int/bool/...) up to maxArrayRank (jagged/multidim primitive arrays
+	//     like int[][][] are cheap — a small fixed set of element types),
+	//   * System.String up to maxArrayRank (also a built-in element type, so multidimensional string
+	//     arrays like String[][] stay resolvable),
+	//   * the boxed Nullable<T> value types up to maxArrayRank (also built-in element types mapping to
+	//     java/lang/<Boxed>; a small fixed set, so multidim boxed arrays stay resolvable too).
 	static void EmitPrimitiveArrayEntries (TypeMapAssemblyData model, int maxArrayRank)
 	{
 		foreach (var primitive in PrimitiveArrayProxies) {
@@ -694,6 +744,74 @@ static void EmitPrimitiveArrayEntries (TypeMapAssemblyData model, int maxArrayRa
 				AddArrayProxyAssociations (model, proxy, proxyReference);
 			}
 		}
+
+		// System.String maps to java/lang/String but is a built-in element type injected at runtime by
+		// TrimmableTypeMapTypeManager.GetBuiltInTypeForSimpleReference, so it is neither a scanned Java
+		// peer (EmitArrayEntriesForPeer) nor a keyword primitive. Emit its array proxies here (Primitive
+		// is null, so it gets the reference-array family) so GetTypes ("[Ljava/lang/String;") yields
+		// System.String[] / JavaObjectArray<string> / JavaArray<string> on NativeAOT, matching CoreCLR.
+		// String is a single, fixed built-in element type (not part of the scanned-peer explosion), so —
+		// like the keyword primitives — it goes up to maxArrayRank. This keeps multidimensional string
+		// arrays (String[][], "[[Ljava/lang/String;") resolvable, matching the other type-map backends.
+		for (int rank = 1; rank <= maxArrayRank; rank++) {
+			var proxy = new ArrayProxyData {
+				TypeName = ManagedTypeNameToArrayProxyTypeName ("System.String", rank),
+				ElementType = new TypeRefData {
+					ManagedTypeName = "System.String",
+					AssemblyName = "System.Runtime",
+				},
+				Rank = rank,
+			};
+			model.ArrayProxyTypes.Add (proxy);
+			var proxyReference = AssemblyQualify ($"{proxy.Namespace}.{proxy.TypeName}", model.AssemblyName);
+			model.Entries.Add (new TypeMapAttributeData {
+				MapKey = GetArrayProxyMapKey (proxy.ElementType),
+				ProxyTypeReference = proxyReference,
+				TargetTypeReference = proxyReference,
+				AnchorRank = rank,
+			});
+			AddArrayProxyAssociations (model, proxy, proxyReference);
+		}
+
+		// Nullable counterparts of the primitive value types map to the boxed java/lang/<Boxed>
+		// references and, like System.String, are built-in element mappings (no scanned peer, no
+		// primitive proxy). Emit reference-array proxies (Primitive is null) so GetTypes
+		// ("[Ljava/lang/Boolean;") yields bool?[] / JavaObjectArray<bool?> on NativeAOT. The element
+		// key uses the normalized generic form (simple assembly names) that
+		// TrimmableTypeMap.BuildManagedTypeKey produces at runtime for Nullable<T>, while the model
+		// keeps the generic instantiation structured so the emitter writes a real Nullable<T> type
+		// signature. Like the primitives and System.String, these are a small fixed set of built-in
+		// element types (not the scanned-peer explosion), so they go up to maxArrayRank and keep
+		// multidim boxed arrays resolvable.
+		foreach (var nullablePrimitive in NullableArrayProxies) {
+			for (int rank = 1; rank <= maxArrayRank; rank++) {
+				var proxy = new ArrayProxyData {
+					TypeName = $"Nullable_{nullablePrimitive.Name}_ArrayProxy{rank}",
+					ElementType = new TypeRefData {
+						ManagedTypeName = "System.Nullable`1",
+						AssemblyName = "System.Runtime",
+						GenericArguments = [
+							new TypeRefData {
+								ManagedTypeName = nullablePrimitive.ManagedTypeName,
+								AssemblyName = "System.Runtime",
+								IsValueType = true,
+							},
+						],
+						IsValueType = true,
+					},
+					Rank = rank,
+				};
+				model.ArrayProxyTypes.Add (proxy);
+				var proxyReference = AssemblyQualify ($"{proxy.Namespace}.{proxy.TypeName}", model.AssemblyName);
+				model.Entries.Add (new TypeMapAttributeData {
+					MapKey = GetArrayProxyMapKey (proxy.ElementType),
+					ProxyTypeReference = proxyReference,
+					TargetTypeReference = proxyReference,
+					AnchorRank = rank,
+				});
+				AddArrayProxyAssociations (model, proxy, proxyReference);
+			}
+		}
 	}
 
