Scaladoc external references jdk11

[ashawley]

It's no longer possible for scaladoc to reference the Java class library from Java 9, now, which was discovered here ThoughtWorksInc/sbt-api-mappings#8 by the Akka team. The Akka docs have a few Java refs in their api docs, e.g. https://doc.akka.io/api/akka/current/akka/japi/Util$.html

Presumably, the Java-9 rt.jar hack would work from scala/scala-dev#139, but in the long-term scaladoc will need module-path support and a way to point to modules like java.base...

scala> java.lang.ModuleLayer.boot.configuration.modules.stream.filter(
         m => m.reference.descriptor.name == "java.base"
       ).forEach(
          m => println(m.reference)
       )
[module java.base, location=jrt:/java.base]

[sjrd]

Here is a workaround that we've been using in the Scala.js build for a while: https://github.com/scala-js/scala-js/blob/aede3c83fc6ab9132f475b98a662d0aaaa77dfb8/project/Build.scala#L233-L237

[ashawley]

Ok, good to know. Thank you. I gave your hack a go in ThoughtWorksInc/sbt-api-mappings#14.

[ashawley]

Looks like the hack works for 2.12, but not 2.11.12 for some reason. Is that your experience as well?

[sjrd]

Well we have scala-js/scala-js#3152, but otherwise it seemed like it was working fine (for other projects in our build, beside library). I'm not sure that I actually carefully checked the output, though. I am only certain that it builds.

[ashawley]

Ok, I tried looking through the Jenkins builds for scalajs, but I don't think Java 9 is in the matrix. I'll try the library project locally on Java 9....

Yeah, doesn't look like the hack works on 2.11

https://travis-ci.org/ashawley/scaladoc-test/jobs/335874903

[ashawley]

This probably won't be fixed, but works in 2.12.

It doesn't work again in 2.13, but this can be superseded by #11839.