[Xamarin.Android.Build.Tasks] Add opt-in R8 runtime remapping - #12692
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Context: #12535 R8 obfuscation changes JNI names that managed bindings still use. Add an experimental alternative to assembly rewriting by translating those names through the existing runtime remapping machinery. Run a naming-only R8 seed before ILLink or ILC and apply its mapping during final R8. Select CoreCLR remaps from linked assemblies and NativeAOT remaps from retained ELF literals, then link the NativeAOT table after ILC. Extend lookups for reverse types, descriptors, fields, and peers. Expose AndroidEnableR8Obfuscation, defaulting to false, and AndroidR8ObfuscationMode, defaulting to runtime-remapping. Reserve experimental-rewriting with a clear error until its separate pipeline is available. Diagnose incompatible configurations with XA4329. Preserve JNI bootstrap and resource keep rules, track incremental table and native-link inputs, and support switching obfuscation back off. Include task, configuration, device regression tests, and documentation. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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Copilot review overview
🔵 Needs a closer look
It makes cross-cutting changes across MSBuild targets, build tasks, native runtime lookup code, and public API surface that require careful human validation beyond automated review.
Review tier: Lite
Findings: 3
New issues introduced by this change (3)
| Severity | Finding |
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src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/GenerateJniRemappingNativeCodeTests.cs — ❌ error: Avoid the null-forgiving operator (!) in tests as well; it hides real nullability issues… |
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src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/R8Tests.cs — |
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src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/R8Mapping.cs — |
What changed in this PR
Adds an experimental opt-in for R8 obfuscation in .NET for Android by generating and consuming runtime JNI remapping tables (rather than rewriting managed assemblies), enabling obfuscated DEX outputs while preserving managed JNI name expectations.
Changes:
- Introduces a two-pass R8 pipeline (seed mapping pre-trim + final R8
-applymapping) and generates JNI remapping XML/native tables for CoreCLR and NativeAOT. - Extends runtime remapping to cover reverse type lookups, rewritten method descriptors, and field remapping; shares native lookup code between CoreCLR and NativeAOT.
- Adds/updates tests and documentation for new public properties and XA4327/8/9 diagnostics.
| File | Description |
|---|---|
| tests/MSBuildDeviceIntegration/Tests/R8RuntimeRemappingTests.cs | Device test validating obfuscated members/types and incremental/missing-output recovery. |
| src/Xamarin.Android.Build.Tasks/Xamarin.Android.D8.targets | Wires new R8 inputs/outputs and enables mapping input/output + obfuscation flag. |
| src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets | Adds opt-in properties, validation (XA4329), incremental inputs, and AAPT rules tracking changes. |
| src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/R8Mapping.cs | Extends mapping parsing/projection for class/method/field data used by remapping generation. |
| src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/NativeAotJniRetention.cs | NativeAOT ELF-based literal retention to conservatively select required remap entries. |
| src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/JniDescriptorText.cs | Converts Java source-form types to JNI tokens + builds method descriptors. |
| src/Xamarin.Android.Build.Tasks/Utilities/JniRemapping/JniAssemblyRewriter.cs | Adds scan-only entrypoint for linked-assembly analysis (no rewriting). |
| src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/R8Tests.cs | Adds unit coverage for keep-option and config generation behavior. |
| src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/GenerateTrimmableTypeMapTests.cs | Verifies NativeAOT proguard generation respects allowobfuscation. |
| src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/GenerateJniRemappingNativeCodeTests.cs | New tests for native remap table emission, ordering, and legacy compatibility. |
| src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/InvalidConfigTests.cs | Tests defaults + invalid configuration errors for new MSBuild properties. |
