Recommended Scalac Flags For 2.13
13 May 2019
Following in the footsteps of @tpolecat’s wonderful “Recommended Scalac Flags for 2.12”, and previous version for 2.11, I’d like to share with you an updated list for Scala 2.13.
Scala 2.13 has removed a significant number of old lints and compiler flags, so you will find the previous list no longer works as-is with Scala >= 2.13.0.
This list is current as of Lightbend Scala 2.13.0-RC1.
scalacOptions ++= Seq(
"-deprecation", // Emit warning and location for usages of deprecated APIs.
"-explaintypes", // Explain type errors in more detail.
"-feature", // Emit warning and location for usages of features that should be imported explicitly.
"-language:existentials", // Existential types (besides wildcard types) can be written and inferred
"-language:experimental.macros", // Allow macro definition (besides implementation and application)
"-language:higherKinds", // Allow higher-kinded types
"-language:implicitConversions", // Allow definition of implicit functions called views
"-unchecked", // Enable additional warnings where generated code depends on assumptions.
"-Xcheckinit", // Wrap field accessors to throw an exception on uninitialized access.
"-Xfatal-warnings", // Fail the compilation if there are any warnings.
"-Xlint:adapted-args", // Warn if an argument list is modified to match the receiver.
"-Xlint:constant", // Evaluation of a constant arithmetic expression results in an error.
"-Xlint:delayedinit-select", // Selecting member of DelayedInit.
"-Xlint:doc-detached", // A Scaladoc comment appears to be detached from its element.
"-Xlint:inaccessible", // Warn about inaccessible types in method signatures.
"-Xlint:infer-any", // Warn when a type argument is inferred to be `Any`.
"-Xlint:missing-interpolator", // A string literal appears to be missing an interpolator id.
"-Xlint:nullary-override", // Warn when non-nullary `def f()' overrides nullary `def f'.
"-Xlint:nullary-unit", // Warn when nullary methods return Unit.
"-Xlint:option-implicit", // Option.apply used implicit view.
"-Xlint:package-object-classes", // Class or object defined in package object.
"-Xlint:poly-implicit-overload", // Parameterized overloaded implicit methods are not visible as view bounds.
"-Xlint:private-shadow", // A private field (or class parameter) shadows a superclass field.
"-Xlint:stars-align", // Pattern sequence wildcard must align with sequence component.
"-Xlint:type-parameter-shadow", // A local type parameter shadows a type already in scope.
"-Ywarn-dead-code", // Warn when dead code is identified.
"-Ywarn-extra-implicit", // Warn when more than one implicit parameter section is defined.
"-Ywarn-numeric-widen", // Warn when numerics are widened.
"-Ywarn-unused:implicits", // Warn if an implicit parameter is unused.
"-Ywarn-unused:imports", // Warn if an import selector is not referenced.
"-Ywarn-unused:locals", // Warn if a local definition is unused.
"-Ywarn-unused:params", // Warn if a value parameter is unused.
"-Ywarn-unused:patvars", // Warn if a variable bound in a pattern is unused.
"-Ywarn-unused:privates", // Warn if a private member is unused.
"-Ywarn-value-discard", // Warn when non-Unit expression results are unused.
"-Ybackend-parallelism", "8", // Enable paralellisation — change to desired number!
"-Ycache-plugin-class-loader:last-modified", // Enables caching of classloaders for compiler plugins
"-Ycache-macro-class-loader:last-modified", // and macro definitions. This can lead to performance improvements.
)