How can I split build.sc into multiple files?

[micheal-hill]

I'm not sure if this is a question that's already answered elsewhere, but I didn't come up with much after searching through docs and the discussion forum. I'm trying to convert some workflow from sbt to mill

Is it possible to split my build.sc into multiple files? I'd like to have a hierarchy something like:

root
│  build.sc
└─ project             // arbitrary name; but indicates code that is important for the build script/config
│    utils.sc          // [1] contains some helper functions that are used by both `CommonModules.sc` and `build.sc`
│    CommonModules.sc  // [2] contains `trait ScalaCommon extends ScalaModule`
└─ app-module          // arbitrary name; represents a submodule of the project
     build.sc          // [3] module definition that is specific to this submodule

So far, it seems that:

1. Can be done using ammonite's import syntax import $file.project.utils
2. The import itself works, however it requires a second import to obtain ScalaCommon from the file. More importantly, it seems to break mill if I try to use it; resulting in an error: Modules, Targets and Commands can only be defined within a mill Module
3. I couldn't figure out a way to make this work at all

In each of the above situations, I've tried both $cp and $file syntax imports from ammonite - not sure if there's something else I should try too.

[lefou]

2. The import itself works, however it requires a second import to obtain `ScalaCommon` from the file. More importantly, it seems to break mill if I try to use it; resulting in an error: `Modules, Targets and Commands can only be defined within a mill Module`

The second import is normal, but the error not. Defining trait which contains targets should work. Only objects (the real modules in mill) need to be located in the build.sc.

To get to the cause of your specific error, you might need to share some code.

3. I couldn't figure out a way to make this work at all

Mill supports foreign modules which should the way to support your project layout. Note, that you may not be able to refer back to the importing build.sc from the foreign module (in terms of tasks/targets). Also, I have to say I've never tried this myself and @lihaoyi once said, that foreign modules are much less used and therefore less tested than all the other stuff.

[itegebo]

When splitting, do all files need to have the .sc suffix? Also, what's the reason for a different suffix?

[lefou]

Yes, all files need the .sc suffix. .sc is typically used for Scala scripts, e.g. in Ammonite but also for workbook files (Eclipse (scala-ide), IntelliJ IDEA), whereas .scala is Scala source code to be fed to the compiler.