[Feature][Android] Support for consumer proguard files in AARs

[jcayzac]

Following this comment I'd like to request support for adding consumer proguard files when creating AARs.

Currently there's no obvious way for packaging a consumer proguard file, something that's standard when using gradle and AGP to build a library.

Anatomy of an AAR file shows the proguard.txt packaged inside the AAR, to be eventually merged with the proguard configuration of the consuming application.

[ronshapiro]

Is this on the horizon? Is there a pointer to where this should be implemented?

Update: These files seem to be on the right track:

• bazel/src/main/java/com/google/devtools/build/lib/rules/android/AndroidLibrary.java

  Lines 233 to 241 in e2d200f

  	new AarGeneratorBuilder(ruleContext)
  	.withPrimary(primaryResources)
  	.withManifest(aar != null ? aar.getManifest() : primaryResources.getManifest())
  	.withRtxt(primaryResources.getRTxt())
  	.withClasses(classesJar)
  	.setAAROut(aarOut)
  	.setThrowOnResourceConflict(
  	ruleContext.getFragment(AndroidConfiguration.class).throwOnResourceConflict())
  	.build(ruleContext);

• bazel/src/main/java/com/google/devtools/build/lib/rules/android/AarGeneratorBuilder.java

  Line 89 in 9a5d1af

  public void build(ActionConstructionContext context) {

• bazel/src/tools/android/java/com/google/devtools/build/android/AarGeneratorAction.java

  Lines 216 to 217 in 5a33000

  	static void writeAar(
  	Path aar, final MergedAndroidData data, Path manifest, Path rtxt, Path classes)

[aj-michael]

Fix pending in https://bazel-review.googlesource.com/c/48690/