Towards Scala 3 support.

[dubinsky]

Fixes #16527, #15491

• switch to the latest Zinc;
• detect Scala 3 library dependency;
• configure Scala 3 compiler and bridge as appropriate;
• Scala 3 compiler bridge is distributed as a binary and does not need to be compiled.

Context

Contributor Checklist

• Review Contribution Guidelines
• Make sure that all commits are signed off to indicate that you agree to the terms of Developer Certificate of Origin.
• Make sure all contributed code can be distributed under the terms of the Apache License 2.0, e.g. the code was written by yourself or the original code is licensed under a license compatible to Apache License 2.0.
• Check "Allow edit from maintainers" option in pull request so that additional changes can be pushed by Gradle team
• Provide integration tests (under <subproject>/src/integTest) to verify changes from a user perspective
• Provide unit tests (under <subproject>/src/test) to verify logic
• Update User Guide, DSL Reference, and Javadoc for public-facing changes
• Ensure that tests pass sanity check: ./gradlew sanityCheck
• Ensure that tests pass locally: ./gradlew <changed-subproject>:quickTest

Gradle Core Team Checklist

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation
• Recognize contributor in release notes

[SethTisue]

are this and #18001 independent efforts?

[dubinsky]

are this and #18001 independent efforts?

Yes, they are.

[tgodzik]

Eclipse will not currently work anyway :/ so no need to update this.

[dubinsky]

:)

[dubinsky]

The main goal of this pull request - support for Scala 3 - was not achieved: some classpath manipulations are needed, as demonstrated by #18001, which does makes Scala 3 work.

This pull request also attempts to update Zinc to the latest version. This turned out to be:

• more involved than anticipated (one test is still broken);
• not needed to add support for Scala 3 (again, as demonstrated by Add support for Scala 3 #18001).
  Depending on if, when, and how smoothly Add support for Scala 3 #18001 is merged (and released), I might attempt a follow-up pull request for Zinc update (as suggested by @tgodzik in Add support for Scala 3 #18001 (comment)) - unless someone who actually knows Zinc beats me to it ;)

Clean-up of the Scala-library-version-recognizing code in the Scala plugin might get its own follow-up pull request (again, as suggested by @tgodzik in #18001 (comment)), but this change is less pressing and thus is less likely to happen :)

For the above reasons, this pull request is not relevant. Closing.