[TrimmableTypeMap] Implement runtime TypeManager, ValueManager, and JavaConvert by simonrozsival · Pull Request #10967 · dotnet/android

simonrozsival · 2026-03-18T17:37:58Z

Summary

Adds the runtime-side support for the trimmable typemap: type resolution, peer creation, native method registration, and AOT-safe collection marshaling. All behind RuntimeFeature.TrimmableTypeMap (defaults to false).

New runtime types

JavaPeerProxy / JavaPeerProxy<T> — AOT-safe proxy attribute base. Generated proxy types extend this and provide CreateInstance() for peer creation and GetContainerFactory() for collection marshaling.
IAndroidCallableWrapper — RegisterNatives(JniType) interface for ACW proxy types to register JNI native methods.
JavaPeerContainerFactory — AOT-safe factories for arrays, lists, collections, and dictionaries without MakeGenericType().
TrimmableTypeMap — Central class owning the TypeMapping dictionary. Encapsulates all proxy attribute access: peer creation, invoker resolution, container factories, and native method registration bootstrap.
TrimmableTypeMapTypeManager — JniTypeManager subclass delegating type lookups to TrimmableTypeMap. RegisterNativeMembers throws UnreachableException (JCW static blocks handle registration).

Type resolution

GetProxyForManagedType(Type) resolves managed type → JNI name via IJniNameProviderAttribute (shared interface for [Register] and [JniTypeSignature]) → TypeMap dictionary → proxy. Results cached in ConcurrentDictionary.
TryGetJniNameForType shared between TrimmableTypeMap and TrimmableTypeMapTypeManager.
ActivateInstance uses JNI GetObjectClass → GetJniTypeNameFromClass → TypeMap lookup for constructor activation (proxy types have self-applied attribute, not the target type).

TypeMap dictionary initialization

The runtime's GetOrCreateExternalTypeMapping<Java.Lang.Object>() handles assembly resolution automatically via the System.Runtime.InteropServices.TypeMappingEntryAssembly runtimeconfig property (set in Trimmable.targets). No manual Assembly.Load pre-loading is needed — the runtime walks TypeMapAssemblyTargetAttribute attributes from the entry assembly recursively.

Native interop refactoring

RegisterJniNatives passed via init args — Initialize sets args->registerJniNativesFn (null when TrimmableTypeMap=true). Eliminates the create_delegate call for RegisterJniNatives, letting the trimmer remove it cleanly in the trimmable path.
C++ registerNatives stub — Host::Java_mono_android_Runtime_registerNatives no-op for the trimmable path (managed code handles registration via Initialize).
Null guard on jnienv_register_jni_natives call site.
Initialize is now the singlecreate_delegate entry point from native code.

RegisterNatives bootstrap

mono.android.Runtime.registerNatives(Class) Java native method added
TrimmableTypeMap.Initialize() registers the JNI callback during init (behind explicit if (RuntimeFeature.TrimmableTypeMap) guard for trimmer compatibility)
When Java loads a JCW class, OnRegisterNatives resolves the proxy and calls IAndroidCallableWrapper.RegisterNatives() to bind UCO function pointers

AOT-safe JavaConvert

JavaConvert.GetJniHandleConverter() uses JavaPeerContainerFactory for IList, ICollection, IDictionary
JNIEnv.ArrayCreateInstance() uses factory path

Peer creation

JavaMarshalValueManager (renamed from ManagedValueManager) overrides CreatePeer for the trimmable path — calls proxy.CreateInstance() directly, bypassing GetUninitializedObject
GetSimpleReferences walks base type chain for managed-only subclasses without [Register]

Wiring

RuntimeFeature.TrimmableTypeMap feature switch with ILLink substitutions
JNIEnvInit (CoreCLR) and JavaInteropRuntime + JreRuntime (NativeAOT) create the new managers when the feature is on
JavaMarshalValueManager (renamed from ManagedValueManager) gets proxy-based peer creation in TryConstructPeer

Dependencies

Add RegisterNatives overload for raw function pointers java-interop#1391 (RegisterNatives with raw function pointers — follow-up optimization)
Manifest generator: [TrimmableTypeMap] Add ManifestGenerator #10991
Build pipeline: [TrimmableTypeMap] Build pipeline: targets, scanner, task, assembly store #10980

