🥅 Keeper¶

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

Keeper hooks into 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. See the changelog to check what versions are supported with each release.

Installation¶

Keeper is distributed via Maven Central. Apply the keeper Gradle plugin in your application’s build.gradle. Keeper requires Gradle 7.0 or higher and AGP 7.1.0 or higher.

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

plugins {
  id("com.android.application") // <- Keeper only works with com.android.application!
  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"

Full configuration defaults can be found on the Configuration page.

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 TraceReferences CLI and outputs the inferred proguard rules into a new intermediate .pro file.
Finally - the generated file is wired in to 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.

Core Library Desugaring (L8) Support¶

Library Desugaring (L8) was introduced in Android Gradle Plugin 4.0. To make this work, the R8 task will generate proguard rules indicating which j$ types are used in source, which the L8DexDesugarLibTask then uses to know which desugared APIs to keep. This approach can have flaws at runtime though, as the classpath of the test APK may not have the right j$ classes available on its classpath to run app code it is invoking. To work around this, Keeper does two things:

Keeper merges generated L8 rules from both the androidTest and target app to ensure they cover all used APIs. These merged rules are given to the target app L8DexDesugarLibTask.
L8 will still, by default, generate a dex file of backported APIs into both the test app and target app, which can cause confusing runtime classpath issues due to L8 generating different implementations in each app. Keeper works around this by forcing the use of a single dex file in the target app and preventing the inclusion of a backport dex file in the test app.

This L8 support is automatically enabled if android.compileOptions.coreLibraryDesugaringEnabled is true in AGP.

License¶

Copyright (C) 2020 Slack Technologies, LLC

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.