| src/Xamarin.Android.Build.Tasks/Tasks/R8.cs | Adds seed mapping mode, applymapping support, and conditional dontobfuscate removal. |
| src/Xamarin.Android.Build.Tasks/Tasks/GenerateR8JniRemapping.cs | Generates JNI remapping XML from R8 mapping + existing remaps; supports NativeAOT retention path. |
| src/Xamarin.Android.Build.Tasks/Tasks/GenerateR8JniManifestProguardConfiguration.cs | Generates manifest keep rules to stabilize seed mapping applicability. |
| src/Xamarin.Android.Build.Tasks/Tasks/GenerateProguardConfiguration.cs | Emits allowobfuscation on keep rules when runtime remapping is enabled. |
| src/Xamarin.Android.Build.Tasks/Tasks/GenerateNativeAotProguardConfiguration.cs | Emits allowobfuscation for NativeAOT-generated keep rules when enabled. |
| src/Xamarin.Android.Build.Tasks/Tasks/GenerateJniRemappingNativeCode.cs | Extends generated tables to include reverse types + fields; exposes info for tests. |
| src/Xamarin.Android.Build.Tasks/Resources/proguard_xamarin.cfg | Adds/adjusts keep rules needed for stable seed/final graphs and bootstrap types. |
| src/Xamarin.Android.Build.Tasks/Resources/proguard_trimmable_nativeaot.cfg | Aligns NativeAOT baseline keep rules with remapping needs and seed/final stability. |
| src/Xamarin.Android.Build.Tasks/Properties/Resources.resx | Adds XA4327/8/9 localized strings for errors/warnings/validation. |
| src/Xamarin.Android.Build.Tasks/Properties/Resources.Designer.cs | Updates generated resource accessors for XA4327/8/9. |
| src/Xamarin.Android.Build.Tasks/MSBuild/Xamarin/Android/Xamarin.Android.Aapt2.targets | Moves AAPT proguard rule tracking to incremental parent target. |
| src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.targets | Imports new R8 JNI remapping targets last to override pre-trim outputs as needed. |
| src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.NativeAOT.targets | Includes new properties in incremental stamps; passes obfuscation state into proguard generation. |
| src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.CoreCLR.targets | Reworks linked-assembly proguard inputs; adds remapping-assembly prep + incremental inputs. |
| src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.LlvmIr.targets | Adds remapping enable flag into proguard generation and incremental inputs. |
| src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.R8JniRemapping.targets | New MSBuild pipeline for seed mapping, remap XML, and NativeAOT late-linked table build. |
| src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.NativeAOT.targets | Links remapping object into NativeAOT shared library and updates incremental inputs. |
| src/native/nativeaot/include/runtime-base/internal-pinvokes.hh | Adds internal pinvokes for reverse-type and field lookup. |
| src/native/nativeaot/host/jni-remapping-tables-stub.cc | Provides weak empty table symbols for apps without remapping objects. |
| src/native/nativeaot/host/internal-pinvoke-stubs.cc | Removes now-shared remapping pinvoke stubs from NativeAOT host stubs. |
| src/native/nativeaot/host/host.cc | Plumbs jniRemappingInUse via shared JniRemapping::is_in_use(). |
| src/native/nativeaot/host/CMakeLists.txt | Adds shared remapping sources and stub table compilation to NativeAOT host build. |
| src/native/native.targets | Includes shared remapping sources/headers in NativeAOT flavor build inputs. |
| src/native/mono/xamarin-app-stub/xamarin-app.hh | Updates stub ABI structs to include target_signature + field remapping structures. |
| src/native/mono/xamarin-app-stub/application_dso_stub.cc | Updates stub table initializers for new method signature field. |
| src/native/mono/runtime-base/internal-pinvokes.hh | Adds internal pinvoke declarations for reverse-type and field lookup. |
| src/native/mono/pinvoke-override/pinvoke-tables.include | Extends pinvoke table entries/count for the new remapping exports. |
| src/native/mono/pinvoke-override/generate-pinvoke-tables.cc | Adds new internal pinvoke names to generator input list. |
| src/native/mono/monodroid/internal-pinvokes.cc | Adds MonoVM-safe placeholder exports for new remapping entrypoints. |
| src/native/clr/xamarin-app-stub/application_dso_stub.cc | Extends CLR stub tables to include reverse types + fields + signature pinning. |
| src/native/clr/runtime-base/jni-remapping.cc | Implements binary-search remapping lookups (types, reverse types, methods, fields) + is_in_use(). |
