Allow customizable scala version dependency through dependency provider

[rfan-debug]

Description

Currently, the scalapb version and scala-compiler version are hard-coded in the repository.bzl dependency file. It blocks users from upgrading their scala application from scala 2.12 to 2.13, because dependencies compiled in 2.12 is not binary-compatible in scala-2.13 code.

Is there any plan to allow passing in customer-defined dependency version for scala compiler + scalaPB? I wish we could provide customized dependencies underneath through some dependency provider.

[aaliddell]

In the short term, it's difficult, as the combinations explode when trying to support multiple versions per language. In the long term, Bazel 6.0 will introduce bzlmod, which will allow offloading all the dependencies. This will allow users to update their versions without changes needed here.

In the very short term, if you need that specific version, you can vendor the code used here for one version and adapt it to the new version. When I do the next cycle of picking up new versions, scalapb will be checked and updated if possible.