It is a non-transitive R class world

After Duplo modularization, we observed that the duty producing a transitive R class was taking a big period of time to execute. To get rid of this job altogether, and because the non-transitive R class is marketed to have as much as 40% incremental build time improvement, we determined emigrate our codebase to make use of it.

When you’re not aware of nonTransitiveRClass, beforehand often called namespacedRclass, it’s an Android Gradle Plugin flag that allows namespacing R courses so that each module’s R class solely consists of assets declared within the module itself, and never assets from the modules or libraries it is dependent upon. This flag is enabled by default for brand spanking new initiatives since Android Studio Bumblebee.

On this publish, we’ll stroll by way of how we transitioned to non-transitive R class and among the advantages — each anticipated and sudden — that we noticed.

Establishing conventions


Since assets can’t all be referenced utilizing the present module’s R class anymore, we first wanted to align on how we needed them to be referenced within the non-transitive R class world. Utilizing the fully-qualified identify for R courses to reference assets, e.g. getString(slack.l10n.R.string.at_everyone), was cumbersome and verbose, so we settled on utilizing import aliases as a substitute for that goal:

import slack.l10n.R as L10nR

class Clazz(context: Context) 


Sadly, import aliases are a Kotlin-specific characteristic and never accessible in Java. Nevertheless, contemplating that solely 4% of our codebase was nonetheless in Java, we agreed that utilizing the fully-qualified identify to reference assets not declared within the present module was a adequate answer, and would function motivation emigrate these courses to Kotlin down the road.


Preliminary technique

We had been planning on utilizing Android Studio’s Refactor > Migrate to Non-Transitive R Classes characteristic to refactor all R references to be fully-qualified, after which use this script to undergo the refactored information and alter the fully-qualified references to make use of import aliases.

Nevertheless, on the scale of our codebase, with greater than 400 modules, Android Studio took all night time on an Intel Macbook Professional (we hadn’t but moved to M1 Macs) to do a part of the work and prompted the UI to turn out to be non-responsive after, so we pivoted to a distinct migration technique.

Chosen technique

Nearly all of our assets are outlined in two modules: the strings are in :l10n-strings and most different assets are in :slack-kit-resources. So, we proceeded with the next technique:

  1. We first used Android Studio’s Discover & Change with the regex ([[|(|]| )R.string. to interchange string useful resource references with $1L10nR.string. and the regex ([[|(|]| )R.(colour|dimen|drawable|font|uncooked|model|attr).sk_  to interchange different useful resource references with $1SlackKitR.$2.sk_.
  2. Then we ran a modified model of the aforementioned script to iterate over information that used both L10nR or SlackKitR as a useful resource reference and added the required import aliases to them. The wanted dependencies had been added to the modules that had been beforehand relying on both :l10n-strings or :slack-kit-resources transitively by way of the R class. The undertaking began compiling efficiently once more.
  3. We enabled non-transitive R class by including android.nonTransitiveRClass=true to the foundation file, and manually up to date the few remaining useful resource references that had been failing compilation.
  4. As the ultimate step of the migration, we enabled a non-transitive R class dependent optimization that generates the compile time solely R class utilizing the app’s native assets by including android.enableAppCompileTimeRClass=true to the identical file.

Developer expertise

Discoverability enhancements

To assist builders work as successfully within the non-transitive R class world as they did earlier than, we discovered the 4 most typical import aliases within the codebase, by working grep -o -h -r -E 'import w+(.w+)+.R as [a-zA-Z0-9]+R' . | kind | uniq -c | kind -b -n -r, and added them as live templates that begin with r for discoverability.

Aliases live templates

Not like file and code templates, reside templates can’t be made accessible to everybody who works on the undertaking by way of Intellij. To work round this, we copied the reside templates file from Android Studio’s templates listing in ~/Library/Software Assist/Google/AndroidStudio<model> and checked it into our Git repository beneath the config/templates listing. As a technique to import it into Android Studio at any time when a brand new model is put in, we then used this script, which runs as a part of bootstrapping the native improvement setting, to repeat the live templates file again to the templates listing.

Conference enforcement

Along with the reside templates, we additionally developed three lint checks, that constructed on high of the conventions that we agreed on, to enforced the next:

  1. Solely the native module’s R class could be imported with out an import alias.
    • For instance, slack.uikit.assets.R can’t be imported exterior :slack-kit-resources with out an import alias.
  2. Import aliases for R courses ought to be constant throughout the codebase.
    • For instance, slack.uikit.assets.R can solely be imported as SlackKitR, not SKR or anything.
  3. R courses/assets can’t be referenced utilizing their fully-qualified names, however quite by way of import aliases.
    • For instance, getString(L10nR.string.at_everyone) must be used as a substitute of getString(slack.l10n.R.string.at_everyone).

All three lint checks have auto-fixes, so fixing any ensuing lint points is a breeze.


Migrating to non-transitive R class had many advantages, essentially the most notable being a ~14% enchancment in incremental construct instances following a useful resource or format change.

It additionally lowered APK/DEX measurement by ~8.5%, which is about 5.5MB of code!

APK size difference graph

Along with the advantages coated above, which had been anticipated, the transition had some oblique advantages that had been sudden:

  • It uncovered situations the place some assets had been declared in a single module however solely utilized in one other, which allowed us to maneuver them for elevated module cohesion. 
  • It made it simpler to determine the place assets are coming from, which enabled us to slender down inaccessible UI components and triage them.


All in all, the migration to non-transitive R class has been an enormous success for us, and developer sentiment is optimistic because of all its advantages and the tooling we applied as help.

We advocate you make the transition to non-transitive R class to reap the advantages we’ve outlined in case you are engaged on a multi-module undertaking or plan on introducing modules to your undertaking.

When you like engaged on stuff like this, we’re hiring!