Define multiple sbt sub-projects which share sources, resources and jars

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sbt-ShadowyProject is a sbt-plugin to define an additional project which refers to another (original) project sources, resources and jars.

You can copy(shadow) your original sub-project(shadowee) into a different one(shadower), with modifying original settings.

How to use:

// project/plugins.sbt
addSbtPlugin("com.taisukeoe" % "sbt-shadowyproject" % "0.1.0")
// build.sbt

lazy val yourMainProject = (project in file("core"))

lazy val shadow = project
  .shadow(yourMainProject) // enriched by sbt-shadowyproject
  .modify(/* define how to modify original settings with modification algebras */)
  .settings(/* add shadowee specific settings */)
  .light // applied all modification and settings to `shadow` sub-project

In case you needn't copy nor modify original shadowee settings, you can call project.shade(yourMainProject).light instead.

NOTE: sbt-ShadowyProject build.sbt file is a good real world example.


This aims to split sbt settings for slightly different purposes, even for the same sources. Combination is up to you - mandatory-for-build and useful-for-maintainance, safer-coding ando flexible(,but not so safe)-coding, or strict-scalacOptions and loose-scalacOptions-with-Scalafix.

While there are tons of scalac-options which allow us to pursue safer coding, some of them might be too strict.

For example, -Xfatal-warnings (or -Werror in Scala 2.13 or above) scalac option is widely used to escalate warnings to errors.

It works great in situations when you want to confirm if current code is clean, such as CI.

On the other hand, marking every unused import as an error every time seems to be a bit strict.

Refactoring often introduces unused imports or variables, which don't have to be fixed immediately. Rather, it would be much easier to run Scalafix RemoveUnused rule, just before you commit your changes.

If that's a case, you can set -Xfatal-warnings to your original sub-project(shadowee), and set Scalafix configuration without -Xfatal-warnings to your shadower project.


DeepShadow is an experimental feature that you want to gather all sources from your dependency.

Imagine the following build.sbt is given.

lazy val a1 = project
lazy val a2 = project.dependsOn(a1 % "compile->compile;test->test")
lazy val a3 = project.dependsOn(a2)
lazy val a4 = project.dependsOn(a3 % "compile->compile;test->test")
lazy val a5 = project.dependsOn(a4 % "compile->compile;test->test")

lazy val deepShadowA5 = project

sources files in compile or test scope are as follows.

sbt> show deepShadowA5/compile:sources

[info] [info] * /your/temp/dir/project_dependency/a5/src/main/scala/A5.scala
[info] [info] * /your/temp/dir/project_dependency/a4/src/main/scala/A4.scala
[info] [info] * /your/temp/dir/project_dependency/a3/src/main/scala/A3.scala
[info] [info] * /your/temp/dir/project_dependency/a2/src/main/scala/A2.scala
[info] [info] * /your/temp/dir/project_dependency/a1/src/main/scala/A1.scala
sbt> show deepShadowA5/test:sources

[info] [info] * /your/temp/dir/project_dependency/a5/src/test/scala/A5Test.scala
[info] [info] * /your/temp/dir/project_dependency/a4/src/test/scala/A4Test.scala
[info] [info] * /your/temp/dir/project_dependency/a3/src/test/scala/A3Test.scala

So that you can run a task with your favorite config (e.g. compile with your favorite scalacOptions or run Scalafix with preferable settings) against all sub-project sources at once.


ShadowyProject assumes original project settings:

  • don't have files to be added to sources or resources TaskKeys directly.
  • don't have files for its generators, managed sources or resources which are not located under sourceManaged or resourceManaged directories.

Otherwise, ShadowyProject cannot refer them automatically and requires to add them to ShadowyProject settings explicitly.

Modification Algebras

SettingTransformer traits define the ways to modify original settings.

Shadow has a public modify method to add a SettingTransformer, while Shade has only a private constructor parameter for it.

There are pre-defined transformers like:

  • RemoveScalacOptions
    • RemoveXFatalWarnings
  • ExcludeKeyNames
    • RemoveTargetDir (applied to all Shadow projects at default)
  • ExcludeConfigScoped

SettingsTransformer and Action Algebras have a plus(+) operator and satisfy an associative law.