[build] Pass class files directly to D8 and R8

[simonrozsival]

Related: #10958

Summary

• stop creating obj/.../android/bin/classes.zip after javac for app builds
• pass generated .class files directly to class-parse, javac, and D8/R8
• remove archive creation from the Javac task
• retain JAR generation only for library/AAR output and legacy jar2xml
• use the Java compile stamp and loose binding classes as dex target incremental inputs

D8 and R8 both accept individual .class files as program inputs. The Windows command-line limit was originally reported as Xamarin Bugzilla #59651. PR #888 initially addressed it by passing the class directory to dx.jar; PR #911 then introduced classes.zip because j8.jar also needed to consume the classes without exceeding the command-line limit. D8/R8 response files make that workaround unnecessary.

Application projects containing bound AndroidJavaSource files also avoid an intermediate binding JAR: class-parse consumes the loose binding classes directly, the regular Java compilation uses their directory as a classpath entry, and D8/R8 receives the class files as program inputs. Library projects still create a JAR because it is packaged into their AAR; legacy jar2xml also continues to require a JAR.

Performance

Balanced 5+5 clean MAUI Debug Android builds using --no-restore:

Typemap	ZIP-based mean	ZIP-free mean	Improvement
LLVM-IR	47.448s	43.630s	3.818s / 8.0%
Trimmable	50.846s	46.736s	4.110s / 8.1%

The Javac task mean fell from 4.235s to 2.757s for LLVM-IR and from 6.890s to 3.278s for trimmable because it no longer packages the class output.

The final loose binding-class implementation was also compared directly with the earlier implementation that still created a binding JAR in application projects:

Bound Java app, clean Debug	Binding JAR	Loose classes	Improvement
LLVM-IR, 10 runs each	10.791s	10.597s	0.194s / 1.8%
Trimmable, 5 runs each	12.620s	12.164s	0.456s / 3.6%
No-op incremental, LLVM-IR, 10 runs each	2.022s	1.696s	0.326s / 16.1%

Binding Javac time was unchanged, while passing the class file directly to class-parse was 106–120ms faster on average. No application build in the loose-class sample produced a binding JAR.

Validation

• focused D8Tests: 2 passed
• clean Debug D8 MAUI build
• incremental Debug D8 MAUI build
• clean Release R8 MAUI build
• bound Java application builds with D8 and R8
• binding library project consumed by an application
• verified D8 and R8 builds produce signed APKs without classes.zip or an application binding JAR

[Copilot]

Pull request overview

This PR updates the Android build pipeline to avoid generating an intermediate classes.zip for application builds, instead passing compiled .class files directly into D8/R8 via the existing response-file mechanism. This aligns the build tasks with D8/R8 supported inputs and reduces unnecessary I/O during javac.

Changes:

• Stop producing obj/.../android/bin/classes.zip for app builds; use .class files from $(_AndroidIntermediateJavaClassDirectory) as D8/R8 program inputs.
• Update _CompileToDalvik incremental inputs to use the Java compile stamp ($(_AndroidCompileJavaStampFile)) instead of classes.zip.
• Adjust D8 task API/response-file generation and update D8 unit tests accordingly.

Show a summary per file

File	Description
src/Xamarin.Android.Build.Tasks/Xamarin.Android.D8.targets	Passes @(_JavaClassFile) (compiled .class files) directly to D8/R8 instead of classes.zip.
src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets	Removes the classes.zip intermediate property and switches dex incremental input to the Java compile stamp.
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/D8Tests.cs	Extends the D8 response-file unit test to cover .class inputs.
src/Xamarin.Android.Build.Tasks/Tasks/D8.cs	Replaces ClassesZip with ClassFiles and emits .class paths as program inputs in the response file.
src/Xamarin.Android.Build.Tasks/MSBuild/Xamarin/Android/Xamarin.Android.Javac.targets	Stops deleting/passing classes.zip for app Java compilation, leaving binding JAR generation intact elsewhere.

