Summary

• Fix updateSbtClassifiers to use the correct Scala version when building cross-compiled sbt plugins with explicit scalaVersion

Problem

When cross-building sbt plugins with explicit scalaVersion set in build.sbt, the updateSbtClassifiers task fails because it uses the launcher's Scala version instead of the appropriate Scala version for the target sbt version.

For example, with this configuration:

lazy val root = (project in file("."))
  .enablePlugins(SbtPlugin)
  .settings(
    scalaVersion := "2.10.7",  // Explicit for IDE support
    crossSbtVersions := Seq("0.13.17", "1.0.0"),
  )

Running sbt "show updateSbtClassifiers" would fail with:
Error downloading org.scala-sbt:scripted-plugin_2.12:0.13.17

It should look for scripted-plugin_2.10:0.13.17 since sbt 0.13.x uses Scala 2.10.

Solution

Modified sbtClassifiersTasks in Defaults.scala to:

1. Check if the project is an sbt plugin (sbtPlugin.value)
2. For plugins, derive the Scala version from pluginCrossBuild / sbtBinaryVersion using PluginCross.scalaVersionFromSbtBinaryVersion
3. For non-plugins, continue using the launcher's Scala version (original behavior)

Test plan

• Added scripted test dependency-management/i8026-update-sbt-classifiers-cross-plugin
• Verified existing tests pass:
  • dependency-management/update-sbt-classifiers
  • dependency-management/i8405-update-sbt-classifiers-plugins
  • dependency-management/sources
  • dependency-management/cache-classifiers
  • plugins/plugin-cross
• MiMa binary compatibility check passed
• Unit tests passed

Fixes #8026

Contribution by Gittensor, see my contribution statistics at https://gittensor.io/miners/details?githubId=148254234