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💀 Emerge Reaper

Reaper is an SDK that uses production data for detecting dead code.

Features

  • Automatically detect and delete dead code in production.
  • View statistics on real-world code usage.
  • (Upcoming) Automated code deletion.

For full details, see the Emerge Reaper docs.

Quickstart (~10 min)

Setup Emerge Gradle plugin

Add the Emerge Gradle plugin to your application's build.gradle.kts file:

plugins {
  id("com.emergetools.android")
}

emerge {
  // If not explicitly set, Emerge uses the EMERGE_API_TOKEN env variable
  apiToken.set(System.getenv("EMERGE_API_TOKEN"))

  reaper {
    // Specify all variants of your app you'd like to add Reaper to.
    // We recommend setting the release variant you ship to the Play Store.
    enabledVariants.set(listOf("release"))
    publishableApiKey.set(System.getenv("EMERGE_PUBLISHABLE_API_KEY"))
  }
}

You must add the variant you intend to add Reaper to to the enabledVariants list for reaper to work properly. Behind the scenes, the Emerge Gradle plugin will instrument your code for the specified varaint(s) to drop breadcrumbs that Reaper can use to detect dead code.

publishableApiKey is a token included with reports uploaded from the field to Emerge. Your team's key can be found here.

Emerge recommends enabling reaper on any variant you ship to the Play Store or other release distribution.

See gradle-plugin for more information.

Add Reaper SDK

Add the Reaper SDK to your application's build.gradle.kts file:

dependencies {
  implementation("com.emergetools.reaper:reaper:<latest_version>")
}

Build a release build

Emerge needs a valid release AAB to generate a list of all possible classes within your app.

./gradlew :app:bundleRelease

By adding your variant to the reaper.enabledVariants property, the Emerge Gradle plugin will instrument your that variant's code and upload the resulting AAB from the bundle task to Emerge.

Emerge will then analyze the AAB, parsing all classes in the app. This process can take a few minutes.

Upon receiving Reaper reports from production data, Emerge will automatically mark used classes as used.

Release your app with Reaper

That's it! Build and ship the AAB you generated in the previous step with Reaper enabled to start detecting dead code.

As reports come in, Emerge's Reaper UI will show unused code from real user reports. We recommend waiting a few days after a release before acting on the data to ensure enough time for a wide range of user sessions to have used your app.

How it works

Reaper uses production data to detect dead code by determining what code is used at runtime.

It works by instrumenting code using our Gradle plugin, which instruments class initialization functions. Upon a class being initialized, Emerge will mark that class as used in an in-memory store. This marking is done by recording a hash of the class name, so no actual class names are recorded.

Upon a user backgrounding the application, Emerge will send the list of hashes of used classes to the Emerge backend. Emerge will then process each report received, marking classes as used if any user session reports that class being used.

Releasing Reaper SDK

Releasing a new version

  1. Update the emerge-reaper version in /gradle/libs.versions.toml
  2. Update the /reaper/CHANGELOG.md
  3. gt c -am "Prepare for Reaper release X.Y.Z" (where X.Y.Z is the version set in step 1)
  4. gt ss
  5. Get PR approved and merge
  6. Create a new release on GitHub
  7. Tag version reaper-vX.Y.Z
  8. Release title Reaper vX.Y.Z
  9. Paste the content from /reaper/CHANGELOG.md as the description

The reaper-release workflow will automatically publish the new version to Sonatype upon new release publish.

From there, the release will need to be promoted to the main repository from the Sonatype UI.