ghik / silencer

Scala compiler plugin for warning suppression

Scala has no local warning suppression (see e.g. scala/bug/issues/1781 for discussion). This plugin aims to change the situation. The direct motivation for this plugin is to be able to turn on -Xfatal-warnings option in Scala compiler and enforce zero-warning policy but still be able to consciously silent out warnings which would otherwise be a pointless noise.

Usage

If you're using SBT, simply add these lines to your build.sbt to enable the plugin:

libraryDependencies ++= Seq(
  compilerPlugin("com.github.ghik" %% "silencer-plugin" % silencerVersion),
  "com.github.ghik" %% "silencer-lib" % silencerVersion % Provided
)

Silencer currently works with Scala 2.11.4+, 2.12.0+ and 2.13.0-M4+. Also note that since both silencer-plugin and silencer-lib are compile time only dependencies, Silencer can also be used in ScalaJS and Scala Native without having to be cross compiled for it.

Annotation-based suppression

With the plugin enabled, warnings can be silenced using the @com.github.ghik.silencer.silent annotation. It can be applied on a single statement or expression, entire def/val/var definition or entire class/object/trait definition.

import com.github.ghik.silencer.silent

@silent class someClass { ... }
@silent def someMethod() = { ... }
someDeprecatedApi("something"): @silent

The @silent annotation suppresses all warnings in some code fragment. There is currently no way to silent out only specific classes of warnings, like with @SuppressWarnings annotation in Java.

Global regex-based suppression

You can also suppress warnings globally based on a warning message regex. In order to do that, pass this option to scalac:

scalacOptions += "-P:silencer:globalFilters=[semi-colon separated message patterns]"

Filename based suppression

Another option is to suppress all warnings in selected source files. This can be done by specifying a list of file path regexes:

scalacOptions += "-P:silencer:pathFilters=[semi-colon separated file path patterns]"

NOTE: In order to make builds independent of environment, filename separators are normalized to UNIX style (/) before the path is matched against path patterns.

By default, absolute file path is matched against path patterns. In order to make your build independent of where your project is checked out, you can specify a list of source root directories. Source file paths will be relativized with respect to them before being matched against path patterns. Usually it should be enough to pass project base directory as source root (i.e. baseDirectory.value in SBT):

scalacOptions += s"-P:silencer:sourceRoots=${baseDirectory.value.getCanonicalPath}"

Another good choice for source roots may be actual SBT source directories:

scalacOptions += s"-P:silencer:sourceRoots=${sourceDirectories.value.map(_.getCanonicalPath).mkString(";")}"

Status

Silencer is successfully being used in AVSystem open source and closed projects, e.g. AVSystem Scala Commons Library