Scala 2.12.2 emits a ton of useless “Warning: para

Question

This is a question so I don't have to traverse the entire Internet to find the answer, as scalac options are currently not published.

How do I disable these warnings starting in Scala 2.12.2, when I have a global "-Xlint"?

Answer 1

$ scalac -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.
  params     Warn if a value parameter is unused.
  implicits  Warn if an implicit parameter is unused.
Default: All choices are enabled by default.

So

-Ywarn-unused:-params,_

But:

$ scalac -Xlint:help
Enable or disable specific warnings
  adapted-args               Warn if an argument list is modified to match the receiver.
  nullary-unit               Warn when nullary methods return Unit.
  inaccessible               Warn about inaccessible types in method signatures.
  nullary-override           Warn when non-nullary `def f()' overrides nullary `def f'.
  infer-any                  Warn when a type argument is inferred to be `Any`.
  missing-interpolator       A string literal appears to be missing an interpolator id.
  doc-detached               A Scaladoc comment appears to be detached from its element.
  private-shadow             A private field (or class parameter) shadows a superclass field.
  type-parameter-shadow      A local type parameter shadows a type already in scope.
  poly-implicit-overload     Parameterized overloaded implicit methods are not visible as view bounds.
  option-implicit            Option.apply used implicit view.
  delayedinit-select         Selecting member of DelayedInit.
  by-name-right-associative  By-name parameter of right associative operator.
  package-object-classes     Class or object defined in package object.
  unsound-match              Pattern match may not be typesafe.
  stars-align                Pattern sequence wildcard must align with sequence component.
  constant                   Evaluation of a constant arithmetic expression results in an error.
  unused                     Enable -Ywarn-unused:imports,privates,locals,implicits.

So

-Xlint:unused

Or also more surgically:

-Xlint:-unused,_ -Ywarn-unused:imports

There's a PR to improve ergonomics, so you can set/unset in arbitrary combinations, but this is the incantation for 2.12.2.