Add support for specifying the Java toolchain for invoking R8 about gr8 HOT 8 CLOSED

I can make a PR for this later in the evening today

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I forked the task (only needed a handy R8 invoke task :)), that's exactly what I'm doing (invoking on Gradle the JVM Gradle is running on) while runtime jars are passed in from the launcher. I guess it would make sense to name it differently or actually use it for launching?

For invoking afaik the Worker APIs had nice facilities to create isolated tasks that run on a different JVM.

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Good callout 👍 . Any idea what options to expose override this? I guess it should take a path?

gr8 {
  javaHome.set("path/to/java/home")
}

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ideally should expose setting the toolchain launcher itself, while defaulting to the toolchain provided by the Java extension by default, check the section "Toolchains for JVM projects" here:

https://docs.gradle.org/current/userguide/toolchains.html#sec:plugins

that way if someone does something like

java {
  sourceCompatibility = JavaVersion.VERSION_11
  targetCompatibility = JavaVersion.VERSION_11

  toolchain {
    languageVersion.set(JavaLanguageVersion.of(11))
    vendor.set(JvmVendorSpec.AZUL)
  }
}

you can get that toolchain picked up automatically.

If you have a Property<JavaLauncher> you can turn it into a java.home File with something like:

val javaHome = launcher.get().executablePath.asFile.parentFile.parentFile

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Property<JavaLauncher>

Thanks that sounds perfect 👍

Do we want to be able to run R8 using e.g. Java 20 while still passing it Java 11 runtime jars? That'd save launching a new JVM if your main build is using 20. But maybe it's not worth it?

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invoking on Gradle the JVM Gradle is running on while runtime jars are passed in from the launcher

Nice. I think that's a good default, no need to downgrade the JVM just to get the runtime jars.

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Awesome, thanks!

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Closed with #16

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