How to add a generated code from build folder to the path in a Gradle Android Library plugin

Question

I've got an Android Library module, and in the build.gradle.kts script I've made a plugin class, inside the apply method of the plugin I am doing:

import com.android.build.gradle.LibraryExtension

val libExtension = project.extensions.findByType(LibraryExtension::class.java)!!
libExtension.libraryVariants.all {
     val variantName = this.name
     val sourceDir = "${project.buildDir}/generated/my-plugin/$variantName"
     libExtension.sourceSets[variantName].kotlin.srcDir(sourceDir)
}

(where variantName is “debug” or “release”)

I thought this code would add the folder as a source folder, but it doesn't (and therefore the kotlin class I have in the folder is not available).

Under the build folder of my android library module:

My folder (not working / not blue):

A correctly working folder in the build directory, created by another plugin:

Answer 1

Ok so the code in the question works, I'm not so crazy ><.

When I split this out into the demo it showed it working.

Here is the code that does not work:

import com.android.build.gradle.LibraryExtension

val libExtension = project.extensions.findByType(LibraryExtension::class.java)!!
libExtension.libraryVariants.all {
     val variantName = this.name
     val sourceDir = "${project.buildDir}/generated/my-plugin/$variantName"
     // This task generates some code and puts it in the sourceDir
     val tp = project.tasks.register<MyTask>("${variantName}MyTask")
     tp.get().doLast {
         libExtension.sourceSets[variantName].kotlin.srcDir(sourceDir)
     }
}

I am assuming the "doLast" is what's stopping it working in the IDE. My guess is that if I generate the files first and then set the folder as a sourceset the IDE isn’t triggered into action. But if I set it as a sourceset first, and then generate the files, it kinda kicks in? 🤷

Leaving the question here anyway, as I found it hard to even find anyone talking about this.