Plugins¶

Global plugins¶

The ~/.sbt/0.13/plugins/ directory is treated as a global plugin definition project. It is a normal sbt project whose classpath is available to all sbt project definitions for that user as described above for per-project plugins.

Using a library in a build definition¶

As an example, we'll add the Grizzled Scala library as a plugin. Although this does not provide sbt-specific functionality, it demonstrates how to declare plugins.

libraryDependencies += "org.clapper" %% "grizzled-scala" % "1.0.4"

$ sbt
> reload plugins
[info] Set current project to default (in build file:/Users/harrah/demo2/project/)
>

> set libraryDependencies += "org.clapper" %% "grizzled-scala" % "1.0.4"
...
> update
...
> session save
...

> reload return
[info] Set current project to root (in build file:/Users/harrah/demo2/)

lazy val root = project.in( file(".") ).dependsOn( assemblyPlugin )
lazy val assemblyPlugin = uri("git://github.com/sbt/sbt-assembly")

lazy val assemblyPlugin = uri("git://github.com/sbt/sbt-assembly#0.9.1")

> eval grizzled.sys.os

import grizzled.sys._
import OperatingSystem._

libraryDependencies ++=
    if(os ==Windows)
        ("org.example" % "windows-only" % "1.0") :: Nil
    else
        Nil

Introduction¶

A minimal plugin is a Scala library that is built against the version of Scala that sbt runs (currently, 2.10.3) or a Java library. Nothing special needs to be done for this type of library, as shown in the previous section. A more typical plugin will provide sbt tasks, commands, or settings. This kind of plugin may provide these settings automatically or make them available for the user to explicitly integrate.

Description¶

To make a plugin, create a project and configure sbtPlugin to true. Then, write the plugin code and publish your project to a repository. The plugin can be used as described in the previous section.

A plugin can implement sbt.Plugin. The contents of a Plugin singleton, declared like object MyPlugin extends Plugin, are wildcard imported in set, eval, and .sbt files. Typically, this is used to provide new keys (SettingKey, TaskKey, or InputKey) or core methods without requiring an import or qualification.

In addition, a Plugin can implement projectSettings, buildSettings, and globalSettings as appropriate. The Plugin's projectSettings is automatically appended to each project's settings. The buildSettings is appended to each build's settings (that is, in ThisBuild). The globalSettings is appended once to the global settings (in Global). These allow a plugin to automatically provide new functionality or new defaults. One main use of this feature is to globally add commands, such as for IDE plugins. Use globalSettings to define the default value of a setting.

These automatic features should be used judiciously because the automatic activation generally reduces control for the build author (the user of the plugin). Some control is returned to them via Project.autoSettings, which changes how automatically added settings are added and in what order.

Example Plugin¶

An example of a typical plugin:

build.sbt:

sbtPlugin := true

name := "example-plugin"

organization := "org.example"

MyPlugin.scala:

import sbt._
object MyPlugin extends Plugin
{
    // configuration points, like the built in `version`, `libraryDependencies`, or `compile`
    // by implementing Plugin, these are automatically imported in a user's `build.sbt`
    val newTask = taskKey[Unit]("A new task.")
    val newSetting = settingKey[String]("A new setting.")

    // a group of settings ready to be added to a Project
    // to automatically add them, do
    val newSettings = Seq(
        newSetting := "test",
        newTask := println(newSetting.value)
    )

    // alternatively, by overriding `settings`, they could be automatically added to a Project
    // override val settings = Seq(...)
}

Usage example¶

A build definition that uses the plugin might look like:

build.sbt

MyPlugin.newSettings

newSetting := "example"

Example command plugin¶

A basic plugin that adds commands looks like:

build.sbt

sbtPlugin := true

name := "example-plugin"

organization := "org.example"

MyPlugin.scala

import sbt._
import Keys._
object MyPlugin extends Plugin
{
  override lazy val settings = Seq(commands += myCommand)

  lazy val myCommand =
    Command.command("hello") { (state: State) =>
      println("Hi!")
      state
    }
}

This example demonstrates how to take a Command (here, myCommand) and distribute it in a plugin. Note that multiple commands can be included in one plugin (for example, use commands ++= Seq(a,b)). See Commands for defining more useful commands, including ones that accept arguments and affect the execution state.

Global plugins example¶

The simplest global plugin definition is declaring a library or plugin in ~/.sbt/0.13/plugins/build.sbt:

libraryDependencies += "org.example" %% "example-plugin" % "0.1"

This plugin will be available for every sbt project for the current user.

In addition:

1. Jars may be placed directly in ~/.sbt/0.13/plugins/lib/ and will be available to every build definition for the current user.
2. Dependencies on plugins built from source may be declared in ~/.sbt/0.13/plugins/project/Build.scala as described at .scala Build Definition.
3. A Plugin may be directly defined in Scala source files in ~/.sbt/0.13/plugins/, such as ~/.sbt/0.13/plugins/MyPlugin.scala. ~/.sbt/0.13/plugins//build.sbt should contain sbtPlugin := true. This can be used for quicker turnaround when developing a plugin initially:
   1. Edit the global plugin code
   2. reload the project you want to use the modified plugin in
   3. sbt will rebuild the plugin and use it for the project. Additionally, the plugin will be available in other projects on the machine without recompiling again. This approach skips the overhead of publishLocal and cleaning the plugins directory of the project using the plugin.

These are all consequences of ~/.sbt/0.13/plugins/ being a standard project whose classpath is added to every sbt project's build definition.