| src/native/clr/pinvoke-override/precompiled.cc | Maps new internal pinvoke entrypoints to implementations. |
| src/native/clr/include/xamarin-app.hh | Declares remapping table symbols and adds field + reverse type structures. |
| src/native/clr/include/runtime-base/jni-remapping.hh | Declares shared lookup surface including reverse type and field lookup. |
| src/native/clr/include/runtime-base/internal-pinvokes.hh | Declares new remapping pinvokes for CoreCLR runtime. |
| src/native/clr/host/internal-pinvokes-shared.cc | Centralizes shared remapping pinvoke implementations for CoreCLR/NativeAOT. |
| src/native/clr/host/internal-pinvokes-clr.cc | Removes remapping implementations now provided by shared file. |
| src/native/clr/host/host.cc | Uses JniRemapping::is_in_use() for init flag and includes remapping header. |
| src/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMapValueManager.cs | Ensures FindClass uses replacement type name when remapping is enabled. |
| src/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMapTypeManager.cs | Adds reverse-type handling for Java-to-managed lookups; uses replacement type for signatures. |
| src/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMap.cs | Uses reverse type for proxy lookup and replacement type for FindClass checks. |
| src/Mono.Android/Microsoft.Android.Runtime/JniRemappingLookup.cs | Adds reverse type + field lookup plumbing and supports target-method-signature. |
| src/Mono.Android/Android.Runtime/RuntimeNativeMethods.cs | Adds LibraryImport declarations for reverse type + field lookup pinvokes. |
| src/Mono.Android/Android.Runtime/AndroidRuntime.cs | Exposes GetOriginalTypeCore via reverse-type lookup. |
| external/Java.Interop/tests/Java.Interop-Tests/Java.Interop/JniPeerMembersTests.cs | Adds tests validating remapped field names and pinned target signatures. |
| external/Java.Interop/tests/Java.Interop-Tests/Java.Interop/JavaVMFixture.cs | Extends test runtime type manager with field replacement support. |
| external/Java.Interop/src/Java.Interop/PublicAPI.Unshipped.txt | Records new public API surface additions for replacement fields + original type. |
| external/Java.Interop/src/Java.Interop/Java.Interop/JniType.cs | Adds TryGet{Static,Instance}Field helpers to support remapped field probing. |
| external/Java.Interop/src/Java.Interop/Java.Interop/JniRuntime.ReflectionJniTypeManager.cs | Adds null default implementation for field replacement in reflection manager. |
| external/Java.Interop/src/Java.Interop/Java.Interop/JniRuntime.JniTypeManager.cs | Adds ReplacementFieldInfo + original type + replacement field APIs. |
| external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.JniStaticMethods.cs | Uses replacement lookup keyed by original type name (compat + remapping). |
| external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.JniStaticFields.cs | Adds remapped static field probing and fallback to original lookup. |
| external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.JniInstanceMethods.cs | Tracks original vs effective JNI type names; remaps ctor/method lookup accordingly. |
| external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.JniInstanceFields.cs | Adds remapped instance field probing and fallback behavior. |
| external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.cs | Tracks original type name and performs replacement lookups across base types/types. |
| Documentation/docs-mobile/TOC.yml | Adds XA4327/8/9 docs to TOC. |
| Documentation/docs-mobile/messages/xa4329.md | Documents invalid/unsupported configuration errors and resolutions. |
| Documentation/docs-mobile/messages/xa4328.md | Documents remapping incompleteness warnings (conflicts/signature conversion). |
| Documentation/docs-mobile/messages/xa4327.md | Documents remapping generation failures and troubleshooting steps. |
| Documentation/docs-mobile/messages/index.md | Adds XA4327/8/9 to messages index. |
| Documentation/docs-mobile/building-apps/build-properties.md | Documents AndroidEnableR8Obfuscation + AndroidR8ObfuscationMode properties. |
Files not reviewed (1)
- src/Xamarin.Android.Build.Tasks/Properties/Resources.Designer.cs: Generated file
Suppressed comments (1)
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/GenerateJniRemappingNativeCodeTests.cs:112
- ❌ error: This uses the null-forgiving operator (
info!) afterAssert.IsNotNull, which the compiler can’t reason about. Prefer?? throwso nullability is enforced without suppressions.
