Wartremover : Installation & Setup

Add the following to your project/plugins.sbt:

addSbtPlugin("org.wartremover" % "sbt-wartremover" % "3.1.6")

NOTE: sbt-wartremover requires sbt version 1.0+. for sbt 0.13.x

NOTE: wartremover 3.x requires Scala 2.12.+. please use wartremover 2.x for Scala 2.11

Now, you can proceed to configure the linter in your build.sbt. By default, all errors and warnings are turned off. To turn on all checks that are currently considered stable, use:

wartremoverErrors ++= Warts.unsafe

To turn on all available errors (some have false positives), use:

wartremoverErrors ++= Warts.all

Similarly, to just issue warnings instead of errors for all built-in warts, you can use:

wartremoverWarnings ++= Warts.all    // or Warts.unsafe

You can also use scopes, e.g. to turn on all warts only for compilation (and not for the tests nor the sbt console), use:

Compile / compile / wartremoverErrors ++= Warts.all

To choose warts more selectively, use any of the following:

wartremoverErrors ++= Warts.allBut(Wart.Any, Wart.Nothing, Wart.Serializable)

wartremoverWarnings += Wart.Nothing

wartremoverWarnings ++= Seq(Wart.Any, Wart.Serializable)

Suppressing Errors & Warnings

To exclude a specific piece of code from one or more checks, use the SuppressWarnings annotation:

@SuppressWarnings(Array("org.wartremover.warts.Var", "org.wartremover.warts.Null"))
var foo = null

// suppress all warts
@SuppressWarnings(Array("org.wartremover.warts.All"))
var bar = null

To exclude a file or directory from all checks, use wartremoverExcluded in your build.sbt file:

wartremoverExcluded += baseDirectory.value / "src" / "main" / "scala" / "SomeFile.scala"
wartremoverExcluded += sourceManaged.value

Other ways of using WartRemover

Apart from using the sbt plugin to set it up for your project, WartRemover can also be used in the following ways:

as a command-line tool,
as a compiler plugin with manually provided scalac options,
to derive macros.

Command-line

Compile the command-line tool via sbt "++ 2.12.19" core/assembly and then use the provided wartremover shell script:

$ sbt "++ 2.12.19" core/assembly

  ...

$ ./wartremover -traverser org.wartremover.warts.Unsafe core/src/main/scala/wartremover/Plugin.scala
core/src/main/scala/wartremover/Plugin.scala:15: error: var is disabled
  private[this] var traversers: List[WartTraverser] = List.empty
                    ^

Compiler plugin (manually)

Add the following to build.sbt:

addCompilerPlugin("org.wartremover" %% "wartremover" % "3.1.6" cross CrossVersion.full)

scalacOptions += "-P:wartremover:traverser:org.wartremover.warts.Unsafe"

By default, WartRemover generates compile-time errors. If you want to be warned only, use an only-warn-traverser:

scalacOptions += "-P:wartremover:only-warn-traverser:org.wartremover.warts.Unsafe"

If you don’t want to perform the checks in some file, you can use:

scalacOptions += "-P:wartremover:excluded:ABSOLUTE_PATH_TO_THE_FILE"

The excluded option accepts a colon-separated list of absolute paths to files to ignore.

To use your custom WartTraverser, you’ll need to provide a classpath where it can be found:

scalacOptions += "-P:wartremover:cp:someUrl"

Gradle

Support for Gradle is provided by the Gradle-Wartremover plugin:

buildscript {
    dependencies {
      classpath 'cz.augi:gradle-wartremover:putCurrentVersionHere'
    }
}
apply plugin: 'wartremover'

The plugin can be also applied using the new Gradle syntax:

plugins {
    id 'cz.augi.gradle.wartremover' version 'putCurrentVersionHere'
}

It automatically uses the safe Warts for all Scala code.

Apache Maven

You can use WartRemover in Maven by employing it as a compilerPlugin to scala-maven-plugin:

<build>
  <plugins>
    <plugin>
      <groupId>net.alchim31.maven</groupId>
      <artifactId>scala-maven-plugin</artifactId>
      <version>3.2.1</version>
      <configuration>
        <compilerPlugins>
          <compilerPlugin>
            <groupId>org.wartremover</groupId>
            <artifactId>wartremover_2.13</artifactId>
            <version>3.1.6</version>
          </compilerPlugin>
        </compilerPlugins>
        <args>
          <arg>-P:wartremover:only-warn-traverser:org.wartremover.warts.Unsafe</arg>
        </args>
      </configuration>
    </plugin>
  </plugins>
</build>

See the notes on the compiler plugin above for options to pass as <arg>s.

Scala 2 Macros

You can make any wart into a macro, like so:

scala> import language.experimental.macros
import language.experimental.macros

scala> import org.wartremover.warts.Unsafe
import org.wartremover.warts.Unsafe

scala> def safe(expr: Any) = macro Unsafe.asMacro
safe: (expr: Any)Any

scala> safe { null }
<console>:10: error: null is disabled
              safe { null }
                     ^

Wartremover A flexible Scala linter