Test coverage

255/255 generator tests pass
End-to-end HelloWorld app runs on device with Activity, layout XML, FindViewById<Button>, Click events
Runtime tests require device integration (tracked by [TrimmableTypeMap] Functional validation #10793)

Trimmer size regression prevention

Add ILLink substitutions for IsMonoRuntime and IsCoreClrRuntime — enables trimmer to eliminate runtime-specific branches
JavaMarshalValueManager: remove TrimmableTypeMap? field, use TrimmableTypeMap.Instance singleton
TrimmableTypeMap: private ctor, Initialize() static method, Instance throws if not initialized
TrimmableTypeMapTypeManager: no constructor parameter, uses singleton
No TrimmableTypeMap type references outside feature guards — clean trimming for MonoVM/NativeAOT

simonrozsival

🤖 AI Review Summary

Verdict: ⚠️ Needs Changes (CI pending)

Found 0 code issues. CI is still running (dotnet-android and Xamarin.Android-PR in progress). Review will need to be re-evaluated once CI completes.

Code review

✅ No null-forgiving operator (!) usage
✅ All new files have #nullable enable
✅ Proper Mono style (tabs, space before () and [])
✅ Namespace style consistent with existing files
✅ Feature flag with ILLink substitutions follows established pattern
✅ Interlocked.CompareExchange + Debug.Assert for single-instance safety in both TrimmableTypeMap and JavaMarshalValueManager
✅ JNI callback delegate properly rooted in static field (s_onRegisterNatives)
✅ OnRegisterNatives calls Environment.FailFast on error (unrecoverable state)
✅ All TODO comments reference tracking issues (#10794 or java-interop #1391)
✅ TypeMapException is sealed
✅ TryGetType uses [NotNullWhen(true)] annotation
✅ 255/255 generator tests pass
✅ Mono.Android.dll builds locally

Architecture notes

Clean encapsulation: all proxy attribute access goes through TrimmableTypeMap — JavaPeerProxy is not leaked to callers
JavaMarshalValueManager (renamed from ManagedValueManager) takes TrimmableTypeMap? in constructor — immutable, no settable property
TrimmableTypeMapTypeManager delegates all lookups to TrimmableTypeMap
RegisterNatives bootstrap: Java → managed callback → proxy → IAndroidCallableWrapper.RegisterNatives(JniType) → UCO function pointers
All behind RuntimeFeature.TrimmableTypeMap (default false) — zero impact when off

Review generated by android-reviewer from review guidelines.

Copilot

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jonathanpeppers

This file grew:

"lib/arm64-v8a/lib_System.Private.CoreLib.dll.so": {
-- "Size": 633928++ "Size": 691720
},

It's probably OK, but I wonder what did it.

simonrozsival · 2026-03-20T14:23:26Z

Re: the System.Private.CoreLib size increase — my best guess is that JNIEnv.ArrayCreateInstance was referencing TrimmableTypeMap.Instance unconditionally (without a RuntimeFeature.TrimmableTypeMap guard), which prevented the linker from trimming the entire TrimmableTypeMap dependency chain — ConcurrentDictionary, Assembly.Load, GetCustomAttributesData, Marshal.GetDelegateForFunctionPointer, etc. I've added the feature guard in the latest push to match the pattern in JavaConvert.cs. We'll see after the next CI run if that brings it back down.

- JavaPeerProxy / JavaPeerProxy<T> — AOT-safe proxy attribute base - IAndroidCallableWrapper — RegisterNatives(JniType) for ACW types - JavaPeerContainerFactory<T> — AOT-safe array/list/collection/dict - TypeMapException — error reporting Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Proxy types now extend JavaPeerProxy<T> instead of JavaPeerProxy. TargetType and GetContainerFactory() are inherited from the generic base. Generator references TrimmableTypeMap for ActivateInstance and RegisterMethod. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Add TrimmableTypeMap class with core typemap functionality: TryGetType, TryCreatePeer, GetInvokerType, GetContainerFactory, ActivateInstance. Add TrimmableTypeMapTypeManager delegating to TrimmableTypeMap. Rename ManagedValueManager to JavaMarshalValueManager. Add proxy-based peer creation in TryConstructPeer via TrimmableTypeMap.TryCreatePeer. Add RuntimeFeature.TrimmableTypeMap feature switch with ILLink substitutions. Wire into JNIEnvInit (CoreCLR) and JavaInteropRuntime + JreRuntime (NativeAOT). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Add registerNatives(Class) native method to mono.android.Runtime.java so JCW static initializer blocks can trigger native method registration. Add to TrimmableTypeMap: - RegisterBootstrapNativeMethod() registers the JNI callback during init - OnRegisterNatives() resolves the proxy and calls IAndroidCallableWrapper.RegisterNatives(JniType) to bind UCO ptrs - RegisterMethod() helper for per-method registration (TODO: batch) Wire RegisterBootstrapNativeMethod() call in JNIEnvInit after runtime creation. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