Context: #12692 Follow the existing Intune contract: member lookup keys contain the replaced owner type and the original managed member name and descriptor. Generate R8 member entries and collision keys in that same form rather than teaching every consumer to try both original and replaced owners. Remove JniPeerOriginalTypeName, the duplicate constructor identity, and the now-unused Java.Interop reverse-type hook. Keep reverse lookup for peer activation and derive desugared companion names in the Android remapping helper where the original name is actually needed. Cover residual-owner keys, descriptors, MAM conflicts and duplicates, and real renamed-class construction and member access on both runtimes. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Runtime remapping keeps original JNI names in managed code, so it does not need an early naming pass. Remove the seed compilation, seed R8 invocation, applymapping support, and early manifest-rule generation. Generate remapping tables from the one final R8 mapping. Defer CoreCLR native linking until those tables exist. For NativeAOT, compile IL early and link each RID after the shared R8 pass without running ILC again. Keep post-ILC table filtering, ordinary MAM assets, and opt-out behavior. Add invocation-count and ordering coverage, including multi-RID builds, no-op builds, missing mapping/table recovery, and changed R8 rules. Context: #12535 Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Use content-based writes and generation stamps so managed-only rebuilds do not unnecessarily rerun R8. Preserve missing-output recovery, no-op incrementality, and cleanup across per-RID builds, with regression coverage. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Replace null-forgiving operators in the native remapping tests with explicit assertion guards, and separate adjacent test attributes and mapping helper declarations. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Resolve merged and per-manifest keep-rule paths against the captured project working directory during asynchronous AAPT execution. Preserve unchanged rule timestamps and use the existing packaged-resource output to recover missing rules without adding another stamp. Cover resource-only changes, no-op builds, and missing-rule recovery. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Delegate field remapping through AndroidTypeManager and supply the Android fixture with the field and target-descriptor mappings already used by desktop JVM tests. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
simonrozsival
marked this pull request as ready for review
September 8, 2026 13:34
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❌ Needs Changes — 1 error found.
The remapping pipeline is well covered and the runtime/native lookup design is coherent, but field-entry conflict detection currently omits the JNI descriptor from the key. Under R8 class merging this can discard a valid field remap and cause runtime lookup failure. CI has no observed failures, with the latest build checks still in progress.
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Include the original JNI descriptor in generated and existing-XML field claim keys. Keep fields from merged owners distinct even when their residual descriptors match, while preserving duplicate suppression and same-signature conflict warnings. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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⚠️ Needs Changes
Found 2 errors in JNI field remapping: inherited remaps can override hidden derived fields, and the newly enabled field fixtures run on MonoVM even though its field-remapping entry point is a stub. The overall cross-runtime design and focused coverage are substantial, but these correctness gaps should be addressed before merge.
CI has not run for the latest commit: the dotnet-android check is currently action_required (awaiting pipeline authorization); CLA passes.
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Consolidate duplicate class and member mapping checks into retained regression cases. Drop standalone count/symbol and property checks, and reduce malformed-input permutations while keeping representative failures, Intune compatibility, retention, ordering, and end-to-end coverage. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Preserve main's net11 test relocation and carry the obfuscation cases into GenerateNativeAotProguardConfigurationTests. Adapt the scan-only JNI remapping entry point to the shared planner's FieldRvaTable input. Retain main's lazy JNI caches and libc++ removal alongside single-pass R8. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Preserve Java field-hiding semantics and enable reverse and field remapping on MonoVM, including field-only configurations. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Mirror the dedicated field-remapping fixtures in the on-device remap table so the hiding and inherited-fallback tests exercise the intended mappings. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Use AndroidR8ObfuscationMode as the sole opt-in, place its behavior-preserving default with the shared R8 defaults, and keep runtime-specific derivation and validation late. This prepares the branch to add runtime-remapping to the mode contract from PR #12668 after it merges. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Preserve the shared private-members default, isolate runtime-remapping rules, and reconcile mode validation and packaging coverage. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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❌ Needs changes
Found 4 errors in the new runtime-remapping paths:
- Member lookup can select a renamed base member before an unchanged hiding member on the current type.
- Java-to-managed lookup can resolve a residual-name/original-name collision to the wrong managed type.
- MonoVM wildcard and parameter-only remaps can shadow more-specific descriptors because of generated sort order.
