Problem building scala 2.13.1 with Gradle 6.2 (worked with 5.6.2) - scala

Question

I want to use Gradle 6.2 because of the recently fixed scaladoc issue.
Here is a build scan of my Gradle build using version 5.6.2 and Scala 2.13.1 - which works fine.
Without changing the Gradle build file at all, other than changing the version to 6.2, I now get this error:
> Could not resolve all dependencies for configuration ':zinc'.
> Conflict(s) found for the following module(s):
- org.scala-lang:scala-library between versions 2.12.8, 2.12.2, 2.12.1 and 2.12.0
- com.google.protobuf:protobuf-java between versions 3.7.0 and 3.3.1
- org.scala-lang.modules:scala-xml_2.12 between versions 1.0.6 and 1.0.5
I studied the suggested dependency graph but don't know how I am supposed to resolve the conflicts. I don't know why it is trying to use scala 2.12 at all.
Here is the corresponding build scan for this failing build.
I see that dependency configurations like "compile" are now deprecated. I tried changing to the newer preferred configurations, but I'm not certain that I mapped them all correctly.
I tried this:
dependencies {
implementation "java3d:vecmath:$vecmathVersion"
testImplementation 'junit:junit:4.12'
compileOnly("org.scala-lang:scala-library") {
version {
require "2.13.1"
}
}
testImplementation 'org.scalatest:scalatest_2.13:3.1.1'
testRuntimeOnly 'org.pegdown:pegdown:1.6.0'
}
but get the same error as above.

Answer 1

Please see this post for a bit more detail about how gradle works with Scala dependencies.
I suggest simplifying your dependencies section first, and using a specific version of scala, to get it working. I don't see why you you only want the scala-library at compile time and not runtime? The Gradle Scala plugin requires it to be a generally compile-time dependency: https://docs.gradle.org/current/userguide/scala_plugin.html.
The same documentation says that Gradle uses 2.12 to compile 2.13 sources... so I suspect that the 2.12 dependency is creeping in because you did not explicitly declare your scala-library version.
Without knowing the value of $vecmathVersion, I suggest the following:
dependencies {
implementation group: 'java3d', name: 'vecmath', version: '1.3.1'
implementation group: 'org.scala-lang', name: 'scala-library', version: '2.13.1'
testImplementation 'junit:junit:4.12'
testImplementation 'org.scalatest', name: 'scalatest_2.13', version: '3.1.1'
testImplementation 'org.pegdown:pegdown:1.6.0'
}