in Kotlin, Kotlin Multiplatform, Libraries |

Run Custom Gradle Task After “build”

After running ./gradlew build on my Kotlin Multiplatform project, I wanted to copy the JavaScript build artifacts (.js & .html) to publish a demo where someone could test my library via a web browser. A custom Gradle task is is a great way to write your own behavior to accomplish this using the Gradle build system.

My Custom Gradle Task

I found the Gradle documentation for how to copy files, and was able to write this custom task "myTaskName" to do it. You can then just run ./gradlew myTaskName and it’ll run the task independently. The problem was that I didn’t know how to get it to always run after ./gradlew build ran.

/** Copies files from "build/distributions" to "demo" directory */
tasks.register<Copy>("myTaskName") {
    println("Copying Build Artifacts!!!")
    from(layout.buildDirectory.dir("distributions"))
    include("**/*.*")
    into(layout.buildDirectory.dir("../demo"))
}

TL;DR – Use finalizedBy()

  • finalizedBy – Runs my task AFTER “build”. ✅
    • tasks.named("build") { finalizedBy("myTaskName") }
  • dependsOn – Runs “build” BEFORE my task, if my task is executed explicitly.
    • tasks.named("myTaskName") { dependsOn("build") }

To give you more details and to go into my process of how I figured it out, here are a few options I tried while figuring out how to run this custom task after every execution of the “build” Gradle task.

1. finalizedBy ✅

You can use finalizedBy() to say what task you should run after a named task. I think this reads nicely because it calls out the task dependency separately from it’s declaration. This will appropriately run after the build task executes as I needed.

tasks.named("build") { finalizedBy("myTaskName") }

2. shouldRunAfter 🤔

Another possible way to do this is with shouldRunAfter() which can just be added inside the block where you register your custom task. This will run after the build task executes. HOWEVER: I had to call .get() after registering my task to get it to work in order to have this actually run, which just feels wrong… Someone feel free to explain why, but I’m guessing this is some sort of lazy initialization happening if I don’t call “.get()”. Because of this, I don’t like this solution personally.

tasks.register<Copy>("myTaskName") {
    shouldRunAfter("build") // Tells Gradle to execute after "build" task
    // My Custom Task Code
}.get()

3. dependsOn() 🙃

You would think dependsOn() may work, but it’s the opposite behavior than what I wanted. It’s saying that “myTaskName” needs “build” to have run before it executes. It’s the opposite task dependency relationship from finalizedBy(). This wasn’t the behavior I wanted for this use case because I wanted it to copy the artifacts after every time a ./gradlew build was run, but could be useful depending on your use case.

tasks.named("myTaskName") { dependsOn("build") }

Wrap Up

None of this is rocket science, but if you try to Google for how to do it, it may take you a while to figure out how to do it. Using Option 1, finalizedBy() was the solution that worked for my use case! I hope this saved you an hour or more!

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