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[TrimmableTypeMap] Add AOT-safe array and collection factories using MakeArrayType and MakeGenericType #12030

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ca78fa2
[TrimmableTypeMap] Add AOT-safe array and collection factories
simonrozsival Jul 9, 2026
db04690
[TrimmableTypeMap] Address safe collection factory review
simonrozsival Jul 9, 2026
9e0ce62
[TrimmableTypeMap] Document NativeAOT factory assumptions
simonrozsival Jul 9, 2026
0c62664
[TrimmableTypeMap] Share primitive value type factories
simonrozsival Jul 9, 2026
53d50fb
[TrimmableTypeMap] Clarify array factory AOT justification
simonrozsival Jul 9, 2026
b959f4a
[TrimmableTypeMap] Fix NativeAOT warning leak and update apk size bas…
simonrozsival Jul 9, 2026
1143044
[TrimmableTypeMap] Address review: file-scoped namespaces, drop unuse…
simonrozsival Jul 9, 2026
d41d005
[TrimmableTypeMap] Fix nullable warnings in SafeJavaCollectionFactory
simonrozsival Jul 9, 2026
187d9fa
[TrimmableTypeMap] Address review: value/value dict test, drop unused…
simonrozsival Jul 9, 2026
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163 changes: 128 additions & 35 deletions src/Mono.Android/Android.Runtime/JNIEnv.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -28,48 +28,14 @@ public static partial class JNIEnv {
static Array ArrayCreateInstance (Type elementType, int length)
{
if (RuntimeFeature.TrimmableTypeMap) {
if (RuntimeFeature.IsCoreClrRuntime) {
// CoreCLR runtime type loader can construct any T[] dynamically.
// IsDynamicCodeSupported is a [FeatureGuard] so this branch is
// dead-coded under PublishAot.
return Array.CreateInstance (elementType, length);
}

if (RuntimeFeature.IsNativeAotRuntime) {
// NativeAOT: resolve via per-rank typemap + generated array proxy.
if (TrimmableTypeMap.Instance.TryGetArrayProxy (elementType, additionalRank: 1, out var arrayProxy)) {
return arrayProxy.CreateManagedArray (length);
}
}

int arrayRank = GetArrayRank (elementType, out var leafElementType);
throw new NotSupportedException (
$"No TrimmableTypeMap array proxy entry for element type '{elementType}' " +
$"(leaf element type '{leafElementType}', rank {arrayRank}). " +
$"Array lookups use the leaf element type within the per-rank __ArrayMapRank{arrayRank} typemap group; " +
$"ensure the mapping is emitted for that rank (for example by increasing _AndroidTrimmableTypeMapMaxArrayRank) or report an issue.");
return SafeArrayFactory.CreateInstance (elementType, rank: 1, length);
}

#pragma warning disable IL3050 // legacy fallback path
return Array.CreateInstance (elementType, length);
#pragma warning restore IL3050
}

static int GetArrayRank (Type elementType, out Type leafElementType)
{
int rank = 1;
while (elementType.IsSZArray) {
rank++;
var nestedElementType = elementType.GetElementType ();
if (nestedElementType is null) {
break;
}
elementType = nestedElementType;
}
leafElementType = elementType;
return rank;
}

internal static IntPtr IdentityHash (IntPtr v)
{
return JniEnvironment.References.GetIdentityHashCode (new JniObjectReference (v));
Expand Down Expand Up @@ -605,11 +571,29 @@ static void AssertCompatibleArrayTypes (IntPtr sourceArray, Type destElementType

static IntPtr FindArrayClassByElementType (Type elementType)
{
var boxedPrimitiveJniClassName = GetBoxedPrimitiveJniClassName (elementType);
if (boxedPrimitiveJniClassName != null) {
return FindClass ("[L" + boxedPrimitiveJniClassName + ";");
}

int rank = JavaNativeTypeManager.GetArrayInfo (elementType, out elementType) + 1;
var typeSignature = JniRuntime.CurrentRuntime.TypeManager.GetTypeSignature (elementType).AddArrayRank (rank);
return FindClass (typeSignature.Name);
}

