Fix trimmer size regression: remove TrimmableTypeMap field from ValueManager

Two changes to prevent TrimmableTypeMap types from leaking into MonoVM builds:

1. Add ILLink substitutions for IsMonoRuntime and IsCoreClrRuntime.
   Without these, the trimmer can't eliminate runtime-specific branches
   (e.g. the CoreCLR JavaMarshalValueManager path stays in MonoVM builds).

2. Remove TrimmableTypeMap? _typeMap field from JavaMarshalValueManager.
   Access via TrimmableTypeMap.Instance singleton instead. The field
   reference was rooting the entire TrimmableTypeMap type graph even
   when the feature switch was false.

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

Author: simonrozsival

src/Microsoft.Android.Runtime.NativeAOT/Android.Runtime.NativeAOT/JavaInteropRuntime.cs

@@ -61,13 +61,13 @@ static void init (IntPtr jnienv, IntPtr klass, IntPtr classLoader, IntPtr langua
 			var settings    = new DiagnosticSettings ();
 			settings.AddDebugDotnetLog ();
 
-			var (typeManager, trimmableTypeMap) = CreateTypeManager ();
+			var typeManager = CreateTypeManager ();
 
 			var options = new NativeAotRuntimeOptions {
 				EnvironmentPointer          = jnienv,
 				ClassLoader                 = new JniObjectReference (classLoader, JniObjectReferenceType.Global),
 				TypeManager                 = typeManager,
-				ValueManager                = new JavaMarshalValueManager (trimmableTypeMap),
+				ValueManager                = new JavaMarshalValueManager (),
 				UseMarshalMemberBuilder     = false,
 				JniGlobalReferenceLogWriter = settings.GrefLog,
 				JniLocalReferenceLogWriter  = settings.LrefLog,
@@ -89,13 +89,12 @@ static void init (IntPtr jnienv, IntPtr klass, IntPtr classLoader, IntPtr langua
 		transition.Dispose ();
 	}
 
-	static (JniRuntime.JniTypeManager, TrimmableTypeMap?) CreateTypeManager ()
+	static JniRuntime.JniTypeManager CreateTypeManager ()
 	{
 		if (RuntimeFeature.TrimmableTypeMap) {
-			var map = new TrimmableTypeMap ();
-			return (new TrimmableTypeMapTypeManager (map), map);
+			return new TrimmableTypeMapTypeManager ();
 		}
 
-		return (new ManagedTypeManager (), null);
+		return new ManagedTypeManager ();
 	}
 }

src/Mono.Android/Android.Runtime/JNIEnvInit.cs

@@ -135,11 +135,9 @@ internal static unsafe void Initialize (JnienvInitializeArgs* args)
 			BoundExceptionType = (BoundExceptionType)args->ioExceptionType;
 			JniRuntime.JniTypeManager typeManager;
 			JniRuntime.JniValueManager? valueManager = null;
-			TrimmableTypeMap? trimmableTypeMap = null;
 			if (RuntimeFeature.TrimmableTypeMap) {
-				trimmableTypeMap = new TrimmableTypeMap ();
-				typeManager     = new TrimmableTypeMapTypeManager (trimmableTypeMap);
-				valueManager    = new JavaMarshalValueManager (trimmableTypeMap);
+				typeManager     = new TrimmableTypeMapTypeManager ();
+				valueManager    = new JavaMarshalValueManager ();
 			} else if (RuntimeFeature.ManagedTypeMap) {
 				typeManager     = new ManagedTypeManager ();
 			} else {
@@ -163,7 +161,7 @@ internal static unsafe void Initialize (JnienvInitializeArgs* args)
 			);
 
 			if (RuntimeFeature.TrimmableTypeMap) {
-				trimmableTypeMap?.RegisterBootstrapNativeMethod ();
+				TrimmableTypeMap.Initialize ();
 			}
 
 			grefIGCUserPeer_class = args->grefIGCUserPeer;

src/Mono.Android/ILLink/ILLink.Substitutions.xml

@@ -5,6 +5,10 @@
       <method signature="System.Boolean get_NegotiateAuthenticationIsEnabled()" body="stub" feature="Xamarin.Android.Net.UseNegotiateAuthentication" featurevalue="true" value="true" />
     </type>
     <type fullname="Microsoft.Android.Runtime.RuntimeFeature">
+      <method signature="System.Boolean get_IsMonoRuntime()" body="stub" feature="Microsoft.Android.Runtime.RuntimeFeature.IsMonoRuntime" featurevalue="false" value="false" />
+      <method signature="System.Boolean get_IsMonoRuntime()" body="stub" feature="Microsoft.Android.Runtime.RuntimeFeature.IsMonoRuntime" featurevalue="true" value="true" />
+      <method signature="System.Boolean get_IsCoreClrRuntime()" body="stub" feature="Microsoft.Android.Runtime.RuntimeFeature.IsCoreClrRuntime" featurevalue="false" value="false" />
+      <method signature="System.Boolean get_IsCoreClrRuntime()" body="stub" feature="Microsoft.Android.Runtime.RuntimeFeature.IsCoreClrRuntime" featurevalue="true" value="true" />
       <method signature="System.Boolean get_ManagedTypeMap()" body="stub" feature="Microsoft.Android.Runtime.RuntimeFeature.ManagedTypeMap" featurevalue="false" value="false" />
       <method signature="System.Boolean get_ManagedTypeMap()" body="stub" feature="Microsoft.Android.Runtime.RuntimeFeature.ManagedTypeMap" featurevalue="true" value="true" />
       <method signature="System.Boolean get_TrimmableTypeMap()" body="stub" feature="Microsoft.Android.Runtime.RuntimeFeature.TrimmableTypeMap" featurevalue="false" value="false" />