Review details

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

[jonathanpeppers]

The <Javac/> task still has the ClassesZip property and code to create the classes.zip, can we remove that, too?

[simonrozsival]

Done in 3d7d113. Javac no longer has a ClassesZip property or archive-writing code. _CompileBindingJava now creates its required binding JAR separately with MSBuild’s ZipDirectory task.

[simonrozsival]

Follow-up in ceb8a43: class-parse app builds now avoid the binding JAR as well. Their bound .class files flow directly to class-parse, javac, and D8/R8. JAR creation remains only for library/AAR output and legacy jar2xml.

[jonathanpeppers]

/review

[github-actions]

✅ Android PR Reviewer completed successfully!

Generated by Android PR Reviewer for #12438

[github-actions]

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

The loose .class flow is coherently wired through javac, class-parse, and D8/R8, and retaining the JAR for binding projects and jar2xml preserves the required archive consumers. The added app-build assertion must first use an actual bound Java source; as written, it cannot catch regressions in the new _JavaBindingClassFile path.

CI build 1560618 is currently red and still in progress: both macOS package-test APK lanes are failing while several Windows, Linux, and emulator lanes remain active. I could not verify that those failures are related to this change, so this review does not attribute them to the PR.

Generated by Android PR Reviewer for #12438 · gpt56 · 400.8 AIC · ⌖ 8.95 AIC · ⊞ 25.7K
_{Comment /review to run again}

[jonathanpeppers]

I reran to see if that would help, but I think this is broken on APK tests:

EXEC : warning : [options] system modules path not set in conjunction with -source 17 [/Users/runner/work/1/s/tests/Mono.Android-Tests/Java.Interop-Tests/Java.Interop-Tests.NET.csproj]
/Users/runner/work/1/s/bin/Release/dotnet/packs/Microsoft.Android.Sdk.Darwin/37.0.0-ci.pr.gh12438.0/tools/Xamarin.Android.Bindings.ClassParse.targets(51,5): error MSB6006: "dotnet" exited with code 1. [/Users/runner/work/1/s/tests/Mono.Android-Tests/Mono.Android-Tests/Mono.Android.NET-Tests.csproj]
/Users/runner/work/1/s/bin/Release/dotnet/packs/Microsoft.Android.Sdk.Darwin/37.0.0-ci.pr.gh12438.0/tools/Xamarin.Android.Bindings.ClassParse.targets(51,5): error XACLP0000: class-parse: Unable to read file 'obj/Debug/net11.0-android/binding/bin/classes/net/dot/android/test/Example%241.class': Could not find file '/Users/runner/work/1/s/tests/Mono.Android-Tests/Mono.Android-Tests/obj/Debug/net11.0-android/binding/bin/classes/net/dot/android/test/Example%241.class'. [/Users/runner/work/1/s/tests/Mono.Android-Tests/Mono.Android-Tests/Mono.Android.NET-Tests.csproj]
/Users/runner/work/1/s/bin/Release/dotnet/packs/Microsoft.Android.Sdk.Darwin/37.0.0-ci.pr.gh12438.0/tools/Xamarin.Android.Bindings.ClassParse.targets(51,5): error XACLP0000: class-parse: Unable to read file 'obj/Debug/net11.0-android/binding/bin/classes/net/dot/android/test/InterfaceMarshalling%241.class': Could not find file '/Users/runner/work/1/s/tests/Mono.Android-Tests/Mono.Android-Tests/obj/Debug/net11.0-android/binding/bin/classes/net/dot/android/test/InterfaceMarshalling%241.class'. [/Users/runner/work/1/s/tests/Mono.Android-Tests/Mono.Android-Tests/Mono.Android.NET-Tests.csproj]
Build failed with exit code: 1.

[jonathanpeppers]

If we kept <Javac/> writing the classes.zip in some cases for now and just didn't pass it to d8/r8 -- it would be ok to drop the most recent changes.

I didn't realize it complicated some of the binding code paths.