 	static string Brackets (int rank) => rank switch {

@@ -27,10 +27,11 @@ public TypeMapAssemblyGenerator (Version systemRuntimeVersion)
 	/// <param name="useSharedTypemapUniverse">
 	/// When true, uses <c>Java.Lang.Object</c> as the shared anchor type. When false, emits a per-assembly anchor.
 	/// </param>
-	/// <param name="maxArrayRank">Max rank for per-rank array <c>TypeMap</c> entries. 0 disables.</param>
-	public void Generate (IReadOnlyList<JavaPeerInfo> peers, Stream stream, string assemblyName, bool useSharedTypemapUniverse = false, int maxArrayRank = 0)
+	/// <param name="maxArrayRank">Max rank for per-rank built-in element array <c>TypeMap</c> entries. 0 disables.</param>
+	/// <param name="maxReferenceArrayRank">Max rank for per-rank scanned Java peer reference-type array <c>TypeMap</c> entries. 0 disables.</param>
+	public void Generate (IReadOnlyList<JavaPeerInfo> peers, Stream stream, string assemblyName, bool useSharedTypemapUniverse = false, int maxArrayRank = 0, int maxReferenceArrayRank = 0)
 	{
-		var model = ModelBuilder.Build (peers, assemblyName + ".dll", assemblyName, maxArrayRank);
+		var model = ModelBuilder.Build (peers, assemblyName + ".dll", assemblyName, maxArrayRank, maxReferenceArrayRank);
 		var emitter = new TypeMapAssemblyEmitter (_systemRuntimeVersion);
 		emitter.Emit (model, stream, useSharedTypemapUniverse);
 	}

@@ -35,6 +35,7 @@ public TrimmableTypeMapResult Execute (
 		XDocument? manifestTemplate = null,
 		string? packageNamingPolicy = null,
 		int maxArrayRank = 0,
+		int maxReferenceArrayRank = 0,
 		bool generateTypeMapAssemblies = true)
 	{
 		_ = assemblies ?? throw new ArgumentNullException (nameof (assemblies));
@@ -43,6 +44,9 @@ public TrimmableTypeMapResult Execute (
 		if (maxArrayRank < 0) {
 			throw new ArgumentOutOfRangeException (nameof (maxArrayRank), maxArrayRank, "Must be >= 0.");
 		}
+		if (maxReferenceArrayRank < 0) {
+			throw new ArgumentOutOfRangeException (nameof (maxReferenceArrayRank), maxReferenceArrayRank, "Must be >= 0.");
+		}
 
 		var (allPeers, assemblyManifestInfo) = ScanAssemblies (assemblies, packageNamingPolicy, frameworkAssemblyNames);
 		if (allPeers.Count == 0) {
@@ -56,7 +60,7 @@ public TrimmableTypeMapResult Execute (
 		PropagateCannotRegisterToDescendants (allPeers);
 
 		var generatedAssemblies = generateTypeMapAssemblies
-			? GenerateTypeMapAssemblies (allPeers, systemRuntimeVersion, useSharedTypemapUniverse, maxArrayRank)
+			? GenerateTypeMapAssemblies (allPeers, systemRuntimeVersion, useSharedTypemapUniverse, maxArrayRank, maxReferenceArrayRank)
 			: [];
 		var jcwPeers = allPeers.Where (ShouldGenerateJcw).ToList ();
 		logger.LogGeneratingJcwFilesInfo (jcwPeers.Count, allPeers.Count);
@@ -178,7 +182,8 @@ List<GeneratedAssembly> GenerateTypeMapAssemblies (
 		List<JavaPeerInfo> allPeers,
 		Version systemRuntimeVersion,
 		bool useSharedTypemapUniverse,
-		int maxArrayRank)
+		int maxArrayRank,
+		int maxReferenceArrayRank)
 	{
 		List<(string AssemblyName, List<JavaPeerInfo> Peers)> peersByAssembly;
 
@@ -207,14 +212,16 @@ List<GeneratedAssembly> GenerateTypeMapAssemblies (
 			string typeMapAssemblyName = $"_{assemblyName}.TypeMap";
 			perAssemblyNames.Add (typeMapAssemblyName);
 			var stream = new MemoryStream ();
-			generator.Generate (peers, stream, typeMapAssemblyName, useSharedTypemapUniverse, maxArrayRank);
+			generator.Generate (peers, stream, typeMapAssemblyName, useSharedTypemapUniverse, maxArrayRank, maxReferenceArrayRank);
 			stream.Position = 0;
 			generatedAssemblies.Add (new GeneratedAssembly (typeMapAssemblyName, stream));
 			logger.LogGeneratedTypeMapAssemblyInfo (typeMapAssemblyName, peers.Count);
 		}
 		var rootStream = new MemoryStream ();
 		var rootGenerator = new RootTypeMapAssemblyGenerator (systemRuntimeVersion);
-		rootGenerator.Generate (perAssemblyNames, useSharedTypemapUniverse, rootStream, maxArrayRank: maxArrayRank);
+		// The root generator builds the [assembly][rank] anchor matrix, so it needs the overall maximum
+		// rank across primitive and reference element types.
+		rootGenerator.Generate (perAssemblyNames, useSharedTypemapUniverse, rootStream, maxArrayRank: Math.Max (maxArrayRank, maxReferenceArrayRank));
 		rootStream.Position = 0;
 		generatedAssemblies.Add (new GeneratedAssembly ("_Microsoft.Android.TypeMaps", rootStream));
 		logger.LogGeneratedRootTypeMapInfo (perAssemblyNames.Count);