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

@@ -34,12 +34,8 @@ class JavaMarshalValueManager : JniRuntime.JniValueManager
 	public static JavaMarshalValueManager Instance =>
 		s_instance ?? throw new InvalidOperationException ("JavaMarshalValueManager has not been initialized. Call the constructor first.");
 
-	readonly TrimmableTypeMap? _typeMap;
-
-	unsafe internal JavaMarshalValueManager (TrimmableTypeMap? typeMap = null)
+	unsafe internal JavaMarshalValueManager ()
 	{
-		_typeMap = typeMap;
-
 		var previous = Interlocked.CompareExchange (ref s_instance, this, null);
 		Debug.Assert (previous is null, "JavaMarshalValueManager must only be created once.");
 
@@ -512,8 +508,9 @@ void ProcessContext (HandleContext* context)
 			Type? targetType)
 	{
 		if (RuntimeFeature.TrimmableTypeMap) {
-			if (_typeMap is not null && targetType is not null) {
-				var proxy = _typeMap.GetProxyForManagedType (targetType);
+			var typeMap = TrimmableTypeMap.Instance;
+			if (typeMap is not null && targetType is not null) {
+				var proxy = typeMap.GetProxyForManagedType (targetType);
 				if (proxy is not null) {
 					var peer = proxy.CreateInstance (reference.Handle, JniHandleOwnership.DoNotTransfer);
 					if (peer is not null) {

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

@@ -22,29 +22,36 @@ class TrimmableTypeMap
 {
 	static TrimmableTypeMap? s_instance;
 
-	internal static TrimmableTypeMap? Instance => s_instance;
+	internal static TrimmableTypeMap Instance =>
+		s_instance ?? throw new InvalidOperationException (
+			"TrimmableTypeMap has not been initialized. Ensure RuntimeFeature.TrimmableTypeMap is enabled and the JNI runtime is initialized.");
 
 	readonly IReadOnlyDictionary<string, Type> _typeMap;
 	readonly ConcurrentDictionary<Type, JavaPeerProxy?> _proxyCache = new ();
 
-	internal TrimmableTypeMap ()
+	TrimmableTypeMap ()
 	{
-		// The runtime's GetOrCreateExternalTypeMapping handles assembly resolution
-		// automatically via the System.Runtime.InteropServices.TypeMappingEntryAssembly
-		// config property (set in Trimmable.targets). It loads the entry assembly
-		// (_Microsoft.Android.TypeMaps), walks its TypeMapAssemblyTargetAttribute
-		// attributes, and recursively loads each referenced assembly.
 		_typeMap = TypeMapping.GetOrCreateExternalTypeMapping<Java.Lang.Object> ();
+	}
 
-		var previous = Interlocked.CompareExchange (ref s_instance, this, null);
+	/// <summary>
+	/// Initializes the singleton instance and registers the bootstrap JNI native method.
+	/// Must be called after the JNI runtime is initialized and before any JCW class is loaded.
+	/// </summary>
+	internal static void Initialize ()
+	{
+		var instance = new TrimmableTypeMap ();
+		var previous = Interlocked.CompareExchange (ref s_instance, instance, null);
 		Debug.Assert (previous is null, "TrimmableTypeMap must only be created once.");
+
+		instance.RegisterBootstrapNativeMethod ();
 	}
 
 	/// <summary>
 	/// Registers the <c>mono.android.Runtime.registerNatives</c> JNI native method.
 	/// Must be called after the JNI runtime is initialized and before any JCW class is loaded.
 	/// </summary>
-	internal void RegisterBootstrapNativeMethod ()
+	void RegisterBootstrapNativeMethod ()
 	{
 		using var runtimeClass = new JniType ("mono/android/Runtime");
 		JniEnvironment.Types.RegisterNatives (

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

@@ -15,20 +15,13 @@ namespace Microsoft.Android.Runtime;
 /// </summary>
 class TrimmableTypeMapTypeManager : JniRuntime.JniTypeManager
 {
-	readonly TrimmableTypeMap _map;
-
-	internal TrimmableTypeMapTypeManager (TrimmableTypeMap map)
-	{
-		_map = map;
-	}
-
 	protected override IEnumerable<Type> GetTypesForSimpleReference (string jniSimpleReference)
 	{
 		foreach (var t in base.GetTypesForSimpleReference (jniSimpleReference)) {
 			yield return t;
 		}
 
-		if (_map.TryGetType (jniSimpleReference, out var type)) {
+		if (TrimmableTypeMap.Instance.TryGetType (jniSimpleReference, out var type)) {
 			yield return type;
 		}
 	}
@@ -59,7 +52,7 @@ protected override IEnumerable<string> GetSimpleReferences (Type type)
 			[DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
 			Type type)
 	{
-		var invokerType = _map.GetInvokerType (type);
+		var invokerType = TrimmableTypeMap.Instance.GetInvokerType (type);
 		if (invokerType != null) {
 			return invokerType;
 		}