Set default Java version to 17 if scalaVersion is 3.8.0 or higher

[kubukoz]

With the release of 3.8.0-RC1, which only supports JDK17 and above, sbt-typelevel should probably use Some(17) as the default value of tlJdkRelease.

Thoughts?

[kubukoz]

uh, it might be more complex. I just tried this locally:

ThisBuild / tlJdkRelease := {
  if (scalaVersion.value.startsWith("3") && scalaVersion.value.split("\\.")(1).toInt >= 8) Some(17)
  else (ThisBuild / tlJdkRelease).value
}

and now my workflows / mergify configs either all refer to jdk8, or all refer to jdk17 - it depends on which Scala version I'm using at the moment of generating them. Is it even possible to have separate JDK versions within the build?

[armanbilge]

The tlJdkRelease setting is a compiler config flag, so it's okay to be set dynamically: it doesn't go into the workflows.

At least, not directly—the problem is that the workflow Java version setting is currently derived from the release setting 😕

sbt-typelevel/core/src/main/scala/org/typelevel/sbt/TypelevelPlugin.scala

Lines 69 to 71 in ceb8c3e

	githubWorkflowJavaVersions := {
	Seq(JavaSpec.temurin(tlJdkRelease.value.getOrElse(8).toString))
	},