How to share code between project and build definition project in SBT

Question

If I have written some source code in my build definition project (in /project/src/main/scala) in SBT. Now I want to use these classes also in the project I am building. Is there a best practice? Currently I have created a custom Task that copies the .scala files over.

Answer 1

Those seem like unnecessarily indirect mechanisms.

unmanagedSourceDirectories in Compile += baseDirectory.value / "project/src/main"

Answer 2

Sharing sourceDirectories as in extempore's answer is the simplest way to go about it, but unfortunately it won't work well with IntelliJ because the project model doesn't allow sharing source roots between multiple modules.

Seth Tisue's approach will work, but requires rebuilding to update sources.

To actually share the sources and have IntelliJ pick up on it directly, you can define a module within the build.

The following approach seems to only work in sbt 1.0+

Create a file project/metabuild.sbt:

val buildShared = project
val buildRoot = (project in file("."))
  .dependsOn(buildShared)

and in your build.sbt:

val buildShared = ProjectRef(file("project"), "buildShared")
val root = (project in file("."))
  .dependsOn(buildShared)

Then put your shared code in project/buildShared/src/main/scala/ and refresh. Your project will look something like this in IntelliJ:

Full example project: https://github.com/jastice/shared-build-sources