IssueTracker

Local library projects (AARs) consumed as flatDir in applications/other projects, break desugaring because they do not contain dependency information. AGP can try to detect this case and desugar these dependencies together with file-based dependencies.

Alternatively, developers can add AAR dependency as a file based one, and not use the flatDir. In the example above dependency can be added as:

dependencies {
  implementation fileTree(dir: '../library/build/outputs/aar/', include: ['library-debug*.aar'])
}

Artem, can you migrate to file-based dependencies instead of flatDir?

Original issue: https://issuetracker.google.com/140508065#comment23

Orignal comment:
I was able to isolate the issue and make a demo project to reproduce it. Tested on Android Studio 3.6.0-beta01 with AGP 3.6.0-beta01 - issue is still reproducible.

Steps to reproduce:

1. Download and import attached project
2. There will be two modules: app and library
  app depends on 'library' and on 'androidx.lifecycle:lifecycle-common-java8:2.1.0'
  library depends on 'androidx.lifecycle:lifecycle-common-java8:2.1.0'
3. Initial sync will fail because app depends directly on generated AAR. This file would be generated by :library:assemble task inside the /library/build/outputs/aar/
  Run ./gradlew :library:assemble to assemble the 'library' module
4. After library is assembled try Gradle Sync button again. Now it should sync just fine.
5. Create an emulator that runs pre-java8 API, I was testing on Nexus 5 API 21 (required to enable desugaring)
6. Run app on the emulator. Upon launch app will crash.
7. In app/build.gradle comment out this:
  implementation(name: 'library-debug', ext: 'aar')
    And uncomment this line:
  implementation project(":library")
8. Try running app again. With this module dependency app will run fine and activity will be displayed.
9. Revert step #7 to make dependency to be 'aar' again
10. In gradle.properties uncomment following line
  android.enableDexingArtifactTransform.desugaring=false
11. Try running app. With this workaround app will run fine.

Explanation of the bug cause:

  - Lifecycler-common-java8 contains an interface DefaultLifecycleObserver with default implementation on 6 methods
  - 'library' has a class 'MyCustomObserver : DefaultLifecycleObserver' which overrides only 2 methods from DefaultLifecycleObserver
  - 'app' instantiates 'MyCustomObserver' in its Application onCreate() and attempts to call method on it which is NOT overridden in 'MyCustomObserver'

Checking the bytecode for the case when AAR is used I found that 'MyCustomObserver' would only have two methods in it.
In the bytecode for the module dependency (steps #7-8) 'MyCustomObserver' has 6 methods, where 4 of those are synthetic and pointing to static methods generated by D8 in the 'DefaultLifecycleObserver$-CC' class

To sum things up, it looks like D8 cannot figure out where to get 'DefaultLifecycleObserver' while processing 'MyCustomObserver' - because AAR doesn't have any dependencies - and therefore it doesn't generate any synthetic methods for it.