I'm learning custom gradle plugins and I'm struggling with plugin extensions. I'm currently working ...

# gradle

[tim]

I'm learning custom gradle plugins and I'm struggling with plugin extensions. I'm currently working through the gradle guide on making the plugin configurable but i'm getting the following error when running ./gradlew tasks locally:

* What went wrong:
Failed to apply plugin class 'Build_gradle$FooPlugin'.
> Could not create plugin of type 'FooPlugin'.
   > The constructor for type Build_gradle.FooPlugin should be annotated with @Inject.

[tim]

Heres the contents of build.gradle.kts:

abstract class FooExtension {
    abstract val bar: Property<String>

    init {
        println("Hi from FooExt")
    }
}

class FooPlugin : Plugin<Project> {
    override fun apply(target: Project) {
        val extension = target.extensions.create<FooExtension>("foo")

        project.task("hello") {
            doLast {
                println(extension.bar.get())
            }
        }
    }
}

apply<FooPlugin>()

extensions.getByType<FooExtension>().bar.set("foo")

[Vampire]

I think your problem is, that you have all that in a .gradle.kts file.
Because of that the class FooPlugin is an inner class of the class Build_gradle and thus has the instance of the enclosing class as argument to the constructor.
And as now the constructor has a parameter it would need to get the value injected which of course would not work even if the annotation were present.

[tim]

Okay ... I think i'm following. The root issue is that bar isn't initalised .. so i could add something to the contstructor to initialise it init { bar.set("baz") } which should address the issue

[tim]

When the external scope is say a standalone plugin, does the initialisation of the abstract properties occur automatically?

[Vampire]

No, you totally misunderstood

[Vampire]

bar IS initialized, it gets implemented and initilaized by Gradle

[Vampire]

You are looking at the wrong class

[Vampire]

Just copy your FooPlugin into its own file in an included build or buildSrc and it should work as it is then no longer an inner class that needs the instance of the outer class in the constructor

[Vampire]

It is very uncommon to have a plugin class within a build script, because then you could also just do the action

[tim]

okay cool will try that

[tim]

It is very uncommon to have a plugin class within a build script, because then you could also just do the action

Agreed .. but its from the official gradle docs 🤷

[tim]

Okay thanks thats now working as expected

[Vampire]

Ah, your problem is a different one

[Vampire]

You changed the parameter name from the example where it is project to target, but you still do project.task.
So project is the instance of the enclosing script and that's why there is a connection that cannot be initialized

[Vampire]

If you take your initial example here and change project.task to target.task, it works.

[tim]

ahhh that makes sense

[Vampire]

Besides that it is not using task configuration avoidance