When TrimmableTypeMap is available, use JavaPeerContainerFactory from the proxy for IList<T>, ICollection<T>, IDictionary<K,V> marshaling and array creation instead of MakeGenericType/Array.CreateInstance. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Ranks 1-3: direct new T[], T[][], T[][][] — fully AOT-safe. Rank 4+: when dynamic code is supported (CoreCLR), falls back to MakeArrayType + CreateInstanceFromArrayType. Throws on NativeAOT. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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

TrimmableTypeMapTypeManager.GetSimpleReferences now walks the base type chain when a type has no TypeMap entry. This handles managed-only subclasses like JavaProxyThrowable (extends Error but has no [Register]) by resolving to the nearest registered ancestor's JNI name. Without this, error wrapping (RaisePendingException → JavaProxyThrowable) crashes with NotSupportedException before the real exception is visible. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The trimmable path uses proxy.CreateInstance() which creates a fully initialized peer. Override CreatePeer instead of TryConstructPeer to bypass the GetUninitializedObject + reflection pattern. This fixes JavaCast<T> where the pre-allocated shell from GetUninitializedObject was returned with Handle == IntPtr.Zero because CreateInstance created a separate object, ignoring the shell. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

ILLink/ILC needs the feature switch check as a standalone if statement to constant-propagate and eliminate the dead code branch. Compound conditions like 'RuntimeFeature.TrimmableTypeMap && x' may not be optimized correctly. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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

The runtime's GetOrCreateExternalTypeMapping already handles assembly resolution via System.Runtime.InteropServices.TypeMappingEntryAssembly config property. It loads the entry assembly, walks its TypeMapAssemblyTargetAttribute attributes, and recursively loads each referenced assembly. The explicit pre-loading loop was redundant and cost ~70ms at startup (46ms Assembly.Load + 24ms GetCustomAttributesData). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…Manager 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>

…al/trimmable-typemap-runtime-pr

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

[FeatureSwitchDefinition] on the properties already tells the trimmer to substitute these getters, making the XML entries unnecessary. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival · 2026-03-24T15:58:27Z

Good call — removed all the RuntimeFeature entries from the substitutions XML. [FeatureSwitchDefinition] on the properties is sufficient for the trimmer. 7cb0913

simonrozsival

🤖 AI Review Summary

Verdict: ✅ LGTM

Found 2 suggestions (no blockers):

💡 Patterns: TrimmableTypeMap.Instance throws on null, making downstream ?. and is not null guards dead code — 3 locations (JNIEnv.cs:30, JavaMarshalValueManager.cs:512, JavaConvert.cs:152)
💡 Nullable: Use provider.Name.IsNullOrEmpty() extension method (TrimmableTypeMap.cs:101)

👍 Well-structured PR with clean separation between legacy and trimmable paths. Good error handling — FailFast for critical JNI registration failures, InvalidOperationException with context for activation errors. Native/managed JnienvInitializeArgs struct kept in sync. All TODOs reference GitHub issues. Feature switch correctly uses [FeatureSwitchDefinition] for trimmer integration.

CI: Public checks all ✅ green. Internal Xamarin.Android-PR still in progress.

Review generated by android-reviewer from review guidelines.

simonrozsival · 2026-03-24T19:08:06Z

+	{
+ if (RuntimeFeature.TrimmableTypeMap) {
+ var typeMap = TrimmableTypeMap.Instance;
+ if (typeMap is not null && targetType is not null) {


