sbt-dotty plugin fails to aggregate multiple projects

[allanrenucci]

Consider the following scenario:

I have a project structure like this

.
├── bar
│   └── src
│       └── main
│           └── scala
│               └── Bar.scala
│
├── foo
│   └── src
│       └── main
│           └── scala
│               └── Foo.scala
│
├── build.sbt
│
└── project
    ├── build.properties
    └── plugins.sbt

and a build.sbt as follow:

lazy val foo = project
  .in(file("foo"))

lazy val bar = project
  .in(file("bar"))

lazy val root = project
  .in(file("."))
  .aggregate(foo, bar)

If plugin.sbt is empty, then I can type sbt compile and it will compile Foo.scala and Bar.scala. However, if plugin.sbt contains

addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.1.5")

then when I type sbt compile, it will do nothing. I can still do sbt bar/compile or sbt foo/compile

[smarter]

This has something to do with the use of Def.derive in DottyIDEPlugin but I don't understand what. As a workaround you can add:

  .disablePlugins(dotty.tools.sbtplugin.DottyIDEPlugin)

to every sbt project in the build.

[smarter]

Opened an issue against sbt because I'm baffled: sbt/sbt#3580