TL;DR the name sbt doesn’t stand for anything, it’s just “sbt”, and it should be written that way.
When Mark Harrah (@harrah) first created the project he called it “Simple Build Tool”, but in his first public announcement of it he already referred to it as just “sbt”. Over time some have re-defined sbt to stand for “Scala Build Tool”, but we believe that isn’t accurate either given it can be used to build Java-only projects.
Nowadays we just call sbt “sbt”, and to reinforce that the name is no longer an initialism we always write it in all lowercase letters. However, we are cool with 酢豚 (subuta) as a nickname.
sbt 1.9.8 by default suppresses most stack traces and debugging
information. It has the nice side effect of giving you less noise on
screen, but as a newcomer it can leave you lost for explanation. To see
the previous output of a command at a higher verbosity, type
last <task> where <task> is the task that failed or that you want to
view detailed output for. For example, if you find that your update
fails to load all the dependencies as you expect you can enter:
> last update
and it will display the full output from the last run of the update
command.
Sometimes sbt doesn’t detect that ansi codes aren’t supported and you get output that looks like:
[0m[ [0minfo [0m] [0mSet current project to root
or ansi codes are supported but you want to disable colored output. To
completely disable ansi codes, pass -no-colors option:
$ sbt -no-colors
In sbt’s shell run console.
:=, +=, and ++= methods? These are methods on keys used to construct a Setting or a Task. The
Getting Started Guide covers all these methods, see
.sbt build definition,
task graph, and
appending values for
example.
% method? It’s used to create a ModuleID from strings, when specifying managed
dependencies. Read the Getting Started Guide about
library dependencies.
ThisBuild / scalaVersion mean? ThisBuild acts as a special subproject name that you can use to define default
value for the build.
When you define one or more subprojects, and when the subproject does not define
scalaVersion key, it will look for ThisBuild / scalaVersion.
See build-wide settings.
ModuleID, Project, …? To figure out an unknown type or method, have a look at the Getting Started Guide if you have not. Also try the index of commonly used methods, values, and types, and the API Documentation.
The files included in an artifact are configured by default by a task
mappings that is scoped by the relevant package task. The mappings
task returns a sequence Seq[(File,String)] of mappings from the file
to include to the path within the jar. See
mapping files for details on creating these mappings.
For example, to add generated sources to the packaged source artifact:
Compile / packageSrc / mappings ++= {
import Path.{flat, relativeTo}
val base = (Compile / sourceManaged).value
val srcs = (Compile / managedSources).value
srcs pair (relativeTo(base) | flat)
}
This takes sources from the managedSources task and relativizes them
against the managedSource base directory, falling back to a flattened
mapping. If a source generation task doesn’t write the sources to the
managedSource directory, the mapping function would have to be
adjusted to try relativizing against additional directories or something
more appropriate for the generator.
See Generating Files.
See Caching.
See How to define a custom dependency configuration.
See the Additional test configurations section of Testing.
run? This answer is extracted from a mailing list discussion.
Read the Getting Started Guide up to custom settings for background.
A basic run task is created by:
lazy val myRunTask = taskKey[Unit]("A custom run task.")
// this can go either in a `build.sbt` or the settings member
// of a Project in a full configuration
fullRunTask(myRunTask, Test, "foo.Foo", "arg1", "arg2")
If you want to be able to supply arguments on the command line, replace
TaskKey with InputKey and fullRunTask with fullRunInputTask. The
Test part can be replaced with another configuration, such as
Compile, to use that configuration’s classpath.
This run task can be configured individually by specifying the task key in the scope. For example:
myRunTask / fork := true
myRunTask / javaOptions += "-Xmx6144m"
Tool dependencies are used to implement a task and are not needed by project source code. These dependencies can be declared in their own configuration and classpaths. These are the steps:
update.
As an example, consider a proguard task. This task needs the ProGuard
jars in order to run the tool. First, define and add the new
configuration:
lazy val ProguardConfig = config("proguard").hide
ivyConfigurations += ProguardConfig
Then,
// Add proguard as a dependency in the custom configuration.
// This keeps it separate from project dependencies.
libraryDependencies +=
"net.sf.proguard" % "proguard" % "4.4" % ProguardConfig.name
// Extract the dependencies from the UpdateReport.
ProguardConfig / managedClasspath := {
// these are the types of artifacts to include
val artifactTypes: Set[String] = (ProguardConfig / classpathTypes).value
Classpaths.managedJars(proguardConfig, artifactTypes, update.value)
}
// Use the dependencies in a task, typically by putting them
// in a ClassLoader and reflectively calling an appropriate
// method.
proguard := {
val cp: Seq[File] = (ProguardConfig / managedClasspath).value
// ... do something with , which includes proguard ...
}
Defining the intermediate classpath is optional, but it can be useful
for debugging or if it needs to be used by multiple tasks. It is also
possible to specify artifact types inline. This alternative proguard
task would look like:
proguard := {
val artifactTypes = Set("jar")
val cp =
Classpaths.managedJars(proguardConfig, artifactTypes, update.value)
// ... do something with , which includes proguard ...