🤖 💡 Patterns — TrimmableTypeMap.Instance throws InvalidOperationException if s_instance is null, so typeMap is guaranteed non-null here. The typeMap is not null check is dead code.
If the intent is defensive (gracefully fall back to base.CreatePeer if uninitialized), access s_instance directly instead of Instance. Otherwise, remove the null check.
Same pattern in JNIEnv.ArrayCreateInstance (Instance?.GetContainerFactory) and JavaConvert.TryGetContainerFactory (Instance?.GetContainerFactory).
Rule: Method names must reflect behavior (Postmortem #4)

simonrozsival · 2026-03-24T19:08:06Z

+	internal static bool TryGetJniNameForType (Type type, [NotNullWhen (true)] out string? jniName)
+	{
+ if (type.GetCustomAttributes (typeof (IJniNameProviderAttribute), inherit: false) is [IJniNameProviderAttribute provider, ..]
+ && !string.IsNullOrEmpty (provider.Name)) {


🤖 💡 Nullable — Per repo conventions, use the NullableExtensions instance method:
&&!provider.Name.IsNullOrEmpty()){
instead of string.IsNullOrEmpty (provider.Name). The extension integrates with [NotNullWhen] for NRT flow analysis.
Rule: Use IsNullOrEmpty() extension

simonrozsival requested review from grendello and jonathanpeppers as code owners March 18, 2026 17:37

simonrozsival added the trimmable-type-map label Mar 18, 2026

CopilotAI review requested due to automatic review settings March 18, 2026 17:38

Copilotstarted reviewing on behalf of simonrozsival March 18, 2026 17:38 View session

simonrozsival commented Mar 18, 2026
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[TrimmableTypeMap] Unify InTune/method replacement support between AndroidTypeManager and TrimmableTypeMapTypeManager #10968
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jonathanpeppers reviewed Mar 19, 2026
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Comment threadsrc/Mono.Android/Java.Interop/TypeMapException.cs Outdated
Comment threadsrc/Mono.Android/Java.Interop/IAndroidCallableWrapper.cs

simonrozsival force-pushed the dev/simonrozsival/trimmable-typemap-runtime-pr branch 2 times, most recently from a956a46 to a8f3e62Compare March 20, 2026 07:51

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Comment threadsrc/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMap.cs

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Comment threadsrc/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMap.cs

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Comment threadsrc/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMap.cs

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Comment threadsrc/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMap.cs

simonrozsival force-pushed the dev/simonrozsival/trimmable-typemap-runtime-pr branch from a8f3e62 to d2e4bb1Compare March 20, 2026 08:57

simonrozsival mentioned this pull request Mar 20, 2026
[TrimmableTypeMap] Build pipeline: targets, scanner, task, assembly store #10980
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simonrozsival marked this pull request as draft March 20, 2026 14:55

simonrozsival marked this pull request as ready for review March 20, 2026 15:40

simonrozsival mentioned this pull request Mar 20, 2026
[TrimmableTypeMap] Generate AndroidManifest.xml from component attributes (#10807) #10983
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simonrozsivaland others added 6 commits March 21, 2026 09:51

Guard GetContainerFactory calls with RuntimeFeature.TrimmableTypeMap
2b80737
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival force-pushed the dev/simonrozsival/trimmable-typemap-runtime-pr branch from 71ed636 to 2b80737Compare March 21, 2026 23:14

simonrozsivaland others added 3 commits March 22, 2026 07:50

Reset submodule pointers to match main
57711b3
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simonrozsivaland others added 3 commits March 23, 2026 09:00

Fix PR diff: reset submodules, remove leaked build-pipeline files
fea4bc6
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Merge branch 'main' of github.com:dotnet/android into dev/simonrozsiv…
1646ebb
…al/trimmable-typemap-runtime-pr

Update MonoVM APK size baseline for TrimmableTypeMap runtime changes
649ed14
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jonathanpeppers reviewed Mar 24, 2026
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Comment threadsrc/Mono.Android/ILLink/ILLink.Substitutions.xml Outdated

Remove redundant ILLink substitutions for RuntimeFeature
7cb0913
[FeatureSwitchDefinition] on the properties already tells the trimmer to substitute these getters, making the XML entries unnecessary. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival enabled auto-merge (squash) March 24, 2026 18:50

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jonathanpeppers merged commit aa0f6d9 into mainMar 24, 2026
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[TrimmableTypeMap] Implement runtime TypeManager, ValueManager, and JavaConvert - #10967

[TrimmableTypeMap] Implement runtime TypeManager, ValueManager, and JavaConvert#10967
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Summary

New runtime types

Type resolution

TypeMap dictionary initialization

Native interop refactoring

RegisterNatives bootstrap

AOT-safe JavaConvert

Peer creation

Wiring

Dependencies

Test coverage

Trimmer size regression prevention

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