[r8] Enable private-member obfuscation and optimization by default by jonathanpeppers · Pull Request #12668 · dotnet/android

jonathanpeppers · 2026-09-03T18:16:52Z

Description

Enable R8 optimization and selective obfuscation by default while preserving JNI-sensitive Java names without rewriting managed IL.

The selective obfuscation defaults keep Java class names and public/protected member names stable while allowing private and package-private members to be renamed:

-keep,allowshrinking,allowoptimization class **
-keepclassmembers,allowshrinking,allowoptimization class ** {
public protected *;
}

The SDK now ships both Android default R8 configurations and selects proguard-android-optimize.txt by default. Runtime rules explicitly preserve net.dot.android.ApplicationRegistration, which managed code loads by name. NativeAOT also preserves the package-private java.lang.Class fields on mono.android.Runtime because native hosts resolve them by literal name during startup.

Escape hatches

$(_AndroidR8DontObfuscate) and $(_AndroidR8DontOptimize) are private escape hatches only. Setting either to true restores the corresponding previous global behavior (-dontobfuscate or the legacy non-optimizing Android configuration). They are not supported public build properties or alternative configuration modes, and both remain blank by default.

Tests

Added R8ObfuscationTests device coverage for CoreCLR and NativeAOT using an AndroidJavaSource probe. It verifies stable class/public/protected names, renamed private/package-private methods, and successful JNI execution.
Extended AAB metadata coverage for CoreCLR and NativeAOT to verify optimization is enabled by default and disabled by the escape hatch.
Updated the affected XForms CoreCLR/R8 app-size baseline.

Preserve Java class names and public/protected member names while allowing R8 to obfuscate private and package-private members. Keep _AndroidR8DontObfuscate as a private escape hatch that only restores the previous global -dontobfuscate behavior. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: cf67f43d-2eef-46ac-9d52-e9a677671fc8

Copilot

🟡 Changes recommended

The new device test can leave apps installed on failure paths, which risks flakiness and cross-test interference in device CI runs.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR changes the default R8 behavior to allow obfuscation of private/package-private Java implementation details while keeping Java class names and public/protected member names stable for JNI compatibility, with a private MSBuild escape hatch to restore the previous global -dontobfuscate behavior.

Changes:

Add a new selective-obfuscation default by generating base ProGuard/R8 rules at build time (and wiring an internal $(_AndroidR8DontObfuscate) toggle).
Update embedded ProGuard config resources to no longer globally disable obfuscation, and add a NativeAOT-specific keep rule for mono.android.Runtime startup fields.
Add device integration tests validating mapping + DEX output + runtime execution for CoreCLR and NativeAOT.

File summaries

File	Description
tests/MSBuildDeviceIntegration/Tests/R8ObfuscationTests.cs	Adds device test coverage verifying selective obfuscation via mapping/DEX inspection and a runtime probe.
src/Xamarin.Android.Build.Tasks/Xamarin.Android.D8.targets	Plumbs a private MSBuild escape hatch property into the R8 task invocation.
src/Xamarin.Android.Build.Tasks/Tasks/R8.cs	Implements default selective-obfuscation ProGuard directives generation and supports `DontObfuscate`.
src/Xamarin.Android.Build.Tasks/Resources/proguard_xamarin.cfg	Removes the global `-dontobfuscate` default from the common R8 config resource.
src/Xamarin.Android.Build.Tasks/Resources/proguard_trimmable_nativeaot.cfg	Removes `-dontobfuscate` and adds a keep rule for `mono.android.Runtime` fields needed at NativeAOT startup.

Review details

Files reviewed: 5/5 changed files
Comments generated: 1
Review effort level: Lite

Track successful installation and attempt uninstall from a finally block so assertion failures do not leave packages on the test device. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: cf67f43d-2eef-46ac-9d52-e9a677671fc8

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: cf67f43d-2eef-46ac-9d52-e9a677671fc8

jonathanpeppers · 2026-09-04T12:48:10Z

/review

github-actions · 2026-09-04T12:49:33Z

✅ Android PR Reviewer completed successfully!

Generated by Android PR Reviewer for #12668

github-actions

⚠️Needs Changes — 0 errors, 1 warning, 0 suggestions.

The selective R8 rules preserve class and JNI-visible public/protected member names while allowing private implementation details to be renamed, and the runtime-specific keep configuration is consistent with the native field lookups. The new device coverage exercises both CoreCLR and NativeAOT, but its shared logcat marker is not isolated between parameterized cases and can produce a false pass; please address the inline testing comment. CI is green.

Generated by Android PR Reviewer for #12668 · gpt56 · 125.5 AIC · ⌖ 9.02 AIC · ⊞ 25.7K
_{Comment /review to run again}

github-actions · 2026-09-04T12:55:26Z

+ AssertDexDoesNotContainMethod (dexFiles, "packagePrivateEntry");
+ AssertDexDoesNotContainMethod (dexFiles, "privateEntry");
+
+ RunProjectAndAssert (proj, builder, doNotCleanupOnUpdate: true);


🤖 ⚠️Testing — Clear logcat immediately before launching this case (as the neighboring device tests do), or make SuccessMarker runtime-specific. MonitorAdbLogcat() first scans all buffered output via logcat -d, and both TestCases emit the same marker, so the NativeAOT case can satisfy line 134 with the earlier CoreCLR run even if the NativeAOT app never reaches this code.
Rule: Deterministic test isolation

jonathanpeppers · 2026-09-04T19:07:34Z

The changes here, get us this far with a dotnet new maui -sc project template:

Previously, obfuscation was at 0%.

I'm investigating what else is missing, if we should add more changes here or a separate PR.

Use Android's optimized default R8 configuration unless the private _AndroidR8DontOptimize escape hatch is enabled. Ship both configurations and preserve ApplicationRegistration, which is loaded by name from managed code. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: cf67f43d-2eef-46ac-9d52-e9a677671fc8

jonathanpeppers · 2026-09-04T21:09:08Z

This is now getting this far:

CopilotAI lite review requested due to automatic review settings September 3, 2026 18:16

jonathanpeppers requested a review from simonrozsival as a code owner September 3, 2026 18:16

Copilotstarted reviewing on behalf of jonathanpeppers September 3, 2026 18:17 View session

jonathanpeppers mentioned this pull request Sep 3, 2026
[r8-obfuscation] Enable R8 JNI name obfuscation for NativeAOT #12634
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CopilotAI reviewed Sep 3, 2026
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Comment threadtests/MSBuildDeviceIntegration/Tests/R8ObfuscationTests.cs Outdated

jonathanpeppers added 2 commits September 3, 2026 13:39

[tests] Update R8 app size baselines
d9e1584
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: cf67f43d-2eef-46ac-9d52-e9a677671fc8

github-actionsBot reviewed Sep 4, 2026
View reviewed changes

jonathanpeppers changed the title ~~[r8] Obfuscate private Java members by default~~[r8] Enable private-member obfuscation and optimization by defaultSep 4, 2026

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[r8] Enable private-member obfuscation and optimization by default - #12668

[r8] Enable private-member obfuscation and optimization by default#12668
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Escape hatches

Tests

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