static string? GetBoxedPrimitiveJniClassName (Type type)
{
if (type == typeof (bool?)) return "java/lang/Boolean";
if (type == typeof (sbyte?)) return "java/lang/Byte";
if (type == typeof (char?)) return "java/lang/Character";
if (type == typeof (short?)) return "java/lang/Short";
if (type == typeof (int?)) return "java/lang/Integer";
if (type == typeof (long?)) return "java/lang/Long";
if (type == typeof (float?)) return "java/lang/Float";
if (type == typeof (double?)) return "java/lang/Double";
return null;
}

public static void CopyArray (IntPtr src, bool[] dest)
{
if (dest == null)
Expand Down Expand Up @@ -684,6 +668,14 @@ public static void CopyArray (IntPtr src, string[] dest)
_GetDoubleArrayRegion (source, index, 1, r);
return r [0];
} },
{ typeof (bool?), (type, source, index) => GetNullableArrayElement (source, index, typeof (bool?)) },
{ typeof (sbyte?), (type, source, index) => GetNullableArrayElement (source, index, typeof (sbyte?)) },
{ typeof (char?), (type, source, index) => GetNullableArrayElement (source, index, typeof (char?)) },
{ typeof (short?), (type, source, index) => GetNullableArrayElement (source, index, typeof (short?)) },
{ typeof (int?), (type, source, index) => GetNullableArrayElement (source, index, typeof (int?)) },
{ typeof (long?), (type, source, index) => GetNullableArrayElement (source, index, typeof (long?)) },
{ typeof (float?), (type, source, index) => GetNullableArrayElement (source, index, typeof (float?)) },
{ typeof (double?), (type, source, index) => GetNullableArrayElement (source, index, typeof (double?)) },
{ typeof (string), (type, source, index) => {
IntPtr elem = GetObjectArrayElement (source, index);
if (type == typeof (Java.Lang.String))
Expand All @@ -709,6 +701,12 @@ public static void CopyArray (IntPtr src, string[] dest)
};
}

static object? GetNullableArrayElement (IntPtr source, int index, [DynamicallyAccessedMembers (Constructors)] Type targetType)
{
IntPtr elem = GetObjectArrayElement (source, index);
return JavaConvert.FromJniHandle (elem, JniHandleOwnership.TransferLocalRef, targetType);
}

static TValue GetConverter<TValue>(Dictionary<Type, TValue> dict, Type? elementType, IntPtr array)
{
TValue? converter;
Expand Down Expand Up @@ -913,6 +911,14 @@ static Dictionary<Type, Action<Array, IntPtr>> CreateCopyManagedToNativeArray ()
{ typeof (long), (source, dest) => CopyArray ((long[]) source, dest) },
{ typeof (float), (source, dest) => CopyArray ((float[]) source, dest) },
{ typeof (double), (source, dest) => CopyArray ((double[]) source, dest) },
{ typeof (bool?), (source, dest) => CopyManagedObjectArray (source, dest) },
{ typeof (sbyte?), (source, dest) => CopyManagedObjectArray (source, dest) },
{ typeof (char?), (source, dest) => CopyManagedObjectArray (source, dest) },
{ typeof (short?), (source, dest) => CopyManagedObjectArray (source, dest) },
{ typeof (int?), (source, dest) => CopyManagedObjectArray (source, dest) },
{ typeof (long?), (source, dest) => CopyManagedObjectArray (source, dest) },
{ typeof (float?), (source, dest) => CopyManagedObjectArray (source, dest) },
{ typeof (double?), (source, dest) => CopyManagedObjectArray (source, dest) },
{ typeof (string), (source, dest) => {
var s = source as string[];
if (s != null) {
Expand Down Expand Up @@ -942,6 +948,23 @@ static Dictionary<Type, Action<Array, IntPtr>> CreateCopyManagedToNativeArray ()
};
}

static void CopyManagedObjectArray (Array source, IntPtr dest)
{
// Inlined equivalent of JavaConvert.WithLocalJniHandle to avoid allocating a capturing
// closure per element (this runs once per array element for both NewObjectArray and the
// nullable-primitive CopyManagedToNativeArray entries).
for (int i = 0; i < source.Length; i++) {
object? value = source.GetValue (i);
IntPtr lref = JavaConvert.ToLocalJniHandle (value);
try {
SetObjectArrayElement (dest, i, lref);
} finally {
DeleteLocalRef (lref);
GC.KeepAlive (value);
}
}
}

