Because scala3-compiler contains a copy of scalajs-ir, they conflict with each other when being in the same classpath. This was found when trying to migrate the sbt-scalajs to sbt 2, because sbt-scalajs depends on scalajs-ir and on sbt, which depends on scala3-compiler. The related issue is sbt/sbt#7709.

The solution is to shade the compiler version of scalajs-ir under its own package: dotty.tool.sjs.ir. The compiler uses the scalajs-ir internally but it does not need to expose it.