}
It is possible to register additional jars that will be placed on sbt’s
classpath. Through
State, it is possible to obtain a
xsbti.ComponentProvider, which
manages application components. Components are groups of files in the
~/.sbt/boot/ directory and, in this case, the application is sbt. In
addition to the base classpath, components in the “extra” component are
included on sbt’s classpath.
(Note: the additional components on an application’s classpath are
declared by the components property in the [main] section of the
launcher configuration file boot.properties.)
Because these components are added to the ~/.sbt/boot/ directory and
~/.sbt/boot/ may be read-only, this can fail. In this case, the user
has generally intentionally set sbt up this way, so error recovery is
not typically necessary (just a short error message explaining the
situation.)
The following code can be used where a State => State is required,
such as in the onLoad setting (described below) or in a
command. It adds some files to the “extra”
component and reloads sbt if they were not already added. Note that
reloading will drop the user’s session state.
def augment(extra: Seq[File])(s: State): State = {
// Get the component provider
val cs: xsbti.ComponentProvider = s.configuration.provider.components()
// Adds the files in 'extra' to the "extra" component
// under an exclusive machine-wide lock.
// The returned value is 'true' if files were actually copied and 'false'
// if the target files already exists (based on name only).
val copied: Boolean = s.locked(cs.lockFile, cs.addToComponent("extra", extra.toArray))
// If files were copied, reload so that we use the new classpath.
if(copied) s.reload else s
}
See How to take an action on startup.
The following example maintains a count of the number of times a project has been loaded and prints that number:
{
// the key for the current count
val key = AttributeKey[Int]("loadCount")
// the State transformer
val f = (s: State) => {
val previous = s get key getOrElse 0
println("Project load count: " + previous)
s.put(key, previous + 1)
}
Global / onLoad := {
val previous = (Global / onLoad).value
f compose previous
}
}
Setting initializers are executed in order. If the initialization of a setting depends on other settings that has not been initialized, sbt will stop loading.
In this example, we try to append a library to libraryDependencies
before it is initialized with an empty sequence.
libraryDependencies += "commons-io" % "commons-io" % "1.4" % "test"
disablePlugins(plugins.IvyPlugin)
To correct this, include the IvyPlugin plugin settings, which includes
libraryDependencies := Seq(). So, we just drop the explicit disabling.
libraryDependencies += "commons-io" % "commons-io" % "1.4" % "test"
A more subtle variation of this error occurs when using scoped settings.
// error: Reference to uninitialized setting
settings = Seq(
libraryDependencies += "commons-io" % "commons-io" % "1.2" % "test",
fullClasspath := fullClasspath.value.filterNot(_.data.name.contains("commons-io"))
)
This setting varies between the test and compile scopes. The solution is use the scoped setting, both as the input to the initializer, and the setting that we update.
Compile / fullClasspath := (Compile / fullClasspath).value.filterNot(_.data.name.contains("commons-io"))
This error occurs when the published checksum, such as a sha1 or md5 hash, differs from the checksum computed for a downloaded artifact, such as a jar or pom.xml. An example of such an error is:
[warn] problem while downloading module descriptor:
https://repo1.maven.org/maven2/commons-fileupload/commons-fileupload/1.2.2/commons-fileupload-1.2.2.pom:
invalid sha1: expected=ad3fda4adc95eb0d061341228cc94845ddb9a6fe computed=0ce5d4a03b07c8b00ab60252e5cacdc708a4e6d8 (1070ms)
The invalid checksum should generally be reported to the repository owner (as was done for the above error). In the meantime, you can temporarily disable checking with the following setting:
checksums in update := Nil
See library management for details.
This problem crops up frequently. Plugins are only published for the Scala version that sbt uses (currently, 2.12). You can still use plugins during cross-compilation, because sbt only looks for a 2.12 version of the plugin.
… unless you specify the plugin in the wrong place!
A typical mistake is to put global plugin definitions in
~/.sbt/plugins.sbt. THIS IS WRONG. .sbt files in ~/.sbt are
loaded for each build—that is, for each cross-compilation. So, if
you build for Scala 2.11.0, sbt will try to find a version of the plugin
that’s compiled for 2.11.0—and it usually won’t. That’s because it
doesn’t know the dependency is a plugin.
To tell sbt that the dependency is an sbt plugin, make sure you define
your global plugins in a .sbt file in ~/.sbt/plugins/. sbt knows
that files in ~/.sbt/plugins are only to be used by sbt itself, not as
part of the general build definition. If you define your plugins in a
file under that directory, they won’t foul up your cross-compilations.
Any file name ending in .sbt will do, but most people use
~/.sbt/plugins/build.sbt or ~/.sbt/plugins/plugins.sbt.
See Community Plugins for a list of currently available plugins.
