Why are plugins defined with "apply false" in the project-level build.gradle.kts?

[jaemin-Yoo]

Hello,
I'm a junior Android developer studying with the nia project and I really appreciate the quality sample project provided.

I have noticed that the build.gradle.kts(project root) file defines several plugins with apply false.

/* build.gradle.kts(Project: nowinandroid) */

plugins {  
    alias(libs.plugins.android.application) apply false  
    alias(libs.plugins.android.library) apply false  
    alias(libs.plugins.android.test) apply false  
    alias(libs.plugins.baselineprofile) apply false  
    alias(libs.plugins.compose) apply false  
    alias(libs.plugins.kotlin.jvm) apply false  
    alias(libs.plugins.kotlin.serialization) apply false  
    alias(libs.plugins.dependencyGuard) apply false  
    alias(libs.plugins.firebase.crashlytics) apply false  
    alias(libs.plugins.firebase.perf) apply false  
    alias(libs.plugins.gms) apply false  
    alias(libs.plugins.hilt) apply false  
    alias(libs.plugins.ksp) apply false  
    alias(libs.plugins.roborazzi) apply false  
    alias(libs.plugins.secrets) apply false  
    alias(libs.plugins.room) apply false  
    alias(libs.plugins.module.graph) apply true
}

As I understand it, plugins defined with apply false are not applied at the project level, and need to be explicitly applied in the module-level build scripts where they are needed.
If the plugins need to be applied at the module level, I am wondering why they are also defined in the project-level script.

The comment in the plugins block says:

By listing all the plugins used throughout all subprojects in the root project build script, it ensures that the build script classpath remains the same for all projects. This avoids potential problems with mismatching versions of transitive plugin dependencies. A subproject that applies an unlisted plugin will have that plugin and its dependencies _appended_ to the classpath, not replacing pre-existing dependencies.

I understand that this is meant to keep the buildscript classpath consistent, but since nia uses version catalogs, wouldn't the classpath remain consistent even if plugins are only defined at the module level?

Could you please explain the practical reason for defining plugins with apply false in the project-level build.gradle.kts?

Thank you.

[Jaehwa-Noh]

Because of the plugin contains bundle of tasks and that was usually no need at the top of project.
https://docs.gradle.org/current/userguide/plugins.html#benefits_of_plugins

[jaemin-Yoo]

Thank you for your reply.

When not using a version catalog, I defined the plugins with apply false in build.gradle.kts(:project) in order to keep the plugin versions consistent across multiple modules. However, since the nia project uses a version catalog, isn't it unnecessary to define the plugins in build.gradle.kts(:project)?

https://developer.android.com/build/dependencies#add-dependencies-without-catalogs