Meta-Build is ignored by GenIdea

[lefou]

The generated Idea project does not have the necessary source directories under mill-build/src.

[lihaoyi]

GenIdea doesn't go through the proper bootstrap process, the same way that the mill.bsp.BSP logic does in State.scala. It's probably missing a bunch of stuff as a result.

The proper fix would be to make GenIdea go through the proper bootstrap process as well. This might necessitate moving it from mill.scalalib.GenIdea to mill.runner.GenIdea, so it can properly access the mill.runner.MillBuildBootstrap logic that we use for BSP.

Ideally we would be able to share most of the logic between GenIdea and BSP. They're both just dumping classpaths and source folders after all. But it would take some work to merge the divergent implementations

[lefou]

A new module is probably the better option, as it not really part of the runner but some IDE integration. We could make it a contrib, but that's kind-of degrading its support.

[lefou]

Meta-builds now work and code-navigation works even better now than before, where we relied on IntelliJ Ammonite support. If you get asked by IntelliJ IDEA whether you want to enable Ammonite script support for build.sc and friends, you can safely say "no".