SI-7707 SI-7712 Exclude unused warnings from -Xlint

Experience building open source projects like Specs that use
`-Xlint` suggests that this warning is too noisy to lump in
with the others.

We are lacking in more fine-grained control of these things, so
simply turning of `-Xlint` in favour of its underlying `-Y` options
ends up *losing* some other important warnings that are predicated
directly on `-Xlint`.

Furthermore, bug reports against M8, SI-7707 SI-7712, show that
unused private/local warnings, while far less noisy, are still
in need of polish.

This commit moves these warnings to a pair of new -Y options,
neither of which is part of  `-Xlint`..

Let's ask people to opt in for 2.11, and as it stabilizes, we can
consider adding it to Xlint (or the desirable evolution of that)
in the next release.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/compiler/scala/tools/nsc/settings/Warnings.scala b/src/compiler/scala/tools/nsc/settings/Warnings.scala
index 791d44153c..5214f6485f 100644
--- a/src/compiler/scala/tools/nsc/settings/Warnings.scala
+++ b/src/compiler/scala/tools/nsc/settings/Warnings.scala
@@ -30,6 +30,8 @@ trait Warnings {
     warnNullaryUnit,
     warnAdaptedArgs,
     warnInferAny
+    // warnUnused       SI-7712, SI-7707 warnUnused not quite ready for prime-time
+    // warnUnusedImport currently considered too noisy for general use
   )
 
   // Warning groups.
@@ -56,6 +58,8 @@ trait Warnings {
   val warnInaccessible     = BooleanSetting   ("-Ywarn-inaccessible", "Warn about inaccessible types in method signatures.")
   val warnNullaryOverride  = BooleanSetting   ("-Ywarn-nullary-override", "Warn when non-nullary overrides nullary, e.g. `def foo()` over `def foo`.")
   val warnInferAny         = BooleanSetting   ("-Ywarn-infer-any", "Warn when a type argument is inferred to be `Any`.")
+  val warnUnused           = BooleanSetting   ("-Ywarn-unused", "Warn when local and private vals, vars, defs, and types are are unused")
+  val warnUnusedImport     = BooleanSetting   ("-Ywarn-unused-import", "Warn when imports are unused")
 
   // Backward compatibility.
   @deprecated("Use fatalWarnings", "2.11.0") def Xwarnfatal            = fatalWarnings      // used by sbt