public static void CopyArray (Array source, Type elementType, IntPtr dest)
{
if (source == null)
Expand Down Expand Up @@ -1045,6 +1068,14 @@ public static void CopyArray<T> (T[] src, IntPtr dest)
CopyArray (source, r);
return r;
} },
{ typeof (bool?), (type, source, len) => CreateManagedArrayFromObjectArray (type, source, len) },
{ typeof (sbyte?), (type, source, len) => CreateManagedArrayFromObjectArray (type, source, len) },
{ typeof (char?), (type, source, len) => CreateManagedArrayFromObjectArray (type, source, len) },
{ typeof (short?), (type, source, len) => CreateManagedArrayFromObjectArray (type, source, len) },
{ typeof (int?), (type, source, len) => CreateManagedArrayFromObjectArray (type, source, len) },
{ typeof (long?), (type, source, len) => CreateManagedArrayFromObjectArray (type, source, len) },
{ typeof (float?), (type, source, len) => CreateManagedArrayFromObjectArray (type, source, len) },
{ typeof (double?), (type, source, len) => CreateManagedArrayFromObjectArray (type, source, len) },
{ typeof (string), (type, source, len) => {
if (type != null && typeof (Java.Lang.Object).IsAssignableFrom (type)) {
var r = new Java.Lang.String [len];
Expand All @@ -1069,6 +1100,16 @@ public static void CopyArray<T> (T[] src, IntPtr dest)
};
}

static Array CreateManagedArrayFromObjectArray (Type? elementType, IntPtr source, int len)
{
if (elementType == null)
throw new ArgumentNullException ("elementType");

@github-actions github-actions Bot Jul 10, 2026

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🤖 💡 Formatting — Use nameof (elementType) instead of the string literal "elementType" so the argument name stays correct under future renames.

throw new ArgumentNullException (nameof (elementType));

(Rule: Prefer nameof for argument names — repo-conventions)


var r = ArrayCreateInstance (elementType, len);
CopyArray (source, r, elementType);
return r;
}

static Array? _GetArray (IntPtr array_ptr, Type? element_type)
{
if (array_ptr == IntPtr.Zero)
Expand Down Expand Up @@ -1321,12 +1362,48 @@ static Dictionary<Type, Func<Array, IntPtr>> CreateCreateManagedToNativeArray ()
{ typeof (long), (source) => NewArray ((long[]) source) },
{ typeof (float), (source) => NewArray ((float[]) source) },
{ typeof (double), (source) => NewArray ((double[]) source) },
{ typeof (bool?), (source) => NewObjectArray (source, typeof (bool?)) },
{ typeof (sbyte?), (source) => NewObjectArray (source, typeof (sbyte?)) },
{ typeof (char?), (source) => NewObjectArray (source, typeof (char?)) },
{ typeof (short?), (source) => NewObjectArray (source, typeof (short?)) },
{ typeof (int?), (source) => NewObjectArray (source, typeof (int?)) },
{ typeof (long?), (source) => NewObjectArray (source, typeof (long?)) },
{ typeof (float?), (source) => NewObjectArray (source, typeof (float?)) },
{ typeof (double?), (source) => NewObjectArray (source, typeof (double?)) },
{ typeof (string), (source) => NewArray ((string[]) source) },
{ typeof (IJavaObject), (source) => NewArray ((IJavaObject[]) source) },
{ typeof (Array), (source) => NewArray (source) },
};
}

static IntPtr NewObjectArray (Array value, Type elementType)
{
IntPtr grefArrayElementClass = FindObjectArrayElementClass (elementType);
try {
IntPtr array = IntPtr.Zero;
try {
array = NewObjectArray (value.Length, grefArrayElementClass, IntPtr.Zero);
CopyManagedObjectArray (value, array);
return array;
} catch {
DeleteLocalRef (array);
throw;
}
} finally {
DeleteGlobalRef (grefArrayElementClass);
}
}

static IntPtr FindObjectArrayElementClass (Type elementType)
{
var boxedPrimitiveJniClassName = GetBoxedPrimitiveJniClassName (elementType);
if (boxedPrimitiveJniClassName != null) {
return FindClass (boxedPrimitiveJniClassName);
}