- Generated LLVM member-array symbols can collide or become invalid for Unicode JNI names.
The overall single-pass R8 pipeline is thoughtfully integrated across CoreCLR and NativeAOT, with substantial build, unit, and device coverage. All 44 current CI checks completed successfully, but the cases above require adversarial regression coverage before merge.
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Resolve method remaps in exact, parameter-only, then wildcard order; preserve hidden methods before inherited remaps; emit collision-proof native symbols; and make reverse type mappings authoritative. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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The runtime-remapping implementation has broad coverage across Java.Interop, CoreCLR, NativeAOT, MSBuild incrementality, and device/build tests. One MSBuild ordering issue remains: the post-R8 NativeAOT link can run after _CompileToDalvik fails and may consume stale output or obscure the primary failure.
CI is still in progress: the completed checks are passing, with no failures currently reported.
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| ILC object/output paths. The final mapping path is absolute and shared by every RID. --> | ||
| <Target Name="_AndroidLinkNativeAotAfterR8" | ||
| AfterTargets="_CompileToDalvik" | ||
| Condition=" '$(_AndroidR8RuntimeRemappingEnabled)' == 'true' and '$(_OuterIntermediateOutputPath)' == '' and '$(DesignTimeBuild)' != 'true' " |
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🤖 AfterTargets is scheduled even when _CompileToDalvik fails. In that case this still launches the per-RID NativeAOT links, potentially consuming a stale mapping from an earlier build or adding XA4327 errors on top of the original R8 failure. Please gate this target on $(MSBuildLastTaskResult) == true (or order it through a success-only dependency).
Rule: Avoid unguarded AfterTargets
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Context: #12535
Adds experimental R8 obfuscation through the existing Intune/MAM runtime JNI remapping machinery instead of rewriting managed assemblies. Managed bindings keep their original JNI names; generated native tables translate lookups to the names and descriptors in R8's final mapping. This supports trimmed CoreCLR and NativeAOT applications and is an alternative to the assembly-rewriting workstreams in #12632 and #12634.
The shared R8 mode contract from #12668 is now integrated through
main. This PR addsruntime-remappingwithout changing the .NET 11private-membersdefault or the existingdisabledbehavior. Remapping-specific keep rules apply only to the new mode.Opt-in
For a CoreCLR or NativeAOT application:
AndroidR8ObfuscationMode=runtime-remappingis the sole opt-in; there is no separate enable property. The example leaves Debug unchanged, and runtime remapping does not apply to library projects.private-memberspreserves class/interface and public/protected member names while enabling optimization;disabledpreserves all Java names and uses the non-optimizing Android defaults. Runtime remapping also uses the optimizing defaults, with additional JNI safety constraints.Runtime remapping requires R8, trimming, trimmable type maps, and CoreCLR or NativeAOT. Incompatible configurations report XA4329. Unknown mode values report XA1050 when R8 is enabled.
experimental-rewritingremains reserved and unavailable in this SDK; selecting it reports XA4329 rather than falling back.Build and runtime changes
-applymapping; no-op builds do not rerun R8.Coverage
Host tests cover mode policies, configuration validation, mapping conversion, field descriptors, MAM precedence, and retention filtering. Packaging tests exercise all three supported modes on CoreCLR and NativeAOT, including optimizing versus non-optimizing metadata, mapping-file embedding, and no-op rebuilds. Existing device/build integration coverage exercises renamed types, constructors, overloads, instance/static and inherited members, peer activation, single-pass ordering, multi-RID builds, missing-output recovery, and opt-out.
Earlier MAUI
dotnet new maui --sample-contentmeasurements predate this shared-mode integration; no new startup, build-time, or APK-size comparison is claimed for this head.Experimental limitations
NativeAOT literal matching is conservative and can retain extra entries. Arbitrarily computed JNI names may require explicit remaps or keep rules. Conservative public/nested-class, interface, bootstrap, and native-callback keeps limit obfuscation. Existing Intune/R8 conflict handling is not full remapping-chain composition, and ambiguous reverse mappings for merged classes are omitted. This remains an experimental opt-in, not a production-readiness claim.
Fixes: #12535