Better IntelliJ support when working on scalafix

[bjaglin]

Since the introduction of sbt-project-matrix in #1528, there are compilation errors in IntelliJ when working on scalafix itself (apparently for both classic & BSP integrations), which prevents running tests from the IDE.

This is also true for projects bootstrapped with https://github.com/scalacenter/scalafix.g8.

[bjaglin]

A first solution would be to only export some of the modules of the matrix as recommended in sbt/sbt-projectmatrix#25 (comment).

[tgodzik]

What are the BSP errors that you get? Maybe it's fixable on the Bloop/sbt side?

[bjaglin]

@tgodzik I didn't get the time to look at it myself.

@rvacaru can you report your problems here?

[tgodzik]

Just checked and I don't get any errors with Bloop + Metals. Project matrix might be problematic for Intellij as it doesn't like multiple targets with the same directory.

[rvacaru]

@tgodzik @bjaglin
I've just started working on scalafix with both Intellij and VS Code, so far these are my findings when comparing the IDEs:

• Just looking at ExplicitResultTypes.scala

  • Intellij: line 9 import buildinfo.RulesBuildInfo is not resolved, even after running sbt compile on the whole scalafix
  • VS Code: the import works and ctrl click on RulesBuildInfo navigates to the scala file

• Looking at ExplicitResultTypesBug.scala (only in the output folder, not the input)

  • Intellij:
    • line 4 import scala.reflect.runtime.universe._ says runtime isn't a member of reflect
    • line 9 type ClassMirror not found
  • VS Code: runtime package is recognized when hoovering on it and ctrl click on ClassMirror navigates to it

• Looking at Compat.scala objects

  • Intellij errors SeqView expects only 1 arg, but finds 2 (points to scala-library-2.13.8 jar instead of the 2.11 or 2.12 versions
  • VS Code works as expected

• Running or debugging ScalafixImplSuite

  • Intellij fails building with Compat is already defined as object Compat
  • VS Code runs and debugs are working fine