🥅 Keeper

A Gradle plugin that infers Proguard/R8 keep rules for androidTest sources.

Keeper hooks into Proguard/R8 to add extra keep rules based on what androidTest classes use from the target app’s sources. This is necessary because the Android Gradle Plugin (AGP) does not currently factor in androidTest usages of target app sources when running the minification step, which can result in runtime errors if APIs used by tests are removed.

This is (really) useful only if you run your instrumentation tests against your minified release builds! If you don’t run these tests against minified builds, then you don’t need this plugin. The build type that you test against is controlled by the testBuildType flag, which is set to debug by default.

This is a workaround until AGP supports this: https://issuetracker.google.com/issues/126429384.

Note: Keeper uses private APIs from AGP and could break between releases. It is currently tested against AGP version 4.0.0 and 4.1.0-alpha09 (or whatever ci_agp_version env vars are described here.


Keeper is distributed via Maven Central. Apply the keeper Gradle plugin in your application’s build.gradle. Keeper requires Gradle 6.0 or higher.

Keeper can be consumed via regular gradle plugins {} block.

plugins {
  id("com.slack.keeper") version "x.y.z"

Note that we still publish to Maven Central, so you would need to add it to the repositories list in settings.gradle.

pluginsManagement {
  repositories {
    mavenCentral() // woo-hoo!
    gradlePluginPortal() // there by default

Alternatively, it can be consumed via manual buildscript dependency + plugin application.

buildscript {
  dependencies {
    // ...
    classpath "com.slack.keeper:keeper:x.y.z"

apply plugin: "com.android.application" // <- Keeper only works with com.android.application!
apply plugin: "com.slack.keeper"

Note that Keeper must be applied after the Android gradle plugin.

Optional configuration options can be found on the Configuration page.

As of 0.6.0, Keeper requires at least AGP 4.0.0.

Snapshots of the development version are available in Sonatype’s snapshots repository.

Under the hood

The general logic flow:

  • Create a custom r8 configuration for the R8 dependency.
  • Register two jar tasks per androidTest variant. One for all the classes in its target testedVariant and one for all the classes in the androidTest variant itself. This will use their variant-provided JavaCompile tasks and KotlinCompile tasks if available.
  • Register a infer${androidTestVariant}UsageForKeeper task that plugs the two aforementioned jars into R8’s PrintUses CLI and outputs the inferred proguard rules into a new intermediate .pro file.
  • Finally - the generated file is wired in to Proguard/R8 via private task APIs and setting their configurationFiles to include our generated one.

Appropriate task dependencies (via inputs/outputs, not dependsOn) are set up, so this is automatically run as part of the target app variant’s full minified APK.

The tasks themselves take roughly ~20 seconds total extra work in our Slack android app, with the infer and app jar tasks each taking around 8-10 seconds and the androidTest jar taking around 2 seconds.


Copyright (C) 2020 Slack Technologies, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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