Modularization. Part 3. Compilation time

This series consist of

• Part 1 — Application structure overview
• Part 2 — Dagger structure
• Part 3 — Compilation time

Let’s see how multi-module project affects build time. I will compare two different Android Gradle plugin versions 2.3.3 and 3.0.0-beta7. Generated profile (via --profile option) allows to see exact tasks that are executed.

How you assemble matters

Version 2.3.3
./gradlew clean assembleDebug — profile ~28 sec
./gradlew clean :app:assembleDebug — profile ~ 18 sec
My assumption is the following. :app:assembleDebug compiles app module and all dependent modules. In case of clean build, all of them.
Plain assembleDebug do same as :app:assembleDebug plus :persistence:assembleDebug, :base-app:assembleDebug etc. This introduces additional actions which blows up build time.

Version 3.0.0-beta7

./gradlew clean assembleDebug — profile ~13 sec
./gradlew clean :app:assembleDebug — profile ~ 13 sec

Latest plugin version not only faster but also “smarter”. The difference is visible when we compare profile. :app:assembleDebug executes less tasks than assembleDebug. And version 3.0.0 assembleDebug executes less tasks than version 2.3.3 assembleDebug.

Flavors and build types

Let’s take a close look at the generated profile. Version 2.3.3 :app:assembleDebug contains task :user-details:compileReleaseKotlin . That’s strange since we are compiling debug build. Version 3.0.0 contains :user-details:compileDebugKotlin, which is more logical. Same happens with flavors. Versions 3.0.0 can properly propagate compiled flavor to all app-modules. Before all flavors were compiled regardless your choice.

Incremental compilation.

Let’s see how incremental compilation is influenced by module division. When we change LoginActivity from login module, only login and app modules are recompiled. All other modules are “UP-TO_DATE”. When we change Storage from persistence module, all dependent modules (login, base-app, user-details) are recompiled. Navigator modules are not recompiled because they do not depend on persistence module.

Summary

• Only affected code is recompiled. It’s possible to achieve huge build time improvement, by creating multiple small independent modules.
• Use latest Android Gradle plugin version. Version 3.0.0 has a lot of improvements and bugfixes for multi-module projects.

Project can be found on Github.