From mobile apps to microservices, from small startups to big enterprises, Gradle helps teams build, automate and deliver better software, faster.

Gradle Community

Fwiw, you would now use `project.extensions.getByType(SourceSetContainer::class.java)` (or `project.the&lt;SourceSetContainer&gt;()` or similar) for Java projects.

For Android projects, you need to first get the Android extension, something like `project.the&lt;CommonExtension&gt;().sourceSets` (or use `ApplicationExtension` if you know you'd in an Android application).

<@UDC9Q9RD0> the difference between `the` and `extensions` is it is lazy so you don't need `afterEvaluate`?

Not at all. `the()` is a Kotlin DSL extension that only adds syntactic sugar: <https://github.com/gradle/gradle/blob/v7.3.3/subprojects/kotlin-dsl/src/main/kotlin/org/gradle/kotlin/dsl/ExtensionAwareExtensions.kt#L27-L28>

Thx, which dependency do I need for that `the`  extension function?

`gradleKotlinDsl()`, which you get automatically when applying the ``kotlin-dsl`` plugin (which also applies ``embedded-kotlin``, itself applying `kotlin("jvm") version embeddedKotlinVersion` )

Great I got now the import working, next stupid question: how can I import that `CommonExtension`  or `ApplicationExtension`  classes? They are not in my class path by default

I found already the source code here: <https://android.googlesource.com/platform/tools/build/+/master/gradle/src/main/groovy/com/android/build/gradle/AppExtension.groovy>, but that link is no dependency :smile:

You need to add a dependency on the AGP (either `compileOnly` if your plugin could work without it, `implementation` if it's required, this declaration will then set a _minimum_ version, or you could use `compileOnly` anyway and let the user explicitly add the plugin to their buildscript classpath), I'd use the `gradle-api` artifact then, that only exposes public APIs.

Good so I'm on the right track. I just idenfified this dependency name: com.android.tools.build:gradle

I'd suggest rather using `com.android.tools.build:gradle-api` then :wink:

I get now a `org.gradle.api.internal.plugins.PluginApplicationException: Failed to apply plugin 'my.plugin.name'`
`Extension of type 'ApplicationExtension' does not exist. Currently registered extension types: [ExtraPropertiesExtension]`
My plugin is now basically:
```open class MyPlugin : Plugin&lt;Project&gt; {
    override fun apply(project: Project): Unit = with(project) {
        val androidSourceSets = project.the&lt;ApplicationExtension&gt;().sourceSets
        // crash in line above```

ah Javi provided the solution already I need to use `afterEvaluate`

Don't use `afterEvaluate`.
If your plugin cannot work without that plugin applied, then apply the plugin before configuring the extension.

If you just want to react if the plugin is applied, use `pluginManager.withId("...") { ... }`