How can I use Gratatouille to write task actions with side-effects?

[joffrey-bion]

Description

I would like to try to use Gratatouille to make the Gradle GitHub Changelog plugin more correct without adding too much boilerplate.

This plugin fetches GitHub issues information from GitHub during the task execution, which is inherently a non-cacheable side-effect. Can Gratatouille be used for this too?

[martinbonnin]

That's an excellent question and I haven't put too much thoughts into it.

At first sight, I'd say this is currently not working because @CacheableTask is added unconditionally. And probably (but I have not checked) Gradle fails if a task is marked @CacheableTask without declaring any output. We could probably make this a rule: if a task has no output then do not mark it cacheable. I'll take a look next year :)

[joffrey-bion]

Thanks for the reply!

Actually let me amend what I said. The task fetches information from GitHub and produces a changelog file as an output. So there is an output, but part of the input comes from the internet, so it can never be up to date.

[martinbonnin]

Thanks for the follow up!

Am I correct that this is about allowing non-pure functions?

You would still use Gratatouille for parallel execution (all the workers boilerplate), non-overlapping outputs, potentially classloader isolation but with non-pure functions?

I think this makes sense. One could for an example use the output of generateChangelog as input to another Gradle task.

What about adding @GNonPure to disable up-to-date-ness and cacheability?

User code:

@GTaskAction
@GNonPure
internal fun computeChangelog(output: GOutputFile) {
    TODO()
}

Generated code:

// Note no @CacheableTask here
internal abstract class GenerateChangelogTask : DefaultTask() {
  init {
    outputs.upToDateWhen {
      false
    }
  }

  @get:OutputFile
  val output: RegularFileProperty
}

// Worker, etc...

Thoughts?

[joffrey-bion]

Am I correct that this is about allowing non-pure functions?

Yes, I believe we can frame it this way.

I opened this issue because the section of the docs about pure functions seemed to mentioned this as a kind of requirement (even though it's in the "features" section).

So, with that in mind, your suggestion looks good to me, but please keep in mind that I don't know all the implications, so my opinion might not bring much value on this 😅

[martinbonnin]

I have added a pure: Boolean parameter to @GtaskAction. See code here (apologies I had a bunch of things in flight and this didn't turn out as a nice atomic commit).

It can be used like so:

@GTaskAction(pure = false)
internal fun impureFunction(
    input: String,
    outputFile: GOutputFile,
) {
    outputFile.writeText("${Date()}: $input")
}

[joffrey-bion]

Oh nice! Thank you!

[joffrey-bion]

By the way, no rush at all, this is just a side project, and I wanted to clean it up also as an excuse to try Gratatouille. I'll give it a go when you cut a release ;)

[martinbonnin]

Sounds like a plan 👍

Heads up the project is still in the early days. I haven't used it in a real life plugin yet. I want to use it in Apollo at some point but there are still some deprecated features that would be awkward to use with Gratatouille (because they require internal properties and using the global classpath, namely operationOutputGenerator and packageNameGenerator).

Hopefully in 2025 🤞