Edit

RemoveUnused

Removes unused imports and terms that reported by the compiler under -Ywarn-unused

See slick/slick/pulls#1736 for an example diff from running sbt "scalafix RemoveUnused".

Installation

To use this rule:

  • Enable the Scala compiler option -Ywarn-unused. In sbt, this is done with scalacOptions += "-Ywarn-unused".
  • Disable -Xfatal-warnings if you have it enabled. This is required so the compiler warnings do not fail the build before running Scalafix. Unfortunately, it's not possible exclude unused imports from -Xfatal-warnings.

Examples

Remove unused imports:

// before
import scala.List
import scala.collection.{immutable, mutable}
object Foo { immutable.Seq.empty[Int] }

// after
import scala.collection.immutable
object Foo { immutable.Seq.empty[Int] }

Remove unused local variables:

// before
def app = {
  val unused = "message"
  println("Hello world!")
}
// after
def app = {
  println("Hello world!")
}

Remove unused private variables:

// before
object Main {
  private def unused = "remove me"
  def main() = println("Hello!")
}
// after
object Main {
  def main() = println("Hello!")
}

Formatting

This rule does a best-effort at preserving original formatting. In some cases, the rewritten code may be formatted weirdly

// before
import scala.concurrent.{
  CancellationException, // A comment
  TimeoutException
}
// after
import scala.concurrent. // A comment
TimeoutException

It's recommended to use a code formatter like Scalafmt after running this rule.

Configuration

NameTypeDescription
importsBooleanRemove unused imports
privatesBooleanRemove unused private members
localsBooleanRemove unused local definitions

Defaults

RemoveUnused.imports = true
RemoveUnused.privates = true
RemoveUnused.locals = true

-Ywarn-unused

Consult scala -Y in the command-line for more information about using -Ywarn-unused.

For Scala 2.12.6

$ scala -Ywarn-unused:help
Enable or disable specific `unused' warnings
  imports    Warn if an import selector is not referenced.
  patvars    Warn if a variable bound in a pattern is unused.
  privates   Warn if a private member is unused.
  locals     Warn if a local definition is unused.
  explicits  Warn if an explicit parameter is unused.
  implicits  Warn if an implicit parameter is unused.
  params     Enable -Ywarn-unused:explicits,implicits.
  linted     -Xlint:unused.
Default: All choices are enabled by default.

For Scala 2.11.12

$ scala -Y | grep warn-unused
  -Ywarn-unused                           Warn when local and private vals, vars, defs, and types are unused.
  -Ywarn-unused-import                    Warn when imports are unused.
← PreviousNext →