Sbt in project plugin, how to structure them? - sbt

Question

We do have a custom plugin as a single file in our project folder:
acme-project
|- ...
|- project
| |- CustomPlugin.scala
object CustomPlugin extends AutoPlugin {
// ...
That was simple and easy until that plugin started to grow...
In the first step, we added more classes/objects to the same source file. However, it continues to grow and I would like to add more structure via packages.
acme-project
|- ...
|- project
| |- CustomPlugin.scala
| |- SupportingClass.scala
| |- acme
| | |- plugin
| | | |- PackagedClass.scala
My CustomPlugin seems to be able to use the SupportingClass from the folder, whenever this class declare another package. However, I cannot use the PackagedClass :
[error] /~/acme-project/project/CustomPlugin.scala:1:8: not found: object acme
[error] import mega.plugin.PackagedClass
[error]             ^
I tried to add one src/main/scala folder but have the same kind of import errors.
So, I would like to know if there are ways to create large/structured plugins inside a project without making a complete one?
I would like to keep the simplicity of this format where I do not have to publish my plugin. Having it inside a dedicated module would be ok.
Thanks

Answer 1

One way to do this is to restructure your plugin as its own sbt project, then load it as a module dependency in your project's plugins.sbt.
Move the code to its own directory. This can be anywhere you like, e.g.:
acme-project/project/my-custom-plugin/
acme-project/my-custom-plugin/
some-other-path/my-custom-plugin/
Write a my-custom-plugin/build.sbt with at least these settings:
enablePlugins(SbtPlugin)
sbtPlugin := true
scalaVersion := "2.12.16"
name := "my-custom-plugin"
Add it to your project as a module dependency in acme-project/project/plugins.sbt:
// For acme-project/project/my-custom-plugin/
val myCustomPlugin =
project in file("my-custom-plugin")
// For acme-project/my-custom-plugin/
val myCustomPlugin =
ProjectRef(file("../../my-custom-plugin"), "my-custom-plugin")
// For some-other-path/my-custom-plugin/
val myCustomPlugin =
ProjectRef(file("/path/to/my-custom-plugin", "my-custom-plugin")
dependsOn(myCustomPlugin)
You only need one of those val myCustomPlugin = lines, depending on where you put your my-custom-plugin/ directory.