@@ -42,7 +42,7 @@ public sealed class JavaPeerAliasesAttribute : Attribute
 	[AttributeUsage (AttributeTargets.Class | AttributeTargets.Interface, Inherited = false, AllowMultiple = false)]
 	public abstract class JavaPeerProxy : Attribute
 	{
-		private protected JavaPeerProxy (string jniName, Type targetType)
+		protected JavaPeerProxy (string jniName, Type targetType)
 		{
 			ArgumentNullException.ThrowIfNull (jniName);
 			ArgumentNullException.ThrowIfNull (targetType);

@@ -6,6 +6,7 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 using System.Runtime.InteropServices;
+using System.Text;
 using System.Threading;
 using Android.Runtime;
 using Java.Interop;
@@ -543,25 +544,58 @@ internal bool TryGetArrayProxy (Type elementType, int additionalRank, [NotNullWh
 
 	static bool TryGetManagedTypeKey (Type type, [NotNullWhen (true)] out string? key)
 	{
-		var fullName = type.FullName;
-		if (fullName is null) {
-			key = null;
-			return false;
-		}
+		key = BuildManagedTypeKey (type);
+		return key is not null;
+	}
 
+	// Builds the array-proxy map key for a managed type. Closed generic types use a normalized,
+	// version-independent form so the key matches the one emitted by the trimmable typemap generator,
+	// which references types by simple assembly name (no Version/Culture/PublicKeyToken). Without
+	// normalization a closed generic like Nullable<bool> would key on Type.FullName, whose type
+	// arguments carry the full versioned assembly-qualified name and would never match.
+	static string? BuildManagedTypeKey (Type type)
+	{
 		var assemblyName = GetAssemblyNameForManagedTypeKey (type);
 		if (assemblyName is null) {
-			key = null;
-			return false;
+			return null;
 		}
 
-		key = $"{fullName}, {assemblyName}";
-		return true;
+		if (type.IsGenericType && !type.IsGenericTypeDefinition) {
+			var definitionName = type.GetGenericTypeDefinition ().FullName;
+			if (definitionName is null) {
+				return null;
+			}
+			var arguments = type.GetGenericArguments ();
+			var builder = new StringBuilder (definitionName);
+			builder.Append ("[[");
+			for (int i = 0; i < arguments.Length; i++) {
+				if (i > 0) {
+					builder.Append ("],[");
+				}
+				var argumentKey = BuildManagedTypeKey (arguments [i]);
+				if (argumentKey is null) {
+					return null;
+				}
+				builder.Append (argumentKey);
+			}
+			builder.Append ("]], ");
+			builder.Append (assemblyName);
+			return builder.ToString ();
+		}
+
+		var fullName = type.FullName;
+		if (fullName is null) {
+			return null;
+		}
+		return $"{fullName}, {assemblyName}";
 	}
 
 	static string? GetAssemblyNameForManagedTypeKey (Type type)
 	{
-		if (type.IsPrimitive || type == typeof (string)) {
+		// Primitives, string, and Nullable<T> are surfaced through the System.Runtime reference
+		// assembly; the trimmable typemap generator emits their keys with "System.Runtime", so
+		// normalize to it here (the runtime implementation assembly is System.Private.CoreLib).
+		if (type.IsPrimitive || type == typeof (string) || Nullable.GetUnderlyingType (type) is not null) {
 			return "System.Runtime";
 		}
 

@@ -80,6 +80,7 @@
         TargetFrameworkVersion="$(TargetFrameworkVersion)"
         PackageNamingPolicy="$(_TrimmableTypeMapPackageNamingPolicy)"
         MaxArrayRank="$(_AndroidTrimmableTypeMapMaxArrayRank)"
+        MaxReferenceArrayRank="$(_AndroidTrimmableTypeMapMaxReferenceArrayRank)"
         GenerateTypeMapAssemblies="false"
         CleanJavaSourceOutputDirectory="true"
         AcwMapOutputFile="$(IntermediateOutputPath)acw-map.txt"