What's the best way to write a task which allows its user to specify some functionality in their build.gradle? I'm working on a plugin that produces a report on a project's dependencies, but I want the user to be able to customise specific details as the report is being built. My first instinct is to allow the user to specify a function which gets invoked for each dependency as it is being processed. It seems like that function should be an input to the task, but then I run into serialisation issues, if it's not an input, but is marked as internal I worry that up-to-date checking and caching would be broken. Any advice?

It should work if you make your "dependency processor" serializable. E.g. you create an interface:

interface MyDependencyProcessor : Serializable {
    // methods
}

And then user can implement it and pass instance as an input. Another option is that user passes a

Class<? extends  MyDependencyProcessor>

and you instantiate that at the execution of a task. For example https://github.com/melix/japicmp-gradle-plugin uses such strategy afaik (see filters)

That second option sounds like a good approach. I was trying to avoid serializable since that kind of ties the user's hands. Do you know if using

ObjectFactory.newInstance()

would cause the standard dependency injection to occur?

See JavaDoc what it supports: https://github.com/gradle/gradle/blob/dc6e12baff8fbfbe75ee3f5a238831e594d95cb8/sub[…]/core-api/src/main/java/org/gradle/api/model/ObjectFactory.java

Thanks