proguard does not work with android-24 and above

[aj-michael]

Starting with android-24, the android.jar contains class files with version 52.0. when an android_binary has the proguard_specs attribute, we end up passing android.jar to proguard which chokes because the versions of proguard included in the android sdk do not have support for java 8.

$ bazel build //examples/android/java/bazel:hello_world --android_sdk=@androidsdk//:sdk-24
INFO: Found 1 target...
ERROR: /usr/local/google/home/ajmichael/bazel/bazel2/examples/android/java/bazel/BUILD:12:1: Trimming binary with Proguard failed (Exit 1).
ProGuard, version 4.7
Reading program jar [/usr/local/google/home/ajmichael/.cache/bazel/_bazel_ajmichael/35e62ee2c576f0884e321f960b1f1655/execroot/io_bazel/bazel-out/local-fastbuild/bin/examples/android/java/bazel/hello_world_deploy.jar]
Reading library jar [/usr/local/google/home/ajmichael/sdk/platforms/android-24/android.jar]
Error: Can't read [/usr/local/google/home/ajmichael/sdk/platforms/android-24/android.jar] (Can't process class [java/text/CollationElementIterator.class] (Unsupported class version number [52.0] (maximum 51.0, Java 1.7)))
Target //examples/android/java/bazel:hello_world failed to build

$ bazel build //examples/android/java/bazel:hello_world --android_sdk=@androidsdk//:sdk-23
INFO: Found 1 target...
INFO: From Trimming binary with Proguard:
ProGuard, version 4.7
Reading program jar [/usr/local/google/home/ajmichael/.cache/bazel/_bazel_ajmichael/35e62ee2c576f0884e321f960b1f1655/execroot/io_bazel/bazel-out/local-fastbuild/bin/examples/android/java/bazel/hello_world_deploy.jar]
Reading library jar [/usr/local/google/home/ajmichael/sdk/platforms/android-23/android.jar]
Preparing output jar [/usr/local/google/home/ajmichael/.cache/bazel/_bazel_ajmichael/35e62ee2c576f0884e321f960b1f1655/bazel-sandbox/5578460277401154143/execroot/io_bazel/bazel-out/local-fastbuild/bin/examples/android/java/bazel/hello_world_proguard.jar]
  Copying resources from program jar [/usr/local/google/home/ajmichael/.cache/bazel/_bazel_ajmichael/35e62ee2c576f0884e321f960b1f1655/execroot/io_bazel/bazel-out/local-fastbuild/bin/examples/android/java/bazel/hello_world_deploy.jar]
Target //examples/android/java/bazel:hello_world up-to-date:
  bazel-bin/examples/android/java/bazel/hello_world_proguard.jar
  bazel-bin/examples/android/java/bazel/hello_world_proguard.seeds
  bazel-bin/examples/android/java/bazel/hello_world_proguard.usage
  bazel-bin/examples/android/java/bazel/hello_world_proguard.config
  bazel-bin/examples/android/java/bazel/hello_world_deploy.jar
  bazel-bin/examples/android/java/bazel/hello_world_unsigned.apk
  bazel-bin/examples/android/java/bazel/hello_world.apk
INFO: Elapsed time: 2.046s, Critical Path: 1.66s

[aj-michael]

It appears that the proguard in the Android SDK is 4.7, while java8 support was not added until proguard 5.0.

It seems gradle does not use proguard from the SDK, instead it gets a newer version elsewhere.

[aj-michael]

Our choices are:

1. Desugar the android.jar
2. Bundle a newer proguard with Bazel (or possibly require that the user provides it via maven_jar or something)

@ahumesky , do you have a preference?

[aj-michael]

On second thought #1 will not work, because if there are static interface methods in the android.jar, there will be a mismatch between what the methods present when proguarding and the methods present on the device.

[aj-michael]

Bundling proguard.jar would add about 800k to the Bazel binary size

[ahumesky]

Ideally we would just get an updated proguard in the SDK, but in the meantime we can just bundle it. If the SDK gets an updated version then we can unbundle it and switch to that one.

[aj-michael]

Updating proguard in the Android SDK is in the public android issue tracker: https://issuetracker.google.com/issues/37047494

[damienmg]

[breakage label is for regression observed on ci to help sheriff triage new failure]

[aj-michael]

Ah ok, I’ll keep that in mind. Unfortunately we don’t have integration test coverage for proguard I’m bazel. Otherwise this would have been observed on ci