return FindClass (elementType);
}

public static IntPtr NewArray (Array value, Type? elementType = null)
{
if (value == null)
Expand Down Expand Up @@ -1436,6 +1513,14 @@ static IntPtr NewArray (Array value, Type elementType, IntPtr elementClass)
var _value = new[]{(double) value!};
_SetDoubleArrayRegion (dest, index, _value.Length, _value);
} },
{ typeof (bool?), (dest, index, value) => SetObjectArrayElementFromManagedValue (dest, index, value) },
{ typeof (sbyte?), (dest, index, value) => SetObjectArrayElementFromManagedValue (dest, index, value) },
{ typeof (char?), (dest, index, value) => SetObjectArrayElementFromManagedValue (dest, index, value) },
{ typeof (short?), (dest, index, value) => SetObjectArrayElementFromManagedValue (dest, index, value) },
{ typeof (int?), (dest, index, value) => SetObjectArrayElementFromManagedValue (dest, index, value) },
{ typeof (long?), (dest, index, value) => SetObjectArrayElementFromManagedValue (dest, index, value) },
{ typeof (float?), (dest, index, value) => SetObjectArrayElementFromManagedValue (dest, index, value) },
{ typeof (double?), (dest, index, value) => SetObjectArrayElementFromManagedValue (dest, index, value) },
{ typeof (string), (dest, index, value) => {
IntPtr s = NewString (value!.ToString ());
try {
Expand All @@ -1455,6 +1540,14 @@ static IntPtr NewArray (Array value, Type elementType, IntPtr elementClass)
};
}

static void SetObjectArrayElementFromManagedValue (IntPtr dest, int index, object? value)
{
JavaConvert.WithLocalJniHandle (value, lref => {
SetObjectArrayElement (dest, index, lref);
return IntPtr.Zero;
});
}

static unsafe void _SetBooleanArrayRegion (IntPtr array, int start, int length, bool[] buffer)
{
fixed (bool* p = buffer)
Expand Down
96 changes: 13 additions & 83 deletions src/Mono.Android/Java.Interop/JavaConvert.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -57,19 +57,6 @@ static class JavaConvert {
} },
};

static readonly Dictionary<Type, JavaPeerContainerFactory> ScalarContainerFactories = new Dictionary<Type, JavaPeerContainerFactory> {
{ typeof (bool), JavaPeerContainerFactory<bool>.Instance },
{ typeof (byte), JavaPeerContainerFactory<byte>.Instance },
{ typeof (sbyte), JavaPeerContainerFactory<sbyte>.Instance },
{ typeof (char), JavaPeerContainerFactory<char>.Instance },
{ typeof (short), JavaPeerContainerFactory<short>.Instance },
{ typeof (int), JavaPeerContainerFactory<int>.Instance },
{ typeof (long), JavaPeerContainerFactory<long>.Instance },
{ typeof (float), JavaPeerContainerFactory<float>.Instance },
{ typeof (double), JavaPeerContainerFactory<double>.Instance },
{ typeof (string), JavaPeerContainerFactory<string>.Instance },
};

static Func<IntPtr, JniHandleOwnership, object?>? GetJniHandleConverter (Type? target)
{
if (target == null)
Expand All @@ -89,9 +76,14 @@ static class JavaConvert {

if (target.IsGenericType && !target.IsGenericTypeDefinition) {
if (RuntimeFeature.TrimmableTypeMap) {
var factoryConverter = TryGetFactoryBasedConverter (target);
if (factoryConverter != null)
return factoryConverter;
if (SafeJavaCollectionFactory.TryGetCollectionType (target, out _)) {

@github-actions github-actions Bot Jul 10, 2026

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🤖 ⚠️ Performance — The resolved collection type from TryGetCollectionType is discarded here (out _) and used only as a boolean gate. TryCreateFromJniHandle then calls TryGetCollectionType again internally, so for reference-type generic collections (e.g. IList<string>, IDictionary<string,string>) MakeGenericType() runs twice per marshal — and GetJniHandleConverter isn't cached, so this repeats on every FromJniHandle call. Consider having the converter reuse the already-resolved Type (capture it in the closure) instead of recomputing it, to avoid the redundant reflection/allocation on a hot marshaling path.

For value/value shapes this probe is also slightly at odds with the AOT-safety design: TryGetCollectionType→GetClosedCollectionType calls MakeGenericType(JavaDictionary<,>, [int,long]) as an availability check even though creation goes through the rooted ValueTypeFactory path — the probe still relies on the exact instantiation being rooted.

