Fix R8 stripping JNI callback methods causing SIGABRT

[stevenelliottjr]

Summary

Fixes #6045 — Android apps using MediaPipe tasks with R8 minification (isMinifyEnabled = true) crash with a fatal SIGABRT when running inference (e.g. ImageSegmenter.segment()).

Root cause: R8 tree-shakes process() method implementations on lambda-desugared anonymous classes that implement PacketCallback, PacketListCallback, or PacketWithHeaderCallback. R8 cannot see that these methods are invoked from native JNI code (graph.cc CallbackToJava → GetMethodID → CallVoidMethod), so it considers them dead code and strips them. When GetMethodID fails to find the method at runtime, the JNI layer triggers a hard SIGABRT that bypasses try/catch.

The existing ProGuard rule -keep public interface com.google.mediapipe.framework.* { public *; } preserves the interface definitions but does not prevent R8 from removing method implementations on anonymous/synthetic classes.

Fix: Add explicit -keep class * implements <Interface> rules for the three callback interfaces so R8 retains process() on all implementing classes, including lambda-desugared synthetics.

Changes

• mediapipe/java/com/google/mediapipe/framework/proguard.pgcfg — Added keep rules for:
  • PacketCallback.process(Packet)
  • PacketListCallback.process(List)
  • PacketWithHeaderCallback.process(Packet, Packet)

Reproduction

Minimal repro from the issue reporter: https://github.com/rvp-diconium/mediapipe-bug-report

val segmenter = ImageSegmenter.createFromOptions(context, options)
segmenter.segment(inputImage).confidenceMasks() // SIGABRT here with R8 enabled

Logcat shows:

JNI DETECTED ERROR IN APPLICATION: JNI GetMethodID called with pending exception java.lang.NoSuchMethodError

Test plan

• Build the mediapipe_aar target and verify the updated proguard.pgcfg is bundled
• Build the minimal repro app (linked above) with isMinifyEnabled = true against the patched AAR
• Verify ImageSegmenter.segment() completes without crash
• Verify the same with PacketCallback (single-stream) and PacketWithHeaderCallback callbacks