Projects

Multiple Projects in the same Build (Subprojects)

Sometimes a build combines multiple source directories, each of which is their own ‘project’. For instance, you might have a build structure like this:

projectName/ build.sbt project/ src/ main/ … test/ … core/ src/ main/ … test/ … webapp/ src/ main/ … test/ …

In the above project, the code in projectName/src is considered the root project. There are two other modules, or ‘subprojects’, core and webapp.

Configuring a subproject is similar to configuring the root project, except that the subdirectory is specified in the project. This example shows a root project that aggregates a core and webapp project.

lazy val root = (project in file(".")).aggregate(core,webapp).dependsOn(core, webapp)

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

lazy val webapp = (project in file("webapp")).dependsOn(core)

The values passed to file() are the directories relative to the project root.

The webapp project depends on the core project, which is indicated by the dependsOn clause, which takes the core value specified on the line above. dependsOn and lazy evaluation ensure that dependencies are available before projects utilize them. In this case, webapp depends on core, so core will be compiled before the build attempts to compile webapp.

aggregate makes tasks defined in one project available to the project that aggregates it. For instance, executing compile in the root project will also execute compile in core and webapp.

Configure Macros in a Project

In the build.sbt file (or where the project is defined if it is in another location), add the following setting:

scalacOptions += "-language:experimental.macros"

For instance, a project might be defined like this:

lazy val main = project.in(file("."))  // root project
  .settings(scalacOptions += "-language:experimental.macros",
            addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.0" cross CrossVersion.full))

In the above example, the paradise plugin is included in order to provide complete support of Scala 2.10.x.

Display Settings

When in the SBT console, to list all definable settings for a project:

settings

Or, to get a subproject’s (for example, named webapp) settings:

project webapp
settings

The first line above navigates into the specific subproject.

To show the value of a specific setting (for instance, organization):

show organization

This will display the value of that setting.