(Rule: Avoid redundant reflection on hot paths — repo-conventions Performance)

return (h, t) => {
if (SafeJavaCollectionFactory.TryCreateFromJniHandle (target, h, t, out var collection)) {
return collection;
}
return null;
};
}
} else {
var factoryConverter = TryMakeGenericCollectionTypeFactory (target);
if (factoryConverter != null)
Expand All @@ -110,6 +102,11 @@ static class JavaConvert {

[UnconditionalSuppressMessage ("ReflectionAnalysis", "IL2055:RequiresUnreferencedCode",
Justification = "The target generic type is expected to be preserved by the trimmer as the target type in marshaling.")]
[UnconditionalSuppressMessage ("AOT", "IL3050:RequiresDynamicCode",
Justification = "This legacy MakeGenericType() path is only reached from the '!RuntimeFeature.TrimmableTypeMap' branch above, " +
"i.e. on the reflection-based Mono/CoreCLR runtimes where dynamic code is available. NativeAOT always enables the trimmable " +
"type map, so under AOT the branch above (SafeJavaCollectionFactory) is used instead and this helper is never executed. " +
"The AOT-safe generic collection construction lives in SafeJavaCollectionFactory.")]
static Func<IntPtr, JniHandleOwnership, object?>? TryMakeGenericCollectionTypeFactory (Type target)
{
if (target.GetGenericTypeDefinition() == typeof (IDictionary<,>)) {
Expand All @@ -129,73 +126,6 @@ static class JavaConvert {
}
}

/// <summary>
/// AOT-safe converter using <see cref="JavaPeerContainerFactory"/> from the generated proxy.
/// Avoids <c>MakeGenericType()</c> by using the pre-typed factory from the proxy attribute.
/// </summary>
static Func<IntPtr, JniHandleOwnership, object?>? TryGetFactoryBasedConverter (Type target)
{
if (TryGetSingleGenericArgument (target, typeof (IList<>), typeof (JavaList<>), out var listElementType)) {
var factory = TryGetContainerFactory (listElementType);
if (factory != null)
return (h, t) => factory.CreateList (h, t);
}

if (TryGetSingleGenericArgument (target, typeof (ICollection<>), typeof (JavaCollection<>), out var collectionElementType)) {
var factory = TryGetContainerFactory (collectionElementType);
if (factory != null)
return (h, t) => factory.CreateCollection (h, t);
}

if (TryGetDictionaryArguments (target, out var typeArgs)) {
var keyFactory = TryGetContainerFactory (typeArgs [0]);
var valueFactory = TryGetContainerFactory (typeArgs [1]);
if (keyFactory != null && valueFactory != null)
return (h, t) => valueFactory.CreateDictionary (keyFactory, h, t);
}

return null;

static bool TryGetSingleGenericArgument (Type target, Type interfaceType, Type wrapperType, [NotNullWhen (true)] out Type? argument)
{
if (target.IsGenericType && !target.IsGenericTypeDefinition) {
var genericDef = target.GetGenericTypeDefinition ();
if (genericDef == interfaceType || genericDef == wrapperType) {
argument = target.GetGenericArguments () [0];
return true;
}
}

argument = null;
return false;
}

static bool TryGetDictionaryArguments (Type target, [NotNullWhen (true)] out Type []? arguments)
{
if (target.IsGenericType && !target.IsGenericTypeDefinition) {
var genericDef = target.GetGenericTypeDefinition ();
if (genericDef == typeof (IDictionary<,>) || genericDef == typeof (JavaDictionary<,>)) {
arguments = target.GetGenericArguments ();
return true;
}
}

arguments = null;
return false;
}

static JavaPeerContainerFactory? TryGetContainerFactory (Type elementType)
{
if (ScalarContainerFactories.TryGetValue (elementType, out var scalarFactory))
return scalarFactory;

if (typeof (IJavaPeerable).IsAssignableFrom (elementType))
return TrimmableTypeMap.Instance?.GetContainerFactory (elementType);

return null;
}
}

static Func<IntPtr, JniHandleOwnership, object> GetJniHandleConverterForType ([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods)] Type t)
{
MethodInfo m = t.GetMethod ("FromJniHandle", BindingFlags.Static | BindingFlags.Public)!;
Expand Down
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